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  1. #1
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    brush cards for goped ESR 750 silver-case motor melting -- solved

    After searching for a long time for a solution to a problem that I was repeatedly experiencing with the silver-case motors for the goped ESR 750, I thought I would post the solution in case anyone else experiences the same problem.

    Here is what was happening: I would install a new brush card into the motor (or even try a new motor) and then take a ride on the scooter. At first, everything would be fine, but after a mile or two the engine would stop running and not start again. I'd open it up and find that the plastic ring that forms the base of the brush card had melted and deformed, and that part of the plastic was now blocking one of the brushes from advancing to where it could touch the commutator, so the motor couldn't get any power. (The melted plastic was also really stinky!) Sometimes I could file the plastic back into shape so that the brush card could be reused, sometimes not.

    I thought that the motor was overheating, so I tried a variety of things to try to keep it cool. (If you have a different problem than mine, you might find these ideas helpful.) Using a go-prammer, I reduced the maximum current (cur lim hi) setting to 36 (this was an old ESR that came with a black-case motor and the factory setting for the controller was 54). The go-prammer didn't report any problems with the controller. The go-prammer reported current erratically, so I used a clamp ammeter and verified that the motor was not drawing too much current. I also changed the front sprocket from 15 to 13, leaving the rear at 75. I avoiding using full power when I went up hills. And each time I installed a new brush card, I broke it in by running the engine under no load for about 20 minutes. None of this made any difference. I went through five brush cards.

    Then, after the last failure, I took the motor out and noticed, by burning my finger, that one of the two terminals was extremely hot, whereas the other was not. The cause of the problem finally occurred to me. When I had first replaced the original black-case motor after about five years of use, I had screwed the whole thing up and overtightened the outside nuts on the terminals. In fact, I overtightened them so much that I even twisted the ring connectors and the wires coming from the controller around the terminal. I twisted them so much that I actually broke about half the strands of the "black" wire right before they reached the ring connector. (It was a major screw-up.) That meant that the remaining strands had to carry double the current they normally would, and this was causing them to become very hot, causing the terminal to overheat, and melting the brush card.

    The solution was to cut off the old ring connector and cleanly attach a new one to the wire. Now I've run the scooter all over the place and neither terminal overheats and the brush card doesn't melt.

    To summarize: if your brush card is melting, check the temperature of the terminals and check that there is no damage to the wires and ring connectors that attach to the terminals. If they are damaged, they may overheat, causing the brush card to melt. And don't overtighten the outside nut on the terminals!

  2. The Following 2 Users Say Thank You to shrike For This Useful Post:

    chex (10-19-2016),Gopedboy (03-01-2016)

  3. #2
    Join Date
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    Make sure your using the plastic grommets in the right place on the motor connections,
    they are used to insulate the terminals.
    sounds like that may be your issue.

  4. #3
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    Quote Originally Posted by Len View Post
    Make sure your using the plastic grommets in the right place on the motor connections,
    they are used to insulate the terminals.
    sounds like that may be your issue.
    Thanks Len. The grommets were properly seated, but I agree that it is important whenever changing a brush card not to forget the grommets, or you will be in for a big surprise!

    The problem was that half of one of the wires was gone, so it was overheating...

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