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how common is it for a capacitor to blow on a mill?

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  • how common is it for a capacitor to blow on a mill?

    this is the second time that the capacitor on my mill has burn out. the first was about a year ago and took the manufacture about 6 months to send me a replacement. how often do they go bad? should i just try to find a capacitor made in america?






  • #2
    Do you mean on a single phase motor that drives the mill spindle.....or ??

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    • #3
      it's quite common on Asian machines ..read quite a few stories in uk rec models engineering about it ..

      motors fail as well in short time.

      All the best.markj

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      • #4
        Originally posted by Milacron of PM
        Do you mean on a single phase motor that drives the mill spindle.....or ??

        it's the starter capacitor, or that's what they tell me


        Originally posted by aboard_epsilon
        it's quite common on Asian machines ..read quite a few stories in uk rec models engineering about it ..

        motors fail as well in short time.

        All the best.markj
        thanks, first time i called they seem to know it was common

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        • #5
          I replaced both my run and start capacitors on my Chinese mill. I ot them from McMaster Carr.

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          • #6
            Not that uncommon, if the motor is made in china.
            My motor had the option of being wired for either 110 or 220V. I wired it for 220. However it turned out, with a bang, that the capacitor was only rated for 110.

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            • #7
              Originally posted by Rustybolt
              I replaced both my run and start capacitors on my Chinese mill. I ot them from McMaster Carr.
              thanks i'll go check and see if they have mine, last time i looked all over the place and had to wait on the 6 months it took the manufacture to send me one


              Originally posted by Mad Scientist
              Not that uncommon, if the motor is made in china.
              My motor had the option of being wired for either 110 or 220V. I wired it for 220. However it turned out, with a bang, that the capacitor was only rated for 110.
              i'm doing the same with with the 220 instead of using the 110. how do u tell if the capacitor is rated for 110?

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              • #8
                Originally posted by Mad Scientist
                Not that uncommon, if the motor is made in china.
                My motor had the option of being wired for either 110 or 220V. I wired it for 220. However it turned out, with a bang, that the capacitor was only rated for 110.
                Normally, the start circuit STAYS across one winding, so it gets only 120V regardless of it being wired for 120 or 240. Sounds like you wired it incorrectly.......

                40 uF is low for a start cap, but...... In any case, failures are all in the days work for chinese capacitors, which have had all sorts of problems, just like every OTHER chinese product. QC is not their strong point..... high production is.

                A cap like that should be easily available from US sources...... much faster than your dealer got it from china. Grainger probably has it, or can have it in a day. Many other sources exist as well.
                1601

                Keep eye on ball.
                Hashim Khan

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                • #9
                  there is a graiger near my house, i'll give them a try for the capacitor.

                  thanks

                  Originally posted by J Tiers
                  Normally, the start circuit STAYS across one winding, so it gets only 120V regardless of it being wired for 120 or 240. Sounds like you wired it incorrectly.......

                  40 uF is low for a start cap, but...... In any case, failures are all in the days work for chinese capacitors, which have had all sorts of problems, just like every OTHER chinese product. QC is not their strong point..... high production is.

                  A cap like that should be easily available from US sources...... much faster than your dealer got it from china. Grainger probably has it, or can have it in a day. Many other sources exist as well.

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                  • #10
                    Originally posted by hmcl281
                    thanks i'll go check and see if they have mine, last time i looked all over the place and had to wait on the 6 months it took the manufacture to send me one

                    i'm doing the same with with the 220 instead of using the 110. how do u tell if the capacitor is rated for 110?
                    First, look at your picture, your old capacitor is rated for 450 VAC. However, the rated Voltage is not just the line Voltage. An inductive circuit, as in a motor with inductive coils in it, can have Voltages far in excess of the line Voltage. Hence, a 450 Volt capacitor in a machine that is intended to be run on 110 or 220 Volts AC.

                    I would suspect poor QC on the part of the Chinese manufacturers. Get a name brand capacitor with the same ratings from one of the sources already mentioned or any of a number of US companys and try it out. Chances are it will outlast you. If it fails, then try one with a higher Voltage rating.

                    Six months to get a capacitor is rediculous. If you can't locate one with under 2 week delivery, PM me and I will assist.
                    Paul A.
                    SE Texas

                    Make it fit.
                    You can't win and there is a penalty for trying!

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                    • #11
                      It does not surprise me.

                      Capacitors can be made right or they can be made cheaply. When they are brand new you cannot tell the difference electrically. The cheap one fail prematurely.

                      There was a HUGE problem in computer 5 years ago with a fraudulent cap manufacturer that cheapened out on the caps. It was quite apparent when failure rate zoomed above 10% from normal .1%

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                      • #12
                        Very easy to find the right capacitors in the USA. WWW.Graingers.com has every start or run cap you'd ever want.

                        Any chance this case is a run cap? And it's a 3 phase motor wired to run on single phase?

                        Start caps are general larger, but are only in circuit for a short time. Run caps are generally smaller, but stay in circuit and pass continous current during operation.

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                        • #13
                          Wouldn't be surprised if a local motor re-winder didn't have some in stock.

                          Regards Ian
                          You might not like what I say,but that doesn't mean I'm wrong.

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                          • #14
                            The chinese ones blow all the time. This happens especially in the winter where starting loads are higher because of stiff belts and thick oil in the gear box.

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                            • #15
                              Caps for 220v motors are typically rated 370volt but more does not hurt.

                              The start cap should only be in the circuit for a second or two then switched out by the centrifical force operated contacts in the motor. If the motor does not start quickly and the cap stays switched in for too long it will go bang. These electrolytic type start caps are only rated for a few short seconds use each time. (guys building roto-phases know this very well)

                              When its working, how quickly does the machine start and come up to speed? You can usually hear a distinct click from the motor as the rpms increase and the switch trips, it should happen in just a second or two, no more.

                              As for a new cap, fleabay is loaded with new motor start caps, grainers is also a excellent source. There are two common types. One is the electrolytic type which you have and is quite common, the other is the oil filled type which is in a metal can, usually oval. The oil filled type are far more durable and not restricted to the very short duty cycle during starting.

                              You may also consider a larger value cap, in microfarads (uf), that will give the motor more of a kick to get it going. I am betting your problem is a combination of a poorer than average quality cap along with somewhat slow starting motor. Slow starting can be caused by low line voltage, poor connections, too small of a wire size and a few other things.
                              Last edited by Sparky_NY; 03-12-2009, 09:37 AM.

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