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Topic: Wha tdo I need to control a car's heater fan blower motor? PWM? (Read 8651 times) previous topic - next topic


I have a 12volt dc car fan heater blower motor.  I want speed control for it.  I think I need to use PWM.

I read that PWM will make my motor have a buzzing sound.  I don't want this extra noise at all though.
And I do not know how many amps is uses or how many watts it is.

Similar units I saw on ebay (out of cars 20 years old mind you) said 300 watts 11 amps.  This fan is out of a KIA sedan, My guess maybe around 10-12 years old, but who knows I got it from a car wreckers.

So what parts will I need to drive this motor?


300watt fan in a car - what type of space vehicle is that ?  Mains powered domestic units are only 10s of watts.  I suspect you may be looking at an electric heater.

The only way you are going to answer your noise concerns with a "scrap" motor is to suck it and see.

There's plenty of links available on this site about driving DC motors - feed the search animal


I haven't tried it, but my guess would be that you would need to use a PWM frequency outside the audible range if you want to avoid buzzing/hissing. But depending on the characteristics of the motor, you might find that's not an issue anyway.


Automotive A/C heater blower motors are not insubstantial motors and I would not be at all surprised if one could draw 11A.  Stall current could be much greater.

To simply speed control this, PWM going to be your best bet.  You should be looking for a motor driver than can handle above 11A -- there are some Pololu parts that are sized for this and that aren't too expensive.  Making something out of discrete MOSFETs would be the simplest and cheapest, if all you want is speed and not direction control.

It is possible to change the PWM frequency.  Depending on the driver you pick, there may be limits to what would work well.  Also the frequencies available depend on the PWM pins and are available in possibly inconvenient steps.  Have a look at this playground item: http://arduino.cc/playground/Code/PwmFrequency and also do some forum searches, also on the old forum, to see what discussion has gone before.

Personally, I would not get too hung up on the actual frequency of the PWM.  Get things going with the default frequency, which I think is something like 500 Hz, and see if you can live with the whine.  If it bothers you too much, then by all means mess with it.


I was fooling around with the same thing and it's pretty easy. I used a MOSFET from Radio Shack (Forget the number but I believe you'll need a "logic level" FET) and the fade sketch example. You can just change the number in the code from 0-255 and it will vary the motor speed. I experimented with 2 different 12V auto motors and one of them did a lot of "singing" at certain speeds but the other one was pretty quiet.

Those suckers can pull 10 amps or so as stated earlier so you'll need a heat sink on your FET.

You'll just have to try and see.

Good luck!

Someone please correct me if anything I've said is in error. I'm a noob  :smiley-eek:


Well I ended up getting a pwm motor speed controller kit in town.  Yes the motor must draw over 10 amps as it blew the 10 amp fuse in the back of the dmm.  Anyway, the motor makes the buzzing and humming noise.  But, I am not able to wind the motor up to the full 12 volts.  It will just stop at say 9 volts.  Any ideas?


If the 12V isn't across the motor then the loss is across the motor controller output (and/or the wires between, depending.)
Any info on that "pwm motor speed controller kit"?
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!


I think the motor must resonate or something and it just doesn't like the pulsing of the signal.  I then took the motor off and put on a small 5w 12volt car tail light
and it worked properly all the way form 0 volts up to my max of 12.33 volts.

Here is the kit: http://www.jaycar.com.au/productView.asp?ID=KC5502


Well, there's some difference between a "5W" (nom. 1/2A) tail-light and an 11A motor: you're comparing apples to oranges.
The jaycar link didn't specify the semiconductors used on that controller.  Maybe you could take a look at those and note which they are (attached to the heatsinks.)
Either way, I suspect that there's some loss across those "transistors".  The tail-light is a puny load in comparison to the motor.
Given that, the subject's going non-Arduino anyway.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

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