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What's this thing on my electric motor?

  1. Nov 9, 2015 #1
    Just got this beautiful old pump from a fleamarket.
    Does anybody know what the tube shaped thing connected to the motor with a cable is? It goes into some box on the side of the motor.
    The close up shows the only inscription on it. IMG_2513.jpg IMG_2514.jpg IMG_2515.jpg
  2. jcsd
  3. Nov 9, 2015 #2


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  4. Nov 9, 2015 #3


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    It is a capacitor. Most likely a starting capacitor.
  5. Nov 10, 2015 #4

    I would like to rewire it (old wires are). Will I destroy it by opening it?
    (I'm not planning to break it open, but to undo the bolt it has in one end, and split it where it's held together with tape at the other end).
  6. Nov 10, 2015 #5


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    yes that would destroy it
    the outer casing should probably be grounded(mounted to the metal of the motor casing
    the bolt at the other end is where the wire is connected to

    here's a google list of links for wiring it up correctly ....


  7. Nov 11, 2015 #6
    First point to mention, this capacitor is somewhat like a battery in that it can store an electrical charge, but it is designed to quickly discharge in a moment which will create more than an appreciable spark. at 30u (Microfarads) it can give you enough of a shock to certainly burn a hole in your skin and potentially can be lethal. They are designed to charge rather quickly when connected to a power source, and can hold a charge for quite a long time, certainly for hours and will likely still hold an appreciable charge for several days, after being disconnected from power. Safety first. :-)

    Tearing it open isn't guaranteed to destroy it, if you understand how it is assembled but there is no reason for you to rewire what is inside the canister. Indeed they can be rebuilt but if this pump has been used on a regular basis, the capacitor could very well outlive the pump. As long as the pump motor starts, the capacitor is working fine and is best not disturbed.
  8. Nov 11, 2015 #7


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    under 99% of circumstances it is, specially for someone who doesn't know what they are doing
  9. Nov 13, 2015 #8
    Which is why I included the ",if you understand how it is assembled but...

    I suspected OP is not technical enough yet to attempt to repair a component they cannot identify, but other readers may be interested to know more. In the case of Vintage Audio Amplifiers, for example, it is often preferable to rebuild some components rather than simply replacing it with something new that is comparable, both to preserve some measure of value as well as preserving a distinctive tone. :-)
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