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  1. #21

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    That would be true in a generator like they used in the 50's but they are ALTERNATE-ors, meaning they create ac voltage then use a rectifier with diode to change it to dc. Thats electrics 101 buddy.
    01' 1500 LT Z71 ECSB 5.3L
    line-x'd front brush guard with KC Daylighters, 6000k HID lows and highs, rewired highbeams, Trans-go mild shift kit, custom stainless duals, 3500 dually OEM taillights, K&N CAI. Still have OEM fender flairs and leveling kit in boxes waiting for time.


  2. #22
    Master Mechanic zigger215's Avatar
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    Quote Originally Posted by shibby2oo8 View Post
    That would be true in a generator like they used in the 50's but they are ALTERNATE-ors, meaning they create ac voltage then use a rectifier with diode to change it to dc. Thats electrics 101 buddy.
    I know what an alternator is, it's regulated be a diode rectifier bridge, 2 diodes that allow current only to pass...if these diodes fail the alternator stops working. No "reverse" current in this outcome.

  3. #23
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    I have to disagree with you statements in this post. the alternator can surely fail in such a way as to drain the battery. this can be very high or slight . depends on the diodes point of failing.

    these vehicles will hold a charge for over a month with a good load tested charged battery with a properly operating electrical system.

    with an ampmeter monitoring the current flow on shutdown and removing fuses / alternator feed wire etc you can find the drain.

    I have seen shorted battery plates before . also open battery internal connections especially with the sears diehard .

    the idle being managed by the IAC usually works with no issues unless the throttle body is dirty also the passageways in there for the IAC. vacuum leaks will cause erratic idle rpm.including a bad fuel pump.

  4. #24
    Master Mechanic zigger215's Avatar
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    I've never seen it and I've never heard of that happening. His idle is fixed and it was obviously a case of forgotten idle like I suggested. A diode can NOT fail in "certain" ways. It's just a current gate valve. In can only fail one way and that way can't cause a parasitic draw on the battery. I'm done arguing over this thread you can PM me if you want to continue.

    The OP's battery was probably a little old but the alternator is NOT at all even just a little bit his problem...

    Yes batteries can easily have a short within their case between their plates.

  5. #25

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    Quote Originally Posted by zigger215 View Post
    I know what an alternator is, it's regulated be a diode rectifier bridge, 2 diodes that allow current only to pass...if these diodes fail the alternator stops working. No "reverse" current in this outcome.
    There are 6 diodes in a run if the mill alternator, 3 for each side of the field. If a diode fails closed it will back feed and release ac current. It happens alot actually.

  6. #26
    Master Mechanic zigger215's Avatar
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    2 diode rectifier bridges* yes.

  7. #27

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    Terminology aside there can be reverse current.

  8. #28
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    Quote Originally Posted by shibby2oo8 View Post
    Terminology aside there can be reverse current.
    Meh, might as well agree to disagree. We probably agree but there is probably a terminology barrier still

  9. #29
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    well I am happy someone else out here knows what going on in these alternators. diodes can fail in many ways. sometimes they vaporize to dust. or simply become a direct short or perhaps a resistance of any amount...

    but like you say ,,,, I know many alternators do indeed fail at times by reverse current flow due to diode failure.

    - - - Updated - - -

    forgot to say if the alternator is failing this will cause a lower system voltage and with an old fuel pump the fuel pressures will drop. then you can get performance/idle issues.

    fuel pump relay gets resistance on contacts pump motor gets weak etc... slightly lower voltage will create running issues .. voltage and current testing of the alternator and battery load tested etc can sort all this out with out any guessing on the problem.

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