Modifying a fan controller

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Raxxath

Limp Gawd
Joined
May 29, 2007
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I have an ABS Canyon 595 case, which has one of these fan controllers built in. As you can see on that page, it's supposed to drop a 1200 RPM fan to around 720 on the lowest setting, but for some reason my Scythe Slipstreams are running between 900 and 1000 RPM. On the highest setting it runs the 1200 RPM Slipstreams at 1250 to 1400 RPM, which is a bit odd...

I'm kinda wondering why the fans are running so fast, and also if there's a simple way to drop the speed a bit. I don't have a soldering iron or any experience using one, so that's out. Could anything be done with the 4 pin molex power input?
 
Unless either the fans or the controller actually control the speed (and how do you know the exact speed, BTW?), the speed rating on the fans will be approximate.

It looks like the fan controller is a simple one, using diodes to reduce the voltage to the fans. Which means that reducing the input to the fan controller is a viable option. You need is something like this. Use that product to power your built-in fan controller, and you should be in good shape.
 
I have the yellow RPM wires connected to motherboard headers to monitor the speed.

Would doing a 7v mod like this work? I don't want to damage the fan controller or anything...
 
It would work, but you would lose the fan monitoring because the RPM wire would no longer be referenced to ground.
 
Fenris_Ulf said:
It would work, but you would lose the fan monitoring because the RPM wire would no longer be referenced to ground.
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True, and 7V may be too big of a step down in voltage as well. It won't hurt to try the 7v trick in any case, so it's worth a shot.
 
Well, losing the RPM monitoring would kinda suck. Any idea why these fans are running so much faster than what they're specced for? I'm used to seeing fans running ~50 RPM off their rated value, but 200?
 
Raxxath said:
Well, losing the RPM monitoring would kinda suck. Any idea why these fans are running so much faster than what they're specced for? I'm used to seeing fans running ~50 RPM off their rated value, but 200?
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I can only speculate as to what is causing the fans to run fast. Poor quality control? Windings with too few few turns? Shorted windings? Who knows? Given that nothing untoward is happening to other components, we can safely rule out a several-volts-too-high 12V rail from your PSU :)
 
Well, I used that 7v mod and I can run the fans much quieter, but sure enough there's no RPM signal.

It gave me an idea, though. What if I use 3-pin 7v modded wires on each fan cable, only connected to the red/black wire of the fan, while the yellow goes directly to the motherboard? Wouldn't that work?

Edit: I was thinking of something like this. That uses a resistor, right? So there won't be any loss of the RPM signal?
 
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Do you know where to buy this kind of resistor only? Not the complete extension.
 
Fenris_Ulf said:
Use several diodes in series, between 4 and 7 should drop enough volts.
Click to expand...

Except I know nothing about working with diodes. Is there any reason why these wouldn't work? Having two fans attached to each one wouldn't overload it or anything, right?
 
That's probably just 4 diodes in series. It should work fine to drop about 2.8 volts.
 
Raxxath said:
Well, I used that 7v mod and I can run the fans much quieter, but sure enough there's no RPM signal.

It gave me an idea, though. What if I use 3-pin 7v modded wires on each fan cable, only connected to the red/black wire of the fan, while the yellow goes directly to the motherboard? Wouldn't that work?

Edit: I was thinking of something like this. That uses a resistor, right? So there won't be any loss of the RPM signal?
Click to expand...
Yes, that device will indeed work and preserve your RPM signal. Doing the 7v trick and running the yellow wire to the mobo will *not* work--the motherboard senses the speed by counting how fast the fan pulls the RPM wire to ground. When the fan's running from 12V to 5V, it can only pull the RPM line down to 5V. The adapter you linked drops the supply voltage to 9V (probably with diodes, as Fenris_Ulf said), and fan goes from that lower voltage to ground. So it can pull the RPM line down to ground as well.

scatology said:
Do you know where to buy this kind of resistor only? Not the complete extension.
Click to expand...
you want to just buy the diodes? Hit up your local Radio Shack. If you're looking to buy a whole lot more, hit up mouser.com or digikey.com.

Raxxath said:
Except I know nothing about working with diodes. Is there any reason why these wouldn't work? Having two fans attached to each one wouldn't overload it or anything, right?
Click to expand...
Fenris_ulf is saying that the 12-to-9v adapter uses diodes to drop the extra voltage. You ought to be able to run two fans off it, yes.
 
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