How can I control the speed of a DC electric motor.?

Question

I am building an electric bicycle and would like to

build an electric car.

Answer 1

The best way is to pulse width modulate the power to the motor. Series Resistance waists power and controlling the field winding will cause the motor to over heat at low speeds.

Answer 2

There are two ways to control the speed of a DC motor.

The first is by voltage.  When you reduce the voltage to the motor, it produces less torque, and therefore less speed at a given load.

The second way is by pulsing the DC to the motor.  What this is doing is using an AC signal to control a DC motor.  This is not true AC, as the current does not reverse direction, but it has the effect of giving "slices" of DC current to the motor, so that it pulses the torque.  In theory, the motor moves at what would be the average DC voltage of the motor if it were just given direct DC at that voltage.

The advantage of pulsed DC is that the motor can be more accurately controlled, it has a more consistant start up torque, and you do not need to use a variable resistor across the main winding, increasing efficiency.  The disadvantage is that it heats up the motor faster than straight DC in the middle of the speed range.

The advantage of Variable Voltage control is that the control system is simpler, cheaper, and does not heat the motor in the middle of the speed range like pulsed DC.  The disadvantages are lower starting torque, less accurate motor speed control, and loss of efficiency through the rheostat.

Answer 3

you will need a controler such as Curtis or Altrax. check out the sites provided.

Answer 4

What you want is a DC motor with a separately excitable field coil.  By varying the current in the field coil (with a variable resistor) you can vary the speed of the motor.  The field coil uses much less current than the rotor coil so there is not a lot of power loss in the variable resistor.

This is a much cheaper solution to the pulse type controllers other posters have suggested.

Answer 5

You'll need a DC controller. That's a device that produces power 'pulses' to the motor to control how much energy goes in.