Locked Rotor Sound

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FrancisDoody

Senior Member
Location
Durham, CT
Dual voltage single phase six lead motor. Each lead has a number marking on it. #1, #2, #3, #4, no #5, but there is a purple wire in the bundle and finally #8. Want CW rotation, high voltage wiring, Wired L1 to lead #1, Wired L2 to leads #4 and the purple wire which should be lead #5. Joined leads 2 & 3 & 8. #1 and #2 leads are connected to 1/2 of the main (run) winding. #3 and #4 is the other 1/2 of the main (run) winding. #5 and #8 make up the auxiliary (start) winding including the cap and a switch.

The problem is that after making the connection, either High or Low Voltage and apply power you get a locked rotor sound. The motor will not start.

Has anyone seen this before?

Thanks
Fran
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
130316-1513 EDT

If there is no rotation, then either the motor is mechanically locked in some fashion, or there is no rotating or induced magnetic field.

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GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
gar said:
130316-1513 EDT

If there is no rotation, then either the motor is mechanically locked in some fashion, or there is no rotating or induced magnetic field.

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Click to expand...
i would start by verifying that the cap is good. Either open or shorted would prevent the motor from starting.
 
kwired

kwired

Electron manager
Location
NE Nebraska
GoldDigger said:
i would start by verifying that the cap is good. Either open or shorted would prevent the motor from starting.
Click to expand...
And that the cutout switch is closed. May also want to verify continuity of all three windings.

Since the start is paralleled with half of the run winding, the other half of run winding is likely good (to a certain extent anyway) or you would have total open circuit and no current would flow at all. You would still probably get some rotation out of a motor with no connected load.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
130316-1713 EDT

A true single phase motor (only an oscillating magnetic field) will rotate at full load if you can some how get it up near full load speed.

To automatically start a single phase motor you have to create some semblance of a rotating field, at least for starting.

So fundamentally for starting some sort of two phase operation is created. Two ways are used, and both use another set of mechanically displaced coils. Either a capacitor is used for phase shift, or the second coil has an LR time constant much different than the run winding.

The capacitor type may use a single capacitor with no centrifugal switch and be a capacitor start and run motor. Or there may be two capacitors and one is switched off after speed is reached. Or one capacitor that is switched off after speed is achieved.

The purely inductive type of phase shift has very high start current and is switched off at near run speed. If not switched off the start coil would burn up.

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FrancisDoody

Senior Member
Location
Durham, CT
This motor is on a Powermatic Table saw manufactured in 1959. It has a Baldor motor rated at 1 1/2 HP. The shaft turns freely indicating that the bearings are fine. I believe that the capacitor needs to be checked. I will put a meter on it next time I get out there.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
In the case of our local school the older saw had parts you could actually see. Contacts that could be cleaned by spraying cleaner on a piece of paper and sliding it between the points while holding them closed. Do not use any abrasive. Yes, I charged for the Magic performed.
 
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