alternator output

Discussion in 'Electrical and Ignition' started by robert flippo, Jul 8, 2018.

  1. robert flippo

    robert flippo Well-Known Member

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    Rebuilt a 318 74 duster, put an 80 amp alternator on it, a new one due to the fact i put ac bracket from a 90 ramcharger ,had to put a different alternator to match bracket, my alternator gauge is pegged to top at 40+,,but with ohm meter i read 13.9 volts at battery when running, was 12.5 before starting car, my question is, do i need to disconnect alternator gauge since it's pegged, and is that normal?,,Also should i replace alternator gauge with volt gauge and splice the red and black together that went to alternator guage?
     
  2. BillGrissom

    BillGrissom Well-Known Member

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    You should bypass the dash ammeter. Search for "MAD Bypass", gazillion posts here. The stud connectors can melt even w/ normal 30A output, so 80A would stress them. Any corrosion and heat builds up. Even worse, the bulkhead connections can melt under full alternator current (exc. 1963 & 65 cars w/ buss feed-thrus). 13.9V when running is "about right" for the voltage regulator set-point. I see ~14.3 V in my newer cars. 12.6 V is correct for a fully-charge battery w/ engine off. Some replace the dash ammeter w/ a voltmeter (modified wiring of course). Until then, use a cigarette lighter voltmeter, as I do in my modern cars which have no built-in gages to monitor charging. $15 for a nice digital one or $5 for a Harbor Freight cheapie w/ LED lights.

    I posted a method to keep the ammeter working normally at low currents, then shunt higher output straight to the battery to protect the cabin wiring, using large diodes, but that is beyond most people's abilities to understand and execute.
     
  3. robert flippo

    robert flippo Well-Known Member

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    i appreciate the quick response, i hadn't been driving the car until i found out for sure, was use to working with low voltage dc current, just not in a 44 year old car with factory splices in the wiring,
     
  4. 67Dart273

    67Dart273 Well-Known Member

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    It's likely your battery is down a ways and charging that hard, but ^^above is right, the factory ammeter and wiring were NEVER designed for that kind of output Get started by reading the MAD article. Some guys don't like the way that is done but it IS a very good overview of the problem and why.

    Catalog
    Also do a search on "fleet wiring" which is heavier ammeter wiring on 65A optional cars

    See this thread

    68 Dart Voltage Reg "issues" - Where is factory mounting location

    mopar "fleet wiring" - Google Search

    Here's a shot out of the '72 shop manual this is B body not A body but shows the fleet wiring option

    fleet-jpg.jpg

    Here's an old thread on ammeter to voltmeter conversion. Pleas read it, as it covers a lot of ground

    Ammeter to Voltmeter...who does it?
     
  5. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    Besides damaging the car's wiring, high current charging will heat the battery itself and can damage it, or at minimum boil off some off some of the acid. An alternator will supply its maximum output. On a stock alternator, running at idle, the output is limited by the low speed. It's possible your new alternator is putting out over 40 amps. Although its unlikely to hit the rating of 80 amps at idle speed, it will get there at even normal driving rpms. If the battery is very low, its best to charge it from a charger, and control the rate of charging.
    Here's a series of photos showing a low battery drawing current from a battery charger.
    Alternator amp rating.