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How USB charging works, or how to avoid blowing up your smartphone
- By Jamie Lendino on March 25, 2015 at 11:53 am
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The tech world has finally coalesced around a charging standard, after years of proprietary adapters and ugly wall wart power supplies. Well, sort of: We're already seeing some fragmentation in terms of the new USB-C connector, which could eventually replace USB, as well as what is thankfully turning out to be a short-lived obsession Samsung had with larger USB Micro-B connectors for its Galaxy line. But aside from that, and with the obvious exception of Apple's Lightning connector, micro USB has destroyed the industry's penchant for custom ports.
Ten years ago, you always had to make sure you had the correct power supply for each of your gadgets. Usually, that power supply wasn't even labeled. Today, you can charge your phone at your friend's house, plug your Kindle into any computer, and download photos from a digital camera directly to your TV, all thanks to a standardized connector. In its place, though, there's a new problem: USB power. Not all USB chargers, connectors, and cables are born equal. You've probably noticed that some wall chargers are stronger than others. Sometimes, one USB socket on a laptop is seemingly more powerful than the other. On some desktop PCs, even when they're turned off, you can charge your smartphone via a USB socket. It turns out there's a method to all this madness — but first we have to explain how USB power actually works.
New specifications
There are now four USB specifications — USB 1.0, 2.0, 3.0, and 3.1 — in addition to the new USB-C connector. We'll point out where they significantly differ, but for the most part, we'll focus on USB 3.0, as it's the most common. The other important fact is that in any USB network, there is one host and one device. In almost every case, your PC is the host, and your smartphone, tablet, or camera is the device. Power always flows from the host to the device, but data can flow in both directions.
Okay, now the numbers. A USB socket has four pins, and and a USB cable has four wires. The inside pins carry data (D+ and D-), and the outside pins provide a 5-volt power supply. In terms of actual current (milliamps or mA), there are three kinds of USB port dictated by the current specs: a standard downstream port, a charging downstream port, and a dedicated charging port. The first two can be found on your computer (and should be labeled as such), and the third kind applies to "dumb" wall chargers.
In the USB 1.0 and 2.0 specs, a standard downstream port is capable of delivering up to 500mA (0.5A); in USB 3.0, it moves up to 900mA (0.9A). The charging downstream and dedicated charging ports provide up to 1500mA (1.5A). USB 3.1 bumps throughput to 10Gbps in what is called SuperSpeed+ mode, bringing it roughly equivalent with first-generation Thunderbolt. It also supports power draw of 1.5A and 3A over the 5V bus.
USB-C is a different connector entirely. First, it's universal; you can put it in either way and it will work, unlike with USB. It's also capable of twice the theoretical throughput of USB 3.0, and can output more power. Apple is joining USB-C with USB 3.1 on its new MacBook, and so is Google with the new Chromebook Pixel. But there can also be older-style USB ports that support the 3.1 standard.
The USB spec also allows for a "sleep-and-charge" port, which is where the USB ports on a powered-down computer remain active. You may have noticed this on your desktop PC, where there's always some power flowing through the motherboard, but some laptops are also capable of sleep-and-charge.
Now, this is what the spec dictates. But in actual fact there are plenty of USB chargers that break these specs — mostly of the wall-wart variety. Apple's iPad charger, for example, provides 2.1A at 5V; Amazon's Kindle Fire charger outputs 1.8; and car chargers can output anything from 1A to 2.1A.
Can I blow up my USB device?
There is a huge variance, then, between normal USB ports rated at 500mA and dedicated charging ports which range all the way up to 3,000mA. This leads to a rather important question: If you take a smartphone which came with a 900mA wall charger, and plug it into a 2,100mA iPad charger, as an example, will it blow up?
In short, no: You can plug any USB device into any USB cable and into any USB port, and nothing will blow up — and in fact, using a more powerful charger should speed up battery charging.
The longer answer is that the age of your device plays an important role, dictating both how fast it can be charged, and whether it can be charged using a wall charger at all. Way back in 2007, the USB Implementers Forum released the Battery Charging Specification, which standardized faster ways of charging USB devices, either by pumping more amps through your PC's USB ports, or by using a wall charger. Shortly thereafter, USB devices that implemented this spec started to arrive.
If you have a modern USB device — really, almost any smartphone, tablet, or camera — you should be able to plug into a high-amperage USB port and enjoy faster charging. If you have an older device, however, it probably won't work with USB ports that employ the Battery Charging Specification. It might only work with old school, original (500mA) USB 1.0 and 2.0 PC ports. In some (much older) cases, USB devices can only be charged by computers with specific drivers installed.
There are a few other things to be aware of. While PCs can have two kinds of USB port — standard downstream or charging downstream — OEMs haven't always labeled them as such. As a result, you might have a device that charges from one port on your laptop, but not from the other. This is a trait of older computers, as there doesn't seem to be a reason why standard downstream ports would be used, when high-amperage charging ports are available. Numerous vendors now put a small lightning icon above the proper charging port on laptops, and in some cases, those ports can even stay on when the lid is closed.
In a similar vein, some external devices — hard drives and optical drives, most notably — require more power than a USB port can provide, which is why they include a two-USB-port Y-cable, or an external AC power adapter. Otherwise, USB has certainly made charging our gadgets and peripherals much easier than it ever has been. And if the new USB-C connector catches on — and it looks like it will — things will get even simpler, because you'll never again have to curse after plugging it in the wrong way.
Sebastian Anthony wrote the original version of this article. It has since been updated with new information.
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http://www.cardinalphoto.com David Cardinal
Well explained, but what's the deal with devices like the HP Touchpad that get ornery (and refuse to charge) from time to time with non-HP chargers. Do they require a certain amperage, or type of port? I've had my older smartphones do that sometimes in the car as well.
http://www.mrseb.co.uk Sebastian Anthony
Basically, it looks like wall chargers communicate to the device that they ARE a wall charger by shorting the data lines (D- and D+). When the device sees shorted data lines, it knows that it can draw up to 1.5A — that's what the Battery Charging Spec dictates.
If the Touchpad doesn't do that, then my guess is that HP isn't implementing the spec exactly. Apple used to negotiate amperage by communicating using the power supply (2V = up to 1A, 2.5V = 1.5A, or whatever). Maybe HP is trying something like that.
Would guess that the older smartphones don't implement the Battery Charging Spec.
The spec says they only *have* to source 0.5 A, and then they can drop the voltage to 2 V, and then shut off.
Well specs indicate the available current by voltages on the D− and D+ lines.
When D+ = D− = 2.0 V, the device may pull up to 500 mA. When D+ = 2.0 V and D− = 2.8 V, the device may pull up to 1 A of current. When D+ = 2.8 V and D− = 2.0 V, the device may pull up to 2 A of current
The Battery Charging Spec doesn't. It just shorts the D+ and D- lines together. You're thinking of iPods, which don't follow the standard.
Interesting article, thanks. But I have a question.From the article: "In terms of actual current (milliamps or mA), there are three kinds of USB port dictated by the current specs: a standard downstream port, a charging downstream port, and a dedicated charging port. The first two can be found on your computer (and should be labeled as such), and the third kind applies to "dumb" wall chargers. "
What's the difference between the standard downstream port and the charging downstream port ? Is there really a need for these two ?
http://www.mrseb.co.uk Sebastian Anthony
From what I gather, standard downstream is basically a normal USB 1 or 2 port. 'Charging downstream' was introduced with the Battery Charging Spec (2007). Functionally, they are the same — but the charging port, as it can go up to 1500mA (instead of 500mA) charges devices faster.
As for whether the standard port is used any more, I don't know :) It certainly seems like it is deprecated.
OK, thanks for the clarification :)
http://www.cardinalphoto.com David Cardinal
I found that with some laptops, external drives can get enough power from some but not all of the USB ports. Don't know if that is/was a deliberate design where only some have the higher power rating, or a fluke due to the actual layout/wiring.
http://www.mrseb.co.uk Sebastian Anthony
Yeah, have noticed the same thing. Fairly sure it's because some ports (perhaps on older computers?) are standard USB 2.0, and some have the increased Battery Charging Spec ports.
That's why some external HDDs/optical drives come with Y cables that you plug into two USB ports, for extra power!
http://www.cardinalphoto.com David Cardinal
Buffalo came out with an interesting drive that had a capacitor in line so spin-up could be done even on a low power port, then the drive could run on the low power after that. I think they even sold the capacitor separately, but it seems like with the newest drives the manufacturers either have gotten the power down a bit or integrated a capacitor, as the need for Y-cables seems to be decreasing a bit.
http://www.cardinalphoto.com David Cardinal
I found that with some laptops, external drives can get enough power from some but not all of the USB ports. Don't know if that is/was a deliberate design where only some have the higher power rating, or a fluke due to the actual layout/wiring.
Don't forget it was the European Union who took issue with the many different cell phone changers, and forced cell phone manufacturers to standardize.
Paul Peterson
Australia made this demand too.
http://www.mrseb.co.uk Sebastian Anthony
Aye, gotta love the EU on these kinds of things. They're very sensible.
Mel M. Liu
So why wasn't the EU or Australia able to fix Apple too?
http://twitter.com/snaipperi snaipperi
Apple is happily using a loophole in the agreement, which means they're okay as long as they offer a simple adapter. Oh yeah, and that piece of metal costs £9.
http://www.facebook.com/johnxcassidy John Cassidy
Apple are such a bunch of c0ckmuchers with their proprietary hardware and software. When will people realise that Apple products are more style than substance?
Scott Kennelly
. . . when other companies make computers and other things that are just as good as the stuff Apple makes (i.e. something better than Thunderbolt). Intel developed it (probably because Apple demanded it), and Apple used it. I'm sure other companies can use it too, but they're too stupid or cheap to do that. The fact is though that Thunderbolt uses the mini display port, so they converted a port that already existed to make it more useful AND backward compatible. THAT's intelligent innovation. How can you have a problem with that?
I wish they had adopted a tactile plug orientation standard;
we would all love to quit guessing which side goes up.
lightning does?
You don't know, so you're asking someone who also doesn't know?
Yeah, "that works."
We need to make tunneling USB connectors!
Actually there are reversible USB plugs, and they look just like the bottom picture: http://www.trendhunter.com/trends/double-u-usb-port
We need to make tunneling USB connectors!
Actually there are reversible USB plugs, and they look just like the bottom picture: http://www.trendhunter.com/trends/double-u-usb-port
On all µUSB plugs I've seen (or felt), the underside has two little bumps on it, while the top side is completely smooth.
Henrik Danielsson
Well, you can't plug it in wrong by making a wrong guess, unless you really force it in there, same as it's always been with monitor/printer connectors…
This was done to keep implementation costs down, also a reason why USB became popular with manufacturers. Yes, they've regretted this choice from a user POV, but USB connectors which go both ways are on the market now.
Paul Peterson
You forgot Motorola.
Motorola wanted to insure you used only their chargers so many Motorola phones over the years would not charge on any USB charger.
For AC adapters, they had to be for Motorola devices, for Windows PC's you had to install Motorola's USB driver for your device to charge.
http://www.mrseb.co.uk Sebastian Anthony
Yeah, it used to be a lot more complicated. Basically, prior to the Battery Charging Spec, USB devices had to digitally negotiate the ampage. If an OEM wanted to, it could program the USB controller on the device to only talk to an "authenticated" USB host/charger.
Nathan Brown
Lol. Remember the Moto Milestone problem of the touchscreen going crazy?
I found this started to happen after using a non-propriety charger, and then was made worse by the crappy slide cable and humidity… I wonder if Moto were trying to enforce Moto charger use, or just used substandard tech on the charging assembly?
I saw something similar very recently on my iPhone 4. I had long back bought a cell phone case for my old 3GS which came with a free wall charger.
Last week I couldn't find my phone charger (wall plug), so I tried using this cheap wall charger and while the charger was plugged in my OS started behaving. Wont let me switch apps, touch screen behaved crazy and stuff. I did a few tests to ensure that it was the charger which was bad (I restarted my phone and tried with the bad charger again to reproduce the problem, then checked with apple charger and then used the bad guy again to be sure it always causes trouble).
I immediately threw the bad charger in trash.
This was more of a bug, but there was a Verizon Android upgrade to the Samsung S4 which made low current car chargers non-functional. If you had a 1 amp car charger it simply wouldn't work to provide any current/charge, where prior to the update it did work. I didn't see that same issue with any computer/USB ports, but I didn't really go looking for it either, and they eventually fixed the problem. The phone though will still warn you that you're using a low current charger.
Ty Gardiner
I am confused about the comment "using a more powerful charger should speed up battery charging." Isn't it correct that the device DRAWS the current from the charger, not the other way around? If that is correct, plugging a device into a charger capable of delivering a higher amount of amps would have zero impact on the charge time.
If the port only provide 500 mA, the device can't draw more than that. If the port can provide 1.5 A, the device could request/draw 900 mA and charge faster than it would on a 500 mA port.
If the port only provide 500 mA, the device can't draw more than that. If the port can provide 1.5 A, the device could request/draw 900 mA and charge faster than it would on a 500 mA port.
But that's not how the post sounds. It sounds like the device will have a current being put into it as high as the charger supports, which is not the case since devices simply draw what they need.
If the port only provide 500 mA, the device can't draw more than that. If the port can provide 1.5 A, the device could request/draw 900 mA and charge faster than it would on a 500 mA port.
Electrical current is directly comparable to water current. In other words, if you hook up a fire hose nozzle to a garden hose, it won't provide any higher current than the garden hose nozzle. But hook it up to a fire hose, and it will. On the other hand, hook a garden hose nozzle up to the fire hose, and it won't.
confusing analogy. Maybe something for like this
Garden tap = 500mA port, Fire hydrant = 2000mA port
garden/fire hose = usb cable (no relevance?)
My mouth = phone.
Question 1:
My phone comes with a 500mA charger. = I can drink from a garden tap
Is it safe to plug my phone into a 2000mA charger? = Can i drink from a fire hydrant? Will the hydrant decrease it's flow of water to what ever i can accept?
And reading from reading some comments below, it says something about chargers exploding from hungry phones?
Question 2:
If I usually drink from a fire hydrant, could i make a garden tap 'explode' from drinking from it?
Brad Wood
The key is in Ohm's law. E = I R or voltage equals amperage (current) times resistance. The charger only forces the voltage. The amperage of a charger is just its CAPABILITY. It's up to the device being charged to request however much current it wants based on the resistance or impedance of the phone.
So, voltage is fixed at 5V. Let's say a phone has a charging impedance of 7 Ohms, that means it will try to draw 714 milliamps (or .7 amps) of current from the charger. E / R = I so 5 / 7 = .714
So, if you're using a 500mA charger, then the device only gets 500mA even though it would like more.
If you're using 1A charger, than the device gets to pull its full 714mAs.
If you're using a 5000 Amp charger- the device still just pulls it's 714mA!
That is because the charger doesn't *push* current. It simply provides a voltage difference (or pressure if you will) and is also rated at its MAX possible current, but the actual current that is pulled by the device is entirely decided on the devices charging impedance.
Therefore, the amperage rating of a charger can never be "too high".
Henrik Danielsson
True, but some phones may not regulate their draw properly, causing them to overheat.
Not true. The garden hose will make the water coming from the fire hose have even more pressure, but with a smaller amount of water running all at once. That's not quite the same as the way electric current behaves.
Yes and no. The charging circuit may be perfectly able to draw a higher current than intended by the phone manufacturer.
Ty Gardiner
I am confused about the comment "using a more powerful charger should speed up battery charging." Isn't it correct that the device DRAWS the current from the charger, not the other way around? If that is correct, plugging a device into a charger capable of delivering a higher amount of amps would have zero impact on the charge time.
http://twitter.com/myrmidonical myrmidonical
I've noticed with my Samsung Focus that if I charge it with a non-Samsung charger, the charging indicator will never clear after I disconnect from the charger until the next time I use one made by Samsung. Battery life is usually 10%-20% reduced as well. I assume these two issues are related. Has anyone else had this issue with Samsung?
going to assume the correct charger has a voltage output of 5.2 VS the other with a output of 5V.0, thus not being able to charge the battery all the way up.
Correction, the new USB "Battery Charging spec 1.2″ dictates that 1.5A is the MINIMUM power supply for a charging downstream port. Up to 5A is permitted. See table 5-2 on p.44 of the spec.
http://www.mrseb.co.uk Sebastian Anthony
Ah, I was trying to work that out actually, but couldn't quite get my head around it. So, wall chargers (dedicated charging ports) can do up to 5A — but a charging downstream port (in a PC) can only do 1.5A, right? (Something about increased power damaging the data integrity on the data lines).
Thanks for commenting!
No, the minimum is 0.5 A.
Sawyer Norquist
To clarify and expand on other comments, the power drawn actually depends on the device drawing the power. Assuming the charger doesn't arbitrarily raise the voltage, it cannot force a given amperage into the device being charged. Ohm's law dictates that as long as the voltage is consistent, the resistance determines the amperage; in this case the device puts load on the charger (basically closing the circuit while introducing resistance) and that determines the amperage of the system.
What the charger rating means is just the MAXIMUM amperage it can provide. In truth (again, assuming voltage doesn't exceed the ratings), I'd guess your phone is more capable of making your charger explode. If your phone tries to draw more amperage than the charger can handle, it could cause significant overheating. Any half-decent charger should limit itself in this scenario, but el cheapo chargers can still be made to… malfunction (ah, childhood memories…)
In other news, I nearly threw a party when I first learned that chargers were moving to a standard spec.
http://twitter.com/konaya Benjamin Tayehanpour
What you are saying is all true, but in the very unlikely event that something goes terribly wrong inside your device (such as a short-circuit) you wouldn't want the short-circuit current to be too high, eh?
Summary: Higher maximum amperage won't kill your device, but if your device is old and won't accept a charge current higher than 500mA, it's an unnecessary risk to give it the chance to draw much more than that.
I don't think you understood very well what Sawyer Norquist was explaining. The device will draw whatever current it needs, the charger doesn't exactly have a say. If the charger cannot handle the amount of current, it will overheat and possibly melt or even explode.
If the charger happens to be your computer's USB ports, they will burn (unless they have a failsafe). Personally, I'd rather have the device burn that my laptop, thus I prefer my USB ports to be able to handle higher currents.
USB ports usually have some sort of electronic circuit breaker. If you exceed 500ma, the USB port automatically shuts off and must be reset. My 10 yr old Dell laptop did this when I tried to plug too many things into a large USB hub. Also, when a USB devices fails, it may trip the port. I had a failed USB hub do this.
but in the very unlikely event that something goes terribly wrong inside
your device (such as a short-circuit) you wouldn't want the
short-circuit current to be too high, eh?
The charger's maximum current will make no difference in this situation. Max current will be drawn, something will burn up, and the circuit will become open.
Simon Taylor
Are the USB ports on a desktop PC really limited to 500mA though with only specific ones as dedicated charging ports? If true, I don't see the point in artificially limiting the current when any ATX PSU can easily provide more than enough amps. Is it something to do with the thickness of the +5V and GND traces on the motherboard that go to the USB ports?
I understand why USB ports on a laptop are current limited with maybe 1 higher power port for external HDDs/charging/etc. There's only so much current the internal voltage regulation circuitry can handle before it overheats. Also most laptop PSUs are less than 4A and of course you want to use as little power as possible when running on the battery.
There were two issues involved when they created the batttery charging specs
1) backwards compatibility – very important as the older 1.0 standard didn't allow much power and some devices can be damanged
2) wiring/trace sizes – low-end/cheap boards saved money by going with the absolutely smallest traces/wire size that would carry the load.
Related to these two issues in PC's is the power regulation of the board itself. Remember the capacity issue that many boards suffered a few years back? Overloading the power regulation of a board can easily blow the board itself – CPU and/or chipset fry while GPU's and such go up in smoke. Very expensive and a potential fire hazzard in your home/office.
Don Barker
Thanks for the clarification! I always harboured a fear that I might damage a device, although I learned all the electronics I could stand in the USAF. It was the current rating I always sweated.
How about USB charging ports on emergency hand cracked generators like the Eton FR160r weather radio? I've heard these can damage phones if not done properly. True?
http://socialentrepreneurship.change.org/actions/view/twenty-first_century_metric_america_in_your_state BeholdersEye
I think and look at specs, they are all under .5 amps, that is why you need to crank a long time…. Hook up to my bike please I know I will not be cranking for hours at a time…
Jim N
I knew there were some differences in chargers but I would never have suspected that different USB ports on the same computer would be different.
So how can I determine which is the best charging USB port on my desktop or laptop?
James Moore
on a desktop box, rule of thumb is the usb ports nearest the PSU (usually the ones you'd plug a keyboard and mouse into) are the ones that deliver the highest port currents. Ports that sit off the motherboard (eg on breakout plates or front panels) are generally data ports, probably not safe to plug in an external hard drive never mind your ipod. Laptops with sleep-charging ports will usually be indicated in the user manual (my Toshiba and my Asus both have it advertised on the box!)
http://twitter.com/pjd65 PJD
Does anyone know what is up with the NookColor? It will ONLY charge from its own wall charger. It looks like USB & a standard USB cable works find for data with a PC or laptop, but even with its own cable, it will not charge from a PC and other wall chargers do not charge it.
http://pulse.yahoo.com/_J6N335G6OBCPMGDLCCH56UBECM David
For the NookColor, it might be that it needs the 1 to 2 Amps that is supplied by its own charger (have a look at what's printed on it). I have a Lenovo Thinkpad Tablet, and its charger supplies 2.1 Amps, and it will only "trickle charge" from a standard USB port supplying the standard 500ma (0.5 Amp).
Not sure about the NC, but I can plug my Nook Tablet in with a "standard" USB and it appears to take a charge. This is with the USB connected to my PC and not a power supply though.
Not sure about the NC, but I can plug my Nook Tablet in with a "standard" USB and it appears to take a charge. This is with the USB connected to my PC and not a power supply though.
Benjamin Druhot
The Nook Color's power brick shorts the data pins, which is something the Nook looks for. As noted elsewhere, that's within USB spec; the Nook is just unusually picky in ONLY charging from something that shorts the data lines. Many other chargers put resistors on them instead, to make them communicate properly with various iDevices (again, as noted elsewhere.)
The PS Vita is another gadget that does the same thing. A Vita and Nook Color can use each other's chargers, since they're both looking for that data short, but not most other non-computer chargers.
I guess the bottom line is "If it fits, it ships." Presumably, slight voltage differences on the chargers: 5.0, 5.1, 5.2, don't matter.
http://www.therebelchick.com The Rebel Chick Jenn
I really need to get these new outlets!
Based on the picture they are iphone only. Iphone and android phone use different charging methods
They are NOT iPhone only. They're USB outlets and will charge pretty much any device.
Dude READ MY COMMENT…. Iphone and Android devices use DIFFERENT charging methods. For High speed charging aka AC Charging, iphone and android use different methods!
A iPhone charge will only 'slow' charge a android phone as it doesn't use the right high speed charging method.
The same in reverse, a android high speed charge will only slow charge a iphone!
BTW Hope you feel like a great big man for replying to a comment from over a year ago with ZERO value add
I'd say correcting a misleading reply IS indeed adding value. Yes, a year later, because people will read comments no matter what year we are in; I read them.
Either way, your current reply doesn't even address nor nullify what I've said; you actually confirmed it. If you notice, I never said anything about charge speed, (or that they would charge all devices as quickly as their original chargers or AC fast-chargers for that matter); I said those outlets WILL charge other devices, period.
And by the way, not all phones capable of being charged by USB are either iPhones or Androids. My current crappy Symbian doesn't give a crap about iPhone/Android charging methods and IS charged by those outlets, confirming once again they are not iPhone only. (Also, not all gadgets capable of USB charging are smartphones, but that is besides the point given the article's content).
By the way:
"For High speed charging aka AC Charging, iphone and android use different methods!" -> Talking about USB, there's AC nothing. It's DC current.
Anyway, that is besides my point. I won't argue about it anymore, since we're talking about different things. Whoever reads this later seeking information take it with a grain of salt and should be able to make its own judgment.
Hi, I have a Rc helicopter from silverlit which the transmitter includes 8 AA batteries which means 12 V of charging (the helicopter charges from the transmitter) but the provided a usb cable to save up the batteries but the thing that usb port is only 5 V and the helicopter charging from transmitter is 12 and the usb power hasn't the sufficient amount of power to charge it properly. any suggestions? I mean can I make my custom charger by buying some components and make a charger suits the helicopter without using the transmiter to charge? thank you very much..
http://www.mrseb.co.uk/ Sebastian Anthony
I have no idea what you're talking about. A USB socket should charge an iPhone and Android equally.
Clearly you shouldn't have been writing this if you don't have a understanding on how charging works for signalling high current charging. All chargers will charge at slow charge rate aka 500mah for android and iphone. To move to high speed aka 1000/2000mah the charger needs to signal the device it can supply this higher current.
Of course apple uses its own format by providing voltage values on the data lines and android uses the usb charging standard which is the data pins shorted. Clearly these are not compatible as one requires the data pins connected and one doesn't.
Great article, but it seems to me that the choice of micro-usb as the de-facto standard is a big mistake. I have had to replace 4 HTC phones because of problems with the USB port when charging. It is difficult to tell if a usb-micro plug is right side up (whatever that means) and it is apparently easy to bend pins etc.. in the port. Beieve me after the 2nd phone I was careful. The ohter issue is it doesn't appear that port/connector was ever designed to take the stress of using a cradle…
Love the universality of USB hate the choice of connectors.
http://www.cardinalphoto.com David Cardinal
DF–I have to agree that micro-USB is pretty bad as far as the physical connection. It's great that there is a standard, but I cringe whenever I need to put my phone in a car cradle, and usually have to try 1.5 times to plug the charger into my phone or tablet since there doesn't seem to be a standard for which way the jack should work. Thank goodness for my Touchstone wireless charging dock for my TP at least. More wireless charging options would be great, but the industry has been very slow to move after some initial promise.
http://www.mrseb.co.uk Sebastian Anthony
The standard for USB connectors is always 'trident up' — i.e. the USB symbol should face upwards. The trident on Micro-USB is the narrower side of the connector. But yeah, that's always been the problem with USB: There's no easy way to feel which way is the right way up (unless you can feel the trident… but YMMV…)
http://www.mrseb.co.uk Sebastian Anthony
It's worth noting that not all OEMs implement the 'trident up' standard tho' :P
http://www.cardinalphoto.com David Cardinal
Yes, that's part of my problem. One of mine is upside-down, so I always have to remember which one:-)
http://www.cardinalphoto.com David Cardinal
Yes, that's part of my problem. One of mine is upside-down, so I always have to remember which one:-)
http://pulse.yahoo.com/_EKNZKJ5LBTYYEUH4NCSPTGFGGE Eric
Could you be kind enough to list that device here?
I bought 2 cables without the trident (probably unlicensed) which still function fine after almost 2 years of daily use… (Thanks Buy.COM – saved a great deal)
All of my cables included with phones and a tablet have had the trident and it's always been designed to face up, alternatively, unless you smoke too much pot you should be able to remember which way it goes after using it 3-5 times…
(unless you have a memory disorder like Agnosia,
Alzheimer's, or something like Dimentia)
SA: The ones that don't go with standards probably don't have a large market share for that, and other reasons… RE: trident up.
http://www.cardinalphoto.com David Cardinal
Eric–I hate to bust your theory but the two devices (which I use every day) that are reversed from each other are the Samsung / Google Galaxy Nexus and the ASUS / Google Nexus 7. One has the flat side up and one down. So yes I remember which is which, in theory, but still recharging both at the end of the day requires flipping the connector, which seems more than a little silly to have to do.
http://www.mrseb.co.uk/ Sebastian Anthony
OR… you could flip the device!
Late to the party
Have you ever had a device that was "backwards from expected"? I've had several, and they mess with me forever. For a while I can remember "this device is backwards", but after a time I learn the orientation, and eventually I try to make it "backwards" which would be back to normal, which is wrong for that device! Aaah!!
Mathew Horne
Which way is up? Lol. On both my htc rezound and my Nexus 7, the larger, flat side of the micro-USB connector should be to the screen side of the device. In the dark, I just brush my thumb over the connector to feel for the… I'll call them the barbs. It was the same on the Droid X I had for awhile, but the other way around on the HTC Incredible. I would suggest just noting what is it like on your devices, and then remember. I regularly connect my connect my micro USB cables in the dark.
For my two bits about charging amperage vs devices verses wall chargers, none of my devices seem to care what they're plugged into. I can plug them into the HTC Chargers, the Motorola charger, the Nexus charger, or the USB connector on a power inverter in my car. i did notice that the Nexus 7 was consuming power faster than the computer could charge it earlier today; it's wall charger can provide 2 amps current vs the .5 of the USB port.
http://www.cardinalphoto.com David Cardinal
DF–I have to agree that micro-USB is pretty bad as far as the physical connection. It's great that there is a standard, but I cringe whenever I need to put my phone in a car cradle, and usually have to try 1.5 times to plug the charger into my phone or tablet since there doesn't seem to be a standard for which way the jack should work. Thank goodness for my Touchstone wireless charging dock for my TP at least. More wireless charging options would be great, but the industry has been very slow to move after some initial promise.
I've had the cable connectors fail several times, but that's exactly what they're designed to do. The cable side is designed to fail before the device side, so all you have to do is replace the cable.
Nice article
.To charge my cell phone in my car, I can buy a 10 watt USB car charger, a 5 watt, or smaller. The 120 VAC charger that came with the phone has an output of 5 watts. If I connect the phone to a higher wattage charger, will the charging circuit draw higher current or do these new smart phones control the rate of charging?There are LEDs on car chargers to indicate the state of charge. Are the status LEDs controlled by the charger or the phone? Are the data pins in the charging cable used with the charger?I am looking for a high quality, well regulated, surge protected car charger. I have lost a couple of dumb phones in the past after charging them with car chargers. Thanks.
I don't see it mentioned here, so I figured I'd mention it: using a low-quality USB AC adapter can be bad for your phone, especially if it can supply a decent amount of current. Low-quality adapters often either have wacky voltages (too high or too low), lots of ripple (varying voltage), or both.
Also, in the second-to-last paragraph, "two-USB-port Y-able" should be "two-USB-port Y-cable".
http://www.mrseb.co.uk Sebastian Anthony
Thanks for the info — fixed the post!
http://twitter.com/dhc1950 Dan Crawford
My "semi-intelligent" phone fried after I plugged it into a USB adapter in my car. After about 30 minutes I smelled an odor like overheated wiring. The phone battery was hot and the phone was inoperable. Trying a new battery didn't help. The SIM card was unscathed, so I forked out $150 bucks for a similar phone and was back in business. Lesson learned: all USBs are not alike, or the "U" for universal ain't universal after all. I didn't have specs on milliamps or other details about the USB car charging device. It came with a high-tech travel mug which had a USB cable to keep the coffee warm.
Probably this was a case where the car charger lacked adequate voltage regulation or selection, and allowed a voltage a bit higher than 5 VDC, perhaps even edging up to the nominal car electrical system voltage of 13.8 VDC (otherwise known as 12 VDC). Obviously not good. I have a feeling a lot of the car chargers use simple voltage-divider resistor networks to try and come close to 5 VDC, but fully nailing down what goes on with them is one thing that led me to this article. Maybe some use a zener diode at the output to regulate. Who can say?
http://www.facebook.com/people/Michael-Schmitt/100001798884431 Michael Schmitt
Check out this pdf from Texas Instruments: http://www.ti.com/lit/an/slva520/slva520.pdf
http://profile.yahoo.com/PQZP6LNZVUWX45WXYFMLZVCEZE Jim
I once had a professor at the University of Illinois that likened electronics to water flow. And I think this was one of the guys that invented the first computer or transistor. Volts was the water pressure and amps was the size of the pipe. So, if you have a bigger pipe (1 amp vs .5 amps), you can fill up the bucket faster. But if you have more pressure (10V vs 5V), you can break the bucket.
Scooter Ponzani
Sooo, I shouldn't charge my 5V devices with the 10V charger that came with my iPad. Trying to figure this stuff out. ("I'm a musician, Jim, not an electrician.") Great article and discussion, folks. It has helped.
http://www.mrseb.co.uk/ Sebastian Anthony
As far as I know, it's a 10 WATTS charger, not 10 volts. It should be fine to use your iPad charger with other USB devices.
Its a little grey and the 'standard' is conflicting…. Based on this
USB2.0 dedicated charger ports can deliver upto 1.8A so the kindle is within spec.
But this says its limited to 1.5A
Gotta love standards!!!
http://profiles.google.com/cblasko Chris Blasko
More like "gotta love peer edited websites like Wikipedia that are not authorities on any topic".
Tomer A
Hi, I would like to build some kind of "USB charging station", meaning to be able to charge many mobile phones simulataniously through an AC powered USB HUB or adaptor, without a laptop involved, only directly from the AC power.
My idea is to use as less AC connectors in order to be able to charge as many mobile phones as possible simulataniously and still at normal charging speed.
Do you think this is possible? would I need any special tricks or can it just work for example with an AC powered 10X USB hub that can be found on the market for charging 10 mobile device simultanoiusly and efficiently?
My goal is to achieve the ability to eventully charge 500-1000 mobile devices simulataniosly and efficiently, with a minimum of AC power points and minimum cables lying around and creating chaos.
do you think I could make it through that kind of system? or is a completly stupid idea?
do you have any other idea how to do that?
I'll be happy to hear your opinions and ideas.
http://twitter.com/AlwaysThinkin Luke Cushanick
Are there many monitors that come with charging ports? It seems like all mine monitors only supply downstream ports when they could clearly spare a little juice for recharging devices!
Rick Alleva
interesting that my samsung trender phone will now charge only with wall charger and not my car or newer high speed laptop usb port…it often goes on and off….but will charge with my much older (6+yr) laptop…go figure.
Rick Alleva
interesting that my samsung trender phone will now charge only with wall charger and not my car or newer high speed laptop usb port…it often goes on and off….but will charge with my much older (6+yr) laptop…go figure.
I just purchased a GPS USB unit and the only charger it came with is a car charger. I have a USB card reader with a cord that fits the GPS. Will it hurt anything to charge it using that cord connected to my computer? The charging light comes on.
http://www.mrseb.co.uk/ Sebastian Anthony
Yep, should be fine!
Simon Kiruiya
The current drawn is a factor of the voltage and the internal resistance of the device/machine being powered.
So, if the voltage is kept constant – you CANNOT damage your device/machine.
BUT if for whatever reason you raise the voltage – you fry your equipment
AND if you lower it – you risk doing the same especially for motors as they WILL draw more current and burn out their windings
Simon Kiruiya
The current drawn is a factor of the voltage and the internal resistance of the device/machine being powered.
So, if the voltage is kept constant – you CANNOT damage your device/machine.
BUT if for whatever reason you raise the voltage – you fry your equipment
AND if you lower it – you risk doing the same especially for motors as they WILL draw more current and burn out their windings
I have discovered there is a huge discrepancy in micro USB cables too. Some of them will charge my HTC Desire absolutely fine when using a wallwart charger and others charge it very very slowly, taking up to 2 days to fully charge it (and then only with the screen turned off).
Any ideas why this should be so? are some designed only for data transfer?
Perry Bond
Slightly different question. I have a RC helicopter with a USB charging cable. The battery in the helicopter states 3.7 volts, yet I know the usb port is 5v (or is it 5.1)
I charged it off a mains adapter (UK 230v) and it fried the the battery. The manufacturer says that I shouldn't have used a mains adapter, but just a computer USB.
Two questions
1. Is there a problem charging a 3.7v battery from 5v USB?
2. Is there a difference between PC's USB's and mains adapters?
I hope it is OK to ask this question here
http://www.mrseb.co.uk/ Sebastian Anthony
In general, every USB plug should work with every USB socket. I think 5v USB should charge a 3.7v battery just fine :)
This is something I've always wondered about.
Does the 5V source simply get connected to the battery terminals in the phone? Or is there some charging electronics in the phone doing DC to DC down-regulating?
I have tried charging my Samsung GS2 from most of the USB ports of a Dell Optiplex 990 SFF chasis, and all seem to be delivering the normal 500mAh.
Would I be able to get more charging current by adapting a two-USB-port Y-cable like those that come with external CD writers?
http://www.mrseb.co.uk/ Sebastian Anthony
Yes, probably! Try it and let me know if it works :)
Yesterday was the second time to recharge my Kindle ebook I hooked it up to the 1.1 USB jack on my 4 year old Dell desktop computer, turned on the computer, and was unable to get from the Dell screen to Windows XP. The computer was frozen. Alone and with the help of a Dell tech by phone we tried unplugging all USB connections, hitting F2, F8, F12, etc. After an hour, when the tech was ready to give up, I suggested unplugging and then replugging the ac cord to the computer while it was still operational, and this rebooting finally got me into Windows again. Why he never thought of this I do not know. Note this is the second time this has happened. The first time a Dell tech was successful but I feel certain he did not suggest what we did the second time and did not recall his solution. I was using the Kindle supplied USB wire. Nothing unusual. Sorry to be anecdotal here but I am not a computer maven these days. Why did this occur? And was I taking a chance on rebooting the computer this way? I did have the approval of the tech.
So, based on what I've read here, am I to understand that if I hooked my cell phone up to a charger that could deliver 1000 amps (but never over 5 volts!) it would charge just fine with no damage to battery or circuits?
http://www.mrseb.co.uk/ Sebastian Anthony
Yep, I think that's right :)
Umut "Turk" Kocaman
Thank you for the detailed article. I use my iPad charger to charge my iPhone and never had any problems. Now getting ready to go on a trip and do not want to carry my Sony HD Video camera charger which already has a small USB cable built in it.
Therefore I was hoping I would just plug that into my iPad charger and charge it without blowing it up. Should work, thanks.
http://www.mrseb.co.uk/ Sebastian Anthony
It should be fine :)
Steve Haworth
Cool article. Very informative. Well written.
http://www.mrseb.co.uk/ Sebastian Anthony
A drive _draws_ as many amps as it can take. The USB charger doesn't _force_ amps into the device. The rating on a charge is the max amperage that can be delivered.
Borys Modlinski
I charged my phone with 2.1A charger and i think it fried something because every time i use my phone while charging screen goes crazy like when i scroll it zooms and there is mirror touch (when i touch something at edge of the screen something is also clicked on opposite edge).
http://www.mrseb.co.uk/ Sebastian Anthony
Sounds weird… but sorry, I don't know if that has anything to do with the charger. I would guess not. But try it with another charger?
Tom Hayden
I think this is due to your charger producing a lot of ripple (search above). I have a cheepo charger that came with a desk-dock I bought from China on FleaBay that does exactly this to my phone.
+Tom Hayden – Thanks for the explanation. Yes, with some USB chargers, the device goes haywire and cannot be used when charging, so I have always been curious about the cause. So, simply buy a charger that can supply a steady stream of voltage and the problem will be solved?
I bought a USB 2 – 4 ports to connect my Samsung G Tab 2 7.0 (USB 1) using the tablet's USB to a generic keyboard. It does not work. I tried the USB on something else and it worked. I read that the settings on the tablet's USB should be changed from device to host; however, I could not find such settings on my tablet. Any ideas?
http://www.mrseb.co.uk/ Sebastian Anthony
I would guess there simply isn't enough power coming out of the splitter.
http://twitter.com/JexterTuazon Jexter Tuazon
Well then, can i use my Sony Ericsson EP800 charger to my iPhone 4 ? Charger:
100-240VAC ~ 150 mA 50-60Hz
5.0VDC = 850 mA.
Julian Lebensold
I just got my Google (Asus) Nexus 7. They say to only use their charger and their cable. Since the cable is also used to sync, would it be safe to use another (generic 2.1 amp) charger as long as I use a USB cable with the two data lines shorted?
http://www.mrseb.co.uk/ Sebastian Anthony
You should be able to use any USB cable to charge, and any (proper) USB cable to sync!
They probably just say 'use our charger and cable' for legal reasons.
Jack Pommer
Great article! I've read a dozen articles on this subject and this one is the clearest and most comprehensive. We have so many old power supplies laying around that I've been converting them into universal USB chargers/power supplies. With a limited knowledge of electronics, I've been worried about ruining a device (especially when altering supplies to meet the finicky Apple requirements for my kids' IPods). Thanks for the help.
http://www.mrseb.co.uk/ Sebastian Anthony
You're welcome!
"a standard downstream port, a charging downstream port, and a dedicated charging port. The first two can be found on your computer (and should be labeled as such)…
For a start, while PCs can have two kinds of USB port — standard downstream or charging downstream — OEMs rarely seem to label them as such. "
Very zen.
Oliver Ghalebi
With the device determining how much power to draw, I have a question in reverse. Can I charge a tablet (Nexus 7) that is supplied with a 2 amp charger, with a 1 amp charger, wall/car or otherwise. Do the device and the charger communicate? Or is the shorted data pin simply a signal for the tablet to draw as much current as it can.
http://www.mrseb.co.uk/ Sebastian Anthony
Yep, you can charge it with a 1A charger — it will just charge a little slower :) And if you're actually using it at the time, it might not charge at all.
Alex Worden
You clearly don't understand electricity from your statement:
This leads to a rather important
question: If you take a smartphone which came with a 900mA wall
charger, and plug it into a 2100mA iPad charger, will it blow up?
This isn't the important question at all! More important is if you attempt to plug your iPad into a charger that *can't* deliver the amps it expects. With regular transformers, this will result in the internal coils melting and causing a short-circuit, delivering 120v AC to your device (and frying it) and potentially it's current human user!
What I don't understand is… why doesn't this happen? Amps are a function of volts / resistance. How do these chargers protect themselves from delivering more amps than they're capable of?
Andres G.
And i think you dont understand transformer saturation. The internal switching transformer wil not be able to cope with the current so you get lower voltage and a hell of a ripple, translating in not a good charge or not charging at all and a bit of overheating in the coil but not enough to burst into flames (rated for that).
More in my concern is why some manufacturers don't recommend a 2A charger for their 1A rated products (ex: gopro, iphone). Isn't the charging circuit the one regulating the current? or they are not regulating the current at all and letting the charger choose the rate via the data pins (really dangerous)?
http://twitter.com/captiveinfla Jane Eskay Waldmann
I may have read too fast but I don't see where you say our iphones will blow up. You seem to be saying they won't. In "layman's" terms can our phones blow up and on what devices?
Great article and comments.
I have a wall charger that is rated at 2.0 amps. I have a tablet (PlayBook) that came with a 1.8 amp charger. I can plug a USB cable into the wall charger and the PlayBook responds with a lightning rod icon on the battery. I different USB cable, when plugged into the wall charger and the PlayBook responds with a plug icon on the battery. That, according to the PlayBook info means the charge rate is slow. How is the USB cable determining the charge rate? Same wall charger, same PlayBook.I've tested some other cables, some respond with the lightning bolt (fast charge) and some with the plug icon (slower charge). I can't see any markings on the cable that would indicate any difference.i just found a cable that would did not respond with any battery icon. Using an app, it indicated the battery was charging but at a very slow rate.Again, no indication on the cable that showed any differences.I know there are data only cables, but those have a clear marking of a battery with a line through it.
I just used a new wall charger I bought that is rated at 2.0 amps. Using the same procedure as I did with the 1.8 amp wall charger, I got the same differences between the cables.
Could it be that some USB cables are limited to how much current they will carry, perhaps because of undersized wiring in the USB cable?
http://www.mrseb.co.uk/ Sebastian Anthony
Hehe, interesting!
Yes, it would suggest that the wires themselves aren't capable of carrying 2 amps (though I don't know how the device would detect that? Maybe it measures resistance on the wires or something?)
Might be that the device is only set up to fast charge using dedicated charging cables? (Where the data pins aren't used.)
Thanks for the reply.
It might be that the higher capacity batteries draw enough current that the resistance of the wires reduces the voltage below a fast charge minimum. .
It isn't dedicated cable related, because the cables that gave the fast charge were from iGo, with a removable micro USB tip.
I looked at the many cables I have and was looking for some sort of code or icon that would indicate if it could be used for fast charging. I couldn't find anything at all, except the ones that indicated data only.
I have an app for my smartphone that measures if the source is charging the phone, it has 2 indications. One is 'connected to an external power source charging' , the other is 'charging but at a reduced rate' These are consistent with the lightning bolt icon and the plug icon on my PlayBook. Both the lightning bolt and the plug come on when the app indicates an external power source. No icons appear when the app indicates reduced rate, even though is is connected to an external source.
I have both a plug in power source and a battery power source rated at 2 amps. Each acts the same, so the device can charge from either a charger plugged into an outlet or a battery source, as long as it is rated at 2 amps or higher.
I'm more and more thinking it is smaller power wires in the cables that can't charge the higher power phones or pads. The standards industry should require some capacity indications.
http://www.cardinalphoto.com David Cardinal
Emsel — Some good sleuthing there. I have a box full of chargers & cords to go with my box full of electronics and it drives me nuts with all the different behaviors of combinations of — unmarked — cables with the chargers & devices. Unfortunately there doesn't seem to be a single uber-cable that will do everything right (for example a charge-only cable is sometimes a better bet for fast charging, but it can't carry data…), or else I'd just order a dozen of them and throw the rest away. Let me know if you find one!
http://www.facebook.com/kleinarne Arne Klein
My guess is that the PlayBook works the same way, or similarly at least, as HTC phones. To make sure they don't overload USB ports and potentially fry the entire controller, the phone requires the data pins to be short circuited. High Power chargers usually provide shorted data pins, but a cheap USB cable sold with a charger might have only the power wires, but not the data wires, so from the phone's point of view, they are separated rather than shorted. As a result, the phone limits itself to slow charging (500mA) to prevent itself from frying the USB port.
Any USB data cable (I.e. o e that can be used to connect a device to a computer) should be able to charge your device with high speed as long as your charger can handle it.
The same is not true for Apple devices though – as the article states, they require a specific voltage on the data pins to go to high speed charging.
I have experienced this too. Especially here in Asia, where one can find a wide variety of USB cables (including the cutesy "tangle-free" flat ones) but I have always wondered if there be any CABLE standard specifications too?
Using the official SGS3 Samsung charger & micro usb cable that came with my SGS3, I plugged a male to female USB cable that I had spliced so I could check current, voltage, etc of various usb devices. Anyway, I put my ammeter in series with the + power (red) line and I'm only seeing around 200-250maH on my meter! What is going on here? I've tried this with another meter (with the same result) so it doesn't seem to be anything wrong with my ammeters. Also, my phone was at 37% battery last time I tried this.
Here's a picture of how I have it setup…charger on the left, usb cable going to phone on right, ammeter is attached to the alligator clips.
Any help is greatly appreciated! Thanks!
Hi. Thanks for the article. 2 questions for you (or anyone else with the answers):
1. With most wall chargers having data shorted pins, why are so many CAR chargers WITHOUT data shorted pins? I don't understand that.
2. To work around all these car chargers with open data pins, you need a shorted USB cable. I've seen guides on how to cut into the cable and short the wires, etc etc – but how, if at all, is this any different from simply covering or removing the pins at the host connector? ie, with paper / electrical tape / plucking out with tweezers?
Tom Hayden
Shorted means connected together. Removing them is exactly the same as leaving them 'open' and so achieves nothing…
I have a question about this. I have a droid device, Samsung S3 and I have the charger it came with, the charger I had previously for my older phone (Evo 4G) and a random usb charger that I am not sure where it came from but it is from Motorola. every time I charge my phone with its own usb cable it charges but the battery as soon as I unplug it goes from 100% to 99% in a second. Same using my evo usb cord charger however when I use the motorola it charges a bit longer and 100% stays on for a while and the battery seems to actually last much longer. I tested it by unplugging the phone at 100% with its own usb cord then it went to 99%, I immediately plugged in the motorola one and the phone started charging then it showed battery charging from 97% still an hour later and still charging the phone. But I know this time it is actually fully charging the phone. Any comments in terms of some usb chargers being better than others? if so how do I know which ones. OH something I forgot to mention, this is when I have changed the battery, it's not the one the phone came with.
+maykel I am interested to know the answer too… my Samsung Galaxy Note goes from 100% to 99% within 10 minutes after leaving any USB charger (whether wall or PC) and some USB cables take forever to charge it. Case in point – I have a 3-metre long USB cable which takes 8 hours to charge my Note yet it only ends up at 80% #battery maximum.
http://www.mrseb.co.uk/ Sebastian Anthony
If I had to guess, that's probably a software issue. Or the battery not communicating with the phone properly. I doubt it has anything to do with the charger (USB chargers are very DUMB. All of the logic is in the phone, not the charger).
Most likely, it was a cheap battery — or the phone hadn't been programmed to 'accept' larger/non-standard battery sizes.
just to clear on one point as long as the usb charger i"m using has a 5volt output at 750m
A it wouldn't matter if it's a blackberry charger i'm using for a samsumg galaxy s..right..and as long as the mini usb port matched right?
http://www.mrseb.co.uk/ Sebastian Anthony
Yep, should be fine. 750ma will be quite a low charger tho'.
just to clear on one point as long as the usb charger i"m using has a 5volt output at 750m
A it wouldn't matter if it's a blackberry charger i'm using for a samsumg galaxy s..right..and as long as the mini usb port matched right?
Dear Sebastian. I have tried to charge my iphone 5 using a car charger, 2.1 A. This is the second time. Last night i did it and nothing happened. This morning, i tried it again,, and after a while it heats up. I am also using bluetooth at that time and turned my wifi on. The journey lasted around 45 minutes.
Is this normal?
Should i not charge it anymore using that 2.1 A output?
And is it safe for the phone itself after this experience?
http://www.mrseb.co.uk/ Sebastian Anthony
That's just a combination of the phone being charged AND the CPU/screen being used intensively. Phones are just like small computers after all — they produce less heat, but they still produce some!
If you ever use GPS + 3G + your screen turned on (navigation, for example), you will probably notice your phone getting pretty warm.
I am trying to make a iphone charger out of a shake generator for my school science fair and i am wondering if i need to worry about my battery getting messed up. Thanks!
I randomly found this article online and read it trying to find an answer to a problem. My HTC Sensation goes hay-wire on my gf's wall charger (think it's a generic charger). The phone will respond frantically to any input and will even randomly open apps and change phone settings on it's own accord etc..
I didn't see the cause of this particular issue reading this article, but if anyone has any ideas, love to hear it. Reply at firstname.lastname@example.com
Hi, I'm also looking for information regarding this issue. When I connect my Chinese Droid (W007 model) with a different wall charger the screen goes nuts and start to open apps and doing all kind of things on its own. I'm trying to find some information about what is the factor that produces this behavior, is it volts? mAh? Anyone?
http://jesse.la/ Jesse Wilson, MCM, CPM, ACPM
A ghost in the machine, most likely. Be nice to your phone… wouldn't want to get on his bad side!
http://jesse.la/ Jesse Wilson, MCM, CPM, ACPM
A ghost in the machine, most likely. Be nice to your phone… wouldn't want to get on his bad side!
http://twitter.com/konaya Benjamin Tayehanpour
Sounds like a bad charger. It probably generates enough ripple for the screen digitizer to go mad. You should stop using it, as it could easily damage your devices in the long run.
http://twitter.com/ArabiTam Tam A.
Is this arrangement of iPad-to-iPhone charging possible? (see link for photo)
http://www.mrseb.co.uk/ Sebastian Anthony
Possibly. Depends if the iPad is outfitted with the hardware/software to become a 'USB host'.
I would guess yes, it's possible.
helpful article thank you
http://www.facebook.com/people/Daniel-Watkins/629637578 Daniel Watkins
So basically these devices that use lithium ion batteries and USB chargers, the chargers act as a hybrid between a constant voltage and constant current charger?
If the charger is capable of supplying whatever current the battery could suck up at a specific voltage, then it would be a constant-voltage charging process. But, since I guess a lot of these devices charge faster with a charger rated for higher current, this leads me to believe that the voltage going into the device is actually less than 5V (kind of shorting out the charger in a sense), so most of the time it is a constant-current charging process until the battery starts to get charged up and resistance of the battery increases and the charger can then actually output 5V, then it is a constant-voltage process.
Cool stuff.
If an expert could elaborate on how these cheap lithium ion battery chargers work, including the cheap camera battery chargers on ebay where you stick the battery in the 2-pronged charger and over time the light changes from red to green, email me at firstname.lastname@example.com
http://www.facebook.com/people/Joseph-Perkins/100001836663921 Joseph Perkins
Basically, look for chargers of decent price (in the US, these will be about $15 to $25) or a name brand (usually one and the same – IO Gear, Logitech, etc)
http://www.facebook.com/people/Joseph-Perkins/100001836663921 Joseph Perkins
Most laptops can power 2.5 inch drives off their ports (the MyPassport or HP drives, for instance). These are usually "USB 3.0″ That's simply because 2.5 Inch drives only need 5V while 3.5 Inch drives frequently need 12V for the motor and either 5V or 3.3V for the interface (PATA versus SATA power schemes).
http://www.facebook.com/patrick.gallagher.7923 Patrick Gallagher
Seems like my Apple USB wall plugs blow up after my brother connects his Android to them. I see by this article it is not possible. Just a coincidence? What is the most common culprit to blowing up my apple plugs?
According to one of the comment it will, the device is requesting the amp from the wall plug not the other way round.
Genesis Amadeus
my Lenovo Ideatab a2107 comes with a Huntkey 5volt 5amp charger. Diagram shows data pins shorted.
Thanks for the article. Question:
can I plug 6v-300ma mini-speakers to a 5v-150-2000ms usb wall plug for iPad?
http://www.mrseb.co.uk/ Sebastian Anthony
Probably yes.
Though I'm not sure about the voltage mismatch. USB should always be 5V.
cody bratcher
Electrical Shock causing Death (is it the High Volts or the High Amps that do the Damage?)= The Amps are the Killer….
US A/C Home Voltage Standards= 120 volts
Other Country's (European) A/C Standards= 240 Volts
European Standards are Far more better, efficient use etc.
So this Simple Little Adapters make it more confusing saying that more then 5 volts cause so much damage while the amps are not really an issue and it decides for it's self…..
Once I plugged my smartphone charge cable into the plug hub that came with my ipad. After charging overnight, my phone would show that it was fully charged, until I unplugged it from the charger. It would last as little as 30 minutes on the charge. I did this for about a week, and was getting ready to return the phone and/or battery thinking it was defective when I noticed I was plugged into the wrong charger. I'm not techy enough to understand why, but as soon as I changed my charging cable back to the plug in that came with it, all was well again….
http://www.facebook.com/people/Michael-Driver/100001568136916 Michael Driver
That's because it was an Apple product built to APPLE'S standards. In other words obsolete proprietary hardware standards that only Apple hangs onto, which is one of several reasons that Apple is soon going to be in the same place they were not so very long ago. A small, unregarded, niche market company that all but a few hardcore fanboys pretty much ignore. They're already there with their computers. They only have 10% of the US computer market, and 5% of the global computer market. This is due to gross overpricing, overrated hardware, and their computers being nothing more than very expensive status symbols. They're flooding the market with those expensive toys called iPad, just like they did with the iPod. Look where the iPod is now. Dying. IPhone is crap compared to Samsung's offerings. Apple is simply resting on the name Apple. So, in conclusion, it really doesn't matter if they don't comply with the USB standard, they'll soon be of no concern.
Theo Jaklitsch
I got a cheap (maybe knock-off) apple AC-Usb adapter. Used it with my Nexus S and while charging, the display would become unusable thinking I had touched the top left of the screen when I had really touched bottom right, etc. Eventually I found my 3G antenna having trouble connecting to the network even off-charger, I am pretty sure that it was the adapter that did this but I haven't the equipment to check.
TL;DR : Used cheap apple adapter with my Nexus S, ended up with damaged antenna.
After reading these comments about mini usb i suddenly realised what a mob of brain dead lazy loosers people are becoming.
How do they plug power leads in to a wall socket ,or are they from china where they have vertical plugs,
I have eyes just look so easy
http://www.facebook.com/GwiezdneSwiatlo Bartłomiej Fulanty
Try doing that in a dark bedroom, with wife sleeping and when the only source of light is your cellphone.
frank nstake
also try learning the difference between loosers and losers.
frank nstake
also try learning the difference between loosers and losers.
http://www.facebook.com/margaretas Margaret Simpson
Thank you – This is, by far the most helpfull explanation about USB charging options that I could find.
http://www.facebook.com/RaNdYMoSkO Jorge Ortega
So if i get this right, this means i can use my phones AC wall charger (Input : 100-240VAC 50-60Hz 150mA, Output: 5.0VDC 850mA) to charge my GoPro Hero 3? I wanna use it with the usb cable that i got with my GoPro
question i have a nextel i335 when i use a usb 1.0 or 2.1 amp usb port it will say device connected but will not show it as charging. the wall chargers specs says .55 mA so i was wondering if i need a charger with this spec. the thing is i have done searches for i335 compatible chargers and have seen results for usb that use the 1.0 and or 2.1 a spec
http://www.facebook.com/steve.porter.5437 Steve Porter
Will charging your phone with your computer usb port everyday damage your computer?
http://www.facebook.com/benjamin.p.christiansen Benjamin Christiansen
I just purchased the Nexus Orb (The Nexus 4 Wireless Charger) from the Google Play store. It's input is 5Vdc/1.8A and output is 5Vdc/1.0A. The connection is micro usb. Can I use a car charger to power this device?
http://twitter.com/ptrsmith4 Con Trik
Is it possible to damage or even completely destroy the usb port of my laptop when I use it in order to charge the battery of a tablet, by the extra ampergage? Thank you very much.
http://twitter.com/ptrsmith4 Con Trik
Is it possible to damage or even completely destroy the usb port of my laptop when I use it in order to charge the battery of a tablet, by the extra ampergage? Thank you very much.
Talichuba Walling
Hey, I would like to post a comment down here related to USB. Recently, I had an iPhone problem. When I was browsing the internet in my iPhone 3GS, with my phone connected(charging) to my laptop via USB. Suddenly, my phone just went blank(dead). It won't start…I had tried almost everything(though info from the net)…but I was unable to get it working.
So, I took it to the repair shop…his diagnosis was that it was due to over charging via USB(it seems the charge from the PC's USB is inconsistent), it is still in the repair shop…the problem later on was the dock connector was damaged, and the battery damaged(actually the battery was a new one). Anyway, all I want to ask is, is there a risk in charging from the PC's USB overtime(to long/frequently)? Please explain, what is the better option for my phone…wall socket/usb?
Anticipating your reply. Thank you.
I had a nexus 4 and i charged it with my friend's samsung music player's charger which is also a micro usb charger. When i woke up in the morning, I felt a burnt smell and it came from nexus 4 :( :(. I am heavily disappointed. Will it cover under warranty? According to your post,, it should not affect the phone hardware right?
iTech Mark
Good evening, I very much appreciate this article. We are working on a project for a New Porsche dealership and we are playing with the idea of installing custom charging stations into the furniture for clients visiting the the store and waiting for service to be completed on their car.
I am having a tough time locating a company that can sell me quality hardware to install this into custom made furniture?
Any help or direction would be great!
Mo Khera
Excellent and very informative article – and most of the commenters seem to have the right attitude too
Hafeez Luqman
My Gigabyte motherboard has "3x USB Power" feature and its charging my phone very fast. Thanks for this article.
Hafeez Luqman
I observed that cables also matter in charging phones quickly. Some cables don't charge a phone quickly.
http://www.facebook.com/nilcouac Happy Neil
Many thanks for this article, this is very helpful and explains why old device are not compatible with new usb wall chargers.
Antonio Mastrolia
I noticed that on some laptops, usb-charged hard drives fail to start if the laptop is on battery. As soon as you plug in the charger, it seems that the drive has enough amperage and powers up. Why is that?
I Spawn At Home
Nice article. I read it because I'm trying to get some documentation regarding making my own solar energy panel and connecting it to my phone for charging :). Got any tips? xD
But yea, nice article nonetheless
This is exactly why you MUST use the USB Y Cable provided with the Fujicell 500F electronic battery charger and external power source. It will charge not only AA & AAA batteries but also run and extend talk and operating time for up to 11,200 mah of storage power for I-Phone 4 / I-Pods, Androids, Tablets, Readers and many more devices – but you have to use the cable that comes with it + plus an applicable micro USB adapter.
It has universal voltage adpater and so you can use it workdwide 100v in Japan to 240 volts in the UK or Australia.
Some have tried to use Apple connectors instead of rthe supplied cable. The Apple resistors in their connector cables are made deliberately different so that you may think you have to buy more expensive Apple chargers and accessories – but you dont.
At $18.98 on eBay and I think Amazon too, this U/L listed charger is a steal and a must have if you are on the road and not near a power oint or in the middle of blackouts or power cuts.
hi and thanks for the great info. you mentioned that the age of phone/phone charging may be affected with high amp charging.
I am wanting to buy a wall charger that has max 4000mah output for my tablet.
would that significantly affect a tablet over say 5 years period?
what is your recommended charging output amp for a charger for a tablet.
I have the exact opposite issue with my samsung smartphone: it charges fine when it is hooked up to the usb port on a real computer, but won't charge with either a car charger or the wall charger that came with the smartphone. Any ideas? I am puzzled.
http://www.nicodetourn.com/ Nico Detourn
I did a search for: usb ac adapter charger voltage determining.
This article was at the top of the results and was just what I was looking for to make sure I could both charge and power my Sony ICD-SX712 voice recorder using the AC adapter that came with my HTC Incredible without blowing it up.
Yay! Thank you.
Please confirm: I can charge mobile phone that came with 0,7A charger using 2,0A charger and this will not harm either the phone, battery or the charger and it will not shorten the life cycle of battery (that means that my battery will not die sooner, it will last for lets say 2 years as it would if I would be charging it with the original charger). Is the above stated correct? And following this: I it also ok to charge mobile phone that came with 2,0A charger using 0,7A charget and this will not harm either the phone, the battery and its life cycle nor the charger? Thank you for you answer.
What about the opposite: Charging with an under-powered charger (e.g., charging an iPad with a 500 mA charger, or a smartphone with a 700 mA charger). I understand this means slower battery charge times, but is this good for the lithium battery's life-span? or does it not really matter? The the amprage is too low, will it damage the battery?
Luke O'Malley
I have a 'wire' to connect my 'cigarette lighter' to a min USB plug. It is used for my TOomTom. Will it be safe to use on my smartphone?
Thank you . I got a dual usb car lighter adapter with 2 ports. 1st with 1amp & 2nd with 2.1amp. So this should be safe to use with 1amp GPS & 1.5amp camera?
Thank you
I actually did blow up a Samsung phone about 5 years ago by trying to charge it with a car charger that I later found out was meant for a usb powered self-heating car mug. The phone popped loudly, send out sparks and stank of burned circuitry. I was pissed that my boyfriend had told me to charge my phone with this charger. I don't know what the amperage wad but if it was meant for a heating device then it was no doubt putting out enough juice to fry the insides of my phone.
Amperage doesn't matter. It can't force current through the device. It probably had a non-standard voltage or pinout.
Further, if you want to calculate how long it will take for your
charger, the equation is mah/amps*.06 =
minutes to charge. For a 4500mah battery with 2 amp charger., 4500/2 * .06 = 135 minutes to charge.
SoftwareHardware24 .
Nice Article,
i load my phone mostly with a mobile battery charger. It loads with 2.1A and the most normal cable are slower.
This is my external battery: http://external-battery-charger.com/external-battery-charger/anker-astro-pro14400-mah
The reason standard data usb ports are also used (insread of making all usb ports charging-capable) is noise. The power level at the port introduces noise. Circuits have to be specifically engineered to compensate for the RF noise of nearby power (literally only a few milimeters between the outer and inner pins). Also, power has to be routed to that port differently inside the computer so as not to affect nearby circuits. Smart charging ports also have internal switches to make data transfer more noise-free when the connected device is fully charged. This is why on some tablets the touch screen acts erratically when the usb is plugged into cheap and noisy chargers. If you look at a motherboard that feeds both usb data and charge-capable usb ports there is a visible difference in the adjacent electronics and circuitry. This is also why really cheap laptops rarely have charge-capable usb ports. The noise introduced affects the transfer rate, though the file integrity is typically handled by the software. Part of the reason 3.0 is so much faster is the use of more pins, and you will notice the data pins, specifically the + pins are further away from the ground and power. Plus 3.0 ports are better designed for noise inherently.
Jill Shilvock
Not really connected to your interesting piece, but relevant I feel, why is the design of the mini usb charger crap? I have one where the lead is not attached to the plug and unless I sit and hold it in place it doesn't make proper contact. Many times Ive left it charger only to return to find my phone and andriod tablet dead. It is driving me mad.
mabel leong
There is a phenomena where phone lithium ion battery charged with usb 2.0 cable causes overcharging which cause chemical damage to the structure of the lithium battery. Can this be prevented by monitoring the charging process? or is the structure will be damaged whenever it is charged with a significantly higher voltage due to the heating effect of the charging process? Had a Li ion battery swelled up after a few months of charging with a usb cable connected to laptop. T_T
Ed Burton
I have a wireless mouse that uses a micro-USB charger. I left the cable at work but I have my Android phone charger sitting here also with a micro-USB. Feeling adventurous I plugged it in and sure enough the charging LEDs light up! All well and good. However, I do remember only rechargeable batteries used to have large warning everywhere about only using the charger supplied. Is there any danger charging a device supplied with a USB cable charger from a wall mounted phone charger? The wall charger outputs 5V and 0.7A so I suspect everything is fine.
Not sure of the where and whys – but whilst you say you can't blow up a device – I on 2 separate occasions ( ie 2 phones) a few years back managed to 'fry' my US Motorola Atrix whilst trying to charge them in the UK – both times had to go an buy a new phone for the rest of my trip.
I've had a couple of phones that will not charge from one of the wall wart USB power devices. Sometimes they cycle through on/off settings, and more usually, they ask me to choose what type of data connection I want. So, the phone thinks the charger is a computer, and it will not charge. Other devices charge from the same connector.
I'd like to know what type of device is needed to guarantee a charge-only connection.
James Kenny
Twice I have plugged in a USB cable connected to a pc, to my Chinese phones, and both times the phone will not then recognise USB as a device and will only charge when powered off.
What's going on when some smartphones display that the connected charger is not recommended? What aspect of the charger would the phone be complaining about and would it be bad for the phone or just maybe slow down the charging process?
Taha Benashur
Is it a good idea to plug a usb hub in a 1amp 5volt usb port and plug 3 devices in the usb hub to charge in the same time ??
Rick Jenkins
Awesome explanation. This answered quite a few questions I had. Thank you!
deipak tanwarr
When i am charging my android phone through USB charger on a PC running on Windows, what is the possibility of my phone getting infected with a virus (assuming the PC is infected)?
Ethan Jarlewski
Your comment about "downstream blah blah ports 'should be labeled' " is pure BS. They are NEVER labeled! I've been in the industry 30 years and NEVER have seen such labels. I want to smoke whatever you've been smoking. Unless you may have seen some such labeling on Macs – but, from my experience, there's never been any ports labeled "downstream" anything – and I do see that you've given an update (albeit in an Appendix) to signify that fact.
http://www.ilogic.gr/blog NLS (NULUSIOS)
Been in the industry 30 years too (actually EXACTLY 30 years this year) and indeed have not seen most (like 99.99% of motherboards/laptops label the USB ports. I HAVE seen motherboard AND laptops though (rare but do exist) that label some ports as sleep and charge or "usb charging" ports. I distinctly remember at least one motherboard (and the mode was even selectable by a jumper) have that.
I post for another reason though. You need to cut down on sugar a bit.
Sharon Jarrett
I have a Samsung galaxy s3 phone (²yrs old). I have a 1A/5v USB wall charger that I used a 3-4 ft cord with. I bought a 10′ cord and found that is t seemed as if it wasn't charging. My question is if I increase the wall charger to 2a will it work for the 10′ cord? What do you suggest I use? Does the length of the cord effect how fast a device will charge using aclwer amperage?
Given Ohm's Law, how is it possible for any device to draw more current at the same 5 volt supply? This handshaking seems a bit anal, given that it would be easier to install a limit on the supply than on the draw. All of this gives dumb dongles more credit than they are due, because they are smarter and more generous than a smart USB connection.
http://www.cardinalphoto.com David Cardinal
Lower impedance is one way to increase the current. AFAIK, the current is limited by the host (for its own protection if nothing else). I assume the handshake is an additional capability on top of that. Maybe a HW designer can chip in with why both are needed?
Of course, a lower impedance (or resistance) in the load would necessarily draw more current. IMHO, it is silly to worry about how much current the host device can provide when the maximum under USB1, 2, or 3 is 5 amperes, a minuscule 25 watts. Things might get more dodgy when USB 3.1 pushes the supply voltage to 12 or 20 volts, but then, 3.1 is a new standard which few USBs currently comply with.
I see a lot of physics missconceptions in this forum. If you can understand physics, you can understand how charging works… So kids, it all boils down to the laws of electric charge:
1) The forces in nature will tend to neutralize each other to reach an equilibrium.
2) Electrons will flow trough the path offering the less resistance.
This are the reasons why both lightning bolts and your cellphone actually works…
Your cellphone battery is rated for 3.7Volts and the USB port standard is 5 Volts.. this is what makes the electrons flow from the charger to the battery. Since there is a 1.3 volt (potential difference) between the two parts, electrons simply go to where they should fill the gap.
Now that you understand why electrons MOVE from one side to the other, just count HOW MANY electrons are moving.. this is given by the AMPS and will mainly determine at what rate will your battery recharges.
You can charge an ipad´s battery in 1 month with a 20mA source… or you can charge it in 4 hours with the 2100mA source… it doesn´t really matters, as long as the voltage of the source is slightly higher than the battery, in order to to keep the electrons flowing towards the battery.
Offcourse… materials suffer and will take damage if they are exposed to more power than they were designed to. This is the reason why your ipad can take up to 2100mA and not 20A (thou it would be cool to see it charged in 9 minutes)…
"Your cellphone battery is rated for 3.7Volts and the USB port standard is 5 Volts.. this is what makes the electrons flow from the charger to the battery"
This statement is completely wrong. LiPo cells are a nominal 3.7volts, but can reach as high as 4.2volts. The charge circuit is part of the phone, not the thing that you plug into the wall. The 1.3 volt difference between USB and LiPo is nothing to do with how the battery charges.
Thank you for this article. It's a big help for those wondering why.. I would like to suggest to buy a good USB Charger for your phone. It's available in amazon store.
what's with micro USB pin connectors breaking in such a short period of time which would be the strongest type to buy that will actually last long?
so it dosent matter at the end of the day ?
Choe Technology
CHOE Qi Wireless Charger Kit for Galaxy S4 only on $35.00 for more info. take a look on Amazon ChoeTech Store – http://www.amazon.com/dp/B00DRB2ENK
Is it ok to charge my new (well almost new) kindle Fire with my Samsung Galaxy Y phone charger?
David Cheang
Can anyone help advise on this please? I plan to do a 2week trek and will need to charge my camera batteries on the go. Thinking of using a solar panel to charge a battery pack like this: http://www.amazon.co.uk/EC-TECHNOLOGY%C2%AE-Ultra-high-Thunderbolt-Incredible/dp/B00F5Q4F0U/ref=sr_1_1?ie=UTF8&qid=1402655004&sr=8-1&keywords=portable+battery+pack
And then in turn use the pack to charge my camera battery which is a fujifilm NP-95 like this: http://www.digitalmediastore.co.uk/batteries/camera_batteries/fujifilm/Fujifilm_NP95_compatible_rechargeable_battery_from_DotFoto__WIN-FJNP95B-D
It will all be via USB connections. Anyone see potential problems arising? Don't fancy this exploding in my back pack if it is a risk.
Mark Wheaton Rheault
I just plugged my iphone 5s charger in over night at a resort – heard a loud pop in the middle of my sleep – smelt burning. Looked everywhere but could not see it so I thought maybe it was a neighbor in the connecting unit – nope. It was my brand new iphone 5s charger completely covered in black. Burnt.
Edgar Suazo
u probly pluged it into the rong wall socket they have 220 volt wall sockets that burn anythin u plug into them .those sockets are reseved for certian things
Power supplies are rated AC 100-250v 50-60hz, so its unlikely.
Luka Krnjaic
YEAH but if i put mobilephone like ALCATEL into the computer for charging , does battery or mobile expload
Could you do a tear down of the more advanced usb car chargers, it would be interesting on how these are made and work
Ian Fischer
I have heard that charging with a higher than spec charger shortens the life of your battery and by extension the life of your device because you are over powering it. Is this true?
The story goes, the iPad requires extra current to charge when the screen is on vs off and That Steve jobs had all the MacBooks changed to detect an iPhone / iPad and automatically dump extra current to it. As far as I know every Mac since the iPad 1 does this. There is no way to disable this feature, that i know of. You can see this feature by going into about this Mac, system report and clicking on USB
On a standard device it will say
Current available 500ma
Mininuum current required 500ma
When you connect an iPhone it will say
Extra current 500 ma
When you connect an iPad it will say
Extra current 1600ma
Ross Banick
It's technically correct to say the wall warts can "output" 2.1Amps, but, for the layperson, it should be noted that these non-standard devices won't actually source that amount of current unless the device being charged "needs" it.
The article should explain to the layperson that having too more "current output" capability than you need isn't the same as having too much "voltage output", than you want.
Most, if not all charged devices, will have their own current limiters (if for no other reason as to not unduly heat up the batteries), so, in practice, what you want is the highest current output rating (usually in watts, which is the voltage times the current) you can get.
Just be careful, manufacturers are sneaky when listing output capabilities. If it doesn't specifically say that the wattage is for each port simultaneously, then you must assume that the wattage is divided by each port. Hope this makes sense.
Addison Dorrance
So like it says "5 volts" if iI charge it w/ 6 volts worth of aa batteries/6 volt Solar panel will that 1 volt make a difference?
http://socialentrepreneurship.change.org/actions/view/twenty-first_century_metric_america_in_your_state BeholdersEye
I would like to know how to charge and plugin a keyboard/mouse/trackball on the same port. They only give you one USB port on phones or tablets. And you can not say it can not be done, cause if you connect your phone/tablet to a desktop computer, it will charge and you can transfer data between the two at the same time…so why not a trackball if you add power to it, like a powered hub…..
what id you connect a Multi USB hub to one port and charge more than 2 devices technically from the same USB port?
i had dposted a comment earlier i wonder where that goes?
Bruce Ratcliffe
GREAT details! I have a slightly different concern: I'm building Pb-acid battery-powered
cell phone chargers for my students. These batteries output 6 (not 5) volts. Will 6 V damage a cell phone that is supposed to charge at 5 VDC?
Thanks for any insight,
Bruce Ratcliffe, Fresno
One thing not mentioned in the article is that not all USB cables are up to the task of providing a current over 1 amp. This was something I learned when the higher current car chargers started appearing. I don't remember the gauge of wire required for higher current USB, but not all USB cables have the heavier gauge cable for the two power lines.
Hi, thanks for this great article but I have some doubts. Since you mention USB 2.0 max current is around 500mA. So, even if we are using 1A or 2A charger, it is still charging at 500mA? The charging current is still 500mA, not 1A and not 2A. How can the charging be faster?
Hope to get some answer to this question. Thanks.
Your mother
Suck it
Eureka Gomez
I just recently bought my usb 2 data cable for my apple devices from http://bit.ly/storeapple . Do you think it is still good or I should stop using it or it still depends on the adapter I am going to use? I use the original adapter though. Please help me. Thanks.
Thank you for the explanation! Do you know if a cable like SONICable will work? It has a button to switch on and off the data lines. In a way switch between being a cable for a standard/charging downstream port, and a cable for a dedicated charging port. But will the computer really sense the difference, i.e. if no signal provide 1500 mA instead of 500 mA from the USB port to the mobile phone? Sounds doubtful to me…
the different voltage will blow your phone, the Amp number won't do anything.
shubham jain
well explained sir…….but my only question is…..how much (maximum amperes) charger, a standard smartphone can support ???
Barbara Fuentes
Interesting and useful. I have a TicToc music player that's only ever charged on computers, never wall chargers. Suddenly since the Lollipop 5.0.2 (Android for Nexus 7) update, my tablet is nearly as finicky. Reading this article helps me understand this. I wonder if my laptop will charge it while turned off? Worth a try…


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Tuesday, August 23, 2011
Flatbread Pizza Co.
Finding good gluten free pizza is sometimes difficult. Finding good gluten free pizza on a tropical island, kinda increases your margin of difficulty. Well, Maui sunseekers, search no more. I have found something spectacular. This wood-fired pizza joint is the bomb. Okay, did I just say that? Well, it is the bomb. So there. Flatbread offers a gluten free crust which is amazing. I ordered the kalua pig pizza. It comes will all natural, local ingredients like goat cheese, homemade BBQ sauce, pineapple, red onion, and shredded pork. OMG. This was unreal. It melted in my mouth. The flavours all complimented each other perfectly. I couldn't stop eating! My son and I polished this baby off in no time. Which meant: no leftovers:( Possibly the best pizza I've had...ever. Which begs the question: Can I sell my house to afford weekly airfare just for pizza?
In the cute little town of Paia...don't miss the surfers at nearby Ho'okipa beach. And DON'T miss this place!
Posted by Nicole Rogers at 8:27 AM
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On Wednesday, February 23 at 11am (Pacific) AASHTO and FWHA sponsor a webinar on a new report, "Reducing Greenhouse Gas Emissions from U.S. Transportation"issued by the Pew Center on Climate Change and commissioned by the National Cooperative Highway Research Program.
The report identifies reasonable actions across three fronts - technology, policy, and consumer behavior - that could deliver up to a 65 percent reduction in transportation emissions from current levels by 2050. Authored by David L. Greene, of the Howard H. Baker, Jr. Center for Public Policy and Steven E. Plotkin, of Argonne National Laboratory, the study provides three plausible scenarios of improved transportation efficiency and reduced GHG emissions through 2050, with technology progress and policy ambition increasing from the first to third scenario.
The webinar presenters will be report authors Greene and Plotkin, and also Paula Hammond of the Washington State DOT, who will provide commentary on the implications of the report for state DOTs.
The webinars are free and open to the public. Please register in advance here: https://www1.gotomeeting.com/register/966945377.
Labels: climate change, green transportation
Posted On 2/17/2011 10:00:00 AM by Larry Ehl |
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The opening scenes of "The Spiral Staircase" where we first meet Helen (Dorothy McGuire) takes place in a hotel ballroom that has been set up as a make shift Movie Theater. The hand written sign states there are two showings, 4:30 and 7:30. There is a silent film flickering on the screen, a woman is on the piano accompanying the storyline. In the back, we see a "projectionist" hand cranking the film through the projector. Finally, there is the audience sitting on hard wooden benches enthralled by the flicking of this infant art. It is a great scene for film lovers who get a glimpse at what it was like when the movies were young.
While the movie is playing, up in one of the hotel rooms a young woman is changing her clothes, the closet door is open and we get an eerie feeling she is not alone. The camera moves toward the clothes and suddenly we can sense there is someone in the closet. The next shot is an extreme close up of a wide-open eye, almost hidden between the hanging clothes. In the eye we see the reflection of the woman who is about to be murdered.
It's a brilliant opening to a magnificent thriller that Hitchcock would have been proud to have made. Instead, the film is the child of another master of dark suspense, Robert Siodmak and the master of shadows and light, Nicholas Musuraca. It is Musuraca's evocative lighting, his painting shadows on the walls, combined with the masterful camera placement of Siodmak that make this film so thrilling. A combination of low-angles and stark lighting against wrought iron fences and circular a staircase creates an eeriness that sends chills down the spine. The entire film is painstakingly crafted and well acted. The film is both a throwback to works like "The Old Dark House" where there are drenching rains, crackling thunder, candles that mysterious blow out, and the more current cinema of directors of recent thrillers like John Carpenter.
Though the plot is standard fare, the fine direction and magnificent cinematography make it all quite terrorizing. Helen is a mute servant for the sick and elderly bed-ridden Mrs. Warren (Ethel Barrymore). Also living in the mansion are the ill matriarch's womanizing son Steve (Gordon Olivier), her stepson, Professor Albert Warren (George Brent), his assistant Blanche (Rhonda Fleming), an abusive old biddy of a nurse (Sarah Allgood) , Mrs. Coates the housekeeper (Elsa Lanchester) who likes to hit the bottle and her groundskeeper husband, Mr. Coates. There is the new doctor in town, Dr. Parry (Kent Smith) who wants to take Helen to Boston for treatments that will hopefully restore her voice, the result of a childhood trauma.
When another beautiful handicapped woman is murdered in town, the third in a series, it becomes apparent a serial killer is on the loose focusing on "imperfect" women. Fearing Helen might be next, Mrs. Warren tells her that she should leave town immediately, go somewhere safe. However before she can get out……..well, let me stop here, I don't want to spoil it.
Most of the story takes place inside the Warren's large Victorian style home. The murder suspects are plentiful. There is the womanizing Steven who is having a fling with his brother's secretary Blanche, or maybe it is the "kind" Professor Warren, or maybe it is the groundskeeper Mr. Coates who sneaks leering peaks at Helen. Who the killer is becomes fairly obvious but this does not distract from the fun.
The movie is based on a novel called "Someone Must Watch" by Ethel Lina White who also penned the original story that was the source for Hitchcock's film, "The Lady Vanishes." The novel was first turned into a radio play with Helen Hayes. The screenplay was written by Mel Dinelli who would go on to write other suspense films like "Cause for Alarm", "The Suspect" and "Beware, My Lovely." The screenplay would not only change the novel's setting from England to New England but would also move the setting back from contemporary times to the early turn of the 20th Century to give it a more gothic feel. At one point, Ingrid Bergman was considered for the lead role.
The cast is a good one starting with Dorothy McGuire's performance as Helen. Though mute, McGuire manages a wide range of emotions in a compelling performance. Surprisingly, Ethel Barrymore was nominated for an Oscar for her role as the belligerent bed-ridden matriarch of the Warren family. Not that she is bad, she's fine, it just seems like the role did not require the best use of her talents. The rest of the cast includes George Brent as the stepson, Gordon Oliver as Steven her playboy son, Rhonda Fleming is Professor's secretary who has a fling with Steven and a rib tickling performance from Elsa Lanchester as the inebriated Mrs. Coates.
"The Spiral Staircase" became a blue print for many disabled woman thrillers that would follow in its path, "See No Evil," "Sorry, Wrong Number," "Wait Until Dark" and "Whatever Happened to Baby Jane?" to name a few. The film was remade in 1975 with Jacqueline Bisset and again in 2000 as made for television movie with Nicollette Sheridan. Almost needless to say neither reached the level of the original film.