I'm tearing my hair out with my Chinese lathe - a Clarke CL300, same as Sieg C2.

I'm almost convinced that the motor is kaput but don't want to tip any more money down this hole without some more confidence that my diagnosis is right.
Original problem was intermittent buzz from pcb, almost like a relay not latching - motor would not run but then on another day it would.
I changed the Mosfets without fixing it.
I bought a new pcb control board that did fix it but now the motor sparks badly and blows the fuse even without being under any load.
So far - replaced brushes - new ones now show signs of sparking but otherwise good, sliding in carriers and making good contact with armature
checked motor for continuity, shorts etc - all ok
motor runs slowly but ok on 24v battery in both directions - I know this isn't much of a test but it's the only dc source I've got
driving motor as generator only produces 19v at 3000 rpm (driven by mains drill). Again not much of a test but seems very low as motor is rated at 5000rpm 220v dc
Max output from pcb controller with no load is 107v to 203 v in forward, -108v to -133v in reverse
I then wired up a 50w mains halogen bulb to the output to put some load on it. It turns smoothly from off to bright but is brighter in forward position than reverse - voltage measured with lamp in circuit max 194 fwd 111 reverse.

Sometimes when switching from reverse to forward with speed controller set to zero there is a small output sufficent to light the lamp, but this is intermittent.

It seems to me that I need a new motor and there is a fault elsewhere in the speed controller. It's not going to be locost to fix!

look for burnt segments on the commutator, normally shows as a line on the trailing edge of a segment

may not be that obvious but heavy arcing is most likely a shorted winding

Also check for broken wires where the armature windings are staked into the commutator segments. The symptoms do point to the motor.

My moneys on the motor

A good idea for future reference, is to dress and undercut the commutator before you put the new brushes in. This will help to prevent excessive arcing and thus overheating. The motor will last much longer.

Is there a starter capacitor for the motor? Worth a check and reasonably easy to check.

My 2 reils worth

I doubt it as it is a DC brush motor, sounds like a shorted winding on the armature to me.
Paul

quote:

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Originally posted by wilkingj
Is there a starter capacitor for the motor? Worth a check and reasonably easy to check.

My 2 reils worth

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