Fan-tastic Fan modifications (speed control)

[ioan]

I made some modifications to my Fan-tastic Vent to have more control over the fan's speed (and noise). I used a voltage regulator - LM317, one resistor and one potentiometer. Here is the schematic:



Now from the potentiometer the speed can be set from very very slow and quiet to full speed.

Initially I tried to control the speed using PWM but that actually makes it noisier. This solution with LM317 works perfect.

[IndyTom]

Thanks for the tip about PWM. That was what I was planning to do with I got to that point on my build, but I guess now, I will use your circuit since it is proven.

TOm

[eamarquardt]

Using a voltage regulator isn't a good way to go as motors can overheat when the correct voltage isn't used. A PWM provides pulsed full voltage that is easier on the motor. If your fan was buzzing with a PWM it is an indication that the frequency of the PWM was resonant with your motor. A PWM with variable frequency will, most likely, be able to be adjusted that it can control the speed of your motor and not hum.

That said, the FF folks just use a resistor and all that does is vary the voltage just like your regulator. So it works good enough for the folks that built the fan.

The LM317 is good up to 1.5 amps. The model 8000 FF draws 1.9 amps on low and up to 3 amps on high. You might be pushing the envelope for a single 317.

Cheers,

Gus

[ioan]

If your fan was buzzing with a PWM it is an indication that the frequency of the PWM was resonant with your motor. A PWM with variable frequency will, most likely, be able to be adjusted that it can control the speed of your motor and not hum.

I used a microcontroller and tried several frequencies for PWM and I couldn't make it quiet enough. Just like you said, I was afraid that is going to overheat so I run the fan with the voltage regulator on the lowest speed for a whole night - to test it - and the motor was not even warm. Of course, the voltage regulator needs a heat sink, it will get pretty hot when the output voltage is really low.

[eamarquardt]

If your fan was buzzing with a PWM it is an indication that the frequency of the PWM was resonant with your motor. A PWM with variable frequency will, most likely, be able to be adjusted that it can control the speed of your motor and not hum.

I used a microcontroller and tried several frequencies for PWM and I couldn't make it quiet enough. Just like you said, I was afraid that is going to overheat so I run the fan with the voltage regulator on the lowest speed for a whole night - to test it - and the motor was not even warm. Of course, the voltage regulator needs a heat sink, it will get pretty hot when the output voltage is really low.

Sounds like you did your legwork. Perhaps you can run two 317s in parallel with a common pot. I dunno but it's worth a try. As inexpensive as they are it won't cost much if you fry a couple. My only thought is that it may fail while your camping and be inconvenient. But, if you've gotten this far, I'm sure you could bypass the controller and run it on full high.

Cheers,

Gus

[Shadow Catcher]

After the discussions on the forum and the struggles folks have gone through to slow down their Fantastic Fan I opted for two three speed computer case fans much lower power demand and whisper quiet. At a claimed 100CFM each (I am a bit doubt full, but more than enough)

[ioan]

Here is a video with the fan and the difference in noise between high and low speed:
http://www.youtube.com/watch?v=Y4FQebTqsdI

In the low speed the fan makes barely any noise (in the video it seems a lot noisier than it actually is).