Reply to CGMiner thread about fan set to 0%

[gyverlb]

ref: https://bitcointalk.org/index.php?topic=28402.msg518624#msg518624

With cgminer 2.0.2, even with --gpu-fan 50-100 (for restricting fan speed between 50 and 100%), the fan speed is set to 0% shortly after startup on all GPUs (I have 5 on the rig exhibiting the pb, one being without fan associated : a 5970). So I can confirm the problem reported in the thread referenced above.

The fan speed up only when hitting the target temperature and the rate at which the temperature climb can prevent cgminer from speeding the fan early enough and some GPU can fail.

Other quirks :
- my 5970 doesn't seem to accept the fan speed targets and only accelerates or slows down (speed set to 100% only increments the speed, doesn't set it to 100) the other cards don't have this problem.
- Another quirk is that for the same 5970 card the inability to set the speed right away generates a yo-yo effect : the fan speed and temperature oscillates quite widely (30 to 70% and 15-20°C range).

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[gyverlb]

Seems you need 5 posts to be able to post elsewhere. What a waste of time... Should I reply to myself 4 times then ?

[ParrotyBit]

Seems you need 5 posts to be able to post elsewhere. What a waste of time... Should I reply to myself 4 times then ?

Not if I reply to you first!

[gyverlb]

so 2 to go...

[MadHacker]

well just add your 2 cents to other threads...
that will also get your post count up...
also perhaps you might accidentally help some on in the process.

my 2 cents 

[PLaci1982]

Did you tried the new 2.0.3 yet?

[gyverlb]

Just started using it. I managed to avoid the yo-yo effect by setting a lower bound for gpu fan speed not far from its 'ideal' speed but below. Helps stabilizing the temperature too, which probably make the rig more stable.

[vapourminer]

Did you tried the new 2.0.3 yet?

this. it was a bug. 2.0.3 works as intended, starts at the upper fan range value and works its way down.

[gyverlb]

It's hard designing a correct algorithm for adjusting fan speed.

One of the things that make it hard is thermal inertia. The fan doesn't cool the chip directly : it cools a radiator that cools the chip, so the chip temperature can continue to ramp up for several seconds although the fan is set to a "good enough" speed : the radiator doesn't have time to cool down enough for it to start cooling the chip. So the fan can be adjusted by 10s of % before the effect is felt -> this is one of the reasons for the "yo-yo" effect.

Having a lower bound fan speed near the ideal speed is enough to prevent too much speed adjustments. But it's not ideal : the correct lower bound is linked to the ambient temperature...

[vapourminer]

It's hard designing a correct algorithm for adjusting fan speed.

One of the things that make it hard is thermal inertia.

true. BTUs take time to work their way from the chip through the sink and into the air. cgminer 2.0.3 is aggressive on ramp up though. I like the authors thinking.. safety 1st when it comes to temps. I use 45-85 auto fan (on the dedicated 5830) with a high temp shutdown at 92

with the other PCs that have other duties I have several modes to choose from in batch files. some keep it quiet (60% max fan speed, vary the gpu clocks to keep 72 C temp), others keep it maxed out (maintain max clocks at 85% fan as long as you can). cgminer rocks.