Fan Control??

STI_FFY · 08-09-2009, 03:34 PM

I was thinking it might be possible to power 4-wire fans directly from the 13.8V instead of the fan headers so as to preserve headroom (and reduce noise) on the 12V computer rail. The 4-wire spec says no more than 13.2V for the fan supply, but the fan might tolerate 13.6 (the voltage my Subaru produces).

While thinking about this it also occurred to me that since the case fan of this motherboard (Zotac 9300-D-E) is not controlled, it might be possible to tie the PWM control signal from the CPU fan port into a 4-wire case fan PWM input.

Thus both fans (CPU and case) would be powered with 13.8V instead of 12, and all controlled via the PWM signal of the CPU fan port. The tach signals would be routed to the CPU and case fan headers per usual.

Has anyone tried either scheme (13.8V fan power or multi-fan control from a single PWM signal)?

bratnetwork · 08-09-2009, 03:39 PM

i would not recommend send 13.8 volts to a fan that i designed for 12. if you dont want to power it from the MB then just put in a cheap simple 12 volt regulator from radio shack to to keep from frying the fan

STI_FFY · 08-09-2009, 03:58 PM

Quote: Originally Posted by bratnetwork

i would not recommend send 13.8 volts to a fan that i designed for 12. if you dont want to power it from the MB then just put in a cheap simple 12 volt regulator from radio shack to to keep from frying the fan

I doubt that 0.4 volts over spec will be an issue. If necessary I could use one of my old ITPS units to provide fan power.

What I want to know is if anyone has actually tried either method I described, and what their experience was/is.

STI_FFY · 08-09-2009, 04:19 PM

As an example of input voltage tolerance, here is a spec sheet for a top motor fan. Note that the tolerable input voltage is spec'ed as 7 - 13.8.

The 4-wire fan I chose for this experiment is also manufactured by Dynatron (Top Motor), so I suspect it has similar specs though none were stated.

If no one responds in the affirmative to my question, I will post the results once this plays out.

DarquePervert · 08-09-2009, 04:41 PM

Honestly, I wouldn't worry about it.

STI_FFY · 08-09-2009, 04:58 PM

Quote: Originally Posted by DarquePervert

Honestly, I wouldn't worry about it.

To which it were you referring?

kapone · 08-09-2009, 06:36 PM

I think you'll be fine. That slight bit of extra voltage shouldn't hurt anything. However, it WILL make the fan faster, and consequently louder. And at its spec limits, some of these fans are REALLY loud (depending on the fan).

DarquePervert · 08-09-2009, 08:13 PM

Quote: Originally Posted by STI_FFY

To which it were you referring?

The voltage you're feeding to the fan(s).

STI_FFY · 08-10-2009, 12:12 AM

Quote: Originally Posted by kapone

I think you'll be fine. That slight bit of extra voltage shouldn't hurt anything. However, it WILL make the fan faster, and consequently louder. And at its spec limits, some of these fans are REALLY loud (depending on the fan).

The PWM will counter this effect. The fan should never be running anywhere near full speed.

STI_FFY · 08-10-2009, 12:17 AM

Quote: Originally Posted by DarquePervert

The voltage you're feeding to the fan(s).

I agree. The voltage I will be applying does not exceed the fan manufacturer's spec.

STI_FFY · 08-23-2009, 05:02 PM

FYI - for anyone who might be interested:

I installed 2 DF127015BH 70mm 4-pin case fans into the side of my CaseTronic C128 (replacing the 3-wire fans that were there). I connected the input voltage pins of these fans to the car battery voltage (13.6V in my Subaru). The tach signals are not being used, since my Zotac 9300-ITX does not care about case fan rotation rate. The PWM inputs of these fans are tied together and connected to the PWM signal controlling the CPU fan.

This all works fine, the case fan speeds are controlled by the CPU fan controller and the relatively high-current case fans do not draw current from the regulated 12V supply of my M3-ATX. I left the CPU fan powered by the 12V supply, since I don't know the specs of that fan.

Update: After hibernating the system (turning off the ignition) I noticed that the case fans continued to operate slowly. This is because the fans default to their slowest speed when the PWM goes flatline. I overlooked this possibility, and now realize that the fans will be drawing power while the car is turned off.

It would be better to control the fan power with the ignition. I will incorporate a small relay to turn the fans off when the ignition line is cold. I prefer not to draw much current on the ignition sense line so I won't power the fans directly from that signal.

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