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Technical Think Alternator Charging to Much

Discussion in 'Traditional Hot Rods' started by qmdv, Jul 28, 2019.

  1. On a 32 Ford Roadster I have a flathead engine. I am running a very early MOPAR alternator with Mopar regulator, non solid state. Well yesterday was a milestone event as I fired it up for the first time.

    The battery voltage was just over 12 volts. I have an amp meter in the dash and it showed 30 amps charging. Not sure how system is supposed to work . Does it full charge to the battery until the voltage is up to a certain point or does does the charge rate go down as the battery voltage goes up

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  2. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,739

    Ebbsspeed
    ALLIANCE MEMBER

    Charge current will be pretty high right after you start the engine. Depending on the state of the charge in the battery it may stay there for a while, or drop down to a few amps once the battery is charged. Also, if your accessories, ignition, etc are powered from the battery side of the amp meter it will also be showing whatever loads those items draw. The charge rate will drop as the battery voltage reaches it's charged value.
     
    Last edited: Jul 28, 2019
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  3. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,872

    Boneyard51
    Member

    If you just started it and the battery is down a little 30 amps is just about right.






    Bones
     
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  4. Its both...

    Regulator gives what is needed and 30 amps is not really all that much. If I recall correctly that should be a 60 amp alternator.
     
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  5. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,872

    Boneyard51
    Member

    To answer you question in a nutshell, yes as the voltage in the battery comes up the rate of charge( amps) will go down. When the battery is “ fully” charged the amp will be very little, similar to a trickle charge. If your amp meter is wired to measure amperes that the accessories draw, it will show some amperes according to the draw of the accessories, ie lights, heater, A/C etc. If wired to show amps going into the battery it won’t show much after battery is charged.




    Bones
     
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  6. 6sally6
    Joined: Feb 16, 2014
    Posts: 801

    6sally6
    Member

    Alternator charging too much?!! So what........so does my wife!!! Like me, you just gotta get use to it.:)
    6sally6
     
  7. The only load that does not go through the Amp meter is the starter (of course). Interesting read on early Mopar alternator. Mine is an early Essex But it does not give amperage for early 60's alternator. https://alternatorparts.com/chrysler-alternator-history.html I like these alternators cus they just look the part of the early hot rod. I remeber an early Mopar add where they started a car and pulled out the battery while it was running then drove the car from coast to coast. Never turning it off.
     
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  8. Truck64
    Joined: Oct 18, 2015
    Posts: 3,669

    Truck64
    Member
    from Ioway

    Current starts out high, voltage low. The current tapers down as the battery accepts a charge, and the voltage rises.

    You can connect a voltmeter directly to the battery posts. Typically something between 13.8 to 14.3 volts is right in the zone. Turn on all the lights and accessories, heater blower etc., and spool engine up to a fast idle 2000-2400 rpm and measure again. Voltage might sag some, but should hang in there.
     
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  9. Mr48chev
    Joined: Dec 28, 2007
    Posts: 25,625

    Mr48chev
    ALLIANCE MEMBER

    Ammeter actually just tells you which way the current is flowing and how much is flowing. As they said 30 amps isn't too much on that setup when you start it for the first time as long as it dropped back down after the battery got charged back up. As Truck 64 said 13.8 volts to 14.3 volts is right in the ball park while years I was told 14.2 is right on the money.
    Check the charge voltage and if it is within specs life is good.
     
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  10. Truck64
    Joined: Oct 18, 2015
    Posts: 3,669

    Truck64
    Member
    from Ioway

    The "correct" voltage is actually a moving target, based on temperature. Charging voltage needs to be a lot higher in cold weather.
     
  11. Mr48chev
    Joined: Dec 28, 2007
    Posts: 25,625

    Mr48chev
    ALLIANCE MEMBER

    I'll say NO on that one. in 60 years of being a car freak. over 20 years of mechanicing, 13 years of teaching high school auto mechanics with a good number of text books from different authors in my collection and reading thousands of articles that is the first time anyone ever claimed that. Ideally the battery only wants 14.2 charge volts give or take a couple of points no matter what the outside temp is. It may demand a bit more for a few moments to get some of the charge back in after a severely hard cold start but that isn't "ideal" .
     
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  12. Truck64
    Joined: Oct 18, 2015
    Posts: 3,669

    Truck64
    Member
    from Ioway

    It has to do with the internal resistance of a battery increasing as the temperature goes down. They need a higher voltage, they take longer to charge, and they can't pass as much current, reducing performance. This internal resistance must be overcome by a relatively higher voltage as temperatures decrease to get the same end result.

    Notice charging and OCV tables use 77° F. as the "standard" battery temperature on which the nominal figures are based, but there is a correction or temperature compensation factor applied anytime the temperature is something other than 77° F., it's not a big deal in temperate areas, but it needs to be a lot higher in cold weather. Seeing 15+ volts in extreme cold is normal and necessary, the battery will never reach 100% without it.

    This temperature compensation applies not only to charging, but also when measuring the open circuit or resting voltage, performing specific gravity testing of the electrolyte, load testing, etc. Charging voltages that would boil a battery dry in the summertime are basically only a trickle or "float" charge in extreme cold.
     

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