# DC motor help

Discussion in 'Electronic Basics' started by James, Apr 27, 2005.

1. ### JamesGuest

I'd like for someone to explain how a two speed DC motor works. I have
an idea but what I really want to know is how to increase it's speed
if possible. Or what determines how fast the motor spins.

This is a windshield wiper motor. The wipers on my 1980 Fiat Spider
never did work that great when new. On the fastest speed, the wiper
motor runs about 46 RPMS. On a "typical" car, 46 rpms would be the
slow speed.

The linkage is not binding, the brushes are good, it just never did
work that great from the factory. I've got 13.7 volts at the motor,
but I haven't tested it under load.

Doesn't matter if the wiper motor is running disconnected from the
linkage or if the wipers are running against a dry windshield.

There are three brushes. One is soldered to the body so it has to be
the ground. When power is applied to the grey wire which is connected
one brush, the motor spins "slow". Then power is suppied to the blue
wire connected to the other brush the motor spins faster.

This is what I can't understand. How applying power to one brush makes
it spin 30 RPMs and when power is applied to the other brush makes the
motor spin 46 RPMs. Since all three brushes contact the commutator.

I did some experimenting to see what would happen if I applied power
to both brushes at the same time. To see if this would make the motor
spin faster than 46 RPMs. I figured the worst that would happen would
be I would blow a fuse. The motor actually slowed down and no fuses
were blown.

If I were to increase the number of windings on this armature (not
myself but by a shop that rebuilds starters and alternators) would
this increase the speed of the motor? There is room for more copper
wire. Or use thicker wire.

I'm assuming this will cause the motor to draw more amps but if that
happens and I blow fuses, I can always wire in relays.

Some guy rigged up a DC/DC converter and is sending 16.5 volts to his
wiper motor and says the speed increased from 60 to 96 RPMS! But he
won't explain where he got the parts. He says it's still in the
testing mode. I think this would be hard on the motor after awhile.

I just think there is an easier way to make this motor spin faster.

2. ### Lord GarthGuest

In universal motors, the type that has stator coils rather than permanent
magnets,
you can wire the stator and the armature in series and get high speed / low
torque
or you can wire the armature and the stator in parallel and get slower speed
but
higher torque.

3. ### colinGuest

dont forget that more turns = slower, less turns = faster, ie taking some
turns off will make it faster.

Colin =^.^=