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Thread: Puzzling Motor Problem

  1. #1
    Join Date
    Feb 2017
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    Puzzling Motor Problem

    I have a Jet 2HP 230V 8" helical head jointer. The motor won't start on a seemingly random basis. Since the jointer is still under warranty (for a short time yet), Jet is replacing the motor so I'm not complaining. However, I'm troubled by the problem and am concerned that it might not be the motor.

    More details - I can use the jointer repeatedly with no start/stop problems but the very next time I use it the motor won't start. Then it won't start for awhile until one day, it just starts again and the problem persists for a period of time until the motor starts again.

    Here are a list of things which have been eliminated as the cause:

    1. Consistent, adequate power - The power company has verified that 240V is available into the house and I have further verified via a tester that there are also 240V at the outlet. Jet has indicated that the motor requires a minimum of 208V to start. Since the measured power has not been below 240V when the motor won't start, this is not the cause.

    2. Jointer Power Switch - Jet previously supplied a new switch which I installed. The jointer worked for about 5 uses then again wouldn't start. I bypassed the switch at Jet's request and the motor wouldn't start when plugged into the outlet.

    3. Capacitor - Jet previously supplied me with a new capacitor and this was installed at the same time the new switch was installed. Jet indicates that, in their opinion, it isn't a bad capacitor because there is silence when the switch is turned on rather than a humming sound (which would indicate a bad capacitor).

    4. Motor Plug-In - A cord from the motor plugs into the cord from the switch. I have tested this plug-in connection by unplugging and replugging several times and/or holding the plug end securely together. Only once did the motor start, but the random starting of the motor is the actual problem. Right after that it wouldn't start again.

    Any suggestions of other causes besides just a bad motor? I would hate to have the motor installed; then have the same problem. Thanks in advance for any suggestions.

  2. #2
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    The only thing left is the centrifugal switch inside the motor. It’s either dirty or damaged.

  3. #3
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    Mar 2016
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    Elmodel, Ga.
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    This may sound stupid, but have you checked the cord? I had a new machine, (blower motor), not a Jet, that had a bad place on the cord. I could wiggle the cord, or sometimes just move it a little and all was well. Do it again and it wouldn't budge.

  4. #4
    Join Date
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    Quote Originally Posted by Randy Heinemann View Post
    Jet indicates that, in their opinion, it isn't a bad capacitor because there is silence when the switch is turned on rather than a humming sound (which would indicate a bad capacitor).
    The silence also makes it unlikely that the centrifugal switch is at fault. No hum is a strong indicator of no power to the motor.

    Some possible causes, in order of likelihood:

    1. Connections
    2. Switch
    3. Cable
    4. Motor

    You've already replaced the switch so, while you could have gotten another bad one, it's probably not at fault.

    For the connections let's start at your power outlet. You've verified power there. The next point is the power connector on the power cable. If it's a molded connector about all you can is bend the cord tightly where it enters the molded part while running or trying to run the motor. Otherwise open it up and make sure everything is tight. Next are the connections to the switch which you have just replaced so presumably those are good. The molded connectors breaking the cable from the switch to the motor can be checked the same way as a molded connector on the power cord. Last, and a resonable probability, are the connections at the motor. With the power cable unplugged open up the connection box on the motor and make sure all of those connections are secure.

    Finding an intermittent open in a cable can be difficult although Steve's technique can be useful. Using your tester to verify power at the motor in that cramped space and with a motor that could start up at any time is not something I would recommend.

    If you've gotten to this point and the only things left are the cables and the motor it might be worthwhile to have Jet send you a new set of cables to try before trying to replace the motor.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

  5. #5
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    David did an excellent job, but I just want to add. Depending on who wired your house or shop the cheap 49 cent outlets are junk. I would replace the outlet with a good grade heavy duty one. Plan on paying about three bucks or so for good one. Who knows when you open up that box to replace the outlet you might find some loose wires.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  6. #6
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    So motor replacement then.

  7. #7
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    No damage to the cord either from the motor to the switch or from the switch to the plug (which I wired myself anyway).

  8. #8
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    I wired the shop and the 220V outlet later. I don't know about cheap outlets but I didn't shop for the cheapest. However it's what they had. Wouldn't the outlet show there wasn't power when tested if it was bad though?

  9. #9
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    Quote Originally Posted by Randy Heinemann View Post
    I wired the shop and the 220V outlet later. I don't know about cheap outlets but I didn't shop for the cheapest. However it's what they had. Wouldn't the outlet show there wasn't power when tested if it was bad though?
    From my experience in the electrical field since 1962, I have seen things that checked for good voltage even when they are bad. It only takes a very thin wire to show the voltage. It takes a good solid connection to supply the amps needed. If its 220 volt outlet more than likely its fine, but checking the connections might not hurt. Even the ones in the circuit breaker panel.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  10. #10
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    Sounds like you know a lot more about motors than I do. Opening up the motor is a difficult problem. The motor is mounted so that there is only access on one side inside the enclosed cabinet below. That's one of the reasons I wanted Jet to send service out to deal with this. To this point, I wasn't even able to get at all the motor mounts to get the motor loose or out of the cabinet. I tried when Jet Service wanted to assign installation to me. I will ask the service people when they come out to install the new what their experience with Jet is as they have been Jet service in my area for awhile. So, if any checking is being done, they will need to do it before and after the new motor. Problem is random and intermittent which means it might not show up when I want it to.

  11. #11
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    When my JET band saw was new the motor had issues. They finally sent a new one, the wrong one! Had to box up and send back. The one I got then was perfect, and install was not easy but it got done.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  12. #12
    Lack of humming really seems to indicate a power supply issue.

    Can you measure the voltage AT THE MOTOR when it SHOULD be on, but isn't? I bet you'd see no voltage.

  13. #13
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    Lack of humming could also be a dead spot on the armature

  14. #14
    Quote Originally Posted by Dan Friedrichs View Post
    Lack of humming really seems to indicate a power supply issue.

    Can you measure the voltage AT THE MOTOR when it SHOULD be on, but isn't? I bet you'd see no voltage.
    ^+1

    Randy, this is a great place to apply 'law of halves' to trouble-shoot electrical problems. Test in the middle of a given system and determine which 'side' is bad. Test again in the ~ middle of that bad half and isolate the bad half of that half ...... repeat as necessary. The problem's possible location gets narrowed down quickly.

    Test when the motor won't start*:
    - If you have power at the output side of the controls (= approx middle?) , then the problem is in the last half of the system (wiring to the motor, or in the motor). First half is fine.
    - - If you measure the voltage at the motor and there is rated voltage, then the problem is in the motor. (All else is fine.)
    - - If you measure the voltage at the motor and there is no voltage, then the problem is in the wire between the starter & motor.
    - If you have no power at the output side of the controls, then the problem is in the first half of the system (power supply or starter). Second half may be fine, but is yet to be determined.

    ....repeat until you find the 'break' in the system.

    (I use 'half' loosely, pick convenient spots to test voltage that have accessible points (terminals, wire nuts, etc).
    ________
    * Please remove the belt and use good judgement when the controls/JBs/peckerhead are open!
    Last edited by Malcolm McLeod; 11-21-2017 at 1:46 PM.

  15. #15
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    Quote Originally Posted by Jerome Stanek View Post
    Lack of humming could also be a dead spot on the armature
    AC induction motors do not have armature and brushes.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

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