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Thread: Exciter coil - alternator regulator voltage drain

  1. #1
    Join Date
    Jun 2011
    Location
    SW Florida
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    11

    Exciter coil - alternator regulator voltage drain

    My 85 atc250es was starting and running good after I changed the one way bearing for kicker. I am running with no battery but the regulator was connected and would charge correctly. After I rode it several miles it quit running - no spark.

    I checked everything, everything checked good OHMwise. Voltage was another thing the Exciter coil only output 7 - 10 v ac , I could find that at the coil + too.
    While testing the exciter coil I noticed that the ohm reading changed with direction, if I switched the test lead pos on black/red to neg on b/r. One way 278 ohm other way 54 ohm .

    I was thinking exciter cooked thru winding closer to one end so ohms were different with direction. Then I pulled alternator three yellow wire connector apart and checked it’s cranking voltage- over 50 vac on all three same as before. While checking yellows, I rechecked the exciter and found over 50vac there too. I checked exciter resistance again with three yellow wires disconnected and it is 278 ohm in both directions now. Now making spark too.

    With no battery I have taken the reg off the bike. It starts and runs great without it, but if I plug the reg into yellow wires engine dies.
    Strange bunch of indicators and conditions, at least it runs again. Anyone experienced this with your machine?

    2/9/21- Found that yellow wires have continuity to ground.
    Last edited by Otis0; 02-09-2021 at 01:23 PM.

  2. #2
    Join Date
    Jul 2010
    Location
    Arkansas
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    2,196
    The reg/rec probably failed because of not using a battery and could have a direct short.

    A battery isn't just there to start the engine or for the lights to work without it running, it's there to balance the load on the system. Without it, the reg/rec is having to deal with it all and shunt everything to ground. They tend to get excessively hot when doing that.

    Typically, when one part or another goes bad in a charging system and continues to be operated without repair, it takes the other out with it. Bad batteries take out alternators and bad alternators (when their reg/rec fails) take out good batteries.

    Sounds like you'll just have to replace the reg/rec and if you don't want to use a battery, you'll at least want to use a large capacitor. It used to be called a battery delete back when enduro riders started using capacitors in lieu of a battery, to save weight and have a more durable system for hard off-road racing.

    You could always look into using a super capacitor instead of a battery. It won't save any money over a battery, but it won't go bad sitting there for months on end either, although it will loose charge.
    The story of three wheels and a man...

  3. #3
    Join Date
    Jun 2011
    Location
    SW Florida
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    11
    Click image for larger version. 

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ID:	266658Thanks ATC , I just came in to pose that question. if running without a battery would harm it. I should know better.
    I’ve been pondering why the exciter coil ohm reading changes with polarity of test wires? Decided it had to be the diodes in the regulator, so checked continuity between stator yellows and exciter black/red and found 0 resistance .
    The machine runs better than ever with the reg removed, the exciter wire still has 292 ohms to ground but reads 0 ohm to yellow. The yellow reads 325 ohm to ground, makes me think the wires in pigtail come together. Anyway I guess I need to remove stater and put eyes on it.
    When I first started this machine I had a small lawnmower battery attached and found it charged then .

    — Removed stator and it does not look bad to me, I have the harness pigtail uncovered to inspect wires.Click image for larger version. 

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ID:	266656 found soldered splices with minimal insulation squeezed together under steel shield, I accidentally pulled the black/red apart while moving grommets away.
    Yellow wires now - infinity- to stator base , the exciter wire still 290, but exciter to yellow 0 continuity.Click image for larger version. 

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ID:	266657
    Need to borrow another meter to double check exciter.

    Sorry for the confusion
    Last edited by Otis0; 02-10-2021 at 07:40 PM. Reason: Syntax

  4. #4
    Join Date
    Jul 2010
    Location
    Arkansas
    --
    2,196
    You've got some issues going on with that stator if ANY of the yellow wires have continuity to ground. That's a three phase stator and none of them should connect to ground. The yellow wires should only have continuity with each other.

    0 ohm means no resistance, a direct short. The reading should be infinite/no continuity.

    Those solder joints don't seem right to me. Wait for some other 250ES owners to chime in, but most OEM stators will not have that. That looks like someone has replace it an spliced the wires for some reason; maybe cheap aftermarket without a connector.

    Do you have a wiring diagram?


    Again, if the yellow wires have ANY continuity to ground, the stator is done. Running without a battery will do that, after the reg/rec fails, direct shorts, then takes out the stator. Excessive heat melts the insulation on the magnet wire the stator is wound with and shorts the coils.
    The story of three wheels and a man...

  5. #5
    Join Date
    Jun 2011
    Location
    SW Florida
    --
    11
    Sorry atc I misstated my meaning, your right 0 ohm is not infinite. I do have a manual and wire diagram. Thank you for keeping me straight.
    I’m going to solder and insulate the b/r wire and try it. Yes I agree somebody been here before me.

    2/11/21 Soldered the black/red insulated back together runs, but did before.
    Found broke tooth on starter double reduction 43/18 gear, matches one tooth I found in engine. I found one more in engine so has happened before. Still high 290 ohm exciter reading.
    Last edited by Otis0; 02-11-2021 at 04:58 PM.

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