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Question Slow down HP All-In-One PWM CPU fan with a resistor?

Hulk

Platinum Member
Oct 9, 1999
2,987
423
126
I inherited an HP All-In-One q116 computer from my father-in-law. It's a pretty cool little Haswell system. The issue I have with it is that it has an overzealous cpu fan profile. It'll spin up at really low temps.

Speedfan and other software control won't access it. BIOS has no fan speed controls.

My plan is to insert a resistor in the 12V supply to basically lower the current fan profile. The fan is 0.5A so if I insert a 10ohm resistor that will take it from 12V max to 7V max. I realize I'll have to experiment a bit to get this right.

I'm wondering if anyone here has done this and could offer any advice to reduce my trial and error?
 

VirtualLarry

No Lifer
Aug 25, 2001
50,897
6,313
126
So, instead of hearing a fan spin up at really low loads, you'll get a "clicka-clicka-clicka" that repeats, at really low loads. If it works at all, being that PWM are not voltage-controlled.

Edit: Instead of hacking the fan, why not simply replace it with one with a lower noise profile. There must be something available, if it's a standard chassis fan size.
 

BonzaiDuck

Lifer
Jun 30, 2004
14,887
1,023
126
that could be what you want to do, but might there be consequences? Is it possible that HP chose that particular fan to meet the real cooling needs at the top end?

Did you look at the fan? what size is it -- 40mm x 10mm? What amperage? Who makes it?

Can it be replaced with a different fan make and model?

I'm not too electrically savvy. The last time I inserted a resistor into a circuit to change the voltage was a few years ago, with a hot-swap-bay's 12V pinouts to drive a 5V SATA-to-IDE device. It all worked great. This other thing -- you could try it, but I've doubts that it might not spin up to a spec maximum when it's needed.

I have a collection of small fans. I still want to find more uses for two 40x25mm Japanese mag-lev fans that can go to 15,000 rpm. I have some different 40x10mm units, among them some from the Noctua line. I think Noctua makes at least a few small fan models. Of course, if it's a laptop or AIO, the fan might be a niche specification.

Oh. coming back, here . . . Is the noise you hear identifiable as air-turbulence, vibration, or motor-whine? If it's noise being transmitted through contact with another part of its housing, a roll of automotive self-adhesive rubber hose bandage and some scissors might come in handy . . . . . Tedious, though. You might try and deaden the contact between hard surfaces with the fan mount.
 
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Hulk

Platinum Member
Oct 9, 1999
2,987
423
126
Thanks for the insights.

@ VirtualLarry,

I would set this up first with a variable resistor to ensure the lowest setting is enough to get the fan moving. Good point.

@BonzaiDuck,
The fan is in a proprietary housing from HP to fit the unique dimensions of the computer. I'm going to see if the fan can actually be removed/replaced from the custom housing.

Again, thanks for your time/thoughts!
 

BonzaiDuck

Lifer
Jun 30, 2004
14,887
1,023
126
Thanks for the insights.

@ VirtualLarry,

I would set this up first with a variable resistor to ensure the lowest setting is enough to get the fan moving. Good point.

@BonzaiDuck,
The fan is in a proprietary housing from HP to fit the unique dimensions of the computer. I'm going to see if the fan can actually be removed/replaced from the custom housing.

Again, thanks for your time/thoughts!
That's what the forums are for. I'm always coming here looking for comments and opinions.
 

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