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7 posts • Page 1 of 1

Motor Won't Come Up to Speed

#19811 by dusty » Wed Jul 23, 2008 4:42 pm

I have an Shopsmith Emerson Motor that starts to turn slowly and then kicks the breaker. It does the same in reverse direction.

This motor is from a Crafters Station that I am attempting to ressurrect. The wiring harness and a control relay are questionable. I pulled the motor completely to make certain that one (the motor) was not effecting the other (the harness).

I think I have the harness rebuilt. I'm waiting on a relay from the component manufacturer to confirm that.

Can I draw any favorable conclusions about the motor windings based on the fact that the motor does attempt to run. I'd like to think that it kicks the breaker simply because there is insufficient starting torgue due to a bad capacitor.....but.....there doesn't appear to be a starting capacitor.

Is there a starting capacitor buried within the motor? I'm used to seeing an external housing for a starting capacitor but this motor has no such housing.

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"Making Sawdust Safely"
Dusty
Sent from my Dell XPS using Firefox.

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#19812 by dicksterp » Wed Jul 23, 2008 5:07 pm

After spending years as a toolmaker with the GE motor div., I don't recall ever seeing a start capacitor inside a motor. About the only thing buried in the stator windings was a thermocouple. Could be dirt, rotor binding slightly, bearings going bad, possibile bad start winding?, ect. Have it checked by a motor shop.

Dick

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#19813 by beeg » Wed Jul 23, 2008 5:08 pm

Does the shaft turn freely?

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SS 500(09/1980), DC3300, jointer, bandsaw, belt sander, Strip Sander, drum sanders,molder, dado, biscuit joiner, universal lathe tool rest, Oneway talon chuck, router bits & chucks and a De Walt 735 planer,a #5,#6, block planes. ALL in a 100 square foot shop.
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Bob

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#19816 by wa2crk » Wed Jul 23, 2008 6:00 pm

Hi;
Sometime ago I rebuilt a SS machine for my son and it had an Emerson electric motor. This motor had questionable bearings so at the advice of a mechanical engineer who I worked with I changed the motor bearings in the motor. This was a 1 and 1/8 HP motor and the start capacitor was indeed inside the motor. If memory serves correctly it is in the end cap opposite the spring loaded motor sheeve. If your motor is a CDR55 frame then it is the same as the one I worked on.
The fact that the motor tries to start and then trips the breaker is an indication that the start capacitor is bad or the start switch has not reset from the previous startup. If you do not feel comfortable in working on the motor yourself a good electric motor repair facility can repair any motor.
Bill

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#19819 by cowboyplus » Wed Jul 23, 2008 7:46 pm

It would be my first guess that the centrifical switch is not opening after rotation has started, keeping both the start and run windings energized. The shaft travel could be gummed up or the contacts are welded together.

Motors do not have to have a capacitor. Single phase (or any odd phase) motors do not use capacitors. Capacitors are used when an additional phase is used for additional capacity, either starting or start and run, as an independent winding and the capacitor is used to make the additional 90° phase.

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#19822 by a1gutterman » Wed Jul 23, 2008 8:05 pm

[quote="cowboyplus"]...Single phase (or any odd phase) motors do not use capacitors. Capacitors are used when an additional phase is used for additional capacity, either starting or start and run, as an independent winding and the capacitor is used to make the additional 90°]I have to disagree. I own single phase induction motors that use a capacitor start. Universal motors do not use the capacitor start and they are single phase also. Maybe you are thinking of them. Among common ones, your clothes washing machine (single phase) motor uses an capacitor start. They generally call the motor a split-phase motor, but it still operates from a single phase (110V versus 220V) power source.:) Here is a link that describes these motors very well: http://www.allaboutcircuits.com/vol_2/chpt_13/9.html
And this link is very informative too: http://en.wikipedia.org/wiki/AC_motor

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Tim

Buying US made products will help keep YOUR job or retirement funds safer.

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#19823 by cowboyplus » Wed Jul 23, 2008 8:21 pm

a1gutterman wrote:I have to disagree. I own single phase induction motors that use a capacitor start. Universal motors do not use the capacitor start and they are single phase also. Maybe you are thinking of them. Among common ones, your clothes washing machine (single phase) motor uses an capacitor start. They generally call the motor a split-phase motor, but it still is a single phase (110V versus 220V).:) Of course, 2 and 3 phase motors do use capacitor starts too.


A single phase motor with a capacitor, is actually a 2 phase motor and the capacitor makes the second phase from the first (single) phase.

The only time a 3 phase motor uses a capacitor(s) is when true 3 phase current is not available (3 - 120° phases) and 3 phase is simulated using single phase and two capacitors ( a 90° phase and a 180° phase), and it will develope only about ½ the rated HP.

True 3, 5 (the first ac motor), 7, and 9 phase motors never use a capacitor.

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