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  1. #1
    CB750 New Member yarburdin's Avatar
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    Alternator's stator coil outputs 0 volts ac, faulty stator coil?

    Hello Everyone,

    Honda CB 750 k7 here.

    My battery is not charging.

    Did all possible tests found on website.

    Passed all of them, except couple (will be numbered bellow).

    While testing alternator:
    Passed: .6 ohms measured between phases (3 yellow wires) for stator coil, no short on case
    Passed: 7.2 ohms measured between green and white wires on field coil, no short on case
    1. While running bike and with 3 yellow wires disconnected, I get 0 vac between yellow wires

    Also, the isolation of wires coming from the stator coil melted.
    Found this:

    2. The white wire coming from the regulator outputs .2V
    Are we dealing with the burnt stator coil and possibly faulty regulator?

    Attached pics of stator and field coils, as well as the burnt wires coming from the stator coil.

    What do you guys think?

    Click image for larger version. 

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  2. #2
    CB750 Guru amc49's Avatar
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    The field coil looks like crap, look at your last pic. You have a strand of it hanging off in space, it looks like the coil wires have gone through some heat and the other end of that hanging wire may be lower down in the dark where you can't see it.

  3. #3
    CB750 Guru amc49's Avatar
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    https://imgur.com/IgOZOuV

    I added question marks and the yellow line..............

  4. #4
    CB750 New Member yarburdin's Avatar
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    Correct me if im wrong, but those type of coils are varnished, it physically cannot do what you mentioned.

    And if it happened, it happened on the stage of manufacturing.

    Btw, i've bypassed regulator and field coil started to work, exciting stator coil, which outputted desired 15-20 volts ac while bike idle.

  5. #5
    CB750 Guru amc49's Avatar
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    '...those type of coils are varnished, it physically cannot do what you mentioned.'

    That is incorrect, I have seen one with wire coming loose individually, vibration fretting can pull them loose if the epoxy is too thin.

    And which varnish job? The wire alone gets varnished and then when wound the whole unit gets lots of varnish over it. Tell me you think the inside field wires are as deeply coated as your outside stator wiring is. No way there. They should be the same. Better quality units will also cover the OD of the wire with cloth that once the epoxy has dried on soaking through the cloth becomes a hard shell the wires then have to break through to come loose. Your field coil looks like it has virtually no epoxy on it at all.

    The 'loose wire' may be an optical illusion but certainly does not look right. Need a better pic from a different angle.

    Be careful with the reg out of the system, that alt can make up to 70 volts unregulated if you rev the motor up high, as all alternators can in the same state. Bulb and other parts popping voltage.

    I'd be checking that wire if bike was mine, it simply does not look right. You can always add more glue to hold it down if it has come loose. It definitely should not be sticking up like that.

    Something made the stator leads get too hot too, I'd be renewing that.
    Last edited by amc49; 06-17-2020 at 08:20 PM.

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