Nvidia card power draw

[Dr_claws]

Hi All,

Got a quick question I’d love to get some feedback on. So work was kind enough to get me a couple of new Quadros for my deep learning rig. This makes 4 on a 1600W PSU. I did some research and wrote a bash script and set up a systemd service to limit the power draw on the cards. Everything in this regard works fine. My question is this: if I look a max_power in nvidia-smi I’m to assume that this is for the card only (not fans), so what assumptions can I make about power draw from the fans themselves?

 

According to the specs, total TDP for each card is 295W, which I take to mean max power draw for the fans is 35W. But if I limit power draw on the cards, say to 200W, does the max power of the fans scale in proportion—for example, 200/260 = 76.9% * 35W = 26.9 W? Or is there some power curve I can reference to do such a calculation? Could I then factor something like this into calculating any additional “power down” overhead? I guess I’m trying to figure out a smart way to build in a margin.

 

Appreciate any and all help! Thank y’all much.
C.

[AbydosOne]

16 minutes ago, Dr_claws said:

so what assumptions can I make about power draw from the fans themselves?

Fans are usually in the 5W to 10W range (excluding high-flow server fans that will slice your fingers off without a second thought).

 

I would expect board power to be calculated through the VRMs, after the 12V stage the fans are powered from, so you would probably need to account for fan power draw (however minimal) manually.

[mariushm]

Fans are more like 2-3 watts ... 12v x 0.15 .. 0.35A = 2...4 watts , but fans are rarely spinning at maximum rpm so you rarely get maximum power consumption

 

You have several VRMs on the video card, one for gpu, one for memory, other auxiliary ones.

They're usually 92-95% efficient, so you lose some watts there. You have to figure out what the software reports... what the gpu chip takes in or the amount measured at 12v input ... because there should be a difference between the two, the VRM losses.

For GDDR6 or GDDR6X, a value of around 30-50 watts of power consumption for the memory alone would not be far fetched.

 

[igormp]

The value found on the power limit does include the fan consumption, but keep in mind that this value is really small (2~6W at most).

[Dr_claws]

Thanks mariushm, AbydosOne and igormp. These gave me some good threads to pull on. Confirmed that igormp is correct using gpustat. That makes life a lot easier. And, mariushm the power calculations you gave make sense and were what I got for my back of the envelope. Thank you also AbydosOne for the VRM lead. Honestly, I’m still a bit confused by the reported TDP of 295. Maybe that includes some built in overhead for over clocking? At any rate, I’m feeling much more comfortable now. The alternative was to get second power supply and a 24 pin mining adapter and hope I don’t burn the house down

 

Well, thank you all again. Hope you’re having a great Sunday!