Voltage regulator

[Greg Hermann]

>At 04:55 AM 1/2/99 -0600, you wrote:
>>How about using a big pump and cutting the voltage when all that
>>capacity is not required? Will the pump last longer, etc.???
>>
>
>That would be almost as bad as overvoltage...  Under voltage can kill them
>as well.

NO. For a shunt would DC motor, Voltage relates to speed, Current to
torque. Field current and voltage want to be pretty constant for correct
excitation.

Too high a current (cooks the insulation with heat) or a voltage high
enough to break down the insulation are the two failure modes for motor
windings (this applies to all types of motors.)

For series wound DC motors, more complex, but voltage control of speed
still works, and without hurting durability, as long as you do not stall
one (with an overload) with too high a current going through it. You just
cannot expect to get full rated torque at lower applied voltages, cuz you
will not have enough excitation.  Even so, with a liquid cooled motor, like
most fuel pumps are, it is pretty hard to cook one this way.

What you need to watch with a PWM scheme for lowering the voltage to a DC
motor is to have good filtering/smoothing on the output to the motor--the
high frequencies from the PWM switching can be quite hard on the windings
from a mechanical standpoint.

Regards, Greg
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>           David Cooley N5XMT           Internet: N5XMT at bellsouth.net
>     Packet: N5XMT at KQ4LO.#INT.NC.USA.NA   T.A.P.R. Member #7068
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