enter image description here

First, thank you for your time of reading my questions. As the title suggested, my questions are about turning a computer power supply into a lab power supply. I already did my homework and read pages and pages, and also tested the power supply unit itself while took great caution not to get executed by electricity doing so, yet I still have few doubts that I want to get a precise answers before moving on.

1, some say that it will explose; some say that it will be fine; some just doesn't really know. Will it be okay if there is no load connected to the psu? As far as I know, my tested unit didn't explose, but it could be an exception. I need to know this because I don't like the idea of a dummy load that wastes 5 watts.

2, I don't see manual switch, and I used to see those in older units. I love the idea that it's possible to switch the unit on/off using a simple signal. Here is my observation: With no load and with ps-on not connected to ground, after removing the power, I connect ps-on to ground while got a voltage reading on my meter for a brief moment. Here is my question: is the capacitor still hold a high voltage when ps-on is off after removing the ac plug? I think it probably is. The main doubt for me is when I connected ps-on to ground after the removal of the ac plug, will that discharge the lethal high voltage capacitor to a safe level?

3, I notice there are 2 small yellow pots on the board. I think it is use to change the voltage of 2 of the output. if I am correct, can I turn it as a variable voltage source?

4, I notice that there is a small blue capacitor connected between one ac input line to the ground/metal case (shield). I know it's for filtering high frequency noise, but is it safe for me to touch the metal case when I don't have ground connected to anything? Ac does go through capacitors and metal does go through me, I think. Interestingly, when measuring the voltage difference between that metal case and a water pipeline, it reads 65v ac, so it's not safe? should I remove that capacitor?

again, thank you for your time, and please have a nice day.


closed as off-topic by Leon Heller, PeterJ, Ricardo, Daniel Grillo, Dave Tweed Aug 24 '15 at 14:18

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Leon Heller, Ricardo, Daniel Grillo, Dave Tweed
If this question can be reworded to fit the rules in the help center, please edit the question.


1) Any decent PSU should not explode or get damaged by using it in a non-standard way. Usually there is overload/overvoltage protection built-in to prevent damage. A decent supply should just switch off when misused.

2) Most ATX PSUs have a mains switch at the back but some don't. When connected to mains the PSU will put 5V on the 5V_SB (Standby) line. This voltage is used on a PC's motherboard to power some circuits that are connected to the PS's power switch (the small one at the front). When you press this button and the PWR_OK pin is high (indicating that the supply is ready for action) the motherboard pulls PS_ON to ground which will turn the supply fully on.

3) yes but these are usually only for small adjustments, like set the 5 V line between 4.5 V and 5.5 V

4) Don't remove the small blue capacitor ! It is also needed for safety reasons. The fact that you measure 65 V with a multimeter is because the impedance of the multimeter is very high, like 10 Mohms. So any leakage present will result in a high voltage to be measured. It is nothing to worry about !

HOWEVER I would strongly advise against using a PC supply as a lab supply ! The reason for this is that PC supplies can deliver VERY high currents so if you accidently short a supply, like the 5 V line, easily 20 A could flow and any thin wires will start to heat up, melt the PVC isolation resulting in smoke and damage. You are far better of using a wall plug adapter that can deliver 1 A or so, this will be much safer.

For a cheap regulated and current controlled lab supply I recommend a module like this in combination with wall adapter or a laptop charger (these are usually 19V). I have one of these and they are very handy and safe.

  • \$\begingroup\$ You're welcome, enjoy electronics :-) \$\endgroup\$ – Bimpelrekkie Aug 19 '15 at 8:57
  • \$\begingroup\$ @Atmega328: Did you know that you click the "accept" checkmark button? That will give FakeMoustache some extra rep (and you'll get a little bit too!) Please do so when you find an answer acceptable to you; it's part of the etiquette on Stack Exchange. (I'm saying this because you currently have no answers marked accepted to any of your questions.) \$\endgroup\$ – Fizz Nov 5 '15 at 7:59
  • \$\begingroup\$ I have no idea about that. will do it next time \$\endgroup\$ – Atmega 328 Nov 5 '15 at 8:19

Not the answer you're looking for? Browse other questions tagged or ask your own question.