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Hot Rods Anyone have any luck remagnetizing a GM 10SI Alternator?

Discussion in 'The Hokey Ass Message Board' started by Dads426, Apr 11, 2021.

  1. Dads426
    Joined: Jul 14, 2010
    Posts: 24

    from Olney, MD

    We use a GM 10SI alternator on a 64 Dodge NSS car and over the last 10 years we have replaced 3 of them that fail to charge after the Winter storage. The battery is disconnected for about 5 months, so the alternator is not receiving power during this time. I was told that if left connected, the small leakage current through the diodes is enough to keep the field magnetized. There is a procedure to remagnetize the field with the car running by pulling the plug on the alternator and momentarily touching the R terminal to the positive battery terminal, but this hasn't worked. Any suggestions?
  2. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,049


    I'm going to say that who ever you have been talking to has been feeding you a line of BS.
    Yes there can be a slight residual magnetism in an alternator but alternators do not have permanent magnets nor do they need permanent magnetism. They use the voltage from the exciter wire to create the magnetic field.
    I've pulled 10 SI alternators out of the shed that have sat there for 20 years or more and run them with no issues.
    If yours are failing after sitting a few months without a battery I'd say you have an issue with the car that causes that.
    There is a pretty good article on the the alternator initial manetic field here. ac - Source of initial magnetic field in an alternator - Electrical Engineering Stack Exchange
  3. deathrowdave
    Joined: May 27, 2014
    Posts: 2,698

    from NKy

    The alternator has no idea how long it sits . As in if sitting on a shelf for 10 years , bolt it onto an engine , energize the windings and low and behold it works , if the guts are good . A 10 or 12 SI is one of the better and easier to rebuild . Google it and you will see step by step how to do it .
    XXL__ likes this.
  4. Dads426
    Joined: Jul 14, 2010
    Posts: 24

    from Olney, MD

    The 10SI is a one wire alternator. I did replace the internal regulator in one once and it still didn't work. Is the residual magnetism necessary to make it work? Increasing the rpms is suppose to excite the alternator, but it has no effect on it.

  5. trollst
    Joined: Jan 27, 2012
    Posts: 2,068


    A 10si is not a one wire, it is the first internally regulated alternator made by gm. A 3 wire, simple, I have had the same one on my 36 for twenty years, that would be 19 winters, battery hooked up the whole time. Always has worked flawlessly.
  6. enjenjo
    Joined: Mar 2, 2001
    Posts: 2,548

    from swanton oh

    It can be converted to one wire by changing the diode trio to a marine application diode. I've done a few.
    trollst likes this.
  7. Don't certain one-wire alternators, have to be revved up when first started, to start the charging process?
  8. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,211


    it's the internal voltage regulator that gets changed not the diodes...Some one wire alternators did need to be reved when the engine is first started but I believe the most recent version may not..
  9. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,467


    I like the 10DN best. It has a stand alone regulator that keeps batteries nice and charged but no over done..

    If this is a drag car only, I'd look into a magneto..
    Last edited: Apr 12, 2021
  10. TRENDZ
    Joined: Oct 16, 2018
    Posts: 310


    Being a drag car, I assume you have a battery cut off switch. How is the car wired(alternator/ battery wise) to kill the car?
    Yes. A one wire alternator does need residual magnetism to excite the regulator. The lower the residual magnetism, the higher the rpm required to “turn on” the field.
  11. Here is the 'how to' video to excite a self exciting alternator that has lost its magnetism. Sounds weird? Watch the video.
    Dads426 likes this.

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