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?

 

[Jules_Theone]

Yes, if all the lives are joined together and all the neutrals are joined together it should turn on without needing to short any pins together. You might need to connect the voltage sense wire (power good) wire to 5V for it to start properly. The fans starting for a second sounds more like a short or fault detected in the PSU and switches the supply off to protect it. I've seen similar behaviour in newer PSUs where they 'hiccup' - try to start, fault detect, switch off, try to start, fault detected, switch off... repeat. It might be that this PSU doesn't have the auto start function so just stops and waits for the user to manually recycle power.

Also, have you got both PSUs connected in parallel pin-pin (all the +12V are joined together, +5V joined together etc.)? Because have you tried powering up one PSU at a time in case they are interfering with each other?

 

[Reloadron]

To start an AT PSU you need to connect Pin 14 (old Style 20 pin connector) or Pin 16 (new style 24 pin connector) to any common. It is generally a Green wire. That gives the PSU a start command. Also, it might be wise to connect a 10 ohm 10 watt resistor between the 3.3 volt output and ground (common). Also, given a choice I would not parallel the two units at their outputs.

Ron

 

[sghosh]

See I confused anyone with my initial question.

I using AT supply and not ATX, so it has no connector more than 6 pins.

Attaching picture of it, and the white connectors with tabs - one at top left and other at bottom right having 6 pins and all others standard Molex 4 pins connector.

You see I needed to short White + Blue and Brown + Black as per DPDT wiring diagram on SMPS case. This wire usually go directly to old computer power button - different from newer ATX model.

 

[Reloadron]

My bad for not catching that and making an assumption. Those boards were designed to provide 5 and 12 volt power with emphasis on the 5 volt supply. I believe they regulated their outputs off the 5 volt lines. I would try placing a 10 ohm 10 watt resistor on the 5 volt outputs between any red wire and ground. Give that a try and see if it powers up and remains up and the 12 volts becomes stable.

Ron

 

[sghosh]

I connect 250k soldering iron to output of 5V and fans rotate for 1 second and stop. 5 secs after I disconnect AC input, fans rotate again for a second.

 

[Reloadron]

A 250 K soldering is not a load. Do the math. How much current does that draw? I suggested a 10 ohm load. Gee let's see..... 5 volts / 10 ohms = .5 amp get the idea? If the PSU still fails to turn on then the PSU is bad. What will a soldering iron draw?

Ron

 

[alec_t]

A 250 K soldering is not a load. Do the math.

It's not even a soldering iron! At 250V AC it consumes 250mW. The solder will hardly get warm!

 

[shortbus=]

May be this will help you; http://www.marcee.org/Articles/PCPowerSupply.htm While he's telling how to make a battery charger from one, it tells how to use it and switch it on.

 

[Sceadwian]

Given AT supplies have been obsolete for a decent amount of time, there is a chance the power supply is bad to start with, personally the cost of a brand new ATX power supply are so low it's not worth trying to use something that old. I do try to recover all ATX supplies from any PC's I get that are less than 5 years old, but beyond that I tend to just throw them into my disassembly stack for all the heatsink and power components you can get out of them.