PWM Fan controller. Tach must come back to system.

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serpretetsky

2[H]4U
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Dec 24, 2008
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I have 2 4-pin fan outputs from system. I need to either to limit the duty cycle to some max value, or to adjust the duty cycle to limit the tach to some max value. I don't care which.

The tach from each fan MUST come back to the 4-pin fan output from the system (I need the system to still be able to read the speed of each fan).

Cheap is good, i don't need any fancy interface, I don't need any LCD screen, Bare PCB ok, just need some way to limit to a specific duty cycle/tach speed (I'm guessing POT, but little switches/jumpers works too). Need options to limit speeds between 2000rpm to 6000rpm. Or options to limit duty cycles between 10% to 50%. Speed/duty cycle limit can be global for all attached fans.

I looked around briefly but I'm not sure how to tell what the controllers actually do with the individual signals (some look like they don't even bother using 4-pin outputs from the system and just use something like the ide hard drive 4pin molex simply for power) .

Do you guys know what options I have?
 
Your motherboard has 4-pin outputs. Why can't you control your fans from the motherboard? BIOS just not very well designed?

If you split a single motherboard output to multiple fans, you'll get a tach signal back from one of them, but not all of them. (Unless your splitter is super cheap and you do get a signal back from all of them, which will confuse the bajibbers out of the tach input.)
 
This will be used in testing environment where the motherboard/backplane will be turned on/off multiples times. Fans spin up to full speed during POST. Firmware may also be reflashed at various times. Ideally I want a solution that does not rely on the motherboard/backplane. I don't need a splitter. I want individual tach from each fan to come back to its intended 4-pin header. I want individual fan PWM to go to its intendeded fan. But I want to intercept the signals and limit the fan speed to a maximum value.

That controller capt_cope linked basically looks kind of like what I want, but it looks like I would need to buy one for each fan. I was hoping I could at least do 2 fans, and cheaper :p. I was wondering if maybe someone already ran into this specific use case. If not then maybe it's easier to just replace the fans on each system with different fans.
Thanks.
 
serpretetsky said:
This will be used in testing environment where the motherboard/backplane will be turned on/off multiples times. Fans spin up to full speed during POST. Firmware may also be reflashed at various times. Ideally I want a solution that does not rely on the motherboard/backplane. I don't need a splitter. I want individual tach from each fan to come back to its intended 4-pin header. I want individual fan PWM to go to its intendeded fan. But I want to intercept the signals and limit the fan speed to a maximum value.

That controller capt_cope linked basically looks kind of like what I want, but it looks like I would need to buy one for each fan. I was hoping I could at least do 2 fans, and cheaper :p. I was wondering if maybe someone already ran into this specific use case. If not then maybe it's easier to just replace the fans on each system with different fans.
Thanks.
Click to expand...
Yeah after hearing what you're really after I don't think I've ever encountered EXACTLY what you're looking for. Frustratingly close, but not really anything I've ever seen that fill your primary needs.

That being said, If you're handy with a soldering iron and have a basic grasp on circuits you could probably work something up using one of the super cheap PWM controllers on amazon (or better yet an arduino) pretty easily.
 
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