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Thread: motor troubleshooting question.

  1. #1
    Join Date
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    motor troubleshooting question.

    air compressor, 1ph/208v motor.

    running current is 23.8 working under load. 5.3kw. 7.5 hp TEFC

    starting is another thing......
    stutters badly for five or six seconds, then lights up
    and runs smoothly.

    i'm guessing the centrifical switch has either stuck
    open, or closed. if stuck open, there is no starting
    cap.

    if stuck closed, it burnt out the starting cap.

    i usually just remove and take to a motor shop.
    is there a way i can easily test the centrifical switch?

    or, does it sound like something else entirely?

    it was working fine, until they moved it about 7'
    further down the wall. same circuit, same feeders,
    same everything. now, it's like trying to kick start
    a harley with one plug wire disconnected.

    motor's been in service a year and a half.
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  2. #2
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    Can you hear it unloading the air pressure on the head when it turns off?

  3. #3
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    Quote Originally Posted by Barbqranch View Post
    Can you hear it unloading the air pressure on the head when it turns off?
    #1 question.
    Tom
    TBLO

  4. #4
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    Quote Originally Posted by Barbqranch View Post
    Can you hear it unloading the air pressure on the head when it turns off?
    One you get above 5HP, it is not uncommon to have unloaders that hold the suction valve open as opposed to dumping the head pressure. Either way, if the compressor is not properly unloaded, it could be the problem. Does it start ok when the entire system is at zero pressure? If so, unloading is likely your problem.

  5. #5
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    Quote Originally Posted by Barbqranch View Post
    Can you hear it unloading the air pressure on the head when it turns off?

    yes.... but i haven't bled the system down to zero yet. it may be leaving some head pressure there.

    i'll test further tomorrow.
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  6. #6
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    If open capacitor circuit, whether centrifugal switch is stuck or if capacitor is burned out, it probably won't have enough torque to start at all.

    I agree with others to make sure pressure unloader works, also maybe make sure if there is multiple capacitors (series or parallel) that all of them are good.

    Some chance there is a fault in aux winding or even fault in a start capacitor but still works enough to get it started, once up to speed the aux winding is out of the circuit and it runs fine.

    Poor contact in that centrifugal switch is also a possibility.

  7. #7
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    I'm with the others.

    I'd bleed the whole system down to nothing, and clip some test leads on the bottom of the starter to monitor the voltage while you fire it off. Then go from there...

  8. #8
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    Quote Originally Posted by Cow View Post
    I'm with the others.

    I'd bleed the whole system down to nothing, and clip some test leads on the bottom of the starter to monitor the voltage while you fire it off. Then go from there...
    yeps. i'll log voltage and current at the contactor.... i was looking
    at the current when starting, and instead of a spike and drop off,
    it kept fluttering between 50 and 110 or so amps, until it hit synchronous
    speed.
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  9. #9
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    Is the motor actually designed/rated/labeled for 208 volts? A 230-volt motor on a 208-volt circuit might be hard to start.

  10. #10
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    The centrifugal switch you can only check by stripping the motor end bell.

    This is what I found inside a S Ph motor

    MIET ARPS

    I’m English so what do I know?

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