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One PS, multiple Motherboards -- how?

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January 18, 2010 8:12:13 PM

I have come into possession of several 1.8Ghz and 2.4Ghz motherboards that are perfect for running BOINC. The thing is, I don't want to run them each in their individual cases -- that would blow the breaker of almost any room I put them in.

I am looking to make a computing cluster in as small a space as possible. Since the 2.4's have onboard video and LAN, I can run them without any additional peripherals. Without any hard drives or optical drives the power requirements for each would be very low, and the O/S & BOINC data will be provided by network boot from a primary machine. Essentially, the whole setup would look something like this:



One of the issues I have is of power management. What I would like to do is take one 1000w or 1200w power supply and use that to power the whole lot of them. Theoretically possible, but since modern ATX motherboards can control the power supplies that they are attached to, this can be problematic. What if a MB were to issue a shutdown command? The rest would all be spontaneously powered off once the MB which was shutting down told the PS to shut down.

So I am looking for a "Power Supply KVM", for lack of a better description. I am looking for a power bus that you can plug a traditional PS into (that is, plug the 24-pin plug, 4-pin CPU plug and molex connector of the PS into), and which can supply on/off power to multiple motherboards without shutting the whole lot on or off.

Essentially, the PS equivelent of this:



But where each "plug" for each MB is "smart", in that if it receives a power-off command from the MB, it shuts power off to just that MB. That, and it provides the standard 24-pin plug, 4-pin CPU plug and molex connector as its "plug" to the MB instead of a 3-pronger as in the photo.

Suggestions? Has anyone ever built something like that before, even as a personal experiment?

More about : multiple motherboards

a b ) Power supply
January 18, 2010 8:17:54 PM

You'll probably have to find a specialty server product, or you'll be venturing into the DIY Electrician (which is a bad idea). I'm sure there are several reasons why running 2 or more complete systems on a single power supply are a bad idea. But maybe I'll let others with experience on the server end of things reply to this before I say anything else. :) 
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January 19, 2010 2:42:07 AM

I was hoping there wouldn't be a need for a DIY product.

I am sure someone somewhere must have thought about this. The circuitry allowing a MB to shut down a PS is embedded in the PS; it should be a simple matter to replicate that same circuitry outside of the PS itself. That way you can take a butt-normal PS, plug it into a "plug replicator", and have groups of plugs that power individual motherboards; each plug grouping with its own physical on/off switch as well as its own software switch (so that the MB can shut off that group of plugs without shutting off the PS itself or the whole plug replicator system).

As for the specialty server product, is there anything anyone can point me toward? I'm at a loss as to where to look on this one.
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January 19, 2010 2:50:15 AM

I know of many different kinds of splitters. Power splitters, between the MB and PS however, are a total mystery for me. Could you point me in the right direction?
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a b ) Power supply
a b V Motherboard
January 19, 2010 3:04:10 AM

What you propose is difficult, and maybe unwise. If there is a problem with that one PSU, or if any mobo had a problem that pulled a lot of power from the central PSU, ALL your mobo's would be affected. You might actually be better off equipping each mobo with a PSU of its own, but try to match the capacity to the mobo consumption.

You are concerned about overloading the circuit supplying the room. Don't forget that a 1000W PSU supplying a mobo that uses 100 W is actually only consuming about 130 to 150 W (allowing for 80% efficiency PLUS an extra margin for lower efficiency at low loading on the large PSU). Your plan might be like powering 9 mobos each consuming 100W with a PSU of 1200W max capacity running at 75% efficiency. But suppose instead you had each mobo powered by a 150W max capacity PSU able to run 75% efficiency while supplying that 100W, then each PSU would consume 133.3W and 9 of them would consume 1200W. Same thing! Even if their efficiency dropped to 70% the total consumption would still be under 1300W.

Try looking for smaller PSU's with good efficiency ratings. Maybe look at the ones for compact-case HTPC's. Or, look at items specifically designed for server rack systems that don't have high-power components like video cards.
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January 19, 2010 3:18:43 AM

Well, it may be unwise, but I'm pretty sure it's been done before.

I have seen in the past (some time ago, didn't bookmark the URL) an open-concept cluster where the motherboards were open to the air and bolted together on a large framework. Four stacks of them (about 15-20 MB's apiece) in an off-set square. That cluster didn't have individual power supplies, but had a master one for each "stack" with "plug clusters" at each motherboard for hooking each MB up to power individually. These "plug clusters" were individually controlled by each MB, and could be powered down independently of the whole. Powering each "stack" of motherboards was a rather powerful (at the time) 800W PS. This was a single PS which powered a bus, off of which sat the plug clusters. If I remembered correctly, there was also overcurrent cutoffs built into the bus, so a MB which was greedy would be cut off if it began to adversely affect the rest of the stack.

And BTW, this was done at a university where the MB's were cast-offs from the IT department. This wasn't some high-end, six-plus-digit experiment/project.
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January 19, 2010 4:37:35 AM

If one m/b powers down it will still continue to run. Motherboard connects green wire from psu to ground to keep it running. If it powers down it will disconnect these wires but because other m/b's keep running it they will keep wires connected and running. You should however make a diy current limiter for each motherboard so that if it gets short it will be disconnected.

Ideally You would need to run separate cable from PSU to each motherboard to reduce voltage drops intsead of using splitters and extensions but that is a lot of wires.

I would probably use 2x 700-750W PSU's with DIY made cables from the extension/splittercables You can buy and leave it without current limiters. If one m/b fails it will just stop working and rest will keep working. If one gets short it will trigger current limiter on one of the PSUs and switch half of Your system off.
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a b ) Power supply
a b V Motherboard
February 10, 2012 3:15:26 PM

This topic has been closed by Mousemonkey
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