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Charging system question

  • 15-01-2012 8:01pm
    #1
    alanmc
    Registered Users, Registered Users 2 Posts: 1,139 ✭✭✭


    And the post-winter bike shakedown continues. It seems that I can only get 1 maybe 2 starts out of a battery charge. So I'm pretty sure the battery is shagged.

    The question is: I put a multimeter on the battery while holding the revs at 5k ish, and I was only getting 11.5 V. This should be 14V or above, right? Could a bad battery produce this symptom? Or is this definitive proof that my regulator/rectifier is shagged as well?

    One more thing, the bike runs nice and smooth when it is running. Would I be right in assuming the generator is ok?

    Cheers,
    Al.


Comments

  • #2
    Hotblack Desiato
    Registered Users, Registered Users 2 Posts: 35,418 ✭✭✭✭Hotblack Desiato


    alanmc wrote: »
    And the post-winter bike shakedown continues. It seems that I can only get 1 maybe 2 starts out of a battery charge. So I'm pretty sure the battery is shagged.

    That's normal if the battery isn't charging. The battery may or may not be ok, but you can't tell until the charging system is fixed.
    The question is: I put a multimeter on the battery while holding the revs at 5k ish, and I was only getting 11.5 V. This should be 14V or above, right?

    Yeah. It could be a broken stator winding in the generator, or a bad regulator.

    If your multimeter has a 100 or 200V AC range, disconnect the alternator (usually one plug with 3 yellow wires) connect the multimeter to any 2 of the yellow wires coming from the alternator, start the bike and check the voltage between each pair of yellow wires in turn. It should get up to about 70 volts or so and all three readings should be fairly similar. I suspect that at least one of the readings is going to be zero - which means a broken winding and you'd need to get the stator rewound or replace it with a new one. You can also check the resistance of the stator windings with the bike not running, they should all be very similar (a few ohms), a broken winding will show infinite resistance. There should be infinite resistance between each yellow wire and the engine casing (if not then one of the windings is shorting to earth.)

    If the stator is OK then the fault is either a bad connection in the wiring, or a faulty rectifier/regulator.

    Scrap the cap!



  • #3
    alanmc
    Registered Users, Registered Users 2 Posts: 1,139 ✭✭✭alanmc


    Well, the reason I think it's a bad battery is because when I do charge the battery to what my charger says is fully charged and then test the voltage across the terminals, I can see it dropping away before my eyes. In the space of maybe 2 minutes, it drops from near 13 V to just above 11, where it seems to stabilise.

    Also, after I do a manual charge overnight, stick the battery back in the bike and fire her up, the starter struggles to turn.

    But I would have expected a multimeter to show the full 14V across the terminals when holding revs at 5k ... even if the battery is shagged. Would I be right in thinking this?


  • #4
    Hotblack Desiato
    Registered Users, Registered Users 2 Posts: 35,418 ✭✭✭✭Hotblack Desiato


    OK I presumed the battery voltage was normal when you were putting it in the bike. That battery is definitely faulty (probably one of the cells has shorted out) so it will need replacing. Charge up the new battery before installing it, then run the bike and check the voltage again. Should increase with revs up to 14.4 - 14.5V and not rise above that, if the regulator is working right.

    Scrap the cap!



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