Building an 8 gpu rig, need advice on which PSU I should buy

[zorack]

Hey there everyone

I'm planning to build the following rig, and by the way dont worry about profitability I'm 100% sure its profitable where I live:

Biostar TB250-BTC+ motherboard (cheap lga 1151 with 8 pci express)
Pentium 4440
4gb ddr4 2400
HD 120gb sata
8x gtx 970 g1 (I know they arent ideal but I bought em for a really cheap price)
2x EVGA850 BQ (850W 80 Plus Bronze )

The problem is: the 850w PSUs are bronze plus certified, that means at least 85% efficiency at 80% load and 82% efficienty at 100% load, and after doing some research, I found out that gtx 970 gpus usually draw 150w of electricity when mining, and Im planning to connect 4 gpus in each power supply.
Im pretty sure that the psu that will be connected  only to 4 gtx 970 will be fine because they're probably going to draw around 600w , but I am worried about the other one that will be feeding power to  4 gpus + the rest of the computer (processor, memory sticks etc). The 4 gpus alone might use 600w or more, and I'm afraid that when you include the power drawn from the rest of the computer the EVGA850 BQ might not be enough.
There's this one guy who told me I shouldn't worry because he knows someone who uses a 1000w psu to feed a 5 gtx 970 rig, but I still dont know what to do. I would hate having to buy PSUs and then returning it to the seller because I did a bad job picking my rig pieces.

What do you guys think? Should I buy one EVGA 850BQ and one Corsair TX850M (80 plus gold certification: 90% eff at 80% load and 87% at 100% load) instead?

Thanks in advance to anyone willing to help and sorry for all the English mistakes, its not my first language

[Helios45]

Are you planning to run your rig at 100% TDP ? If you pay for electricity you might want to lower your TDP to be more efficient and more profitable and you won't have to deal with any PSU issues

[philipma1957]

Are you planning to run your rig at 100% TDP ? If you pay for electricity you might want to lower your TDP to be more efficient and more profitable and you won't have to deal with any PSU issues

this is the correct answer.

at op just set the gear to 75% tdp

[zorack]

thanks for the contribution helios and philip

Are you planning to run your rig at 100% TDP ? If you pay for electricity you might want to lower your TDP to be more efficient and more profitable and you won't have to deal with any PSU issues

Not really, from the early tests I did yesterday plugging one of the gtx 970 on my personal computer, I was able to get 300 equihash (300 sol/s) mining zcash with 70 or 75% power draw on MSI Afterburner.  

I am not totally sure, but I believe that when I've seen people saying that the 970 draws 150w when mining, they are already reducing the gpu's TDP through afterburner, because from what I've read on technology websites the 970 running heavy games at 100% power can draw up to 220w.

[ckai93]

another option to look at is at server psu. some are platinum rated and comes at usually 1000w+.
i'm just looking into those the other day and it was quite affordable in my area as compared to buying a new standard atx psu.

[zorack]

another option to look at is at server psu. some are platinum rated and comes at usually 1000w+.
i'm just looking into those the other day and it was quite affordable in my area as compared to buying a new standard atx psu.

you mean like this one? https://www.parallelminer.com/product/power-supply-kit-for-3-antminer-l3-plus-litecoin-miners-ltc-94-platinum-high-efficiency-200-240v/
I was considering the idea of getting one of these, but since none of the mining tutorials or forum posts that I read recetly mentioned this idea, I deduced that there should be a good reaso that explains why I didn't see anyone recommending one.

and by the way I am already making changes in the initial post mining rig setup: I found out that the g4560 processor for some reason doesnt work with the Biostar TB250-BTC+, so Im changing it for a pentium g4400
And a really nice user from this forum sent me a PM explaining me that i was wrong about the way psu power works. For example, a  1000w psu that has 80% efficiency at 100% load is actually able to deliver 1000w like its name suggests, the thing is that when its at 100% load delivering 1000w for your equipment it will be consuming 1200w.
That means that buying a 80 plus gold psu will always save me 5% power compared to the bronze ones. Now I think I will pick 2 750w gold plus psus instead of 2 850w bronze. But still not sure what specific models Im getting.

[Helios45]

I have a Biostar TB250 (the 6x PCI-e version) running very well with a cheap Celeron G3900

[zorack]

I have a Biostar TB250 (the 6x PCI-e version) running very well with a cheap Celeron G3900

what altcoin are you mining? I was thinking about getting a celeron but decided to go for a pentium because i've seen some people reporting problems mining with the currently mining software im using (genoil miner) with celeron processors

[zorack]

guys as you can see in the image in the end of this post, I used an online psu calculator to calculate how much energy my system would use excluding the gpus

the result pretty much surprised me: 125w for a pentium 6440, one sata 7200 hard disk, 4gb ddr4 and one kb and mouse usb. Is this correct?  

Taking this information into account, and considering that running the psu 24/7 at 100% load might not be a good idea, I think I should  get one 750w psu for the 4 970 gpus (around 600w), and one 850w psu for 4 gpus 600w + 125w drawn from the rest of the system. Am I missing something?

psu calculator print screen:
https://i.imgur.com/LUDyDzB.jpg

[Helios45]

Mining mainly Equihash and Lyra2REv2 and it is running smoothly

Re yout power calculations, I'm using a power meter and I can confirm that my rig consumes between 50w to 60w when the GPU's are idle

[jillscarbrough]

Yes, Power Meter (like a KILL A WATT) can talk about the real Power consumptions.