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FTG2
New Member

1 Posts
Posted - Feb 04 2012 :  09:44:25 AM  Show Profile  Reply with Quote
On the Pulse Width Modulation DC motor control circuit could R2 be replaced by a thermistor that would change the speed of the motor with relation to how hot the motor was getting?
I plan to use this circuit to limit the speed of a motor used on a small water pump that cools the electric motors on my scale RC ship.
I don't need the pump to run full speed and eat up current so the speed control is the answer however it would be even more flexible if it would only run when the motors started getting hot past a certain point and quit running when the motors cooled below that point. Suggestions on how to modify the circuit??

Aaron Cake
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Canada
6718 Posts
Posted - Feb 12 2012 :  10:22:38 AM  Show Profile  Visit Aaron Cake's Homepage  Send Aaron Cake an ICQ Message  Send Aaron Cake a Yahoo! Message  Reply with Quote
This isn't a real PWM controller, it's a pulse-frequency controller. It works, but not as well as a real PWM controller. Best to use another circuit.

But yes, as you suspect, a thermistor of the proper range could be used to control speed against temperature. It may not work the way you expect though because with no hysteresis it may be prone to runaway. I had a SPAL FAN-PWM controller on my car for the cooling fan that had the same issue. After fighting with it I tore it off and went back to a simple relay.
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