Repair 3phase electric motor(Unisaw)

Hi Mike,
I finally got the motor out of the cabinet, all the wires are paired and numbered and went to check your e-mail
with instructions of how to check the motor with the ohm meter and it got lost. Could you please re-send the instructions
of checking the lines with the ohm meter.

Thanks...............Kerry
 
the site had a crash and we lost some postings, an unfortunate casualty of technology.
i'll see if i can replicate what i said on the lost post.

with the ohm meter set on RX1 or the lowest setting
put 1 meter lead on phase 1 or 7,1 pairings and the other on 8,2 pairing or phase 2, record the reading. there should be low resistance- way below 20 ohms
put 1 meter lead on phase 2 or the 8,2 pairing and the other on the 9,3 pairings or phase 3 record the reading, this resistance should be below 20 ohms
put 1 meter lead on phase 3 or the 9,3 pairing , the other lead to phase 1 or the 7,1 pairing, record the reading, it should also be below 20 ohms.
put 1 meter lead on the 4,5,6 pairing, the other on phase 1 or 7,1 record
put 1 lead on 4,5,6 and the other on phase 2 or 8,2 pairing and record
put 1 lead on 4,5,6 , the other on phase 3 or the 9,3 pairing. record.
all the 4,5,6 to phase X should also have less than 20 ohms

you can also test all pairings to the grounded motor case or frame . there should be no continuity between any phases and the motor case or ground.

lmk if this helps out or makes no sense
 
Hi Mike,

Thanks for the outline, I'm going to do it tomorrow and let you know the results.

Regards...............Kerry
 
Hi Mike,

Here are the results [my multi-meter had Blk(COM) for Ground and Red( lead)] so I tested it both ways
Phase 1 (7-1) + phase 2 (8-2). Blk on phase 1 + red on phase 2 = 2 ohms, Red on phase 1 + blk on phase 2=3 ohms
Phase 2(8-2) + phase 3 (9-3). Blk on phase 2 + red on phase 3 = 5 ohms, Red on phase 2 + blk on phase 3= 2 ohms
Phase 3 (9-3) + phase 1 (7-1). Blk on phase 3 + red on phase 1 = 3 ohms, Red on phase 3 + blk on phase 1 = 7 ohms

Common leads (4-5-6) + Phase 1(7-1). Blk on phase 1+ red on Common lds= 2ohms, Red on phase 1 + Blk on common lds = 3 ohms
Common leads (4-5-6) + phase 2(8-2). Blk on phase 2 + red on common lds= 2 ohms, Red on phase 2 + Blk on common lds = 3 ohms
Common leads(4-5-6) + Phase 3(9-3). Blk on phase 3 + red on commons lds = 2 ohms, Red on phase 3 + Blk on common lds = 3 ohms
All below 20 ohms as you predicted , the readings jumped around in the beginning but finally reduced to the measurements above.


I tested in it with both leads( Red and Blck on the mult-meter )so that there would be no ambiguities. What is the next step that I perform at this point.

Regards.................Kerry
 
just an FYI Kerry, the OHM meter should read the same regardless of polarity when testing an electric motor.
another way of saying it is that the readings should not differ if you start red to black or black to red, it's the same reading. so no big deal either way. just shifting a lead can cause fluctuation in your reading. as long as the reading is stable when you take the reading you are ok.
when testing rectifiers and diodes that's when polarity will make a difference because current flow is blocked in one direction due to the nature of it's construction.

the motor, by your testing results, appears to be good winding wise.
one other test you can perform would be phase to ground test... simply test each wire pairing to ground i.e.
7,1 to ground
8,2 to ground
9,3 to ground
4,5,6 to ground
if there is no continuity on any of these , the motor is not shorted to ground.

if there is no short to ground i would be very suspect of any control component that is switching the single phase 240 volts single phase.


dumb question here... does the motor turn by hand???
 
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Mike,

Yes, it does turn by hand(very easily), another dumb question to test phase to ground Do I use the Ohm meter test as I did before?

Regards.............Kerry
 
Yes, one lead to the motor frame, and one on the wire. Check all 9 wires to ground.
 
What type of numbers am I looking for with the ohm meter, and if there are no readings then what?


Kerry
 
What type of numbers am I looking for with the ohm meter, and if there are no readings then what?


Kerry

Then life is good. That means that the windings are not shorted to ground. A reading of 0 would be a bad thing. No reading or infinite is good.
 
Hi Jim,

I tested all the wires(9) to the motor frame, my multi-meter recorded a 1(this is NOT a reading)it stays on the 1 when I turn the dial on the multi-meter
to the ohm(resistance) position.
You and Mike(Ulma Doctor) have been most helpful, any thoughts what to do now ?

Thanks............Kerry
 
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