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Author Topic: Powering dual 5970s with piggybacked 2nd PSU  (Read 2193 times)
st4rdust
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March 29, 2012, 03:59:16 AM
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I've got a 650w PC Power and Cooling PSU in this rig which would easily handle the load of both 5970s, but the problem is that the PSU only has two PCIe connectors, a 6-pin and 6+2 pin. Each 5970 requires a 6-pin and 8-pin. Anyway, I was trying to find a way around this when I remembered I have a brand-new Apevia 650w PSU sitting in my spare parts closet with 4 6+2 PCIe connectors of its own. It's a 4 rail design, but what I had in mind was something like this:

1. The PC Power and Cooling main PSU powers everything in the computer, except for one of the 5970 cards.
2. The Apevia 650w gets tacked on top of the case, or next to it, some place practical (which definitely is not inside of the case) with the main 20+4 pin motherboard connector shorted and two of its PCIe connectors plugged into the one remaining 5970.

Would this be possible to do with the Apevia PSU's mobo connection shorted? I know that most PSUs will not power on unless this plug is connected, or at least tricked into thinking its connected, so other than that only two PCIe connectors would be used. On a 650w supply with four 12v rails, even that load of a single 5970 can be easily handled I'm sure. I just wanted to run this by anyone who might have experience piggybacking PSUs to gain some insight into the feasibility here. Thanks!

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MrTeal
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March 29, 2012, 04:15:15 AM
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I've got a 650w PC Power and Cooling PSU in this rig which would easily handle the load of both 5970s, but the problem is that the PSU only has two PCIe connectors, a 6-pin and 6+2 pin. Each 5970 requires a 6-pin and 8-pin. Anyway, I was trying to find a way around this when I remembered I have a brand-new Apevia 650w PSU sitting in my spare parts closet with 4 6+2 PCIe connectors of its own. It's a 4 rail design, but what I had in mind was something like this:

1. The PC Power and Cooling main PSU powers everything in the computer, except for one of the 5970 cards.
2. The Apevia 650w gets tacked on top of the case, or next to it, some place practical (which definitely is not inside of the case) with the main 20+4 pin motherboard connector shorted and two of its PCIe connectors plugged into the one remaining 5970.

Would this be possible to do with the Apevia PSU's mobo connection shorted? I know that most PSUs will not power on unless this plug is connected, or at least tricked into thinking its connected, so other than that only two PCIe connectors would be used. On a 650w supply with four 12v rails, even that load of a single 5970 can be easily handled I'm sure. I just wanted to run this by anyone who might have experience piggybacking PSUs to gain some insight into the feasibility here. Thanks!

Mine runs fine with a 450W running one card and another PSU running another.
st4rdust
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March 29, 2012, 04:23:23 AM
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I've got a 650w PC Power and Cooling PSU in this rig which would easily handle the load of both 5970s, but the problem is that the PSU only has two PCIe connectors, a 6-pin and 6+2 pin. Each 5970 requires a 6-pin and 8-pin. Anyway, I was trying to find a way around this when I remembered I have a brand-new Apevia 650w PSU sitting in my spare parts closet with 4 6+2 PCIe connectors of its own. It's a 4 rail design, but what I had in mind was something like this:

1. The PC Power and Cooling main PSU powers everything in the computer, except for one of the 5970 cards.
2. The Apevia 650w gets tacked on top of the case, or next to it, some place practical (which definitely is not inside of the case) with the main 20+4 pin motherboard connector shorted and two of its PCIe connectors plugged into the one remaining 5970.

Would this be possible to do with the Apevia PSU's mobo connection shorted? I know that most PSUs will not power on unless this plug is connected, or at least tricked into thinking its connected, so other than that only two PCIe connectors would be used. On a 650w supply with four 12v rails, even that load of a single 5970 can be easily handled I'm sure. I just wanted to run this by anyone who might have experience piggybacking PSUs to gain some insight into the feasibility here. Thanks!

Mine runs fine with a 450W running one card and another PSU running another.

So you've got the same general setup as what I've described? Just one single graphics card powered by a second PSU while the main PSU handles everything else? Also, is your second PSU paper-clipped to short the 20+4 pin connection or do you have an on/off switch?

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March 29, 2012, 04:31:24 AM
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I've got a 650w PC Power and Cooling PSU in this rig which would easily handle the load of both 5970s, but the problem is that the PSU only has two PCIe connectors, a 6-pin and 6+2 pin. Each 5970 requires a 6-pin and 8-pin. Anyway, I was trying to find a way around this when I remembered I have a brand-new Apevia 650w PSU sitting in my spare parts closet with 4 6+2 PCIe connectors of its own. It's a 4 rail design, but what I had in mind was something like this:

1. The PC Power and Cooling main PSU powers everything in the computer, except for one of the 5970 cards.
2. The Apevia 650w gets tacked on top of the case, or next to it, some place practical (which definitely is not inside of the case) with the main 20+4 pin motherboard connector shorted and two of its PCIe connectors plugged into the one remaining 5970.

Would this be possible to do with the Apevia PSU's mobo connection shorted? I know that most PSUs will not power on unless this plug is connected, or at least tricked into thinking its connected, so other than that only two PCIe connectors would be used. On a 650w supply with four 12v rails, even that load of a single 5970 can be easily handled I'm sure. I just wanted to run this by anyone who might have experience piggybacking PSUs to gain some insight into the feasibility here. Thanks!

Mine runs fine with a 450W running one card and another PSU running another.

So you've got the same general setup as what I've described? Just one single graphics card powered by a second PSU while the main PSU handles everything else? Also, is your second PSU paper-clipped to short the 20+4 pin connection or do you have an on/off switch?

Pretty much exactly, except that the 450W supply only has one 6pin PCIe, so I'm running the 8pin off the 6pin PCIe, and the other off a molex adapter.
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March 29, 2012, 12:00:30 PM
 #5

You should be able to use just the PC&PC PSU with molex->6pin/8pin pcie adapters and save the clutter.  Smiley

Tired of substandard power distribution in your ASIC setup???   Chris' Custom Cablez will get you sorted out right!  No job too hard so PM me for a quote
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st4rdust
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March 29, 2012, 12:32:39 PM
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You should be able to use just the PC&PC PSU with molex->6pin/8pin pcie adapters and save the clutter.  Smiley
I have a few different adapters but my 5970s get temperamental and do not want to power up unless they are getting juiced directly from the PSU. Piggybacking was the only surefire way I could think of to ensure that the cards got adequate power.

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March 31, 2012, 09:46:05 PM
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you can feed the 8 pin power connector with the standard 6 pin molex, it only fits one way so don't worry about fitting the cable wrong.
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March 31, 2012, 09:58:17 PM
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I've got a 650w PC Power and Cooling PSU in this rig which would easily handle the load of both 5970s, but the problem is that the PSU only has two PCIe connectors, a 6-pin and 6+2 pin. Each 5970 requires a 6-pin and 8-pin. Anyway, I was trying to find a way around this when I remembered I have a brand-new Apevia 650w PSU sitting in my spare parts closet with 4 6+2 PCIe connectors of its own. It's a 4 rail design, but what I had in mind was something like this:

1. The PC Power and Cooling main PSU powers everything in the computer, except for one of the 5970 cards.
2. The Apevia 650w gets tacked on top of the case, or next to it, some place practical (which definitely is not inside of the case) with the main 20+4 pin motherboard connector shorted and two of its PCIe connectors plugged into the one remaining 5970.

Would this be possible to do with the Apevia PSU's mobo connection shorted? I know that most PSUs will not power on unless this plug is connected, or at least tricked into thinking its connected, so other than that only two PCIe connectors would be used. On a 650w supply with four 12v rails, even that load of a single 5970 can be easily handled I'm sure. I just wanted to run this by anyone who might have experience piggybacking PSUs to gain some insight into the feasibility here. Thanks!

This is something I am thinking about too.  which two pins on the MOBO connection need to be shorted?
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March 31, 2012, 10:34:52 PM
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This is something I am thinking about too.  which two pins on the MOBO connection need to be shorted?
PWR_ON pin (green cable, pin #16) needs to be grounded.
This should be trivial since both its neighbors (#15 and #17) are ground pins.
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March 31, 2012, 10:37:00 PM
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This is something I am thinking about too.  which two pins on the MOBO connection need to be shorted?
PWR_ON pin (green cable, pin #16) needs to be grounded.
This should be trivial since both its neighbors (#15 and #17) are ground pins.
cool, thanks.

The only thing I can think of is the timing of powering on the PSUs.

I remember reading somewhere the GPU needs to be powered on before MOBO.
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March 31, 2012, 10:50:55 PM
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If you short the PWR_ON pin, that particular PSU will always be on - problem solved.

If you want to spend some cash, you can buy a dual PSU adapter.
Overkill really, especially if your miners are supposed to run 24/7/365.
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March 31, 2012, 10:56:53 PM
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another thing, having a common ground is usually more prudent than leaving them suspended.

this may not be a problem, especially if you mount both PSUs to the same case.
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March 31, 2012, 11:41:06 PM
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This is something I am thinking about too.  which two pins on the MOBO connection need to be shorted?
PWR_ON pin (green cable, pin #16) needs to be grounded.
This should be trivial since both its neighbors (#15 and #17) are ground pins.
cool, thanks.

The only thing I can think of is the timing of powering on the PSUs.

I remember reading somewhere the GPU needs to be powered on before MOBO.


You can just leave your auxiliary PSU powered on. Without the +3.3vdc from the PCIe slot, GPU VRM controllers will not run and switch the fets on/off. So, you'll have the +12v bulk caps powered on but none of the active components will be running until you power the PC on. This is how you run 3-4 PSUs to power quad-SLI GTX 580s under LN2  Cool

Note- Don't go poking about your GPUs with anything conductive. You can still cause damage accidentally shorting +12v to another part of the unpowered GPU.

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April 02, 2012, 09:37:54 AM
 #14

Something like this will do the trick as well

http://cablesaurus.com/index.php?route=product/product&product_id=22



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abbeytim
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April 02, 2012, 10:00:01 AM
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or get one of these  http://www.tigerdirect.com/applications/searchtools/item-details.asp?EdpNo=5681047&SRCCODE=GOOGLEBASE&cm_mmc_o=VRqCjC7BBTkwCjCECjCE




someone has one forsale for 10btc shipped  here

https://bitcointalk.org/index.php?topic=69396.0
discordian666
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April 03, 2012, 06:47:06 AM
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That's a pretty cool device!


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