 |
 |
Variable Speed Motor
Name: andrew m childs
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993
Question:
I am setting up a device that needs to run a motor at variable speeds,
controlled by a knob or slider. How should I do this? I have tried a large
number of combinations of motors, deferent voltage batteries, and various
potentiometers, connected in series or parallel with the motor, but nothing
gives me a wide range of control. What should I do?
Replies:
It really depends upon how closely you want to control the speed of the
motor. The most precise way is by "closing the loop", or creating a servo
system. If you can come by a tachometer (really a very precise DC genera-
tor, you can monitor the speed of the motor by coupling the two together.
By adding a reference voltage (say +/- 10v), and summing that with the
tachometer voltage, you can build an amplifier that will give you quite
precise speed control. For DC motors SCR's can work, although good PWM
amplifiers are better (and considerably more expensive). Several books from
your local library can give you many common circuits for closed loop speed
control, depending upon the size and type of motor you are planning on
using. If you want to use a 3 phase motor, you need to build a phase
invertor that literally changes the frequency of the 3 phase current. A DC
stepper motor would require a phase sequencing circuit with drivers. There
are simpler ways to get rough, less precise speed control from a variety of
motors.
dipper
Click here to return to the Engineering Archives
| |
Update: June 2012
|
|
