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Posts: 2,545
Reply with quote  #1 
IT WORKS! (well, after a fashion)

I started with a 10 amp pwm speed controller from Ebay. I used one of these: 

12V-40V 10A Pulse Width Modulator PWM DC Motor Speed Control Switch ControllerBH 
Is it the best one? NO, but it's what I had. 

And a 2-wire (analog) temperature probe out of my junk box.  It appears to be about 10k.  

The wires from the probe were connected to the control pot on the speed control, one wire to the center connection and one to one side of the pot (I can't tell you which side as it will depend on the controller).  That's all there is to it.

When the temperature probe is heated (I put it in a cup of hot water) it changes the resistance of the control pot and the motor speed increases. (If it slows down you're on the wrong terminal).  I can still adjust the fan speed with the knob as well.

On the test rig I did NOT get full range in the fan speed, because of the mismatch between the 100k control knob and the 10k sensor.  100k probes are available.

Also the motor did not shut off completely, so a snap disk MIGHT still be needed to shut the power at low temperatures. 

Unmodified speed control: IMG_0675.jpg 

Temp probe: IMG_0676.jpg 

In operation:
As pictured it works fairly well.

I tried a 10k pot in lieu of the original 100k, and it did NOT work, and I think I damaged the circuit board in soldering.  Be warned.

I think a speed controller with the control pot on a short cable like this one would be better and easier to work with. https://www.ebay.com/itm/6-90V-15A-DC-Motor-Speed-Controller-Pulse-Width-PWM-Speed-Regulator-Switch/253056259652?epid=1287347415&hash=item3aeb541644:g:JG4AAOSwdnZZ5ila

Improvements welcome!

Willie, Tampa Bay


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Posts: 2,545
Reply with quote  #2 
Back to the drawing board...

The above unit failed and I don't think it was the soldering. I think that when I connected the sensor, it created a possible short across the pot at high temperatures. At normal temperatures it might not be an issue, but what's normal about a solar collector?

I have a couple more speed controls on order, will keep y'all posted.

Willie, Tampa Bay
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