Alternator Question

Interior and Electrical

  1. JohnRogers

    JohnRogers Active Member

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    Alternator Question: During my Vintage Air install it was determined my alternator was bad. I asked for the most powerful alternator available, yeah channeling my inner Tim “Toolman” Taylor. So, I believe a 100amp alternator was installed. The voltage regulator and ballast resistor were also swapped out. I love the bright lights and quick power windows. The gauge seems to show almost constant charging while I’m driving. My radio keeps shutting down and my power sunroof won’t work, both are fine when the car isn’t running.

    Do I have to swap out alternator for something closer to 60amps? Is there something else I’m not considering? Did I mention how much I like the bright lights and quick windows?
     
  2. rcmaniac791

    rcmaniac791 Well-Known Member

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    I installed a chrome (yes, I know) Summit racing brand alternator about 2 years ago. Externally regulated, 100 amp. Everything still works as normal. Might be a silly question, but is the alternator that was installed externally regulated?
     
  3. JohnRogers

    JohnRogers Active Member

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    Interesting, I don't know.
     
  4. Cordoba1

    Cordoba1 Well-Known Member

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    The current-rating of the alternator will not cause any problems. You can install a 300A alternator if you wanted to. However, I'm concerned that your lights seem extra bright, and that your charge indicator is + all the time -- It shouldn't be. Once the battery is charged, say after about 5 minutes of driving, the alternator gauge should settle right in the middle. A constant charge or drain during normal driving indicates a problem. Please check the voltage at idle once the car is warmed up. It should be at about 13.8 volts, maybe up to 14 and change... But more than that, you'll certainly be overcharging your battery, and maybe harming other electrical components. My spidey-sence tells me that maybe your voltage regulator may be bad.
     
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  5. BudW

    BudW Moderator Staff Member

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    A couple of items I can think of. FMJ cars came with three different alternators. The normal 25 to 78-amp version (used for 98% of all Chrysler cars/trucks – from ’70 to 87).
    r111683a_ang_wdp.PNG

    The 100/114-amp version (used on most police, taxis and some special-order cars) used from early ‘70’s until ‘87.
    r211684a_ang_wdp.PNG
    Note: this is huge and weighs as much as the other three designs combined, weigh.

    The ’88-89 had different alternators. A Nippondenso (Denso for short) 90-amp (small but external fan) and a (new) Chrysler design 120-amp. Some people refer to the Denso as a lightweight design (it is by a pound or so). The 120-amp Chrysler design looks more like a GM alternator than anything else. The 120-amp is a lot smaller and lighter than the 100/114-amp design. I “believe” the 120-amp version only came on police vehicles.

    ’88 on Nippondenso (Denso). Note Chrysler only used 90-amp – but aftermarket has bumped of the amperage to 200-amps.
    R110678a_ang_wdp.PNG

    ’88 on Chrysler design (120-amp)
    r111688a_ang.jpg

    Note: all four use external voltage regulators. A person can fit a large array of alternators onto our vehicles – but not all are externally regulated (which can cause problems).


    Both ’88-89 alternator designs use different brackets than the ’76-87 alternator designs. Also, the low amp and high amp versions use different alternator brackets of each year group (so, four different alternator bracket setups).


    The next issue is wiring. The 25-78 amp and 90-amp alternators uses an 8-gauge output wire – which is good for about 50-65 amps (at 14 volts)
    100/114 amp and 120-amp alternators use a 6-gauge output wire – which is good for about 65-85 amps (at 14 volts).

    Now we know how much amperage the wiring can handle – but that is not taking into effect the fusible link attached to each alternator output wire:
    The 25-78-amp alternators use a (red) 14-gauge fusible link.
    The 90 and 100/114-amp alternators use (black) 12-gauge fusible link.
    The 120-amp alternators use (black) 10-gauge fusible link.

    I have seen a lot of people install larger alternators on cars, mainly for vehicles with large radio/amplifiers installed, but really, for any reason – but don't attempt to replace the alternator output wire with a wire size to accommodate the alternator (or is fused accordingly).
    Because of that, I have seen a lot of melted wiring harness and melted fusible links (and underhood fires).

    There is nothing wrong with having a larger output alternator – but please do a little work with the wiring at same time. I don’t want to see anyone’s ride burnt to a crisp, aka: having a “bad day”.


    Lastly, after an alternator (or voltage regulator, or wiring harness modification) has been installed – always check battery voltage both at idle and at 2000 RPM.
    - Battery voltage should be at 13-13.2 volts, engine off.
    - Between 13.5 to 14.8 volts depending on outside temperature when running – and only slightly higher at higher RPM.

    If voltage is above 14.8 volts and it’s not freezing outside – then you have an overcharging problem.
    That said, if the car fender temperature is -20’F (-30’C) then battery voltage when running, can be as high as 14.9 to 15.8 volts and still be OK.
    BudW
     
  6. Aspen500

    Aspen500 Well-Known Member

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    I wish I had a way of describing things like you do, BudW.:cool:
    I equate putting a higher amperage alternator on while keeping the same wiring as running 14 gauge wiring (house wiring I mean) on a 20 amp circuit. It'll be OK if you never have more than a 15 amp load on the circuit but then put a 20 amp load on it and,,,,,,,,,,,possible visit from the big red and/or green trucks with the loud sirens and flashing red lights.

    At work, I've repaired cars that came in on a flatbed and, someone put a 200 amp alternator on (so they can run their BOOM BOOM BOOM stereo)where a 100 amp was originally, and kept the same wiring. Bad things, melted wiring and various other failures. The laws of physics come into play when you try to run 180 amps through a 10 or 12 gauge wire, and the law says it can't be done.