Turning on old style AT SMPS

[sghosh]

I buy two old style AT SMPS to powering my 3A DC Motors.

Shorted the four power pins - Live to live, neutral to neutral.

But when I turn mains power to AT SMPS, fans turning for 1 sec and shuttuing down.

I know in ATX SMPS you short two pins but something similar too you do in AT style?

Thought that in AT SMPS it turn always on as long as you shorted the four power pins - Live to live, neutral to neutral?

 

[betwixt]

Live and neutral are the AC input wires, if you short thiose you get a nasty bang and a blown house fuse!

I think you are referring to the positive and negative (0V) outputs which usually have red and black wires. All of each color are joined inside the PSU so connecting them on the outside is just increasing the current rating of the wiring.

On an AT SMPS there are two other conditions to be met, firstly you must connect a minimum load between +5V and 0V, how much depends on the individual PSU design but usually 0.5 Amp is enough. Withut this load, many will give too much voltage out and immediately shut down for safety. Secondly, you might have to wire a resistor (about 1K) between the orange wire and red wires, it is the "power good" signal from the PSU to tell the motherboard it's safe to start up but in some PSUs it is also used to tell if the board is connected at all.

Brian.