MadSci Network: Engineering

Re: How to reduce back voltage in a motor?

Date: Tue May 25 23:01:49 1999
Posted By: Lawrence Skarin, Faculty, Electrical Engineering, Monroe Community College
Area of science: Engineering
ID: 926818226.Eg

Why would you wish to reduce "back voltage?"  You would not, I suggest.

The fact you can walk on a floor is because a reaction force is created by your 
weight pressing on that floor.  The floor presses back, and you are supported.

Back voltage is the reaction created by a machine performing "electromechanical 
energy conversion."  Most motors involve conductors cutting magnetic "lines" 
and this fact alone generates a voltage.  At start, this back voltage is zero, 
and the current drawn is high.  At light shaft load, the back voltage nearly 
equals the applied voltage, and the current drawn is low.  As the mechanical 
power drawn from the shaft is increased (the subway train may be going up a 
grade), the back voltage lowers, and the electric power into the motor 
increases to provide the mechanical energy needed.

Back voltage is not a bad thing.  It is just the mechanism nature uses to 
preserve conservation of energy in motors.

Larry Skarin

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