90 SHO Alternator Overcharging

Discussion in 'Gen 1 & 2 - Electronics & Audio' started by sperold, Oct 19, 2020.

  1. sperold

    sperold Last to Know Supporting Member

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    With a battery charger, I charged up the battery on my 90 Winter Car, to make sure it did not have to work too hard to recharge the battery.
    Started the car, and my battery light is on.
    Much to my surprise, when I put a gauge on it, the alternator was at 15 Volts at the idle speed.
    I swapped out the battery and the reading was the same.

    What goes on inside the alternator to begin the over-charging situation.
    I do not relish the removal of the alternator and going to a repair shop, so I am asking if there are any things I can do to get it to charge properly.

    Any ideas or advice is welcomed.
     
  2. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    The regulator is bad. idk if the Gen1 cars are this way for sure, but all the Gen2 and later Ford vehicles have the regulator built into the alternator, so I suspect you 90 is the same way. The repair shop can re-build it with a new regulator.
     
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  3. sperold

    sperold Last to Know Supporting Member

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    Yes, the little 90 amp alternator has an internal regulator.

    I hooked the charger up to the battery in the car, so I think I may have contributed to the failure, which makes me remember that no good deed goes unpunished.

    Thanks for the diagnosis, any chance it just died of old age?
     
  4. SHOVNST

    SHOVNST Blood type: SHO+

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    90 and newer have the internal regulator. 89 and older is external.

    .
     
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  5. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    I do not think you charging the battery had anything to do with it. Unfortunately, the regulators were not very durable.
     
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  6. sperold

    sperold Last to Know Supporting Member

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    Big surprise.
    Took the alternator off the car and went to the rebuild shop. They did their run-test and found that it is 15 v at an idle and 15V at any rpm. He said the amps came down as it ran, and there was nothing to be alarmed about and that he would have no problem running it in his car. Especially in the winter.

    When I told him the battery light was on, he insisted that was not the case.

    I remember reading on this forum that overcharging turns on the light, just the same as under-charging.

    Anyone have a recollection of how the charging above 14.5 V turns on the light?
     
  7. sperold

    sperold Last to Know Supporting Member

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    With some luck, i found an explanation of why the battery light is on when overcharging. The post is from ShelbyDoug in 2005 and is titled "Charge Indicator Light help" and the explanation is from
    Hawkeye 18, post #5.

    I went back to the shop and told them if they can still buy a regulator, to put a new one in my alternator.
    The new regulator has to be soldered into place, and it seems that is not a fun job.

    Bad news is everyone will be hunting next week and they won't have a part by then, but that is life.

    https://shoforum.com/index.php?threads/charge-indicator-light-help.110030/
     
    Last edited: Oct 27, 2020
  8. sperold

    sperold Last to Know Supporting Member

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    The shop could not buy a regulator for the alternator, so they put it back together and tested it again. It is still doing the 15V output at all rpm.

    While apart, they showed me green dots all over the windings, and explained that they were breaks in the coating on the wires and the green was corrosion; and it is on borrowed time.

    I put it back on the car and drove it around for half an hour, then felt the battery; and it was stone cold.

    I found another alternator, and plan to have it tested when deer season is over.

    A side note, the shop told me to run a heavy gauge wire directly from the alternator output terminal to the positive terminal of the battery, if I wanted the battery light to go out. But I did not do that, as my bravery only goes so far.

    I will be able to buy a new alternator or a rebuild from RockAuto, but with the border to Canada being closed, it is subject to a lot of extra charges and taxes.
     

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