Generator charging wierdness, any help?

Discussion in 'Old's Cool' started by dorkpunch, Aug 13, 2010.

  1. dorkpunch

    dorkpunch Oops...

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    Aug 2, 2006
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    5,533
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    Been working on a '67 Yamaha YL2C. Its running and (finally) on the road but I have a weird charging issue. It has a charge light that tells you if the generator / alternator / mag / whatever you want to call it is charging the battery. Turn the key on, the light comes on cause the engine isnt spinning. Start the bike, the light goes out. However, apparently the battery gradually looses its charge and the light starts to come on really dim. This will continue to the point where the headlight barely lights and the engine will start to missfire cause the coil isnt getting enough juice. Here's the odd part: when the light comes on, it gets bright at higher RPM (should be charging BETTER at high rpm?) but at just higher than idle it goes out (meaning its charging). Havent actually measured the voltage yet, but anyone got any ideas?
    #1
  2. C Squared

    C Squared Now with TURBO!

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    Measure the voltage... You need more info.
    Check all connections and grounds.

    Regulator may be going bad? Heat sensitive part?
    #2
  3. BarryT

    BarryT Been here awhile

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    Second testing connections!

    I had a charging issue on my 77 bmw and it ended up being the wire the energizes the rotor's field. The wire was corroded and was only hanging on by one strand. Any current through it and it would crap out but the meter would check the line as good.


    barry
    #3
  4. dorkpunch

    dorkpunch Oops...

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    Tested the voltage while running this morning. At idle with the lights off, its got 13v, revving it up brings it up to 13.5v. The charging light is off at idle, but comes on dimly at higher rpm.

    With the lights ON, it drops to 12v at idle, and 12.5v at high rpm. Charging light does the same thing.

    Been reading my manual, turns out it has an ADJUSTABLE voltage regulator?! Thats a new on too me, gonna have to check that. It also has a way to test the regulator so I will try that when my new front sprocket gets here and I have to pull that engine cover off.

    I *should* be seeing around 14v with the motor running, right?
    #4
  5. danedg

    danedg Horizontally Opposed

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    If it has brushes, check those. They might be not held tightly against the armature and might "float" at higher rpms for a bad connection...
    #5
  6. dorkpunch

    dorkpunch Oops...

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    yup, it has brushes, that was listed in the things to check section in my manual too.
    #6
  7. dorkpunch

    dorkpunch Oops...

    Joined:
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    Oddometer:
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    So... I figured it out. tested the voltage again, and noticed that the voltage on the other power terminal that goes down to the electric start would go up to 17v when I revved it up. Took apart the regulator, no adjusment, but if I blocked the switch the voltage would go way up so I was thinking the regulator or the resistors were fried... When I read my manual again. It said something about a red wire, and I didnt remember a red wire, so I got to looking, and FOUND the red wire!!! IT wasnt hooked up. Hooked it up in the right spot, and now its working perfectly. No charging light, got between 15 and 16v at the battery even with the lights on, and the most interesting part: It'll run without the battery!!!

    Amazing what happens when you spend the time to figure something out... I had "figured out" the wiring 15 years ago when I was like 13 or something. :lol3
    #7