My tech rebuilt a 110v sander motor(armature & field) & now it runs backwards. Its a 4 brush motor where the positive feeds thru the winding to two opposite brushes, & the neutral connects to the other 2 brushes.
He tried reversing the power &/ brush feeds feeds without success. Are we missing something or is it possible that the armature is wound wrong?

 

If this is a Universal motor the field has to be reversed WRT the armature.
A Universal motor has the field in series with the armature.
Max.

 

My tech rebuilt a 110v sander motor(armature & field) & now it runs backwards. Its a 4 brush motor where the positive feeds thru the winding to two opposite brushes, & the neutral connects to the other 2 brushes.
He tried reversing the power &/ brush feeds feeds without success. Are we missing something or is it possible that the armature is wound wrong?

I don't know what the technician did (or tried to do) however you may reverse the motor via reversal of the armature/stator phasing...

Best regards
HP

 

As well as a Universal motor there is also a repulsion induction motor that has 4 brushes and this is reversed via moving the brush holders either side of a neutral position.
I have also seen a DC PM motor come back with the armature re-inserted from the opposite end of the PM stator causing reversal.
Max.

 

If this is a Universal motor the field has to be reversed WRT the armature.
A Universal motor has the field in series with the armature.
Max.

Max: I don't understand "reversed WRT". The factory diagram has the positive feeding into the field & out to one bank of brushes 180 deg apart. The neutral feeds the 2nd bank of brushes. I tried reversing polarity( neutral to field, pos to brush),switching feed in/out to field & rotating brush block 90 deg w/o success. I'm baffled. The sander is a Clarke super 7 sander & the wiring couldn't be simpler. The KISS principle is failing me on this one. Bob

 

I have never come across a Universal motor with four brushes, the fact the field appears to be in series with the armature does however indicate a Universal motor.
With this type of motor the field winding connections have to be reversed with respect to (WRT) the armature, this is the only way you can reverse this motor.
It is possible it could be a form of repulsion-induction motor which has four brushes, can you post a photo of the brush gear etc?
Max.

 

Max: I don't understand "reversed WRT". The factory diagram has the positive feeding into the field & out to one bank of brushes 180 deg apart. The neutral feeds the 2nd bank of brushes. I tried reversing polarity( neutral to field, pos to brush),switching feed in/out to field & rotating brush block 90 deg w/o success. I'm baffled. The sander is a Clarke super 7 sander & the wiring couldn't be simpler. The KISS principle is failing me on this one. Bob

In your attempts to correct the phasing, is it possible that you are unwittingly 'reversing' both armature and stator (and, hence, achieving no net effect)? Such mistakes are not uncommon, even among the 'Pros'...

Just a thought
HP

 

I have never come across a Universal motor with four brushes, the fact the field appears to be in series with the armature does however indicate a Universal motor.
With this type of motor the field winding connections have to be reversed with respect to (WRT) the armature, this is the only way you can reverse this motor.
It is possible it could be a form of repulsion-induction motor which has four brushes, can you post a photo of the brush gear etc?
Max.

Unfortunately I don't have a camera till tomorrow to post pictures. The wiring diagram & parts are shown by searching under "Clarke super 7 edger" if that would help. If not, I'll send pics on Saturday.

 

It would appear from the online dwgs that it is a simple Universal motor, the four brushes appear to be just two pairs coupled together on the same comm bar.
So it is back to the reversal of either field or armature connections, with respect to the other.
Max.

 

Got it! Thank you both Max & Hypatia's Protege. I had indeed reversed the field & armature. I greatly appreciate your comments & for not flaming me with such a basic issue. Thanks again! Bob Grand Rental, Manistee, MI

 

. I greatly appreciate your comments & for not flaming me with such a basic issue. Thanks again! Bob

You are allowed one mistake.

Glad you fixed it.
Max.