Help understanding bench psu manual
It's fairly easy.


When you switch on the output voltage ramps up until it reaches the preset maximum voltage or the preset maximum current - whichever comes first.




Figure 1. A typical bench power supply with voltage and current limits adjustable from the front panel. This one also has separate voltage and current readouts allowing simultaneous monitoring of both.

Let's take an example:

I have a 12 V DC motor on a worm gearbox which should draw 0.25 A when running unloaded. I suspect it is stalling but can't spin the output shaft because of the worm gear. Procedure:


Set the PSU to 12 V and 0.5 A current limit.
Connect the motor.
Switch on the output.
If the motor/gearbox is OK the voltage will rise to 12 V and the current readout will settle down at around 0.25 A.
If the motor is stalled the current will be limited by the motor winding resistance - let's say it's 3 Ω. As the voltage rises up we will reach 0.5 A at 6 V. The current limit will come into play and the voltage rise will stop there.


The current limit protects the motor during the test.

Current limiting is also useful in other cases such as testing LEDs without a series resistor or as a constant current source for charging NiCd or NiMnH batteries. For lead-acid battery charging the float voltage can be set to 14 V, for example, and a limit put on the charge current too.