Bench power supply build from ATX power supply acceptable voltage

I built a bench  power supply from an ATX power supply and I am not sure if the voltage is correct.
I am getting 5.74 volts off of the 5 volt supply and 12.7 volts from the 12 volt supply. Is that too high to use or should I try to bring it down a little? When I built the supply I didn't have a 10 ohm power resistor so I used a 6 ohm 10 watt resistor.
Could this be the reason for the higher voltage?

Thanks for any help you can give me.


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Gelfling65 years ago
that 6-Ohm resistor must be getting pretty hot, and I'm no expert, but it might be why you're getting the higher voltages.. (though, <1V is not critical.).. though, your volt meter might be registering higher, too.. (most store bought meters aren't calibrated at the factory.) I have a Fluke meter that ranges the other direction, with a stock 300Watt supply that had a soldered-in (on-board) 33-Ohm, 5W carbon-film resistor across the +5V. Output on the +5 is roughly 4.87, +12 is roughly 11.90...

check the +3.3V.. if it runs higher, check it with a different meter. there, is where you have some critical because the 3.3v chips would run a greater risk of burn-out..
(I.E. If it's running 4V, I'd say it's not a good thing to try running a MP3 player that runs on only 2 AA batteries, because the 1V over, would cause problems.)
Hope this helps a little..
And this comes from a geocacher, who accidentally fried a Magellan Explorist-500LE, by plugging a 9V wall-wart supply (which was supposed to be for a cheapy Net-Book) into the power cord to recharge the Explorist (which the regular wall-wart supply, was supposed to be 5V.) (Oh-yeah, I now have an ancient, $100+ brick now..)
There's a vague chance you only blew the input fuse on the PCB - worth a shot.
@steveastrouk assuming that that is what it is, what would you estimate is the cost to correct?
pennies The works in taking it apart and looking.
I'll have to check.. No ideas where to look inside the explorist.. Hope someone posted something on the net, and it's 'Google'-able.
Did you find out anything further about that? I did the same thing as the power supplies got mixed up when we were moving and I ended up plugging in a 9v to the charger cord and the unit won't start up now. Also, @steveastrouk assuming that that is what it is, what woudl you estimate is the cost to correct?
Your voltages will be high with no load. Don't worry about that at all. And with your resistor, just make sure you have a hi watt one. When I did my power supply out of a PC power supply I got some gnarly ceramic ones from Radio Shack. Your power supply is fine, have at it!
The power supply itself may be keeping the rails a bit high while there is no load. Try plugging in a fan and then see what the power supply reads. Some cheap old and/or old PSUs may have trouble regulating the power so it could be higher or lower then what it should be. The average life of a PC power supply is considered to be about 5 years. The older the PSU gets the less effective the capacitors, that help smooth out the voltage, will be. Not good for a PC but fine for a bench top PSU. But the PSU should keep the voltages at around +/-5% of there rated voltages. if your reading more the +/- 10% then i wouldn't use it. For now your readings are within reason.