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PWM with no tach feedback

K

Kalessian

Senior member
I have a few arctic cooling PWM fans, they all use a clever setup to allow daisy chaining. Too clever for their crappy instruction manual.

Long story short, I accidentally ruined the fan's tach signal.

What happens to a PWM fan when there is no feedback? Judging by noise/feeling the airflow, adjusting the PWM via software still works to some degree, but I suspect it is not performing to spec.

The tach feedback is used to sort of calibrate the fan on the fly, correct?
 
You'll have to manually tell your fan headers what duty cycle to use. Some motherboard bios's let you do this, otherwise you'll need speedfan.
 
I'm not sure what you mean, is 100% duty cycle going to be the same regardless of tach feedback?

I have it set to 100% right now and it's rated up to 2000rpm but I know for sure it is not going that high. The reason I ask this is I'm unhappy with the performance (but really happy with the form factor) and I don't know if I should reorder the same fan or just get a diff. model.
 
Kalessian said:
I'm not sure what you mean, is 100% duty cycle going to be the same regardless of tach feedback?

I have it set to 100% right now and it's rated up to 2000rpm but I know for sure it is not going that high. The reason I ask this is I'm unhappy with the performance (but really happy with the form factor) and I don't know if I should reorder the same fan or just get a diff. model.
Click to expand...

How do you know it's not going at 2000 RPM? Is it not as loud as when plugged directly into your PSU?
 
Hm, I shouldn't have said for sure, but I have 4 140mm fans of various make running 900-1000 rpm and the AC 80mm at 100% is quiet compared to those. Some newegg reviews were saying this gets loud as it approaches 100%, mine definitely does not. Going from 20% to 100% produces barely an audible difference. I mean it could be at 2000rpm but that would make it the quietest fan I've ever owned. At this point I'm guessing it's just a lemon.

I read some more about PWM and it does indeed seem to be that at 100% you get the full constant 12v.

I ordered a replacement of the same model (F8 Pro PWM) and this time I won't break it, so I guess when I test that one I'll have my answers.

EDIT: After reading some reviews, I think I had a misconception about rpms and noise.
 
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