Power supply with no load?

[sgtpeeper]

I just witnessed someone testing a power supply yesterday with the motherboard power connectors removed. The only loads were the drives. She works as a PC repair tech for General Electric, repairing various types of PCs. She tells me GE trained her, and that they said it is okay to to have *NO load whatsoever* on the power supply while testing! She says she's never had a problem, even though I told her this is a no-no.

Does anyone have a clue why GE would tell her this?

Thank you

 

[Souka]

Hmmm, I've never done this myself, but I personally don't see the problem with doing this.


Why would a "NO-LOAD" be bad on the PS? What is the problem?

 

[mee987]

i know nothing about electricity so i cant relly help, but just to clarify -- sgtpeeper thinks that maybe an old psu could handle the load of a single hdd fine, but not work at all when put under the load of a full system

 

[daveshel]

The power supply will not turn on without a load; this is part of its protection. Any drives connected to it satisfy the load requirement and enable it to switch on. There's no danger of testing with no load (unless maybe with a really old power supply). This could be considered a troubleshooting no-no because it introduces another variable when working with a no-boot scenario.

 

[sgtpeeper]

Thanks for the response. I've found a number of seemingly different answers at various sites, but below is something from a book on PC repair, for what it's worth. I don't know how old this info is, however. To answer the question as to what happens when a switching power supply "burns up", I wish I knew.
I need to find a EE or some electronics person and find out.

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According to Scott Mueller, author of Upgrading and Repairing PC's;

Some high quality power supplies have built in load resistors and can run with no external load resistor.

Some high quality ones, like the ones from PCPower and Cooling, have no resistor but only require a very small load on the +5 volt line.

Many of the less expensive ones require a load on the +12, +5, and +3.3 lines to work.

I would say that about covers all possibilities.

He also says that most of the better quality ones have internal circuit protection and will shut down after just a few moments of operation without a load, however the cheaper ones have no protection and will be destroyed after a few seconds of operation.

Talking about ATX power supplies.

 

[Androck99]

Well, I've heard just about as many different reasons both for and against no load operation as the number of people I've asked... A friend of mine had a 12" Kappa Perfect sub in his car and a few months ago, he began working on upgrading the intake, cams, electrical system and who knows what else in his '66 Chevy. This took the mighty Biscayne out of commission for a while so he didn't want his precious sub to go to waste so he asked me to help him ghetto-rig the amp and sub to his computer. Seems simple enough but the only problem is finding a power supply that can run a 300W amp. First, we tried using an old ATX ps and using the old "jumper across the green cable to ground" trick and although this kind of worked, the ATX form factor was way too picky with the proper loads on the different rails. Another problem was that the amp has a stand-by mode that waits about 2 seconds to turn on after the 12V is supplied, this is presumably to keep from overloading the electrical system right after starting the engine... Anyway, I found an old AT ps and went out to Radio Shack and picked up a huge 10 ohm 5W ceramic reisistor and put that guy across one of the 5V rail and it worked like a charm... It's been almost 3 months of daily use and it's still going strong! That's enough to convince me!