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Motor run and start capacitors, need suggestion on buying new ones

Discussion in 'Sensors and Actuators' started by sea, Aug 30, 2013.

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  1. sea

    sea

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    Mar 28, 2012
    I need some help on what brand to buy in these, I just want some good ones to have on hand in case I blow these.

    I will probably just put the new ones in the day I get them because I have had problems with these Chinese capacitors blowing up and I think they must mess up the windings/coils in my motors because I am on my 3rd motor and new capacitors never cure it, the motor usually lasts about a year then one cap blows and I replace the cap but the motor still lags and has to be spun to get things going again, which isn't worth a damn on a mill, I value my fingers lol

    So I thought perhaps there are better quality ones? to begin with before I have this happen again

    These are on my 1-1/2 hp 220 volt metal milling machine

    I don't know much about the make-up or if there is a such thing as low quality capacitors but I am guessing there probably is, the capacitors measure about 3 inches long and 1-5/8 inches across, the kind that uses the metal tabs would be fine, the ones that take the slide on cable ends.

    I got a few pictures below, one of each capacitor ... start and run

    [​IMG]

    [​IMG]

    Thanks for any help and or any explanation of what a good capacitor material make up would be of for my application
     
  2. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    For some reason I can see any pictures you posted. posted.
    The run capacitor is an oil filled , and the start will be an electrolytic ype. Both must be non-polarized. Look at the original capaitors that came with the motor for labeling. You need to match up the ufd's and working voltage of each.

    I would buy the capaciors from an American electrical distributor.
     
  3. sea

    sea

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    Mar 28, 2012
    I don't think either of these are oil filled, ive replaced both before and they look and feel exactly the same weight.

    The pictures come up fine on my end
     
  4. sea

    sea

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    Mar 28, 2012
    The 20 uf one is the one that blows up all the time, well like once a year and the other one looks fine, ive replaced both in the past but the motor still only runs slow and needs a kick to get it up to full speed ... that's when I just replace the motors, so I am guessing when that 20 uf blows it does something internally to the windings/coil
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,361
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    Jan 21, 2010
    Maybe the motor does something to the capacitors.

    Either way, if you can get a duplicate unit from somewhere and see if it's the motor or the caps that are the problem, that would be an ideal
     
  6. sea

    sea

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    Mar 28, 2012
    Oh well I am thinking if you don't replace this 20 mf cap as soon as it starts to go it prolly is the culprit ... they are covered and its tough to really know when it goes with this motor, my thoughts are it goes bad and I just don't know it right away and it stresses out the windings and when it finally does totally fail its screwed up the rest of the motor for good

    Like I said this is the 3rd motor all the same except this newest motor has different letters on the caps

    The 20 mf cap as seen above is the one in the new motor CBB65 ... all the other motors had CBB60 20 mf caps ... anyone know the difference? between them? ... voltage and tolerance is printed same on both caps
     
  7. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    If you are blowing capacitors that ,you have more of a problem than faulty capacitors. The 20 ufd (run) should be an oil filled and, the150 ufd (start) are dry electrolytic. There should be a device which disconnects the start capacitors out of the circuit once the motor gets to speed. Many motors use a centrifugal switch which opens when the shaft reaches running speed. Some motors use a potential relay . A potential relay measures the current thru the winding and opens, taking the capacitor out of the circuit. Either way if the motor doesn't get up to speed the Start capacitors stay connected and will burn up. They are not meant to be connected continuously, Your motor may not be getting up to speed due to bad bearings, or low voltage. You may not have big enough wire / mains service to run more than two motors at a time. I buy my capacitors, potential relays, etc. from MC Master Carr.com . They are a quality industrial supplier and will sell to individuals as well.
    I don't know you expertise/knowledge base. At this point I would check bearings and internal centrifugal switch if applicable. Otherwise you should take the motor to a motor repair shop, they have the necessary test equipment to test bearings, shorted windings, high-pot test etc.
    The Chinese are know to spec'ing everything to the edge/max. Maybe your belts are too tight if belt driven, or there.s not enough oil in the gear box. I'm assuming it's a hobby duty machine. Still, it should work with new components.

    Eddie
     
  8. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    What brand is your Milling machine? Mine is a Grizzly G0484, with a 1.5 HP 220 motor.
     
  9. sea

    sea

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    Mar 28, 2012
    I have a PM45M mill (rf45 clone) looks like a clone of yours

    Its not that there is a thing wrong with the mill right now, its got a brand new motor in it, like I said they usually last about a year, I just wanted to get ahead of the caps on this one, ive been using the mill every day since I got this motor maybe about a month now, daily.

    I have both the old 20uf caps sitting in shop they do not have oil in them, they are dry, when the last one blew it seeped out a very hard silver substance that was hard as a rock, looked like a silver hard foam, just a tiny amount out of the bulge crack, the one I am looking at right now just bulged and blew cap up slightly, no oil in it I tore it apart, I assume oil would be leaking out oil correct? when they blow.

    I use this mill daily, its not sitting around much at all, I think the caps are junk to be honest but once they blow I don't know if I am right on top of it, they might start going bad and I don't know it until total failure and that's was screwing up the motors

    As far as the circuit its correct, I put it in brand new when I got the machine almost 3 years ago to the rated copper and breaker, it has never once tripped the breaker, ever

    Once the start cap blows the motor is replaced, I have torn the motors all down in the past to check out the centrifugal switch (yes that's what they have in them) to check the contacts and make sure switch was working properly using a meter, I did not replace these motors based on a whim, I worked like the devil to figure out whats going on inside ... ive replaced the cables going from switch resoldering and replaced the leads coming off the caps as well, the motors, ive even replaced the motor control switch to a heavy duty one, the off forward and reverse switch

    What they would do is when I turn on switch it would just spin at a constant maybe 10 rpm's when I was using the 2 high gears, usually #2 high I could get it going but the #3 which is 1980rpm on my machine was very hard to get it to spin up (if I could sometimes get it going at 1980 rpm I could mill as long as I wanted to at that speed as long as I didn't turn the motor off and restart) that's when I know the cap is blown, the motors on higher speeds just lose their torque to start up I those higher speeds, it wont spin up enough to get the centrifugal switch tripped I am guessing to kick over to run cap, that's when I know oh crap that start cap is blown, take off cover .. yup blown, replacing it does nothing, motor still runs at same speed wont spin up, its like I didn't put a new start cap in it, its exactly the same 10rpms wont spin up on high gears, the lower gears yeah works good, the motor just loses its start torque once that start cap blows, it must do something to the windings

    I think the motors are just not built to run like I run my mill constantly like that, but they work great until that cap blows, like I said about once a year and I use it a lot
     
  10. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    Definitely sounds like its the start capacitor. The start capacitor is designed to give you a little extra torque when starting.

    I checked mine, and its the same electrolytic 20 mfd. I would try changing it out with a 20 ufd oil filled Areovox brand.

    The physical capacitor damage you describe appears to be high voltage surge, I just had this happen to a VFD capacitor bank. It didn't trip the breaker but ruptured the sides of the capacitors. Maybe your utility has given you a few surges. If so there's not much you can do about it, as the last surge I got, it took out the Surge Suppressor as well.
    Most likely you are getting marginal replacement capacitors.

    I didn't quite follow your explanation of gearing vs. speed. I running my mills and lathe at a low (gear) speed. This way the motor is lightly loaded. I know different speeds are required for production work but mine is only for hobby use. I am not a machinist by trade. I don't use the vertical mill like yours everyday. I probably don't have 40 hours on it yet.

    Never the less, I think you should change that start capacitor to an oil filled.
     
  11. Y2KEDDIE

    Y2KEDDIE

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    You can test the 20 ufd capacitor by putting a 132.6 ohm resistor (or something close in value 125 -150 ohm non inductive) in series with the capacitor on the bench. The closer you can get to 132 ohms the more accurate. Apply AC voltage (any voltage 10VAC from a door bell transformer, or 110 Vac mains. Measure the voltage across the resistor and then the capacitor. The voltages should be close to equal ( +- ).20%. If not the capacitor is open or grossly out of value.
    I determine the value of the resistor by the value of the capacitve reactance.

    Xc = 1/ (6.28) (60 Hz) (.000020 Farads)

    Xc= 1 / .007536

    Xc= 132.6 ohms

    I would test the new capacitors before installing,
     
  12. sea

    sea

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    Mar 28, 2012
    I am finding its very hard to find an oil filled cap with that's round and close to my dimensions
    (3" x 1-1/2")... all I seem to find are oval and they wont fit under my cap covers
     
  13. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    You may have to modify your enclosure. Maybe you can stay with the dry electrolytic if a good quality substitute is available. I will check my resources again.

    Where are you located?
     
  14. sea

    sea

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    Mar 28, 2012
    Hey thanks Eddie for all your help by the way


    Pittsburgh Pa
     
  15. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    Grainger has round 20 ufd 440AC oil filled capacitors: 1-9/16 dia by 3-1/4 p/n: 2MEH1 @ $14.47. Maybe you can sqeeze it into your enclosure. The Oil filled wil have a higher voltage rating, this ma solve your problem.

    Look at Grainger .com.
     
  16. sea

    sea

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    Mar 28, 2012
  17. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    Looks good. You will test and find out. I'm not familar with that brand. Good luck.
     
  18. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    If failures continue I would seriously consider replacing your Chicom motor with a 3PH Baldor driven by a VFD. Once you have one of these you'll never want to go back to a SPH motor. The only reason my SB Heavy10 still has a SPH motor is because I'm a purist regarding vintage machines. This motor shipped with my lathe in 1965 and is still going strong. If and when it goes west it's Baldor 3PH + VFD time. ;)

    Chris
     
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