PSU Wiring

[minihack]

Hi,
While I fully agree that everything is possible and it is an interesting project to re-use a G5 power supply, for me, there are a couple of reasons why even if I did it for fun, I would not want to actually use one for an ATX board.
The first reason is simplicity - as Eelhead says, why bother? If the G5 PSU works you can probably sell it for a reasonable price, maybe more than the price of a new ATX supply, and re-wiring a G5 to an ATX style plug takes ages.
Another big concern though for me would be the life of my mobo. Our mobos are all built to comply with ATX standards and the whole safety issue of when power should come on and when it is "okay" is a shared standard between motherboards and power supplies with signalling between them that governs when a fault is recognised and how it is dealt with. This document explains it a bit: Click.
Macs make up their own standards and they are not ATX. So while it may be possible to hardwire a modded G5 power supply to turn on when the on switch is pressed and to keep it on until you shut down, that hardwiring is unlikely to really result in the signals between mobo and power supply being treated properly. For instance if you look at the page I linked to, what happens if you have hardwired the Power OK signal and in reality the voltages being generated are not okay? Results are unlikely to be good....
Having said all that, it is just my two cents and I wish you luck with your science project!

 

[Catahula]

The G5 supply has all of the voltages at correct current levels as well as standby voltages and proper "Power OK" circuitry. Macs had the standby voltage and "Power On" long before PCs did.

Wiring the PSU to the ATX plug is time consuming. However, even if you buy a new supply, you must spend time modding at least the case to make it work. Boils down to what you want, and how you want to get there. Pros and cons to every method. While I'm actively doing a G5 PSU mod, I'll agree that it has big cons against. Then again, I don't like putting the PSU and cord up high, and the other solution (Eel's) requires about as much time...If you need the juice for overclocking and big video cards, you need a bigger supply than the 600Wt G5 (actually 475 Watts usable) unit, and Eelhead's method is the way I'd go there.

I'll let you know if I can get it to work with the hack.

 

[minihack]

Good luck.

By the way, which one of the Mac signals from the G5 supply is the Power Ok signal ? I mean the one equivalent to the grey wire on an ATX supply and that tells the motherboard that the power supply is working properly.

 

[JohnEnglish]

Since we're talking about PSUs, what are the dimensions of the Mac Pro (Intel, not G5) PSU. I've been looking around online but can find anything that gives, length, width, and height.

 

[Catahula]

"minihack"]Good luck.

By the way, which one of the Mac signals from the G5 supply is the Power Ok signal ? I mean the one equivalent to the grey wire on an ATX supply and that tells the motherboard that the power supply is working properly.

[/color]

On the big plug, P1, it's pin 20 "+5 Sense", and the internal wire is RED. Cheap ATX supplies often just jump this wire to the 5V supply, or use a resistor and a capacitor as a time constant before a transistor switch, so there is a delay before the PSU comes up, This PSU has about a 1 second delay from the time you plug it in until it outputs any voltage.

On an ATX PSU, that wire should go to Pin 8, with the standard color being Gray.

The +5V sense measures just slightly lower than the +5V supply rail (+5.17 no load on the rail, and +5.10 on the sense), as there's circuitry between the rail and the sense, to check over/under voltage, and switch off if need be.

P1 pin 9 is a 3.3V sense, which will go unused. P1 pin 3 is Fantach, which probably won't be used either. The grounds are all just grounds at the PSU, but the grounding scheme of the G5 MOBO is particular to that unit, and is of no concern to us. You do need to add some pins to P1, I just pulled 'em out of P2 and used those. I used 18 gauge wires on all the grounds and high current stuff, and 24 gauge on the lighter stuff. Made it difficult to get the wires through the box!

 

[minihack]

"minihack"]Good luck.

By the way, which one of the Mac signals from the G5 supply is the Power Ok signal ? I mean the one equivalent to the grey wire on an ATX supply and that tells the motherboard that the power supply is working properly.

[/color]

On the big plug, P1, it's pin 20 "+5 Sense", and the internal wire is RED. Cheap ATX supplies often just jump this wire to the 5V supply, or use a resistor and a capacitor as a time constant before a transistor switch, so there is a delay before the PSU comes up, This PSU has about a 1 second delay from the time you plug it in until it outputs any voltage.

On an ATX PSU, that wire should go to Pin 8, with the standard color being Gray.

The +5V sense measures just slightly lower than the +5V supply rail (+5.17 no load on the rail, and +5.10 on the sense), as there's circuitry between the rail and the sense, to check over/under voltage, and switch off if need be.

P1 pin 9 is a 3.3V sense, which will go unused. P1 pin 3 is Fantach, which probably won't be used either. The grounds are all just grounds at the PSU, but the grounding scheme of the G5 MOBO is particular to that unit, and is of no concern to us. You do need to add some pins to P1, I just pulled 'em out of P2 and used those. I used 18 gauge wires on all the grounds and high current stuff, and 24 gauge on the lighter stuff. Made it difficult to get the wires through the box!

Thanks, good to know - I learnt something today. Let us know how it goes.

 

[Catahula]

the two that i got only have one big connector. and the PCB white prints only says 12V.
i do want to use that supply.
Here's what you need to do-

1) Measure all voltages (and I think you already have) with the supply turned ON. Note which pins produce what voltages.

2) Now, with the supply still plugged into the wall, but this time turned OFF, measure all voltages again, and again note which pins produce voltages, and note the voltages.

3) Now, find the pins which produce +5V when the supply is OFF (but plugged in). That's Standby voltage.

4) Now, connecting the voltmeter to the OTHER 5V pins, and see if any measure slightly lower. That'd be POWER OK, if it's even there (we will assume it isn't). You can take an ohm meter and measure resistance between all of the 5V pins when the PSU is OFF and NOT PLUGGED IN. If you get zero ohms (or close to it), then you've got only one leg of 5V, and the multiple pins are used for current carrying capacity.

Note how much time it takes for the power supply to turn on (power wire grounded, voltmeter hooked to the pin, but no AC plug connected. Connect the AC plug and get an idea of the time delay. If you've got a noticeable delay, and +5V, plus or minus 5%, then you can just hook up one of the 5V leads to the "POWER OK" pin and you'll be fine.

-12V @ .8A or so. That's a leg that you may or may not need. It's in the ATX specification, but who knows if it actually gets used. If you need this, the quick and dirty way would be to find a 12V 1 A power supply, wire the + to ground, and now the - is -12V. Wire the power cord to the input of the Mac PSU, and you've got an always on -12V, but I seriously doubt it will matter. If you wish, you could use a 3.3V or 5V or 12V relay to switch the -12V on with everything else. If you do go the extra psu for the -12, do measure the voltage out and make sure it's -12V. If it's too high, you can use a 1 or 1.5A -12V regulator to make it exactly -12V.