633 pwm problem


New member
I've a 633 that I use to control the speed of one fan, but when i set the speed below the 80% I hear a loud mechanical noise coming from the fan. I'm sure that this is due to the pwm...
I tried to mount the fan in many ways, using something to stop the vibrations, but the noise is still unacceptable.

How can I reduce it? Maybe changing the pwm frequency?

Thanks :)
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CF Tech

The PWM is not set up to run at different frequencies.

What kind of fan is it? Do you have a data sheet or link to it?

CF Tech

You can try the capacitor. It will take a big capacitor to supply 0.92 Amps for 1/18 second.

In theory the PWM could be changed in firmware. There would be a tooling charge or minimum order requirement though.


New member
Papst and PWM fan speed control in CFA-633

I have a CFA633 (hardware-firmware "CFA633:h1.4,b1.9") and I use two different kind of Papst fan:

8412NGML - 0,9watt - 45 m3/h - 19db
8412NGM - 1.3watt - 58 m3/h - 26db

The 8412NGML model at low speed is quite silent, also if the pwm on/of is audible; the 8412NGM model is noisy, until 70-80 % , due to the pwm.
Papst fans are very diffused here in Europe, and it would be a very good thing if the CFA633 could fully support them.
There is a firmware update for 633 that can corrects the PWM frequency for this fans?


New member
One more vote to be able to change PWM from the software instead. I had to remove my one and only PAPST fan to get rid of the mechanical sound.
Since it is getting very silent in the house, I can also hear 2 more fans doing the same thing.
Actually, another producer of fan controllers has added it to it's software. (mCubed)
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