runing capacitor

Discussion in 'General Electronics Chat' started by electronis whiz, Jun 29, 2012.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    i'm working on fixing a big industrail stand type fan made by fridgid i guess form the 1970-1980s. it was running then it started making a bunch of noice and slowed down heated up some. oiled the berings tryed it it hummed but wouldn't spin up. we taped the blade with a screw driver and it took but didn't run very fast. In the switch, power conection enclose i removed there was a big metal oval shaped capacitor. I think this is a run capacitor i looked up the values and got run capacitor. here are the numbers on it. york 36 03 78 4 mfd 370VAC 1010. then it says contains combustable fluids use caution in disposal. this makes me think it is an oil capacitor. it does have a red polarity mark. from the symptoms i figured it was this and pulled it out. when i pulled it out i noticed the end with the terminals is kind of bulged out. it has a gob of solder on this side looks like a presure relief but it is iether ok of didn;t get to the pint of breaking.
    is this an oil capacitor? i have seen a few online that look like it but not sure what this is to compare it. i would think if ratings are the same anythin would work as long as it fits the enclosure cover. is that corect? does this sound like a failed one? i have no way of rely testing it with what i have. other than charge to 12v and see if it holds. but that doesn't tell if it is the proper value.
     
  2. DMahalko

    Senior Member

    Oct 5, 2008
    175
    14
    Replacing the capacitor will probably fix it.


    There are different motor designs, capacitor-start only, and also capacitor start with capacitor run. Take a look here to learn how this works:

    http://www.allaboutcircuits.com/vol_2/chpt_13/9.html


    Capacitors from the 1970's and earlier had PCBs which are toxic and must be disposed of as hazardous waste. From about 1980 onward there had to be a "NO PCBs" label to identify if an oil capacitor was a newer safe design.

    I don't know if the "NO PCBs" labeling is still required for new oil capacitors.
     
  3. DMahalko

    Senior Member

    Oct 5, 2008
    175
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    A picture of the label may make identifying it easier. Differences in number size may separate the numbers into groups such as a date code and serial number.

    This: "york 36 03 78 4 mfd 370VAC 1010"

    May mean: York model 36 , Manufactured March 1978, 4 microfarad, 370 volts peak AC rating (handles up to 261v AC RMS), serial #1010
     
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  4. #12

    Expert

    Nov 30, 2010
    16,310
    6,816
    It's an oil filled run capacitor of 4 uf@370 volts. The bulge is a dead givaway that it is bad. The solder blob is the fill hole, not a pressure relief. The red mark doesn't mean it is polarized, it means the internal fuse is on the marked terminal.

    You can't test them with a meter because they change capacitance according to the voltage applied. The only way to test them is to hook them up to 120 volts AC or 240 volts AC and measure the current they allow. Then calculate the capacitance.

    ps, if you want to mess with somebody, tell them the date code is the 36th of March, 1978.
     
  5. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    519
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    dmahalco that is kind of what i was wondering about that all i knew was the values. i tested with ohm meter on 20 m ohm and nothing. also applied 30 vDC in sires with voltmeter and regitered nothing. so i'm pretty sure it's bad.
    i found a few replacements a proline brand and dayton. think i'd prefer to go daton seems i hered of them before. tryed the elna site they didn't seem to have anything like that. any brands i should avoid? probley york, samxon from what i'v seen fro mexperince.
     
  6. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    i looked at that page that is kind of what i was suspecting based on it slowed down and filed to start. I'm probley bot understanding this corect but acording to this it should be imposible for a shaded pole motor like used in small fans and other things to even start without outside force. that is how i under stood it. or does size make this different?
     
  7. DMahalko

    Senior Member

    Oct 5, 2008
    175
    14
    I don't know what you mean by York isn't a good product, from what you've seen?

    This York lasted apparently from 1978 to 2012 .. 34 years? Sounds like pretty good quality to me. :)

    It probably hasn't run constantly that whole time, but 34 * 365 * 24 = 297840 hours of life until failure.

    I'd buy another.
     
  8. DMahalko

    Senior Member

    Oct 5, 2008
    175
    14
    From that All About Circuits page, this sounds like a permanent-split capacitor motor if there's just one capacitor and no centrifugal starting switch.

    The capacitor-start and capacitor-start/capacitor-run motor types will have centrifugal weights on the drive shaft that open a starting switch when the motor starts spinning fast enough, turning off the start-capacitor circuit.


    Without the capacitor, the second winding in a permanent-split capacitor motor isn't doing anything so the starting torque output is maybe 50% or even less, than what is possible with a working capacitor.

    This would also be why you need to give it a push to get it going, and also likely why it doesn't get all the way up to speed without the capacitor. The second coil isn't energized at all without it.

    Also without the capacitor, the motor can probably spin in reverse if you plug it in and give it a helping push to get it moving that way. This would never be possible with a good cap, since the pulsing will always follow a regular 1-2 delayed-pulse step across the two windings.
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,022
    3,236
    A good capacitor will look like an open circuit and draw no current with a DC voltage applied, so your test does not show the cap is bad. The initial application of a DC voltage will show short blip of current, but that's all. You need to apply an AC voltage and check the AC current to determine if a capacitor is open.

    But from your description of the motor operation, it would appear that the cap is bad.
     
  10. crutschow

    Expert

    Mar 14, 2008
    13,022
    3,236
    Without the capacitor, the motor will have no starting torque. The stator magnetic just oscillates with no net rotation to start the rotor. The capacitor changes the phase of the second winding to give a rotating field and thus starting torque.
     
  11. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    519
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    thanks all. got it fixed had to order the cap from granger. like $5 with 10 shipping. for a lille cap that can goe in a med size envolope. seems to be good as new. somthing you get i guess when bying older stuff. still about 150 chaper than a new one, if this din't fix it figured find old motor somwher and weld it on the stand but didn't have to.
     
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