Motor just quit. Suddenly. No smoke, no sparks. Replaced two caps, start and run.

No action, short hum and magnetic motor switch trips off.

Ohm test across black and white leads, Fluke T5-1000 meter, shows dead short.

To the shop for repair or shall I replace it?

$525 to replace.

Thanks guys/gals

Ship.

If you have a place nearby that can repair it, that’s what I’d do. At least let them look at it. And you are fortunate to have that option.

quote:

Originally posted by arfmel:
If you have a place nearby that can repair it, that’s what I’d do. At least let them look at it. And you are fortunate to have that option.

Ditto what he said . Can't hurt to try .

Does the shaft spin by hand?

Are the contacts in the centrifugal switch intact at the back of the motor? Does it actuate correctly?

quote:

Originally posted by shiftyvtec:
Are the contacts in the centrifugal switch intact at the back of the motor? Does it actuate correctly?

I had an air compressor motor that would act the same way . The centrifugal switch was stuck in the RUN position .When the compressor cut off , it would not start unless you smacked the end bell with a wrench and the switch would flop over to the START position .

If you took the leads off and tested and have a dead short, then anything else is not in the picture.

Have you ever put new windings in a motor before?

UPDATE - I Checked caps with multimeter. Appear good. Also tried new caps. No joy. Switch contacts on centrifugal switch were pitted. Cleaned with emery cloth, still no go. Pulled both ends off motor, brushless armature looks good. Only indication of any sparking were on the pitted contacts. Magnetic start/stop switch works fine.

When reassembled and powered up the overload on the mag/switch trips after maybe 2 seconds.

Open fields? Motor is 30 years old. 3hp, 16A. Has had caps replaced in 2009. Bearings are great. While it is not in a production setting (5 days/40 hrs wk). It has seen use probably 50 weeks/year.

I understand what is involved in new windings if we are talking REwinding. Think these might be pressed in as a prewound unit. Might be easier to just replace entire center section - if I could find one.

Checkout Grizzley web site. 3 hp ,220 single phase 3450 rpm for $389. This is the same motor on my Grizzly table saw.

Motored wired 120 or 240VAC? Dedicated breaker? Breaker to a outlet, cord with plug to saw?

Overload trips = high current or bad overload.
Can you use meter to check current?
If high current, is centrifugal switch clicking to run circuit? If it clicks current should drop.
If current does not drop could be bad switch not switching from starting winding or if it switched, shorted turns in run winding.
Trip to motor shop is next probably.

Saw is set up 220v, single phase, dedicated breaker. Breaker to 30A outlet, 30A plug to cord to motor switch. Overload on magnetic switch is tripping before there is enough current to trip the breaker. Panel is Square D (I installed when we built the house 30 years ago.)

Sig - centrifugal switch doesn’t even have time to speed up and disconnect, motor shaft doesn’t get any speed (like zero rpm) before tripping. I did look the switch over and all apprears normal, complete and working.

I repaired industrial woodworking equipment for 18yrs, troubleshot countless motors.

You'll have continuity across a good motor, leads T1 and T2. Symptoms you're describing is one of two things, bad motor or dropped a leg for some reason/trying to run the motor 120VAC.

You might of tried these...

Unplug the motor leads and ground from the magnetic switch. Turn on breaker or plug back in.. Check voltage between L1 and ground, L2 and ground. L1 or L2 can be dead and still read 240VAC across them. One dead, cord/plug/outlet or breaker. If that's OK, turn on the switch. Check voltage T1 and ground, T2 and ground. One dead, bad switch/dirty contacts. If that's OK, hard wire (wire nuts) the motor directly to cord. Turn on breaker. If the motor runs. it's going to jump a bit, stand on it.... Be ready to turn the breaker off immediately if doesn't start. If you don't catch it, that's OK, breaker will do it's job. If the motor runs, most likely a problem with the switch. Switch can pass voltage w/o a load, fail when loaded. 30yr old motor doesn't run and you've changed the caps... I would replace it with a Baldor or Leeson.

Offgrid - will try these first chance I get. They should quickly narrow the possible issues.

Thanks.

Lesson makes the replacement. About $500.

The unisaw motors are special as they have welded taps on them for mounting , you cant just replace it with a standard motor frame. I would run it down to your local motor rewind shop or try what offgrid suggest thats very good info.


I had a motor that did the same thing but would blow capacitors, I ended up changing out the motor start switch because of the burnt contacts as you stated and problem went away. does the motor smell burnt? or are any of the winding off color ?

UPDATE -

Checked each leg through the mag switch to ground - 110v on each. Switch would seem to be fine.

Pulled motor, plug direct connection to motor leads, with green ground - motor turned a little. I could easily count the rpm’s, as they were about 1 or 2 before tripping the breaker.

That was with two new caps. I am sure I didn’t get the caps switched (start vs. run). Don’t think I got the four leads switched on the one.