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TheMawn 2014-04-28 19:21

Of PSU's and GPU's
I don't know how much people around here know about Power Supplies. Perhaps I will be surprised.

Whenever I am actually using my PC for relatively easy display tasks, I switch the instance of mfaktc on my display GPU to medium. This works great for internet videos, movies, and the lighter end of video games.

What I've noticed is that switching from fast to medium does reduce the throughput (from 1700 M/s to 1600 M/s, roughly, in my case). There is a further reduction when I actually start playing a video or something, which makes sense.

However, if I am not using the freed up GPU power for anything (i.e. I am idling on the desktop while mfaktc Medium is running), then my power supply fan goes ballistic. For example, if I play a round of League of Legends with mfaktc on Medium, everything is fine until the round ends and the PSU starts to rev up again. Once I get into another game, the fan quiets down.

Corsair makes a big deal out of their power supplies' fans running at different speeds depending on the load, but I'm sure that's nothing new. Either way, I'm a bit confused as to why the PSU fan revs up so high it's louder than the ten other fans combined.

It only does this when the GPU load isn't maxed out. This either confuses the PSU into believing it is drawing a LOT more power than it actually is, or the PSU is actually getting a lot hotter, but I've checked and found no indication of this.

It's an easy enough issue to just avoid, but it's got me curious. As far as I know, it has always behaved this way. I just never made the link until greed pushed me to running Medium as much as I could instead of turning it off completely.

kracker 2014-04-28 19:28

Mfaktc probably uses more power than most games. It may be because when the game round "ends" it stops using the GPU and mfaktc kicks in more. (imo)

EDIT: Or just get a Kill-A-Watt :razz:

TheJudger 2014-04-28 20:40

Depends on your GPU, mfaktc is "close to a power virus" on GF100/GF110 (e.g. GTX 470/480/570/580/590) but on newer GPUs (e.g. Kepler based GPUs) it is far, far away from being a power virus.
I have access to some Tesla which support power monitoring:
GF100/GF110 based: power consumption close to TDP while running mfaktc
GK110 based: power consumption ~50% of TDP while running mfaktc
OK, consumer cards based on Kepler have a [I]boost clock[/I] thus it will be more than 50% but I *guess* running mfaktc is well below typically games in terms of power consumption on Kepler cards.


TheMawn 2014-04-28 21:18

I would have to imagine mfaktc uses more power in fast mode than in slow, right?

I've set my power limit to 140% on that particular card. Furmark maxes it out but mfaktc gets to about 70% under the overvolt and overclock.

Mini-Geek 2014-04-28 22:01

[QUOTE=TheMawn;372225]I would have to imagine mfaktc uses more power in fast mode than in slow, right?[/QUOTE]

Sure. However, it's entirely possible that game+mfaktc uses less power than just mfaktc. Maybe the fan slows down when you start playing the game, but you notice when it speeds back up when you stop?
To imagine some numbers for the power your GPU is drawing (with the PSU spinning its fan to account for the power requirements):
Playing LoL + mfaktc medium = 70 W
mfaktc medium = 95 W
mfaktc high = 100 W

chalsall 2014-04-28 22:38

[QUOTE=kracker;372206]EDIT: Or just get a Kill-A-Watt :razz:[/QUOTE]

And/or a good amp meter, which can read the current quite accurately "out-of-circuit". Or even just a UPS with a USB data-tap.

Seriously... Empirical measurements go a LONG way in figuring out "that's strange" situations.... :smile:

pdazzl 2014-05-09 22:21

My cheap 700w (and about four years old) actually exploded on me, sparks and all (was running mfakct on one gpu and started spinning up a second gpu). Everything survived fortunately, got a Corsair AX860 and handles the load great, been using it 2 months now. It's quiet but then spins up the fans when the load gets heavier. The modular sleeved cables on it are nice too.

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