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Motor controller help

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JMarrs

New Member
Ok fellas I'm a newbie to the electronics hobby and I enjoy messing with dc motors.
I haven't jumped into building my own motor controllers yet but hopefully soon. But my question is, if I have a 6v-90v pwm
Do I need a 90v power supply to get the max pwm?
 

audioguru

Well-Known Member
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PWM is not a voltage, instead it is a duty-cycle. If the pulses of PWM duty-cycle are near 100% then the motor will have lots of power and spin fast if the power supply produces near the maximum allowed voltage for the motor. But if the pulses of PWM duty-cycle are near 1% then the motor will still have a fair amount of power but it will spin slowly if the power supply produces near the maximum allowed voltage for the motor. If the power supply voltage is less than the maximum allowed voltage for the motor then the motor will not have much power.
 

JMarrs

New Member
Ok so I need to make sure that my supply produces the max allowed voltage for the motor and my pwm has a duty cycle near 100%. That fills in a few more pieces of the puzzle. Thanks
 

MaxHeadRoom78

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Normally you do not size it that tight, it is customary to size the supply at least 10% over the motor voltage, and control rpm accordingly using the PWM
Max.
 

audioguru

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If you apply the maximum allowed voltage to your motor and run it at or over its power rating and it has no cooling then it will curl up and die soon. Read the fine print about heat and how to cool it in its datasheet.
My electric radio controlled model airplanes have a very small motor that produces a lot of power. Flying, the motor has forced air cooling but it gets very hot and the manufacturer recommends full power for short durations and letting it cool down before it flies again. Of course, PWM is used for its speed control.
 

crutschow

Well-Known Member
Most Helpful Member
If you want to go from 0% (full-off) to 100% (full-on) PWM duty-cycle, here's a fairly simple circuit that will do that.
It will need to drive a MOSFET of the appropriate voltage and current rating to control the motor.
 
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