Stumped by a Motor Capacitor

Discussion in 'General Electronics Chat' started by pgrodz, Mar 19, 2013.

  1. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    Good Afternoon Everyone,

    I have pulled most of my hair out trying to figure this out and after much frustration, and a few late-night pints, I'm turning to the pro's for help, guidance, and any suggestions you have.

    The issue: I posted a while back here, stating that the starter capacitor blew out on the motor to a woodworking machine in my shop. After a few mistakes, I obtained the correct capacitor (Grainger model, same as the manufacturer recommended spec) and the machine was back up and running.

    Approximately 2 months later, the capacitor blew again. I pulled out the centrifugal switch, cleaned the connector leads, replaced the capacitor, and everything was honky-dory again...

    Another 2 months, another blown capacitor... This time I took the switch to a motor repair shop. They stated the switch was in good working condition and all I needed to do was file the contact pads so they touched with a maximum amount of surface area. Fixed the switch, replaced the capacitor, everything should be fine...

    Capacitor blew again this morning... And so, I have attached pictures of the centrifugal switch, which I believe is still sticking and causing the start capacitor to overload.

    My questions:
    1. is the carbon burn normal for a centrifugal switch?

    2. I set the weighted spring switch as far from the metal ring as possible to ensure near immediate release of current to the start capacitor... Is there an optimal spacing or positioning for the spring weighted portion of the switch?

    3. I'm trying to troubleshoot other reasons why this might be happening...
    -Can I put a different capacitor in that can handle a longer duration of current?
    -The power coming into the building is 3 phase 240v, goes through several transformers and other set-ups in the neighboring business before coming into my shop at ~215v... could this change in phase/current cause the capacitor to fail?
    -The machine sees a large amount of on and off... could this be contributing to the failure (~2-5 on/off cycles per hour)?
    -Are the Grainger capacitors I keep replacing not reliable?

    Any advice, comments, suggestions, or if you want any more information would be greatly appreciated. The more I try to troubleshoot this, the more I feel like I'm going in circles. Thanks again for any input.
    Paul
     
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  2. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    * And Sorry, I just realized a typo, the power to my shop is reading ~115v at the outlet, not '215v'

    Thanks
     
  3. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    excessive repeated on/off cycles will hurt a motor, but not the 2-5 an hour you mention. What is the HP of your motor, and the actual Voltage / Microfarad of the cap... and the age of the motor.

    It being a wood machine, I assume the sawdust has been cleared out... and the centifuge unit that operates the switch is clean and snappy in operation, so it can kick the start windings out as it is supposed to. The centrifuge will get sticky / sluggish in time.
    Being Graingers, this is usually not a problem, but are the new caps you've been getting made in China ? That is rapidly becoming a worldwide problem in itself...

    keep me posted on this... I worked in motor repair for 12 years before I retired, and this isn't making a whole lot of sense.

    PackratKing.
     
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  4. Sue_AF6LJ

    Member

    Mar 16, 2013
    45
    27
    Keep us all posted on this, your problem has my interest.
     
  5. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    PackratKing,

    The motor is manufactured by Qin Wei Electric Corp... The motor is original and approximately 10 years old, so I'm guessing the internal winding isn't causing any troubles. The motor is a 5hp, 3.7KW, single phase, 220v, 26.6amp unit. We currently have it set up with a 30amp breaker so I know I'm not overloading the whole unit.

    The spring mechanism is still quite snappy, and there is virtually no dust build-up on the switch or springs. There was minor dust accumulation on the actual metal contact points, and the circuit board component, but pretty much what you see in the pictures was what I found when I opened up the motor and removed the switch.

    The start capacitor, model 2MEU6, was manufactured in China for Grainger.

    I wasn't aware of any major issues with Chinese parts coming through lately... Are there issues with inferior metals or something?
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    In the OP, you state it is 215V, in second post, you state power is 115v, now it's 220v?

    The contacts in the photo are fairly pitted/scarred. Can you get a replacement set? Measure the resistance across them while they are closed, it should be in the milli-ohm range.

    --ETA: See This Post in your original thread.
     
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  7. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    The motor is a 5hp, 3.7KW, single phase, 220v, 26.6amp unit.

    Have you got the option of running it on 220 volt... the 26.6 amps seems awful high since it would spike near 60 amps or better to start.....

    Yes, not to be a grinch, Chinese parts can be an issue, they are not famous for quality
     
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  8. Sue_AF6LJ

    Member

    Mar 16, 2013
    45
    27
    I thought the OP said it was running on 220V.
    The current drain is in the ballpark for a 5HP motor.
     
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  9. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    I have a 5 hp motor on my table saw. The label says: 20.8A @ 230 VAC, full load. My power company delivers a bit high so I am running at 249 VAC (measured) and it spikes at 76 amps to start.

    Just a note for you to use a a reference.
     
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  10. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    Hope this solves the confusion about the power, at any regular 110 outlet in my shop, voltage is measured around 113-115v.

    At the outlet for my planer, voltage is measured at around 215-218v. Now I would assume if I'm pulling two hots into the unit they should be double what the single outlet has... 113v-115v (x 2) should give me 226v-230v??

    The motor is rated for 220v power, and to the best of my knowledge, my power isn't coming in higher than normal in the shop.


    PackratKing, as for the contacts on the switch, yes they are starting to pit out... I sanded them smooth with a fine thumbnail file before re-installing it last time...

    Any recommendations on better ways to sand/file the contact leads down?

    thatoneguy, I tried looking for replacement contact leads... but the usual places I get my parts didn't have the correct replacement parts.
     
  11. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    It sounds like your capacitor is used to reduce the motor running current (improving P.F.)...the centrifugal switch disconnects the starting windings after the motor starts coming up to rated speed. The voltage rating of the capacitor should be 370 VAC (min.) for 230 VAC service. My guess is the capacitor corrects maybe 8-10 amps of current. I would try a domestic (not China) capacitor rated at the same mfd., but at a higher voltage (600 VAC).

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
     
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  12. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    Duane,
    Thanks for the advice... quick question, what's the P.F.?

    And I'll take a look for a capacitor you described and post the link on here for you to check out before purchasing it... the first time I bought a DC rated capacitor, not an AC rated capacitor, and I'd prefer not to learn the hard way this time.

    Thanks
     
  13. cork_ie

    Member

    Oct 8, 2011
    348
    58
    Where in the world are you?

    From your posts I get the impression that your supply voltage is standard USA single phase 110V 60 HZ with 220 V on split phase. Is this correct?

    If your saw motor is rated 220 Volt single phase then your capacitor values will not be ideal in a split phase system. Also check the frequency rating for the motor
     
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  14. cork_ie

    Member

    Oct 8, 2011
    348
    58
    The run capacitor is to create lag to artificially generate a quasi split phase system from single phase


    http://www.allaboutcircuits.com/vol_2/chpt_4/2.html
     
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  15. cork_ie

    Member

    Oct 8, 2011
    348
    58
    You assume wrong and I am sure this may be at the nub of your problem

    http://www.allaboutcircuits.com/vol_2/index.html
     
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  16. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    Cork ie,

    I'm in Philadelphia PA, USA. So I'd assume my values are as you stated. I do know the building I'm in was originally used for large scale manufacturing...

    There is a whole series of large service panels, power disconnects, and other boxes I couldn't begin to tell you what they are for. I do know that the Planer was used in a separate shop up the road with no issues for the first 8 years of the life of the machine.

    And the motor is rated for 60hz
     
  17. tinkerman

    Member

    Jul 22, 2012
    136
    34
    Capacitors produce leading current. It's used in the starting circuit to improve the power factor of the motor and also reduces the line current. The starting capacitor is switched out usually at about 75% of full RPM. It's not designed to stay in service more than a several seconds. The run capacitor OTOH is continuous service.
     
    Last edited: Mar 20, 2013
  18. tinkerman

    Member

    Jul 22, 2012
    136
    34

    Not necessarily. The start capacitor is most often connected across one of the two run windings which are in series for 240 volt operation. Thus the start circuit receives 120 volts. For 120 volt operation all the windings are connection in parallel.
     
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  19. Metalmann

    Active Member

    Dec 8, 2012
    700
    223


    About the points,
    I use a small, fine cut, file; for them.
    That way, the points have parallel flats, for the spark.

    Use the file between the points, using only the spring pressure.
     
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  20. cork_ie

    Member

    Oct 8, 2011
    348
    58
    I was referring to the run capacitor referred to the quote included in my post.
     
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