Author Topic: Electric motor help - won't start without 'manual' intervention  (Read 307 times)

Offline mdlbldrmatt135

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I've got this OLD dental compressor in the basement shop. I re plumbed it to a new tank when the original developed a leak.  It seems the motor won't start without "jump' starting it by spinning the pulley on the compressor.

Can anyone guide me thru troubleshooting it?  I can take some pics of it tonight.

The issue with just replacing the motor, is the fact the compressor is mounted above it, using some holes in the motor case.   


Offline goodfellow

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #1 on: March 11, 2019, 10:42:51 AM »
Is it a capacitor start motor? i.e.  Does it have separate "start" and "run" capacitors ? (usually indicated by two humps on top of the motor housing)

Offline mdlbldrmatt135

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #2 on: March 11, 2019, 10:51:14 AM »
It's been so long since I've looked I'm not sure off hand, in other words I's been forever since I've done any (pressure) resin casting.....   Pics will follow tonight.     

Offline fatfillup

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #3 on: March 11, 2019, 05:19:18 PM »
Could also be the centrifugal start switch on the back of the motor if it has one. 

I would test the capacitors first and then pull the rear cover off the back of the motor and look at the switch.  I am no expert by any means but if the switch is stuck open, it could cause the problem you are referring to

Also, do you have a heavy enough cord and or circuit to start it.  Some motors pull a lot of current in start mode and a light cord may not be heavy enough to run it,

Offline goodfellow

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #4 on: March 11, 2019, 06:04:58 PM »
It could also be a split-phase motor -- start windings don't go out often, but it does happen.

Offline bonneyman

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #5 on: March 11, 2019, 06:24:38 PM »
I've got this OLD dental compressor in the basement shop. I re plumbed it to a new tank when the original developed a leak.  It seems the motor won't start without "jump' starting it by spinning the pulley on the compressor.

Can anyone guide me thru troubleshooting it?  I can take some pics of it tonight.

The issue with just replacing the motor, is the fact the compressor is mounted above it, using some holes in the motor case.

Sounds like a specialty motor, made for the OEM. Might be a bit tough to find something like that for reasonable.

If it's not tripping the breaker when you try to start it, chances are nothing is grounded. Windings could be overheated and shorted but you can almost always smell the burn if you get a cover off. Looks and smells OK - pull out an ohm-meter. What resistance reading should you get? Impossible to say over the phone.  ;D Less than infinity and more than zero is a good sign. If you get some ohm reading make sure you're getting power.

Centrifugal switches can be cleaned or replaced, and capacitors are mostly Chinese-made now so cheap as hell. In other words, even if they "test" good I'd replace them anyways.

Here's the on-line version of a motor troubleshooter I've used for years.

http://www.fasco.com/fasco/assets/File/F0007E_Fasco%20Facts.pdf
« Last Edit: March 11, 2019, 06:26:17 PM by bonneyman »

Offline slip knot

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #6 on: March 11, 2019, 08:40:57 PM »
be reeeaaal careful with those capacitors.  short out the connections prior to working on it.

Offline mdlbldrmatt135

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #7 on: March 12, 2019, 04:48:12 AM »
Pics attached.....   I forgot last night... log day at work, and got wrapped up relaxing to Big Bang Theory....

Edit:  poking around on Ebay... I find quite a few, but they all have a geared output shaft as they're listed as gear reduction motors.
« Last Edit: March 12, 2019, 05:39:09 AM by mdlbldrmatt135 »

Offline fatfillup

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #8 on: March 12, 2019, 08:35:19 AM »
Well looks like a split phase motor, I can't help other then suggest a cleaning with a non conduct motor cleaner

Offline mdlbldrmatt135

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #9 on: March 12, 2019, 08:45:20 AM »
On a surprise note... Bodine electric company still exists.  I did send a contact form in as the model/Serial No search turned up nothing.   Maybe they'll reply...

I'm remembering I had left it plugged in at some point and I think it had overheated as I had to depress the overload to get it to start after that.... but it must have done more damage.   

I guess if push comes to shove and it's not repairable, I can redo the re-tanking job I did on this, and come up with a new mount for the compressor relative to a new motor.

It's a nice quiet little compressor.


Edit:   Reply from Bodine:

Being a split phase motor itís most likely the centrifugal switch that starts the motor, as they have a life span of 50K to 175K and that particular motor product line has been obsolete for at least 30 years. Parts are no longer available for them.


« Last Edit: March 12, 2019, 09:23:06 AM by mdlbldrmatt135 »

Offline slip knot

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #10 on: March 12, 2019, 05:11:53 PM »
If its the switch it may just need cleaning. from what I remember its just a set of points that disconnect as the motor spins up.

Offline mdlbldrmatt135

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #11 on: March 13, 2019, 04:57:21 AM »
Looks like I shall pull it apart, once the current project is finished up, and I can clean up some flat space to work on.

Offline fatfillup

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Re: Electric motor help - won't start without 'manual' intervention
« Reply #12 on: March 13, 2019, 08:52:42 AM »
If its the switch it may just need cleaning. from what I remember its just a set of points that disconnect as the motor spins up.

Exactly my experience