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PC power supplies are intended for use in a PC, which has a case connected to mains earth. If you dig out a schematic for pretty much any PC PSU, you will find that the mains isolation is not fantastic. If the switching FETs go short due to an over load, the ouput can become line voltage, and the only protection is a few diodes to crowbar the output and blow the mains fuse.
I've seen the effect this can have on a pc mobo, I'd hate to think a person might be on the recieving end!! (I know, I've been electrocuted more than once)
The other consideration is the current available. 5volts at 30-40 amps is almost enough for arc welding!!
Another point is don't load across the supply rails eg: -12v to +12 to get 24v, these power supplies are not designed for this and will lose regulation and may fail.
If you do decide to build such a power supply, use fuses on the outputs, make sure it's earthed and connect 0v (the black wires) to mains earth inside the PSU.
Linear power supplies (ones with transformers in) are much safer for experimenting, and fully isolate from the mains line.
I bought a 30 amp bench power supply from a local surplus outlet for £15.
I hope this helps.
Just thought i'd add this note while i'm thinking about it: brick type switchmode PSU's (laptop style) are just as bad, even though they look nicer.
Last edited by Simbo; 03-06-2006 at 03:20 PM.
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Linear Mode
