Control the 'speed' of a PC fan (brushless) with Spark?


This may actually be a general electronics question so please excuse a noob :smile:

Can someone tell me if it is possible to use a spark to control the speed of a PC type fan. I believe the fans are ‘brushless’. I’ve googled around and it seems like it would not be possible to use PWM to control the speed of this type of fan?

Can anyone help explain if this can or cannot be done and why?

Thanks in advance,

What kind of fan do you exactly mean?
For 3-wire fan you could have a look at this thread

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You want a “four-wire” fan for PWM control of the speed. Very common in higher end PCs.

You can slow down a two-wire brushless motor somewhat by controlling the voltage you send to it (not with PWM but continuous control) but below a certain point, the switching IC in the hub just stops working and the fan stalls.

There’s an old but true saying with motors: “If she’s not turning, she’s burning!” so be careful.


Thanks for the replies… here is the fan I was trying to use…

You are going to have a very difficult time trying to make that variable speed. I would look for a different fan–they are pretty cheap.

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Thanks @bko, I figured as much… the way I am currently simulating using a PID type controller with this fan is that I assign time ‘windows’ of 10 seconds and then use the PID logic to calculate a number which determines how many seconds of that time window should the fan be on… It’s not quite true variable fan control but maybe it’s enough…

I’ll certainly take a look around for a 4 wire squirrel fan and hope I can find one which will give me a true variable control which I can use for PID controller output…

Thanks again

I don’t think PID will work properly here. I think what might work is using a transistor to control the voltage to the fan (some pc fan speed reducers only are resistors lowering the voltage to the fan). Requires some calculations though. And if you want the speed to be digitally adjustable you would need digital trimpots, not a big deal but still something to consider.