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Aargh stupid electrics!

Discussion in 'Technical and Troubleshooting Torque' started by blackjacket, Sep 20, 2007.

  1. I got the bike (Cagiva Mito) a couple of months back, 2nd hand (2001 model, 8500 k's). From that time, the battery had been a bit weak... sometimes it would be too weak to crank the bike so I'd roll start it. I tested the voltage on the battery, it was around 12V, rising to about 14V when revving. With a booster charge up, it held up until last week.

    Friday night, it refused to crank over at all and at idle, the lights would dim and it woul dtry to stall. I had to prop up the revs at the lights. The headlights on and dodgy front brake switch forcing the brake light permanently on didn't help. The battery was reading 11.7V when off. Okay dead battery, time for a new one I thought. It's probably the original, 6 years old.

    I bought a new one and filled it with acid, let it sit a couple of hours and charged it for a full day. (I'm wondering if the charger did anything at all, because it read out 12.6V before and after).

    So the bike started and ran fine for a day or two. Then today, it's too weak to crank the bike and I'm getting the dimming at idle problem again. Measured the battery when off, it's 11.6V :shock: :shock: When I rev the engine, the highest it goes to is about 12.9V, and it actually starts to drop above around 8k RPMs?

    I've plugged it in to the charger again, though I think I'll train it in to work tomorrow :cry:

    Is my alternator shot? Is it possible to get wrecker ones? I got quotes some time back just in case, and new ones were around $600 >_< Have I killed my new battery? Could all of this be caused by the brake lights being on?

    More bullshit stuffing around this weekend instead of riding :cry: Any help appreciated!!


  2. Possibly not the alternator, but the rectifier, which converts the alternator's AC output into DC to charge the battery. They are usually 3 phase and one or more of the diodes has probably failed.

    You can check with a multimeter and the service manual...if you can get hold of one.

    Best of luck solving it

    Trevor G

    PS The diodes should only pass current in one direction, so that when you measure across them in one direction you should get an open circuit. The other direction (you just reverse the probes) should be a low Ohms reading.
  3. You should be getting more than 12.9V when revving. It could be either the alternator or the Rectifier (regulator).
  4. Okay latest in this sorry saga.

    I left the battery on charge overnight and went to check it this morning. With battery still connected to charger, it read 13.6V, and started dropping to 13.2V when I pulled it off. Looks like my initial charge wasn't actually charging. :evil:

    Installed battery and cranked the bike, it read 13.2V idling and up to 14.6 at high RPMs. So I decided to ride to work.

    Got to work and tested the battery while idling, read 12.6V and up to 14.6V at high RPMs. I'll test it again when I leave work.

    Hopefully it's just that it didn't charge when just filled.. though I would have killed my battery life. :cry:

    Edit: Where can i get a voltage gauge for the bike? It's getting tedious undoing the seat and pulling out the multimeter all the time...