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Author Topic: What Dual PSU's work best for you??  (Read 1134 times)
amazingrando
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October 27, 2011, 08:50:43 PM
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I am building out a few new rigs.  All of my current rigs are 4 GPU, single PSU, so these will be my first dual PSU setups.

6x 5830 rig
I would like both to be capable of also doing CPU mining with a Phenom II X6 (OC'd to 3.6Ghz+)

For the 5830 rig, if they are overclocked quite a bit, I'm guessing power draw is about 200W each.  An overclocked X6 is perhaps 150W, for a total of about 1350W.  So dual 700W?

Also, should I be concerned about the 12V1/V2 rails providing enough power for the CPU and GPUs?  If those two rails provide the CPU, chipset, and 75W per GPU, with 6 GPUs it's going to be a lot (600W/50amp)?

4x 5970 rig
5970's overclocked and overvolted could hit 375W each, perhaps.  4 x 375 = 1500W + 150 for CPU = 1600.  So dual 1000W?

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Gerald Davis


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October 27, 2011, 10:18:39 PM
 #2

Get a kill-a-watt.  You can make any half way accurate power decisions without measuring it.

I run 3x 5970 = 6 GPU on a single power supply.  It pulls .... 880W at the wall.  A 90% efficiency that is only 800W DC.
amazingrando
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October 27, 2011, 10:30:42 PM
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Get a kill-a-watt.  You can make any half way accurate power decisions without measuring it.

I run 3x 5970 = 6 GPU on a single power supply.  It pulls .... 880W at the wall.  A 90% efficiency that is only 800W DC.

Thanks.  I do have a kill-a-watt.  My numbers at the wall socket somehow don't seem to match up with what you've said in other posts, however.  I have a 1000W PSU and a few 5970's.  I'll give that a try this weekend.

Still, doesn't answer my question of a good power supply, whether 650W or 850W, or the question about loading the 12v1/v2 rails.

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Gerald Davis


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October 27, 2011, 10:35:16 PM
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I guess I was confused because of

5830
"I'm guessing power draw is about 200W each."

5970
"5970's overclocked and overvolted could hit 375W each"

Why not simply measure them?

As for the MB load, the best thing to do if find a PS that either has a single rail OR one where you have nothing on the rail powering the MB.  BTW: No high end card pulls 75W from the MB.   Low end cards w/ no power connector may but high end cards pull most of their power through dedicated connectors because they are more reliable.

Using a clamp meter I estimated the power draw at the slot for a 5970 under load to be ~30W.  Everything else comes from PCIe power connectors.

amazingrando
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October 27, 2011, 10:46:08 PM
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I guess I was confused because of

5830
"I'm guessing power draw is about 200W each."

5970
"5970's overclocked and overvolted could hit 375W each"

Why not simply measure them?

Yup, I'll do that.  I've got some test rigs now that I can do that with. Recently all of my rigs have been in the data center which only has 208v and no standard outlet for the kill-a-watt.

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likuidxd
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October 27, 2011, 10:50:19 PM
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I've had my best experience with Antec's High Current 1200W 80+ Gold PSU
1200W of continuous power & 1188W 12V combined maximum output

amazingrando
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October 27, 2011, 11:04:50 PM
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I've had my best experience with Antec's High Current 1200W 80+ Gold PSU
1200W of continuous power & 1188W 12V combined maximum output

I looked at that one and it seemed good.  I'm hoping to go dual PSU.  I think it will make things more modular and save a bit of money on each rig.  I figure I can get two good 650/700W PSU's for $150 versus the $250 for the Antec 1200W.  Given that I'm looking at 10 rigs, that will add up

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October 27, 2011, 11:14:07 PM
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I've had my best experience with Antec's High Current 1200W 80+ Gold PSU
1200W of continuous power & 1188W 12V combined maximum output

I looked at that one and it seemed good.  I'm hoping to go dual PSU.  I think it will make things more modular and save a bit of money on each rig.  I figure I can get two good 650/700W PSU's for $150 versus the $250 for the Antec 1200W.  Given that I'm looking at 10 rigs, that will add up

Not really sure what power supplies your looking at that you can get for that price but 80+ Gold will save you on power cost

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Gerald Davis


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October 27, 2011, 11:16:07 PM
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Not really sure what power supplies your looking at that you can get for that price but 80+ Gold will save you on power cost

Exactly.  Unless your power is free the ROI% on high efficiency powersupply makes it a no brainer.  I have <$0.10 electrical costs and more expensive 80+ Gold comes out ahead in less than a year.  Hard to find high efficiency 600W powersupplies for $75 or any price.
amazingrando
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October 27, 2011, 11:41:56 PM
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Not really sure what power supplies your looking at that you can get for that price but 80+ Gold will save you on power cost

Exactly.  Unless your power is free the ROI% on high efficiency powersupply makes it a no brainer.  I have <$0.10 electrical costs and more expensive 80+ Gold comes out ahead in less than a year.  Hard to find high efficiency 600W powersupplies for $75 or any price.

There is some debate on how easily PSU manufacturers (or their OEM's) cheat the 80plus certification.  You may not be getting the efficiency you think you are:
http://www.hardocp.com/article/2011/10/04/80_plus_irrelevant_to_you_when_buying_psu/

But that aside, take the example of the Rosewill 80plus Bronze 700W PSU which is $65 before rebate:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817152042

The certification states efficiency at 50% and 100%, but let's assume 80% load (560W) with the 120v efficiency seen at 100% load level, in order to be conservative.  An 80plus Bronze will give you 82% efficiency, meaning you'll see 682W at the outlet.

Then take a FSP 80plus Gold 700W PSU for $125:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817104099

Again let's assume 80% load (560W) with the 100% load level Gold efficiency of 87%.  With this you would see 643W at the socket.

This would save you ~40W per PSU.  Assuming I have two in a rig, giving me a combined savings of 80W.

Saving 80W between the two PSUs over the course of one year (8760 hours) will save me $35 at my power rate of 5 cents/kWh.  The cost difference between the two is $120.  Thus it wouldn't pay for itself for more than three years.  If power was 10 cents it would still take 1.5 years.

At this point I would rather save $120 on PSU's and get another GPU (even a 5830).  But to each his own

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Gerald Davis


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October 28, 2011, 12:02:06 AM
 #11

Why would you do that.  I think the point was a SINGLE high efficiency power supply.  At 80% load most 80Plus-Gold power supplies are >90% efficiency.  Depending on where you are on the curve it can be up to 94%.

The unit I have is 92% @ under my rigs load. 92% vs 82% is 10% saved power.  At 4KW combined DC load a 10% energy savings is nearly 3500 kWh.  Not only is that 3500 kWh not paid for each year but it is 3500 kWh of HEAT avoided.  The high end power supplies are simply built better, able to handle the abuse of 24/7 high current.  Most come with 5 year warranty.

less power & electrical cost.
less heat.
simpler setup.
higher end component.
longer warranty.

Now if your delivered power rate is really $0.05 per kWh YEAR ROUND and you have no AC costs then maybe it doesn't make sense but that is a pretty rare scenario.

amazingrando
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October 28, 2011, 12:09:21 AM
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Why would you do that.  I think the point was a SINGLE high efficiency power supply.  At 80% load most 80Plus-Gold power supplies are >90% efficiency.  Depending on where you are on the curve it can be up to 94%.

The unit I have is 92% @ under my rigs load. 92% vs 82% is 10% saved power.  At 4KW combined DC load a 10% energy savings is nearly 3500 kWh.  Not only is that 3500 kWh not paid for each year but it is 3500 kWh of HEAT avoided.  The high end power supplies are simply built better, able to handle the abuse of 24/7 high current.  Most come with 5 year warranty.

less power & electrical cost.
less heat.
simpler setup.
higher end component.
longer warranty.

Now if your delivered power rate is really $0.05 per kWh YEAR ROUND and you have no AC costs then maybe it doesn't make sense but that is a pretty rare scenario.



You're right that the bigger PSU's are generally built better.  For me it's all about profitability.  My power is 5 cents/kWh (plus a monthly $15 demand fee) because it's from hydro power.  I'm pulling down more than 13,500 kWh's per month across my rigs.  I have done the math a few times and it always turns out that I'm better off spending more on power and having more to invest in more rigs.  But my case may be exceptional.  My data center is in the far north so I don't run A/C in the summer, just exhaust fans.

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October 28, 2011, 06:15:40 AM
 #13

I'd say any "good" 500w will have no problem working in tandem,

Maybe You'd want to match them ? same model, but I don't think it's necessary,

To me The only question remaining is,  Will this PSU require a load on the 5v or not ?

It's a good idea to go dual PSU as they are much easier to resell,  Very few people need a 1250W PSU

So you save on purchase and get rid of it more easily,

About the efficiency, I'd say a bronze PSU at 80% load is generally as efficient as a Gold PSU at 95% load.
And anyway In 3 year from now you won't be GPU mining if you're looking for efficiency.

Your 5830 consume +/-10% of 175W

About the rails, No your board may consume ~35W per GPU and 45w for the 5970, and as little as 20w for the CPU (at 0%) and chipset

(These are rough estimate, use your own judgment)
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October 29, 2011, 05:06:57 PM
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I'd say any "good" 500w will have no problem working in tandem,

Maybe You'd want to match them ? same model, but I don't think it's necessary,

To me The only question remaining is,  Will this PSU require a load on the 5v or not ?

It's a good idea to go dual PSU as they are much easier to resell,  Very few people need a 1250W PSU

So you save on purchase and get rid of it more easily,

About the efficiency, I'd say a bronze PSU at 80% load is generally as efficient as a Gold PSU at 95% load.
And anyway In 3 year from now you won't be GPU mining if you're looking for efficiency.

Your 5830 consume +/-10% of 175W

About the rails, No your board may consume ~35W per GPU and 45w for the 5970, and as little as 20w for the CPU (at 0%) and chipset

(These are rough estimate, use your own judgment)

You cant run 2 good 500s on 6 cards. You can be close. You can do 5 like that. But my awsome machine runs on dual 600w coolmater 80+. Never had a moment of down.
Thermaltakes above 650w are nice too for this.

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