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Car Battery Voltage Question

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Apoch

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I have a DC Shunt motor connected to a car battery. How will I be able to vary the voltage so that the RPM of the motor also varies?
 
Use a big, expensive and hot rheostat in series with the motor to control its speed but the torque will be very low and it may not start running at low speed settings.
Or use a simple Pulse-Width-Modulation circuit to control the speed with lots of torque:
 
@audioguru:

I have a couple of questions regarding the schematic that you posted. What should be the wattage of the 100k resistor? What are the specs of the transistor? I think that the current being applied to the motor is high... so, will the circuit be able to handle this large current?
 
Hi Apoch,
The 100K pot has only about 6V across it so dissipates only 0.36mW. A standard 1/2W pot is fine.
Select a Mosfet with a max current spec to match the stalled current at 12V of your motor.

If you use the circuit as a DC lamp dimmer, select a Mosfet with a max current spec to match the cold current of the lamp. It will be about 10 times its lighted current.

You will find that N-channel Mosfets are less expensive than the P-channel one shown. Connect an N-channel Mosfet with its source to ground and the motor connected to its drain and to +12V.
 
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