Motor Problem ......... or not?

[Bob Deroeck]

I'm in the process of recommissioning a 1974 Powermatic 66 table saw I bought last year. I ran the motor for maybe 5 minutes before I bought the saw. Then it sat in my garage for a year while I built my workshop and ran power and gas lines underground.


In the last week I've done maybe 5-10 rip cuts on the saw while making a mobil base and support legs for the extension table. Today after making a couple of cuts, the motor wouldn't start. It hummed and the fan was oscillating a few degrees on either side of the shutdown position, but it wouldn't kick in. I quickly shut it down. Waited a few minutes and tried again. Same result. There was no smoke or burning smell from the motor. The motor is a 3 HP single phase Baldor, built in 1989. From reading posts from the SMC archives, it seems the likely causes of the problem are either the start capacitor, the centrifugal switch that shuts off the start capacitor after the motor attains a certain RPM, or the start windings.

I disconnected the power cord, put on rubber gloves and removed the cover for the capacitors. There was no oil leakage and no smell from the capacitors. I removed each connector from each capacitor and reconnected them. But, all connections were clean and tight, so I doubt poor connnections were the problem. Anyhow, I put it back together and the motor started right up 3-4 times with no problem.


What do you guys think caused the problem? Can start capacitors operate intermittently? My impression was that when they fail, they fail. Is this correct?

I also suspect that when the start windings fail, they fail. Is this correct?


I'm guessing the problem might have been with the centrifugal switch and that it was stuck in the open position when the motor wouldn't start and that my monkeying around with the capacitors (including tapping the capacitor cover with a rubber mallet to free it from the motor case) might have knocked the centrifugal switch closed allowing the motor to start. Does this make sense?

My current plan is to do nothing further and see if the problem happens again. If it does, I'm thinking of taking the motor apart to check the centrifugal switch, the bearings and inspect the windings and rotor. I've looked at the Baldor parts drawing and everything looks pretty straight forward. Are there any things I should be weary of if taking the motor apart, such as things going "sprong" and whizzing past my ear as I remove the guts from the motor case?


Any suggestions are welcome.

Thanks.

Bob

[John McClanahan]

I think you are on target with the switch. If the motor hums for several seconds without tripping the breaker, the switch is sticking, or the start capacitor is internally "open". If the start capacitor in internally shorted, the breaker will trip after a couple of seconds.

[Mike Henderson]

If the motor is not "closed" (such as a TEFC), blow air into the inside and you'll likely clear the dust that's affecting the centrifugal switch.

Mike

[Thomas Hotchkin]

Bob
A couple things, your post did not say that motor was TEFC or not. If it is the then the centrifugal switch, is well protected from dust and dirt. If not, I would be temped to blow it off with compressed air. I have not seen motor capacitors operate intermittently, all of my capacitors failures have been shorts or opens. Just removing and reconnecting the connections at both capacitors may have solved your problem. If there was and open in start windings there would not be any humming coming from your motor. I have not open up a Baldor motor as of yet. All I can say is if the end caps do not pull-off easily add a little heat (hair dryer) at bearing positions. If is does not start again a small tap from rubber hammer on the motor case next to the fan will point to the centrifugal switch. Tom

[Bob Deroeck]

The motor is a TEFC type.


Bob

[Curt Harms]

A bad capacitor may not show physical damage. I had a start cap crap out and it looked fine. It does seem curious that removing and replacing seems to have fixed it though.

[Don Jarvie]

Are you running the motor through a magnetic starter? It may or may not be the problem. Before you take the motor apart you may want to disconnect the wires going into and out of the starter and hooking them up direct and then plug in the motor. If it runs fine then its the starter, if not the motor.

If you go to vintagemachinery.org and go to the electrical section of the WIKI. There is a post called Baldor Motor repair which shows you how to take apart the motor and fix the centrifical switch and put it back together. It may not be the switch but how to take apart the motor is helpful. It may just need a good cleaning.

[Rod Sheridan]

As the motor was hunting between poles the issue isn't the starter, it's in the starting circuit.

From the symptoms and intermittent issue it sounds like a centrifugal switch that needs cleaning and lubricating............Rod.

[Bill Bukovec]

Bob,

Can you give the motor a good smack with a hunk of wood or rubber mallet? If it starts, you know it's the switch.

My jointer motor does the same thing. For now it's easier to smack it than to fix it. I have the problem intermittantly, but someday I will have to fix it.

Good luck,

Bill

[Bob Deroeck]

The problem only happened that one time. Since I whacked the motor case with the rubber mallet to free the capacitor cover, there has been no problem. Maybe I've just got lucky. If it happens again, I'll go directly to the rubber mallet. Meanwhile, I'll check out the post on vintagemachinery.org on Baldor motor repair in case I need to clean and lube the centrifugal switch.

Thanks all for your comments and suggestions.


Bob