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Hot Rods technical alternator overcharging

Discussion in 'The Hokey Ass Message Board' started by studebaker46, Jun 9, 2021.

  1. studebaker46
    Joined: Nov 14, 2007
    Posts: 715


    1941 ford pu with 350 crate engine with a/c with remote condenser with electric fan. has 180 amp alt now all of a sudden starts overcharging. pegging needle on volt meter. 16 v on volt meter any advice appreciated. P.S new batt. Tom
  2. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 12,489

    Johnny Gee
    from Downey, Ca

    Did you have a low battery? Anyway's time to replace or have it repaired.
  3. FrozenMerc
    Joined: Sep 4, 2009
    Posts: 3,087


    Voltage regulator took a shit. If external, easy to replace, if internal, get a new alternator.
    bobss396, mad mikey and porknbeaner like this.
  4. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,513

    from WA-OR, USA

    Might want to take a volt reading with a digital meter to get a precise voltage reading. Some regulators will peak out up to 16 volts under load. One way to check if the regulator has a problem is to check for AC voltage. If there is AC, there's a problem with the regulator (probable shorted diode) that's causing the high output.
    Elcohaulic and anthony myrick like this.

  5. My one wire was showing 15 plus on an auto meter gauge.
    14.4 on a digital volt meter.
    mad mikey likes this.
  6. G-son
    Joined: Dec 19, 2012
    Posts: 1,271

    from Sweden

    A friend sent a video of a tractor with flickering lights a while back, sometimes normal light, sometimes way stronger. Turned out to be the regulator in the generator that had a bad connection to ground so when it didn't sense the actual voltage it bumped up the charging to max. Worked perfectly after some cleaning of the connection.
    Elcohaulic likes this.
  7. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    from Ioway

    13.8 to 14.3 are typical alternator charging voltages at idle. In the summer. Measure directly at the battery posts. Turn the headlights on HI, heater fan on full blast, radio to load up the alternator. Spool up the engine RPM into highway cruise range around 2000 or so. The charge voltage will sag some but it should hang in there. 16 volts is way too high ordinarily, it will boil out your new battery or permanently damage it.

    It does sound like the VR is horked or it lost its ground reference. Charging system or battery defects should always be fixed sooner than later!
    HotRodWorks, mad mikey and VANDENPLAS like this.
  8. jaracer
    Joined: Oct 4, 2008
    Posts: 2,375


    If you are reading 16 volts at the battery posts, you have a problem with the regulator. However, there are a lot of things you haven't mentioned, like what alternator, internal or external regulator? Is it a late model 350 with electronics? The regulator might be in the engine computer if it is.
    Truck64 and mad mikey like this.
  9. Make sure all your grounds are clean and touching clean metal. That means you have to take them apart.
    Truck64 and mad mikey like this.
  10. studebaker46
    Joined: Nov 14, 2007
    Posts: 715


    more info the car does have aftermarket a/c, this was how I noticed it, the blower spiked and I looked at the voltmeter was pegged I will check it out at the batt post in the a.m. Tom
    Truck64 likes this.
  11. My car started doing this, I saw the dash lights getting brighter and then calm down. It was hard to catch it and see the gauge it happened so fast. Finally was able to see it swing to 18v with some help. The internal regulator was bad, local shop replaced it for the right price.
  12. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,718


    If it is a Delco internal regulator it isn't exactly rocket science to replace the regulator. The hard part most of the time is finding the springs for the brushes after they pop out when you take the case apart.
    Try to find the correct Delco regulator and not a cheapie off brand unit though.
    Plus put a pencil mark on the cases in a hidden spot so that you clock the cases right when you put it back together.
    ottoman, Truck64 and anthony myrick like this.
  13. studebaker46
    Joined: Nov 14, 2007
    Posts: 715


    thanks for all info. the suspect alt was a napa rebuilt, out of warranty of course, when I pulled it apart to change out the regulator the battery stud was burnt 1/2 into. so ordered anew tuff stuff alt from speedy bill same price as another rebuilt napa, so all is good now. Mr48chev thanks for spikeing my confindence back in the day I rebuilt a bunch of them. thanks again for all the info Tom
    brEad, Johnny Gee and anthony myrick like this.
  14. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,212


    I have much better luck taking the stock alternators and starters to my local starter shop..
    bobss396 likes this.
  15. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    from Ioway

    "My local starter shop". Lucky you, they seem to be getting scarce.
    Hotrodmyk and '34 Ratrod like this.
  16. 1971BB427
    Joined: Mar 6, 2010
    Posts: 8,674

    from Oregon

    Easy to replace an internal regulator too. Just need 3 nut driver sizes, and about 15 minutes to diaassemble. At least on Delco 10SI and 12SI alternators. Done a lot of them, and nothing special.
    But rebuild kits that include regulator, and brushes are cheap. But complete kits cost almost what a rebuilt alternator costs. So if it's more than a regulator, it's quicker to buy a rebuilt alternator.

    Whatever you do don't waste time at one of the chain auto parts stores getting it checked! I took two recently to Autozone and O'Reilly's to be tested. One had no output, and the other was putting out 18.5 v.! They said both passed the machine's test! I bought a ne 10SI anyway, and it worked fine after putting it on my car.
  17. This is what I do. I used a local shop that was great, that closed maybe in 1990.

    With the stock cars, I had a guy in the area with a 40' x 60' shop behind his house. With a coal bin outside and a coal stove inside. He was old even by 1978, but I stuck with him until I got out of cars for a while. He would do us starters that started even if the car stalled on the track and was up to 240.

    The shop I use in in Amityville NY, a couple of brothers about my age own it, they do really nice work. Converted my truck starter to a high torque. $65 out the door, think my alternator with no core was $55.

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