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Automotive alternator windings & rectifier

Discussion in 'Electrical Engineering' started by Mike Cook, Aug 19, 2013.

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  1. Mike Cook

    Mike Cook Guest

    has photos of an alternator with 4 connections for windings (each of 3 phases
    + common), and the 8 diode rectifier. But wiring diagrams show only 3
    connections and 6 diodes.

    Where does the common winding terminal connect (there is a connection on the
    rectifier plate)? Where do the other 2 diodes connect?

    I handled one of these disassembled units but didn't have time to ohm out the

  2. amdx

    amdx Guest

    Not one of the pages shows four connections brought out from the

    I don't see any 8 diode rectifier.
    Common is created by the way the diodes are connected. >THAT< common is
    connected to the auto frame.

    Wo uld you ask your question again and maybe clarify the situation?
  3. The common in the Wye connection (called "Neutral Junction" in the
    photo on page 18) goes to the 4th pair of diodes (and typically the
    regulator). The other three pairs of winding ends ("Stator Lead Ends")
    go to the other three pairs of diodes.
  4. dumb question.

    what EXACTLY does the charge lamp indicate?

    what triggers it to go on and off?

    can it simply be removed and ignored?
  5. tm

    tm Guest

    One cause that can light the lamp is a broken belt. You would like to know
    as soon as that happens.
  6. David Lesher

    David Lesher Guest

    That pictured alternator is one used on Hondas. ISTM it's a
    Nippon-Densi or such.

    I have too much experience with same. I went through 3-4
    boneyard ones before I bought a rebuilt one from Retarded Auto
    Parts. That brand/model alternator is nice because the diode
    array unscrews easily. No unsoldering needed.

    That particular alternator has 4 pairs of power diodes; the
    center point of the wye has a pair from there as well.... and I
    have no idea why... Jim??

    That said, all recent alternators also have a diode trio of tiny
    diodes. Their function is to rectify enough power to excite the
    rotor. It takes a few amps to drive it. Until it's up to speed,
    that excitation comes from the battery, through the red idiot
    light. When the alternator is up to speed, there is 12V on the
    battery side of the lamp, and 12v on the load side....and it
    goes out.
  7. Those were alternators with only six power rectifiers, right?
    The power rectifiers connected to the Wye common are used to extract
    3rd harmonic power- yielding up to 10% additional current capacity-
    when operating at high speed.

    Best regards,
    Spehro Pefhany
  8. Mike Cook

    Mike Cook Guest

    Not the alternators I've taken apart. The star point is typically a
    But THAT'S why I'm asking here: this Denso alternator (used in MANY Hondas,
    Toyotas, and myriad other makes) does have a common terminal connection to
    the rectifier. The rectifier has EIGHT diodes.

    Yes I agree that common configuration is 6 diodes. That's why I'm confused.
    The system is quite populous and apparently functions. I just don't
    understand how.
  9. One problem with this arrangement... if the red idiot light burns out
    That's why you LOOK at the Idiot Light when you turn the ignition switch on,
    just before you start the engine. A lit ALT bulb means it is present and
  10. Jasen Betts

    Jasen Betts Guest

    current into the regulator not supplied by the altenator.
    basically a working altenator.
    you could replace it with a short circuit
  11. Here's a diagram of what the above link failed to clearly explain

    so somehow tapping neutral is good. I guess those two diodes bypass
    current flowing int coils the wrong way or something? As to how speed
    matters, I'm not following that.
  12. Don Kelly

    Don Kelly Guest

    That doesn't make sense to me. One advantage of 3 phase is the
    elimination of triplen harmonics. Now, with a 3 phase bridge-will there
    be a significant 3rd harmonic voltage? Certainly,if the wye neutral is
    not connected to the DC ground, there is no 3rd harmonic current and
    power. Generally this is a good thing.
    Somehow, I appear to be missing something-could you elucidate? A circuit
    diagram and analysis would help.
  13. Some more info:-

    Best regards,
    Spehro Pefhany
  14. Don Kelly

    Don Kelly Guest

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