Fan controler mod

smokiedabong · Oct 3, 2009

I just bought a NZXT Sentry 2 touch screen fan controller , which is basically a good looking cheap piece of crap . It fails to power the CoolerMAster fan , it just makes a loud droning noise and the other fans that are spinning are louder at low RPM than directly connected , they have a droning noise also .
The controller is a switching regulator and I want to modify it to eliminate the noise . What do you think is a good solution ? Replace the existing capacitors with bigger low ESR capacitors . Add some electrolytics to the output . Or build a secondary circuit with a linear voltage regulator controled by the output to get a clean signal ? I know almost nothing about electronics or switching regulators , just started to learn so I'm asking for your help , thank you .

Resqueline · Oct 3, 2009

I guess this fan controller is a PWM type. These often send the raw, low-frequency PWM directly to the motor. The drone you hear could be the PWM frequency.
You could vary the frequency, searching for a "sweet spot" where the noise becomes unobtrusive. But without a Sentry in hand I couldn't tell you what components to change, and reading reviews about it doesn't make me want to buy one.
You can't put 'lytics directly to the output. That would defeat the PWM completely, but you could increase the frequency and/or put an inductor between the 'lytics and the output. Making the fequency over 20kHz would ensure it's quiet, but as you suggest - a simple RC filter before a linear buffer (a transistor) at the output could be all that's needed.
Still, some fans make a more annoying noise at reduced voltage than at full, even with a perfect DC supply.

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