Quote:
Originally posted by bigben2k
Hum... thanks for the reply, but I thought 1 amp was needed to power up an AT PSU. Is the same true (paperclip trick notwithstanding) for ATX supplies?
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Hey Ben,
I don't have a definitive answer for you. My understanding is that different PSUs handle a no-load state differently depending on their actual circuit design. This applies to both AT and ATX switchers. It is my opinion that a 1 amp load on the 5 v rail is a generic rule-ot-thumb. Do it and you're probably safe, don't and maybe pow!
I had direct personal experience with this about 3 yrs ago. A sparkle 350 watt ATX. Powered it up by grounding the green pwr-on lead in the ATX connector (paperclip trick). I was playing with some different fans. It had been on about 10 seconds and I was reaching for a fan to connect, when pow sparks, smoke and game over!. Since that time I have read countless references from numerous sources warning of not powering up a switcher with no load. Sometimes you get away with it and sometimes you don't.
Sorry, I can't be more specific about the exact current draw - my guess is it varies from one unit to another. I have never had a problem since when using a 1 amp load.
Both of the PSU testers I have use two 2.5 ohm resistors in series (thats all a tester is - a 5 ohm load resistor across 5v line, jumper from pwr-on to grnd and an LED on the pwr-ok line).
I also had a EE at PC Power & Cooling tell me that the 5 and 12 volt rails in most PSUs share a common regulator circuit and pulling a heavy load on one with little or no load on the other can cause the unit to loose regulation. Case in point: Epox 8K7A mobo pulled all power thru 5 v rails - some PSUs had real trouble with this and one recommended solution was to try puttin MORE load on the 12 v rail to bring up the 5...
It apparently worked for some people but not all.