a-hum-won't-start motor with a complication?

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Bob Hammond
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a-hum-won't-start motor with a complication?

Post by Bob Hammond »

Hello,

A 1HP single phase capacitor motor on a dust collector hummed but didn't start. So it was disconnected from the power, the shaft was checked to verify that it turns easily, then the switch & capacitor box was opened. There is a double pole single throw switch, and the line cord is connected to it, and then two jumpers go to a shielded terminal board. The green ground wire is correctly attached to the frame. Bob discovered that the neutral jumper wire from the switch came loose from the terminal board. He reconnected it, and applied power, and the motor hummed but didn't start. Bob disconnected the power, gave the impeller a spin, and reapplied power. The motor slowly wound up to full speed.

The Questions: With the neutral return wire disconnected, how was it possible that the motor hummed? Could there be a fault where energy is returning via the green ground wire? If so, does that mean that the motor should be scrapped or could it be repaired? If it is salvageable, what is the probability that only the starter capacitor needs to be replaceds (about $5-10), or are there other components that are potentially defective?

Bob Hammond
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Re: a-hum-won't-start motor with a complication?

Post by Bob Hammond »

Further testing with an ohmmeter shows that there is no communication between the motor winding's neutral terminal and the chassis/frame ground, and there is very low resistance on the windings. So I conclude that the neutral wire must have been in slight contact with the terminal screw, and when I opened the box and moved the switch then the neutral wire pulled away from the terminal board. So tomorrow I'll buy a capacitor and see if it starts as it should. If not, I may extract and take it to a motor repair shop because it probably would be cheaper to repair because the impeller is bolted directly onto the arbor.

Daryl Kosinski
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Re: a-hum-won't-start motor with a complication?

Post by Daryl Kosinski »

There is a switch inside the motor most likely in the end where the wires go in. This switch is closed when the motor is stopped bringing the capacitor into the start circuit. When the motor reaches full speed the switch opens taking the capacitor and start winding out of the circuit. You need to remove the motor end cap locate the contacts on the switch clean them up with some 600 grit sandpaper. put it back together and it should work. If it doesn't then it could be the capacitor. If these two things do not work then the start winding may be open but that is very unlikely.

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Charlie Schultz
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Re: a-hum-won't-start motor with a complication?

Post by Charlie Schultz »

I don't know if your motor has a centrifugal switch, but on several occasions I've found that dust gets in there and prevents it from closing so that the motor will hum but not start up. The switch is usually at one end of the motor's housing.

Alan Carruth
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Re: a-hum-won't-start motor with a complication?

Post by Alan Carruth »

I've had the same problem on and off with the motor on my jointer. Getting all the dust out fixes it for a while.

Bob Hammond
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Re: a-hum-won't-start motor with a complication?

Post by Bob Hammond »

Thanks much for the advice. Disassembly should provide at least a morning's entertainment.

But before that, I suppose that I should separate the starter winding terminals and see if it has zero or infinite resistance, right? That will tell me if the contacts on the starter switch are closed or open. Hmm, now that I think of it, when it ran correctly, there was a distinct click at shutdown, and maybe a little after startup.

By the way, I got excellent service for a hard-to-replace motor at Lloyd's Electric in Ferndale, MI. The motor was a custom frame Franklin Electric from a 1956 Yates American tablesaw - fully sealed with a cast iron housing (heavy!). He replaced the bearings, cleaned it completely inside and out, and it runs like new, for ~$100.

Bill Raymond
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Re: a-hum-won't-start motor with a complication?

Post by Bill Raymond »

Bob, a centrifugal starter switch will click on startup and at shutdown; those clicks you hear suggest the switch is opening and closing, but not whether or not the contacts are actually conveying the current to the coil or that the capacitor is good. It could be dirty or corroded contacts, or the capacitor could be bad.

Bob Hammond
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Re: a-hum-won't-start motor with a complication?

Post by Bob Hammond »

After removal from the d/c body, I found that the centrifugal brake mechanism is fully exposed on the rear end of the motor. It was immediately obvious that one of the weights was cockeyed. A closer look revealed that one of the compression springs had broken. Although I was able to reseat the weight, I don't think that this will do, because the mechanism is unbalanced. Maybe I can find four comparable springs at a hardware store. The unit is a Jet-650 about 20 y/o, so I'm not sure that they would stock the spring.

Bob Hammond
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Re: a-hum-won't-start motor with a complication?

Post by Bob Hammond »

The broken spring is the short one on the right shoe, and the fragment is in the jaws of the needlenose pliers. I'm happy it didn't drop into the motor.

I spoke with Mr. Lloyd (mentioned above). He told me that finding the spring or brake would likely be very difficult and that Jet would be happy to sell me a new motor. He offered to look it over free of charge and he would search through his heap of old motors and see if he can find something for me. That's what I call old school Detroit customer service.
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Barry Daniels
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Re: a-hum-won't-start motor with a complication?

Post by Barry Daniels »

I have been through the local hardware store spring selection many times and I bet you can find a close replacement for those. It would be worth a shot and won't cost more than a few bucks.
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Bob Hammond
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Re: a-hum-won't-start motor with a complication?

Post by Bob Hammond »

Jet doesn't stock the parts any longer. The repair guy suggested a Grizzly part number for the entire switch, at $5 plus shipping. I'll give Grizzly a jingle to check that it will fit the arbor.

I also measured the springs for the wire gauge, length, and number of turns, and then went to the hardware and picked up a set of similar springs for $3. I expect that if they're a bit weak that the switch will open earlier and close near or at full stop (no braking action, but so what- no harm would be done;its not a saw. If they're too strong then the starter circuit wouldn't be cut out, and that would not be good. So we'll see what happens.

And then there's the third alternative; Clip the other three springs to the same length as the broken one.

Bob Hammond
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Re: a-hum-won't-start motor with a complication?

Post by Bob Hammond »

Before I forget (again), the plastic collection bags for this 14" machine were unavailable locally, and they seemed a bit pricey anyway (5 per $18+shipping). I found that orangebox trash compactor bags work just fine at 30 bags for $10. I cut off the handle 'ears' and fold the excess neatly underneath a bungee cord lasso, and then put the metal strap clamp on too. They would also fit a 16" diameter collection fitting. This setup works fine with a 12' run of rigid 4" pipe with wye branches to the bandsaw, drill press, and lathe.

Bob Hammond
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Re: a-hum-won't-start motor with a complication?

Post by Bob Hammond »

The tech guy at Grizzly was extremely helpful. He found a switch that will work - $4.25 plus $9,95 shipping.

Bob Hammond
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Re: a-hum-won't-start motor with a complication?

Post by Bob Hammond »

There's always a wrinkle. The Grizzly part fit ok, but the motor wouldn't start. Annoyance>disassembly>check>reassembly>annoyance>disassembly>check>reassembly did not bring joy. It turned out the power switch broke (sigh), but I found a direct replacement nearby for $10 (and no shipping costs!). Everything is A-OK now.

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