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Thread: Motor Starter capacitor burnt out

  1. #1
    Join Date
    Jun 2008
    GTA Ontario Canada

    Motor Starter capacitor burnt out

    I guess something does not want me to use my jointer. Get to shop today and after all the effort to get jointer cleaned up from winter rust and sharpen and set knives, I then remember that its the very reason I need my generator. The Jointer I have is a 220v 3Hp grizz 656.

    So sort out a temp hook into the generator and get to start the whole thing up. Discover the belt needs tightening so did that adjustment.

    Then next time I started it poof a cloud of smoke and the Motor start capacitor blew.

    So I am wondering .......was the cap affected by the past winter being stored out in the garage and freezing?

    Has the starter switch failed to take it out of the circuit and it popped? could be but testing the switch which is normally closed and opens when centrifugal force causes it to do so well that's something I don't have a handle on how to do right now.

    Other thing that has me wondering is if the voltage got too high for the cap. Generators don't produce clean power but that would normally be an issue to worry about for the running cap and that's still fine.

    The motor start cap is rated 250v that would seem low to me for a unit that's a 220 motor considering some might run this off higher 240v depending on electric supply.

    Don't know of a company locally that stocks these, Amazon would were not allowed to ship the one I found there to Canada, so I just ordered a new one from Grizz but now I got to wait for the shipping.

    Generator produces 220v and is rated 6.250kw for startup and 5kw for continuous run.

    Motor is 15 amps 220v so roughly 3300 watts should be plenty of spare capacity in generator for a start surge.

    Anyone else here lost a motor start cap and just replaced and had no issues after. Thinking I should have ordered 2 at the same time just in case.

    Would love to believe its just the cap that was on its way out but having a hard time believing it.

    Anyone have any thoughts on whether the generator possibly caused this cap to go?
    Last edited by Rob Keeble; 08-02-2013 at 10:27 PM.

  2. #2
    Join Date
    Dec 2006
    Yorktown, Virginia
    Quote Originally Posted by Rob Keeble View Post
    ....Anyone else here lost a motor start cap and just replaced and had no issues after.....
    The cap blew up (scared the crap outta me) on my Laguna 24 bandsaw. Ordered a new one and hooked it up without any problems....motor started right up.

  3. #3
    Join Date
    Dec 2008
    Santa Claus, In
    I think it was just timing Rob. They don't last for ever.
    If you don't take pride in your work, life get's pretty boring.

    Rule of thumb is if you donít know what tool to buy next, then you probably donít need it yet.

  4. #4
    Join Date
    Oct 2006
    somewhere east of Queen Creek, AZ - South East of Phoenix
    Rob a number of reasons for the cap to blow and you are right about the voltage being on the marginal side. Most I've seen on 220/240 volt circuits are rated for 300+ volts. When the one went on my lathe I just went to the local mote\or rewind shop in my area and picked one that was close in value. its working great for a number of years
    "Thereís a lot of work being done today that doesnít have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesnít have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  5. #5
    Join Date
    Nov 2012
    Wapakoneta, OH
    Having a start cap fail is just something that happens from time to time. Not to say it couldn't be some other problem, but don't jump there from the getgo. My DC has went through 2 in the last 12 months or so, but I can get them easily. I can't even imagine the freezing storage had anything to do with it, but I guess stranger things have happened.

  6. #6
    Join Date
    Dec 2008
    falcon heights, minnesota
    i had the cap give out on my drill press from grizzly, and it fried the motor as well. almost right out of the box, a defective cap. they sent a new cap, didn't solve the problem. sent out a whole new motor and cap, works like a charm. as it was still under warranty, it was free. as for being out in the garage in winters, never had a problem with any of my tools that way.
    benedictione omnes bene

  7. #7
    A small tutorial on start and run capacitors.

  8. #8
    Join Date
    Jun 2008
    GTA Ontario Canada

    Re: Motor Starter capacitor burnt out

    Thanks for the input guys. Alan thanks for the tutorial. I happen to know the technical side of these things Its the practical side thats the issue.
    See the motor starts with a seperate winding and to get more torque they add the cap to make the circuit more efficient. the centrifugal switch is closed when motor is at rest which results in the cap and starter winding being in circuit. When motor is runnjng that swicth is supposed to take the cap out of the circuit by opening. So if that switch is hung up closed which is pretty unlikely then a new cap will get fried on the next start.
    The other thing Don mentioned agreeing with me on is voltage.
    The higher the voltage of a cap just means the dilectric can withstand a higher voltage before breaking down....remember there are two plates to a cap and a dilectric between em. So having a higher voltage cap cannot do any harm it just might end up being physically bigger.
    The key issue is the micro farads. Assuming the design was done properly then thats something that needs matching correctly or the start current and torque wont be there. So my only concern at present is cap voltage looks low as in value eng cheap, and motor is supposed to be tecf and i hope it truly is and that switch is not all clogged up with sawdust like the terminal box was when i took the cap out.
    Time will tell thanks for all the feedback much appreciated.

    Sent from my MB860 using Tapatalk 2

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