DaveC wrote:

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

You didn't by any chance unwire the coupling in the field windings? If
so, it sounds like you have one winding reversed. This will give you the
effect you are seeing. But you did say that you had to hunt for them and
the F1 and F2 legs are on the outside?

Other possible problem is brush alignment.. if you don't have the
brushes orientated so that one crosses over to the next winding while
the other is lagging behind, it'll sit there and hum and some times a
spin of the rotor will start it but most likely will come to a stop.

Are you sure you have field voltage? And also, have you ohmed out
the armature to make sure it isn't shorting to the rotor? It is possible
you could of damaged it while it was in the lathe.

But in any case, what I've done in the past was to use a induction
meter to measure the cross over point on the armature to help align the
brushes.

P.S.
May want to check to make sure you didn't over turn the commutator
and also, it is very possible you had a shorted motor to start with.

Also check the field for ground shorts. YOu need to use a megga meter
for this. Or if you can get your hands on a IR bridge that will work too.

Jamie.