SpudFiles

There are many varieties of motors. Most vacuum motors are of a type called universal. They have brushes, 2 field coils, all wired in series. Some have a tap in the field to add more turns in the coils for higher voltage use. This may be the 3rd terminal. To identify this, the low voltage terminal will have 2 wires on it and the high voltage terminal will only have one as it is the end and not a tap in the middle. These motors work fine on low voltage without overheating. They are used for variable speed such as on a sewing machine, or dynamic loads such as a vacuum cleaner. As a series motor, it is able to reach high speeds.

"It will work but running motors on low voltage can over heat them." This is true for AC induction motors whos speed is dependant on frequency. As the voltage drops, to maintain speed, the current draw increases to the point it is running in an overloaded state causing high current and overheating. Series universal motors simply slow down and draw less current. Series universal motors work on DC or AC. Induction motors try to run at 0 RPM at high torque if fed DC resulting in very high current and rapid overheating.

On your motor, it looks like the middle terminal is the "low" voltage tap. Power would be applied to the outer two terminals for high voltage, and the middle and far terminal for low voltage. Instead of dual voltage, some are two speed and the tap with two wires is the high speed tap and the other with more field turns is the low speed such as a drapery speed for the vac.

Thanks Tech! Any idea why one terminal would just stop working though? The Right terminal works fine, but the middle doesn't run the motor.

No clue on the one terminal as I don"t know the original configuration. It could have been a ground lug used for a noise filter to prevent electrical noise and not part of the windings at all.

Technician1002 wrote:No clue on the one terminal as I don"t know the original configuration. It could have been a ground lug used for a noise filter to prevent electrical noise and not part of the windings at all.

The thing is it worked before. Then one day it just stopped working. Only the right terminal spins the motor, but before if I hooked up power to the middle terminal, the motor ran faster. Now it just barely moves...

Check for shorted stator windings by doing a continuity test between the wire lugs and stator shaft. There should be no continuity between the windings and shaft.

jrrdw wrote:Check for shorted stator windings by doing a continuity test between the wire lugs and stator shaft. There should be no continuity between the windings and shaft.

I'll try that. If that is the problem though... there is no hope

Gun Freak wrote:

jrrdw wrote:Check for shorted stator windings by doing a continuity test between the wire lugs and stator shaft. There should be no continuity between the windings and shaft.

I'll try that. If that is the problem though... there is no hope

Thats pretty much it if the stator or field coil is shorted. If you had a mobile welder, custom built genarator something special then it would be worth getting the stator or field coil re-wound or buying a new stator or field coil. When these little motors start acting up, smelling burnt, getting over heated and turning colors it's cheaper to just buy new.

Well good thing I have 3 other vacuum motors

It just sucks because this is the only one I had with 2 speeds, but I guess that can be solved with a speed controller on any one of the other motors.