Sanborn motor starts fine but bogs down

by James
(Michigan)

Its ,3hp Sanborn compressor. Pump head works fine.


Take belt of motor and motor runs fine.

Put belt on (not over tight) flip the switch and motor starts running get up to about 10-15 lbs pressure and motor starts to bog down and then stops due to thermal switch popping.

Is this a capacitor problem? Start/run or is motor just junk?

Comments for Sanborn motor starts fine but bogs down

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Sep 05, 2016
ahh
by: Doug in s.d.ca

OK. Your plan is good.

Also, based on your description, you should verify that the pullies are not loose on the shaft, and that the belt tension is correct. - both have been known to cause similar problems as far as the noise is concerned.

Sep 05, 2016
Sanborn bogs down
by: Kevin

The flywheel and pump turn by hand with a normal amount of resistance. The motor is one of those "SPL" rated HP. So I am going to re-test with heavier awg wire and measure how mych it draws. I already replaced the capacitor which was burned out. It is set for 110v. I believe it bogs down because it is not getting enough amps or it is out of balance. The over temp safety cuts out. But until then it appears to be building pressure normally.

Sep 04, 2016
Motor
by: Doug in s.d.ca

Based on James's experience, yes 3450 is right.

Sounds like you may have a broken pump. It's unlikely the flywheel would be far enough out to cause very much vibration.

Try removing the belt and see if the runs OK, and try turning the pump (with no load - open the drain valve) to see if it turns fairly smoothly, or has high resistance at some point.

Why does it shut down?

Sep 02, 2016
Is 3450 too high RPM?
by: Anonymous

I got a used one that does this. Is 3450 RPM the OEM spec? Vibrates like all hell and then shuts down. Maybe the cast flywheel is out of balance.

Sep 27, 2015
Motor
by: James

Yes its just my bad English lol. It was the RUN capacitor. Sorry for confusion! Keep up the site. Might need you again!

Sep 23, 2015
Sure.
by: Doug in s.d.ca

Any time.

You said start, but it was the RUN cap, no?

Inquiring minds want to know...

Sep 23, 2015
Motor
by: James

You were correct. It was the start cap. 13 bucks and is working like it was designed to.

Thank you for the most helpful knowledgeable advice! Very much appreciated.

Thank you again.

Sep 05, 2015
capacitors
by: Doug in s.d.ca

Sure.

Let us know how you make out, would you?

Thanks.

Sep 04, 2015
Motor
by: James

Thank you. I'll try that. The compressor used to work but sat untouched for a few years. Much rather replace a 12 $ part vs a 200$ one! thanks for advice again

Sep 01, 2015
capacitors
by: Doug in s.d.ca

OK, you want to check the caps. Good chance the run cap is bad.

Less likely, the start cap is not cutting out after motor starts. That's the switch thing at the enclosed end of the the rotor.

Sep 01, 2015
Motor
by: James

Its a manatek century ac motor compressor duty motor. 115/230v running on 110. 15/7.5a 3450 rpm single phase with external start and run capacitors

Aug 27, 2015
bogs
by: Doug in s.d.ca

Could be run cap if it has one, but we don't know the model.

There's a small chance it's the check valve (which it likely has, but a few compressors don't).

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