Motor Starting Capacitor on Wood Lathe

Discussion in 'Shop Talk' started by Ken Scharabok, Dec 24, 2006.

  1. Ken Scharabok

    Ken Scharabok In Remembrance

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    I blew the capacitor on my Asian-made drill press. Puff of smoke came from motor and I tracked it down to capacitor under a separate cover on the side of the motor. Motor would humm, but not turn chuck without hand rotating it first and now has almost no torque. I'm now trying to track down a replacement capacitor.

    However, to question, a friend has a Northern Tool Asian-import wood lathe. His motor got to the point to where it would only go with hand turning starting assistance and then just quit entirely. Since this is basically what mine did I asked him to check the motor starting capacitor on it. He cannot find one on the motor itself. Can it be elsewhere, such as in the on/off switch area?
     
  2. agmantoo

    agmantoo agmantoo Supporter

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    Ken, not all of the small motors use capacitors.
    Here is a copy and paste describing the differences
    Single-phase motors — These motors are commonly fractional-horsepower types, though integral sizes are generally available to 10 hp. The most common single phase motor types are shaded pole, split phase, capacitorstart, and permanent split capacitor.

    RINGS IN SHADED-POLE MOTOR DISTORT ALTERNATING FIELD SUFFICIENTLY TO CAUSE ROTATION.

    Figure 5 - Rings in shaded-pole motor distort alternating field sufficiently to cause rotation.
    SPLIT-PHASE WINDINGS IN A TWOPOLE MOTOR. STARTING WINDING AND RUNNING WINDING ARE 90 DEGREES APART.

    Figure 6 - Split-phase windings in a twopole motor. Starting winding and running winding are 90 ° apart.
    SPLIT-PHASE START INDUCTION MOTOR.

    Figure 7 - Split-phase start induction motor.

    * Shaded pole motors have a continuous copper loop wound around a small portion of each pole, Figure 5. The loop causes the magnetic field through the ringed portion to lag behind the field in the unringed portion. This produces a slightly rotating field in each pole face sufficient to turn the rotor. As the rotor accelerates, its torque increases and rated speed is reached. Shaded pole motors have low starting torque and are available only in fractional and subfractional horsepower sizes. Slip is about 10%, or more at rated load.
    * Split phase motors, Figure 6, use both a starting and running winding. The starting winding is displaced 90 electrical degrees from the running winding. The running winding has many turns of large diameter wire wound in the bottom of the stator slots to get high reactance. Therefore, the current in the starting winding leads the current in the running winding, causing a rotating field. During startup, both windings are connected to the line, Figure 7. As the motor comes up to speed (at about 25% of full-load speed), a centrifugal switch actuated by the rotor, or an electronic switch, disconnects the starting winding. Split phase motors are considered low or moderate starting torque motors and are limited to about 1/3 hp.
    * Capacitor-start motors are similar to split phase motors. The main difference is that a capacitor is placed in series with the auxiliary winding, Figure 8. This type of motor produces greater locked rotor and accelerating torque per ampere than does the split phase motor. Sizes range from fractional to 10 hp at 900 to 3600 rpm.
    * Split-capacitor motors also have an auxiliary winding with a capacitor, but they remain continuously energized and aid in producing a higher power factor than other capacitor designs. This makes them well suited to variable speed applications.
     

  3. hunter63

    hunter63 Well-Known Member

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    It might not have one, may be a shaded pole motor. Is it 115v?
    If so, it's probably toast.
    Cap are kinda big, so normally are under a cover on the side as I assume yours is? or it may be remote in the switch box. Check the wires to the switch and see if anything is in line
     
  4. Ken Scharabok

    Ken Scharabok In Remembrance

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    Yes, his wood lathe is 115v.

    I have capacitors on my two drill press and metal bandsaw. All three are belt drives. Lathe is probably direct drive. Would that have anything to do with the type of motor on it?
     
  5. Ken Scharabok

    Ken Scharabok In Remembrance

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    Just a follow-up:

    Took my motor into a local electric motor repair shop. A tad less than $20 for a new (and better) capacitor while I waited.

    On my friend's wood lathe, he said it sounded like the internal starter in the motor itself. Estimated about $30 to redo starter or about $80-90 for a motor rewind. Passed information on to friend.

    I'm fat, dumb and happy on my situation. Up to him to take whatever action he wants to now.

    Thank you for advice (which I forwarded on to him).