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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.

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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.

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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.

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  • \$\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

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