There are several reasons you should have an isolation transformer. They can prevent ground loops and also prevent a device under test from having a DC path to ground (or isolate an oscilloscope from DC ground, which can be dangerous in its own right, but that’s another discussion). [Tanner_tech] noticed that finding ballast transformers for sodium vapor street lights is getting easier as more street lights move to LED technology. What to do with these transformers? Build an isolation transformer, of course.
Of course, your dumpster transformer might be a little different than the one shown in the post (and the video, below). [Tanner] shows how to work out the leads you need. A little wood work and a PC power supply case finished the project.
Judging from the comments, some people take [Tanner’s] talk about safety as an implication that a transformer makes working on mains safe. It doesn’t. It makes it safer if you know what you are doing. Working with high voltage isn’t a place to learn by doing.
If you want some practical advice, [Jenny List] has a good read for you. You probably also ought to invest an hour in watching this video that has a lot of practical advice.
Sodium vapor lights sometimes come back to the shop “Cooked”.
Check for “blackened” transformer varnish. Or the typical “cooked” smell.
Better safe than start a fire.
For just a few amps worth, you can use the full 2:1 step up and down 115/230 transformers back to back.
Careful, the step up and step down 115/230 transformers are usually autotransformers. That means no isolation. If you’re not familiar with the difference, Google it, and then you can use a multimeter on the resistance setting to check.
Yah, used “full” in there meaning not auto, but also meant to say more likely to find in older old equipment, AT PSU rather than ATX etc.
Or connect 2 microwave ovens back to back after removing the magnetic shunts.
A 1kW micro wave usually has a 1400W transformer.
You can do this with any 2 transformers with the same winding ratio.
If the ratio between the transformers is slightly different you can use that to compensate for losses.
because having several kilovolt inside the box used to try and to make things safer is just what when you want?
Yes, but that box is not the one you have open and are sticking your test leads into.
It’s Schroedinger’s box until you open it up to observe the inside… why on earth would you want to do that?
Like that this guy is buiding and creating videos like this but damn he needs to up the safety factor a lot.
he has a good idea. but a few problems with his design, first no fuse on input, the on/off switch is quite undersized maybe good for 5-7 amps, and from the diagram on the transformer its designed for 100w usage so he may burn up the transformer first. also i hope he remove the ignitor from the transformer.
Most, if not all, hid lighting transformers are auto transformers. Isolation limits some hazards, but also, if not protected properly can create other hazards. This a poorly executed hack job that could hurt somebody, or atleast give ’em a good shock.
Why do people insist on mounting main voltage devices to wood?
You’re complaining that there’s an actual hack on Hackaday?
There is a difference between a clever hack and a hack job.
I have some large transformers that were for stepping down 3 phase 480 (I think) to 120.
Might cut them up for big coils.
Well I wouldn’t trust them for handling any ‘real’ voltage or current. I really should scrap them.
No no no it’s not that big!
I can carry it, so I probably should have said small!
There are no PCBs I garruntee it.
Many small tube amps also use this trick: use two smallish trafo’s back to back to make the current a little less lethal.
This transformer is quite useless as an isolation transformer. He doesn’t seem to understand what the transformer was needed for in the first place, even though he uses the term “ballast”.
Notice the huge piece of iron between the two coils? That’s a magnetic shunt. The two coils are not on a shared leg of the transformer core, and there only is a loose magnetic coupling between them, or, in other words, there is a very large leakage inductance (uncoupled flux).
Everything will seem just fine with only a multimeter attached, but the voltage will sag quickly when a load is applied.
No, look closer. It’s a common iron central bar with non-ferrous filler on the sides. So it looks like a shunt, but it’s not. It is an unusual design though.
Those fillers on the sides are clearly laminated steel plates.
(Close up @ 2minutes into the video).
Look super close. They are plastic.
Even if upcycle was a cromulent word it’s use in the title is surely incorrect isn’t it?
But wow even suggesting this abortion was built to increase safety is surely a joke?
While we’re on the topic – lol – can anyone suggest a way to ground the outlets in my house? This is in Mexico and the contractor quit while the house was half built. The electrician put in the wiring – again – but he didn’t put in a third wire. All of our sockets are three-hole prong capable, but i’m afraid that middle prong isn’t connected to anything. Is there any way i can ground each outlet without having to run a third wire? There is no room anyway in the plastic tubing they used to route the wires. This is a concrete block construction so there’s not actually much worry about fire hazard, but any appliance that’s plugged in is not grounded of course.
Also GCFI/RCD protection is a good idea.
If the pipes for your wiring are anything like the normal pipes for electricity there is plenty room for the 3rd wire.
The way to go is to first pull out the 2 wires, add the 3rd wire and then put them back in the pipes together again.
You could run the 3rd wire outside the pipes, since it’s not carrying any voltage. But this has issues. Main issue that it’s probably out of regulations (lose insurance if the house burns down?) and with reliability.
But I guess its better than having 3-prong sockets with an open earth connection.
The wire used in most of the US is typically NM-B, or Non-Metallic sheathed cable. Otherwise known as Romex. Romex is double insulated.
That wire comes with the ground inside already, there is no adding of ground.
Previously used wires were “BX” or “AC” (Armored Cable.) Newer Armored cabled includes a separate ground wire. Back a long time ago it includes a thin metal strip that would be wrapped around the metal jacket and in contact with the metal strain relief clamp.
In that case there was no separate ground wire, the metal jacket was the wire.
If rigid metal conduit is used, as is the case in some cities or in, cement construction, perhaps Chicago, the metal conduit itself is suitable for use as the ground conductor.
what type of outlets and wiring do you have? Is it in a conduit? take a picture.
Draw out the circuit, including the electrical panel, DUT and oscilloscope. Don’t forget that the oscilloscope alligator clip lead is connected to the scope’s chassis (earth) ground.
Now trace that all the way back to the electrical panel. There the earth ground is connected to AC mains neutral through the back of the sheet metal electrical panel.
Now either your DUT or your oscilloscope needs an isolation transformer to Galvanically separate it from the AC Mains Line and Neutral.
If you don’t do this your oscilloscope probe “ground” alligator clip will short out whatever non-isolated (AC Mains powered) circuit it is connected to (60 times per second) or (50 times per second,) and will trip your hopefully functioning circuit breaker.
To ‘really’ nit-pick – most [English] words are ‘made up’ anyway.
For the oscilloscope, i’d suggest a suitable ‘scope or probes (isolated or differential).
I do not suggest unsafe methods (like isolating the ‘scopes ground from the mains) – it’s not just failure mode it protects, but the chassis now has a ground ref of the probe ground.
First, all words are made up, get over it, you unovergetter.
Second, if you think the point above is wrong. Why the hell are you using words unknown to Shakespeare, (Who couldn’t spell worth a damme.) like oscilloscope?
You forgot to mention you can also use them to get yourself killed as RCDs won’t detect leakage current on the secondary of the transformer.