Hmmm... so why was 630W not enough for 2 cards?
I guess that's why I am confused. But I hope you are all right because i would love to be able to get another card running and not have to mess with the PSU again
There are so many factors it's really hard to say why that setup didn't work out. It's possible that the 12V rail(s) on the 630W were simply not up to the task (PSU wattage does not tell the whole tale). Antec likes to put multiple +12V rails on their PSUs. Each rail has its own OCP (over current protection) and sometimes on the lower wattage PSUs (650 and under) a single rail simply won't provide enough amperage for mining without tripping. This or any number of other things could have been causing your issue.
I looked into the Antec 850 that you have and it seems decent. It has four +12V rails which are distributed a little oddly but I doubt will cause you problems. According to this review:
http://www.hardwaresecrets.com/article/Antec-TruePower-Quattro-850-W-Power-Supply-Review/555 the OCP for each +12V rail doesn't trigger until 32A (the official rating says 18A). If you decide to try three cards, I'd certainly recommend that you undervolt them if possible to reduce the total load on the PSU and also save on your power bills. The stock voltage setting for cards is usually wastefully high and can safely be backed down a bit to lower temperatures and increase efficiency. It's usually not a good idea to run your PSU at 90%+ of its rated capacity as it greatly reduces the expected lifetime of the PSU. Efficiency and voltage regulation capabilities also drop off sharply around this point.
Anyway, I really do believe that your Antec 850 will be enough still, especially if you can undervolt your cards. Also, you never mentioned what you're mining. SHA256 (Bitcoin) mining uses less power than scrypt (Litecoin) mining.
I'm currently running 3 7950s on an 850W PSU (XFX PRO850W) without issue. I did undervolt my cards quite a bit though. At the stock voltages of 1.2V on these Sapphire cards, I was easily running at 90%+ of my PSU's capacity mining Litecoin (~900W measured at the wall). By undervolting the cards significantly and lowering the memory clockspeeds, I was able to get the total system power usage down to 620W at the wall.
Current setup:
3x 7950s
570Kh/s each, 1,710Kh/s total (scrypt)
.985V core
955Mhz core
800Mhz memory
620 watts, measured at wall (via Kill-A-Watt)
My hash rate is a bit lower than the numbers often bandied about but since my power costs are fairly high, I've realized that efficiency is more important. My cards will run up to 650Kh/s but the extra power used to get there isn't worth it anyway.
With a bit of tweaking, I think that you can make your setup work out as well. As long as you can lower voltages, your 850W will be more than enough. Good luck!
Nice post Xanthe,
I am surprised even with
underclocking your 3 7950s you can get by with only a 850psu. These cards supposedly draw up to 300w under full load (depending on what coin you mine). Then trying to power other peripherals make it seem like your power supply would be running at 100% capacity(or more). Even simple calculators would recommend at least at 1000 for those three cards.
http://support.asus.com/powersupply.aspxAlso, When you draw at such a high percentage of the rated capacity you loose power efficiency. Supposedly running at around 50-70% gives you the best power efficiency. Above those numbers you are burning more electricity in regards to heat. Even using a high efficient power supply..like a 80plus gold.
http://en.wikipedia.org/wiki/80_PlusAnyhow, seems like you have yours dialed in to give you results and performance you are looking for!
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