I would suspect that the replacement brushes are a little short or that the
spring force on the brushes is too weak. I used to go as far as slightly
contouring the brushes to the commutator to make max contact (and reduce
arcing).

David_J

"DaveC" wrote in message
...
A 1/2(?) horsepower 2-brush DC motor was having bearing issues so I
disassembled it and replaced the ball bearings, turned down the commutator
on
a lathe, and installed new original equipment brushes. A good clean-up was
done as there was much grease and carbon dust inside.

Now when I apple power it just growls. If I turn it by hand with power
applied it will turn 1 or 2 revolutions then stop. Before disassembly the
motor ran as expected.

The field and armature are separately terminated at the outside of the
motor
and wired to a motor speed control PCB.

The commutator segments are well-separated. I put an ohm meter on the
brush
terminals and turned the motor slowly. I see 10 ohms across the armature
with
each commutator position (each brush contacts 3 segments). The field
measures
1000 ohms. I thought that a bit high, so I found where the 2 separate
field
windings are connected (in series) and measured each winding separately:
each
is approximately 500 ohms.

There is no mechanical reason the motor should not spin at speed. By hand,
it
turns freely and there is no interference between the armature and field
laminations(?).

The motor is rated at 180 volts DC, 1.5 amps. There are 2 separate field
windings (wired in series) and the commutator has 36 segments.

I've had this motor apart several times but still can't find a reason it's
not operating like it should.

Any suggestions would be greatly appreciated (and the sooner the better
;-)
).

Thanks,
Dave