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Thread: "Any alternator field wire must also be disabled by each master switch"

  1. #1
    Hi,

    Trying to build up a wiring harness, and I don't understand what this instruction is asking for. Can someone explain to me the concept behind this, and perhaps how one would wire a kill switch to do so?

  2. #2
    Hi,

    Trying to build up a wiring harness, and I don't understand what this instruction is asking for. Can someone explain to me the concept behind this, and perhaps how one would wire a kill switch to do so?

  3. #3
    Which engine are you using? I'd say most motorcycle engines use permanent magnets in the rotor for the alternator, but some use a winding to produce the magnetic field. The wire going to this winding is what the rule is referring to. To disconnect it with a killswitch, the killswitch would need to be at least double pole, and you'd probably want to put a flyback diode across the contact of the switch for the field. Let us know what engine you are using and we can tell you if the rule is applicable to you or not.

  4. #4
    The general concept is that they don't want just the battery killed when the kill-switch is thrown, instead a guarantee that power is turned off to the whole car.

    I've seen it happen where the alternator is providing power and it keeps running the engine even after the switch is thrown (because that just removed the battery from the circuit).
    Red & Blue Racing '08

  5. #5
    Actually, cutting the battery out of the loop in a non-permanent alternator can induce some pretty hefty and damaging currents from inductance.

    At best, you can blow a master fuse. Done that. On the highway.
    Wesley
    OU Sooner Racing Team Alum '09

    connecting-rods.blogspot.com

  6. #6
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Wesley:
    Actually, cutting the battery out of the loop in a non-permanent alternator can induce some pretty hefty and damaging currents from inductance.

    At best, you can blow a master fuse. Done that. On the highway. </div></BLOCKQUOTE>
    That's usually called 'alternator load dump' or just 'load dump' and appears a lot in the spec's for protected electronics on road vehicles.

    en.wikipedia.org / wiki / Load_dump

    Regards, Ian

  7. #7
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">en.wikipedia.org / wiki / Load_dump </div></BLOCKQUOTE>

    And it's a good thing, too, else I'd be replacing all kinds of computery bits instead of just a 100A fuse.
    Wesley
    OU Sooner Racing Team Alum '09

    connecting-rods.blogspot.com

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