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Piyono

Help Me Jimmy an AT Power Supply

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AT should turn on just from the switch. Are you sure it's not an ATX which does require a load on the 5V to stay on IIRC?

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Guest russofris

It is an AT and nothing has to be done to the MB connectors. The switch must be wired Black/Brown on one side, and Blue/White on the other.

MAKE SURE THAT IT IS UNPLUGGED BEFORE WIRING UP THE SWITCH!!!!!!!!!!

or it will shock your nutz off.

Thank you for your time,

Frank Russo

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It is an AT and nothing has to be done to the MB connectors.  The switch must be wired Black/Brown on one side, and Blue/White on the other.

Are you sure? I thought so, too, but I Googled several articles saying that an AT PSU wants to see a load across the 5v pins. Nobody specifies which 5v pins, but a load, nonetheless.

I guess I could just plug the sucker in and see if it makes my fans spin.

Also, I've got 3 hard-drive type power connectors on the PSU and four fans to drive. Each fan wants 450mA. I haven't got a DMM handy; how much juice does each leg of the PSU carry? Can two fans be run at full from one connector?

Piyono

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SOME AT ps's need a cont. 5v draw to stay on, others don't. I know, its wierd... :roll:

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SOME AT ps's need a cont. 5v draw to stay on, others don't.  I know, its wierd... :roll:

Well, can anyone tell me which circuit to load and how much to strap on?

As it is the PSU is working inconsistently, sometimes giving me 12v and sometimes not. Granted, I don't have a DMM or resistors to play with -- my test load is the Panaflo connected by bare stranded wires.

If anyone digs up a usefull document online please point me to it.

Thanks.

Piyono

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It is an AT and nothing has to be done to the MB connectors.  The switch must be wired Black/Brown on one side, and Blue/White on the other.

Are you sure? I thought so, too, but I Googled several articles saying that an AT PSU wants to see a load across the 5v pins. Nobody specifies which 5v pins, but a load, nonetheless.

I don't know which pins, but my dad, who is an EE, has often mentioned that switching-mode power-supplies really should have a load across them to work properly.

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On an ATX PSU, you would take a paper clip and bend it in a "U", connect THE green wire to ANY black wire on the 24 wire plug.

On an AT, i dont know. :lol: sorry.

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If it's a standard AT power source, it must have separate cable for switch or a switch.

The 2 connectors of which you put the picture are standard AT motherboard connectors (from left to right on your picture: 3x red = + 5 V, 1x grey = - 5V, 4x black = GND, 1x yellow = -12 V, 1x blue = +12 V, 1x red = + 5V, 1x white = power good ( + 5 V ) ).

how much juice does each leg of the PSU carry? Can two fans be run at full from one connector? 

All the "legs" ( with the same colour ) of the PSU are united inside the PSU. Each leg can carry the maximum power of the PSU. So, you can put all of your fans on one leg.

I don't know which pins, but my dad, who is an EE, has often mentioned that switching-mode power-supplies really should have a load across them to work properly.

Yes, it's true ! If I recall well , you must put something (a consumer ) on +5 V and + 12 V (doesn't matter which wires , as long as they are red and yellow ). You need only to draw a current, something at least 0.5 - 1 A for each voltage to be able to start the PSU.

On +12 V you have the fans, on +5 V you can put a power resistor ( for example : an 10 ohm resistor put on + 5 V => 2.5 A ; the resistor must be able to dissipate at least 20 W; that means it's hot and big ). Or you can put a light bulb ( from a car maybe, but I am not sure ) if you don't have such a resistor.

But this switching-mode power-supplies requires a bigger current for working corectly. It's possible that with a small load the PSU will start, but with voltages out of range. And even to crash if it's not well protected .

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Don't waste your time connecting that for fans! It's not designed for that and could be dangerous!

Instead, purchase a cheap 120V to 12V adapter with say a 1A 12V rating. You plug this into the wall and connect the output line to your case fans. Simple as that.

You could also get fancy and install a jack (coaxial) in your case or in a blank expansion slot cover plate. Wire the backend of this to your fans. If the fans are in removable panels you can use molex connectors to facilitate their easy removal. Just purchase a jack that fits the plug on your AC adapter. If you're like me, you have plenty of these things laying around from dead cordless phones, answering machines, etc. These will work providing they have an output (DC) of at least 9V and 500 mA.

Good luck!

Cheers!

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Don't waste your time connecting that for fans!  It's not designed for that and could be dangerous!

Dangerous? How?

Instead, purchase a cheap 120V to 12V adapter with say a 1A 12V rating.  You plug this into the wall and connect the output line to your case fans.  Simple as that.

The four fans together will require 4×450mA=1.8A. I'd need two 1A wall warts.

You could also get fancy and install a jack (coaxial) in your case or in a blank expansion slot cover plate. Wire the backend of this to your fans.

The PC is to be completely independant of the box, save for the fact that they'll be plugged into the same wall outlet.

Uh... why not just buy some standard power splitters? It's only 4 fans. 20W for all of em.

What's a "standard power splitter"?

On +12 V you have the fans, on +5 V you can put a power resistor ( for example : an 10 ohm resistor put on + 5 V => 2.5 A ; the resistor must be able to dissipate at least 20 W; that means it's hot and big ). Or you can put a light bulb ( from a car maybe, but I am not sure ) if you don't have such a resistor.

I'm no engineer, but I believfe that 10 Ohms across 5V would yield .5A, not 2.5A.

Piyono

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V/R = I = 5/10 = 0.5A

P = I^2 * R = .5^2 * 10 = 2.5W

The numbers are right, but the units wrong.

-Chris

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power splitters for hard drives...

No. The box and the computer are not to share any wiring. The computer PSU cannot power the four box fans.

Besides, the fans I have are already terminated with 3-pin connectors (like the ones on your motherboard). I bought pin headers and a small project phenolic in order to solder myself a little power distribution board.

Piyono

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If you need more power than a standard wall wart then I suggest going with a 75~100W switcher. (these can be found in external SCSI enclosures)

Running an AT power supply without the other rails loaded can result in catastrophic failure of components. This can result in explosion of electrolytic capacitors, flaming resistors, etc. Perhaps not a direct danger to yourself but something that I wouldn't want in my system nonetheless.

Cheers!

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I'm no engineer, but I believfe that 10 Ohms across 5V would yield .5A, not 2.5A. 
V/R = I = 5/10 = 0.5A 

P = I^2 * R = .5^2 * 10 = 2.5W 

The numbers are right, but the units wrong. 

-Chris

:oops: Sorry, I was wrong. I must write my posts in the morning, not in late night.

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If you need more power than a standard wall wart then I suggest going with a 75~100W switcher.  (these can be found in external SCSI enclosures)

Running an AT power supply without the other rails loaded can result in catastrophic failure of components.  This can result in explosion of electrolytic capacitors, flaming resistors, etc.  Perhaps not a direct danger to yourself but something that I wouldn't want in my system nonetheless.

Cheers!

Whoa, cool! Now I know how to dispose of my old, flaky, AT PSUs I have lying around... :)

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If you need more power than a standard wall wart then I suggest going with a 75~100W switcher.  (these can be found in external SCSI enclosures)

I suppose I could use two wall warts...

Running an AT power supply without the other rails loaded can result in catastrophic failure of components.  This can result in explosion of electrolytic capacitors, flaming resistors, etc.  Perhaps not a direct danger to yourself but something that I wouldn't want in my system nonetheless.

... or I could just take an old AT mobo, measure the resistence of all the different motherboard power pins to ground and load the PSU pins accordingly. After all, it's the motherboard pins, that require loading, right? You could, in theory have a computer consisting of just a motherboard and nothing else without fear of the PSU melting down.

Piyono

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