combining computer power supply

Over the years, I've kept a few ATX power supply from old computers. Now,
I'm thinking about upgrading my computer and add more hard disks. The
problem is the current power supply might not be able to support so many
hard disks running at the same time. Instead of buying a new, more powerful
power supply, I am planning to use one old piece (350w) to serve the
motherboard, CD, and 3 hard disks, then another power supply (350w too) to
serve 3 to 4 more hard disks. All components are connected to the same
motherboard. I need to know how I could turn on both power supply with a
single press of the power button on the case. Anyone has any ideas?
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recommendation: invest in larger power supply.
i have several reasons for this recommendation but lets concentrate on one: if your old supply blows up and takes out any one device (hard drive, CD burner, whatever) you are going to be out more then if you had bought a new supply in the first place.
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Thanks Tim,
But I don't want to 'invest' that money yet. That's why I look into the possibility to combine 2 old ones that are still in good shape. I know there are risks involved that I'm willing to take them.
Best Regards.
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Ok - since you're willing to take the risks: Replace the button with a double pole switch. Or if you must use the original button, wire it to sa two pole relay and wire the relay to the supplies.
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I'm sorry. I don't quite get it. Only one power supply can plug to the motherboard, how can I jam the wires together so that the second power supply receive the power-on signal when I press the button? I was thinking about the Power-On (Green), Power-Good (Gray) and 5 VSB (Purple) wires. In other words, the second power supply would only support the hard disks and nothing else, but I need them to be powered up at the same time other hardware are up (and down when it's shut down).
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One problem with using computer PSUs to drive only disks is that the regulation of the 12V rail can be way off spec if you aren't drawing a reasonable load from the 5V and/or 3.3V rails, and disks alone don't draw enough. Sometimes a dummy load or an old motherboard is left connected to overcome this, but it may not affect all PSU's.
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Andrew Gabriel
(Top posting corrected to establish a readable thread)
You plug one supply into the motherboard. It will start with the normal power on button. You plug one supply into the drives. It simply needs the power-on (green) and any ground (black) wire of its (otherwise unused mobo connector) to be joined together.
The first problem is connecting to them. You can cut them and use a "chocolate block" connector. You can use car-type connectors used to tap off wires for things like trailer lights. They are quick and easy to use. You can use a socket off an old mobo, after desoldering and removing it carefully. Loads of ways of connecting to it, I am sure that you will think of something.
Next is, how to connect them together. As suggested, vou can replace the power on switch with one with two sets of terminals, or use the reset button as a second power on switch. Or you can take one of the existing hard drive connectors, from the power supply used to power the mobo, and connect a relay (12v or 5 v, your choice) to it and use the relay contacts to short the wires together. Or you can use a USB port on the mobo to do the same thing. Or you can glue a light piece of plastic sheet to the lever of a microswitch, stick it in the airflow of a mobo fan and use the change in airflow to short the wires together. Or ue a sound-operated switch and shout, "Start" at it.. zillions of ways that you can detect one supply has started up and use that to short two wires together. I am sure that you will think of something..
The points made by other posters about the advisability of using old supplies and the remote possibility that you might not load it enough to achieve reliable operation are very valid.
I do use two supplies, now and again, though.
I get two identical mini-tower cases and bolt them together side by side. I run the file storage hard drives in one case, from their own (new) power supply and the mobo + optical drives + system hard drives in the other case, from their own (new) power supply. It is much cheaper than buying a server case and power supply.
Air flow and cooling is much easier to arrange - although I typically NC mill my own heat transfer devices and stick the pump and reservoir in the mobo space of the second case, with the radiator on the back of the second case (needs no access for connectors or cards). A liquid cooled heatsink on each drive means that I can mount drives top to bottom in the second case.
Currently Seagate 300GByte drives are my favourites, with an additional hardware RAID controller you can run a TByte, mirrored, no problem. With freenas, it makes a nice little, not very expensive, addition to a network.
No way would I do this using old power supplies of dubious parentage for anything like that.
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Thank you for everyone's help in this.
Best regards.
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I have a couple SCSI boxes, stuffed with drives, I use as portable storage. I am using an old AT supply with no problems.
You might be able to just connect the green #14 wires together to get both to power up. I know a bare ATX supply comes up if you ground the green one. That is all the system board does. The only question might be what current does it draw vs the transistor's rating but I bet it is milliamps.
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If you look at a typical circuit for an ATX supply:
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The Power Supply ON terminal (green wire) is held high by 5v from the standby power supply, via a 4k7 resistor. Bringing this pin to ground will start the supply and need approx 1mA sink current.
Commoning two green wires, one from each of two supplies, should be fine. Any mismatch in voltages of the two standby supplies will have a negligable effect, due to the 4k7 resistors.
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Thanks Sue, I figured there was an engineering person who would have that answer. This sounds like a reasonable solution for the OP.
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This is wrong in so many ways. First and foremost you have two different potential inside the case. Electronics as a general rule do not like differences in potentials. The motherboard is on one potential and the hard drive is on another.... POUF goes the magic. Let us know how long it works for ya. I bet it crashes in less than a week.
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As long as these potentials aren't connected together, there should be no problem. After all there are *many* potentials inside the case.
As long as the voltages aren't wired together (grounds must be), no problem.
If it's done right there should be no problem. What exactly is your worry?
Reply to
Keith Williams

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