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How big of a power supply do I need for two 5870's? I see a lot of recommendations and people using 900 watt + for 5970's and such. Will these smaller requirements need that much power?

I'm running 3 5870s off a 700 W PSU with an Intel E6400. At the wall I'm drawing 670 Watts, so I'm close to the limit, if not over it. I was drawing 280 Watts with one 5870, so each card is approx 185 Watts. I'm using a Coolermaster 700W Silent Pro, which is 80+ Gold certified and only cost £79 inc P&P in the UK.

Depending on the rest of your hardware you can expect that 2 5870 GPUs will draw ~200W each under load.

keybaud may I ask what motherboard you are using?

Intel D975XBX. I got it off Ebay a week or so ago with the E6400, 2GB DDR 2 and a 320 GB HDD for the grand total of £55.

Thanks. I am looking for something that has the capacity for 3 cards

You've got a fair bit of headroom left.  670W wall at 87% efficiency is 582W of output, so you've got 118W of extra headroom, assuming your temps are in spec.

Actually 650W is more than enough - you can calculate your consumption at http://www.extreme.outervision.com/psucalculatorlite.jsp (http://www.extreme.outervision.com/psucalculatorlite.jsp)

I am also using the Intel D975XBX also; with an Intel E6300, 2GB DDR2 667, a reference 5850, and a non-reference Sapphire 5870, and this PS is serving me well (I don't have any exact usage figures, though): http://www.newegg.com/Product/Product.aspx?Item=N82E16817371026&cm_re=earthwatts-_-17-371-026-_-Product

I think I just blew a 1200W power supply powering 2x Nvidia 295's just 18 hours after I started GPU mining.  (At least I hope that is all I blew).
It tripped the circuit breaker.

What does reference and non-reference mean in this context? And how does that effect wattage?

What model PSU is it?


A reference GPU uses the 'stock' ATI / Nvidia board and heatsink, non-reference cards typically use boards that may restrict overclocking (By locking the voltage, for example) or they may have a custom cooler fitted.

This link outlines power requirements for many different cards:

http://www.bit-tech.net/hardware/graphics/2009/01/08/nvidia-geforce-gtx-295-quad-sli-review/16

It looks like the Quad SLI I was using draws about 735W at the wall outlet for the basic setup.  

I suspect that coin mining might draw more power than even "loaded OpenGL" due to the "tight loop" nature of hashing.  No breaks waiting on memory,etc.

Thermaltake W0133RU ToughPower 1200W Modular Power Supply

Assuming the power supplies are only 80% efficient, a 1200W supply is can really only provide 960W.
Operating a power supply for extended periods of time near the upper end of its rated range is sure to find the weakest component.

So I would recommend sizing your power supply 30-50% more than it is actually using to prevent it from overheating or failing early.

In my case, I decided to replace it with the ToughPower 1350W supply, it was cheaper and has 10% more margin for error.

No, what that means it can supply 1200W. Thus drawing 1500W from wall at 80% efficiency.

Leaving some headroom is of course recommended. PSUs tend to get noisy at high loads, and tend to be most efficient around 50% load. So it's probably a good idea to leave some 20-30% headroom at least.

On a related note, would a 650w PSU be necessary for running 3x5850's, or could I drop it down to a decent 550w or 500w?  Recommendations?  The other components would just be a 65TDP C2D, single stick of memory, and HDD/fans.  Well, and the motherboard, obviously.

if you going to OC your cards choose 650w PSU

Yeah, good point.  I do plan to overclock them.

btw, if you going to use 5870 bios your card will consume more than 150w. I think it about 160 - 170 w.

I think bitcoin mining is going to quickly separate the men from the boys when it comes to PSU brands.

We are going to see a lot of blown up power supplies!  :D

Thermaltake wasn't banking (pun intended) on bitcoin taking off.

If you only plan on using (2) 5870's, a psu in the neighborhood of 650-750W would be plenty. You can get a 650w corsair tx for $80 after MIR, or the 750W for $95 after MIR from newegg.

I am running 2x 5870s overclocked to 975MHz and a slightly overclocked sapphire 5850 (I've downclocked the memory to 300Mhz on all of them) in my big box. It puts out about 1.1GHash/sec and pulls 555Watts from the wall. Assuming an 87% efficiency rate that's 482Watts. So 2 5870s should be able to run on a 500W PSU.

My dual 5870 rig eats up 440 Watts at the wall and I have a 600W power supply, so I'd say 600W is a good number to have. This way you have a fair bit of headroom and you aren't maxing out or coming close to maxing out the power supply.

This is why you really can't go by the overall wattage ratings. Wattage ratings include all sorts of voltages that don't matter to video cards. You need to look at how the +12V power is distributed.

Look at the TP 1200: +12V1@20A, +12V2@20A, +12V3@36A, +12V4@36A. You're sort of limited on what you can do with several uneven rails like that. If you put a 30A card on that 36A rail, you're left with 6A of unusable power. Put in a second 30A card and you've lost another 6A. Now your 1200W PSU is really only 1056W.

Now look at the Cooler Master Silent Pro Gold 1200W: +12V@98A. One big fat 12V rail means each video card will get what it needs, and there won't be any rails with wasted power.

i recently blew up my corsair 550 W PSU with 2* 5850 and athlon X4 cpu in my computer. now i have a 4 * 5850 mining rig with 950 W PSU and there are no problems whatsoever.