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stmbtwle

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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:
IMG_0677.jpg 
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!


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stmbtwle

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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.

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stmbtwle

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Reply with quote  #3 
Well, the new controls came in and I've managed to get one to work as intended without burning up. I replaced the control pot with a thermistor on one leg and a fixed resistor on the other leg. It works nicely but now I have to figure out how to "tune" it. Once I get that, I'll post the details.
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Rick H Parker

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Reply with quote  #4 
You got proof of concept.

"I replaced the control pot with a thermistor on one leg and a fixed resistor on the other leg."

There are two different types of thermistors.

  • With NTC thermistors, resistance decreases as temperature rises. An NTC is commonly used as a temperature sensor, or in series with a circuit as an inrush current limiter.
  • With PTC thermistors, resistance increases as temperature rises. PTC thermistors are commonly installed in series with a circuit, and used to protect against overcurrent conditions, as resettable fuses.
Take a NTC and a PTC with reciprocal characteristics.  Hook the NTC and PTC in series and your have a three legged thermistor pod. With a fixed resistance across the two.

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stmbtwle

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Reply with quote  #5 
Thanks, that should work.  I was wondering if there was a "reverse" thermistor.  The fixed resistor on one leg works, but prevents me from getting full speed or full stop, depending on how it's hooked up.  If I use too small a resistor, at high temps I get a short and blow the control.

When the auto servo comes in I'm going to try and actuate it the same way.

then to figure out how to control these devices with an Arduino.


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Solar is like the wind. It may be free, but putting it to work isn't!
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stmbtwle

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Reply with quote  #6 
Ok I have the Q&D (quick & dirty) thermal speed control:

I got a 10k Thermistor from ebay
https://www.ebay.com/itm/NTC-Thermistor-accuracy-temperature-sensor-10K-1-3950-Waterproof-Probe-1m-N178/112693354540?
and a 15 amp speed control
https://www.ebay.com/itm/6-90V-15A-DC-Motor-Speed-Controller-Pulse-Width-PWM-Speed-Regulator-Switch/253056259652?
and a 1.7k resistor, 1/2 watt.

The control knob plugs into a socket on the board labeled " 5v 0-5v gnd ". There are also terminals for power and motor. 

I cut the wire to the "gnd" connection and soldered in the 1.7k resistor, and covered it with heatshrink.

Then I connected the leads from the thermistor to the 5v wire and the 0-5v wire.

That's all there is to it.  It works fairly well.

I have about 90% control with the control pot, full speed to "idle" 

The fan won't go to full stop, because of the resistor; if you need full stop at low temperatures you'll need a snap switch as well.  At full speed on the control knob, the thermistor has no effect.  However at any intermediate speed, the thermistor adjusts the speed up or down according to temperature.

Don't leave out the resistor to get full stop.  I tried that last week and fried the control board.

I'm sure a better one can be built, but this is on the "cheap and easy to build" theme. Cost about $12.

If anyone comes up with a better one please post details here.   

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stmbtwle

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Reply with quote  #7 
Here's a diagram:
spd ctrl1.jpg 
If anyone can improve on it (and still keep it simple), I'm open to suggestions.



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Solar is like the wind. It may be free, but putting it to work isn't!
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Rick H Parker

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Reply with quote  #8 
Got an idea but need some measurements.

Remove the pod from the board and measure the pod resistance.
Min-Max speed, resistance pin 2-1.  Wiper to +5
Min-Max speed, resistance pin 2-3.  Wiper to  -5

What temperature do you want the fan to turn off?
What temperature do you want the fan running full blast?

What is the thermistor's make and part number?

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Rick H Parker
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stmbtwle

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Reply with quote  #9 
Picky picky

The pot is 10k

Hard over one way, 2-1 is 0k, 2-3 is 10k. Readings are reversed the other way.

Thermistor is 10k, not marked. See the ebay link.

The idea is for the temperatures to be adjustable with the pot, depending on application. Probably 80F - 130F or thereabouts for an air collector.

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Solar is like the wind. It may be free, but putting it to work isn't!
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Rick H Parker

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Reply with quote  #10 
I can't get the numbers to crunch and balance with the components you have.

It would be easier for you to read the Thermistor and control the PWM board with your Arduino.
Controlling the board is easy enough, get the 0V ground reference from the board and force +5 to -5 on pin #2.

Reading the Thermistor: 3950 in the description is the B-Constant.
Here is a tutor on how to read Thermistors with a Arduino.

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Rick H Parker
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