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Fixed Alternator Output

  1. Aug 5, 2017 #1
    I have a 10SI delco alternator the voltage regulator and diode trio test open to all points I put it togather this way I know it will not charge unless you ground the one side of the brushes then the alternator will put out maximim output. What I want to know if you put resistance between ground and the brushes is it posible to get an alternator with the correct resistance to make a alternator charge a fixed 2 amps?

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  3. Aug 5, 2017 #2


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    The problem with leaving out the diode trio is no there is no way to source current for the field except through the indicator light. That indicator light will allow enough field current to get enough output to source more field current, etc. So if you don't have the diode trio you won't get much. You need to ditch the regulator if you want to manually control the output.
    Are you only interested in output current and not voltage? The regulator is switching. It does not vary the resistance as you intend to do. You may lose a fair amount of power across your resistor.
  4. Aug 5, 2017 #3

    jim hardy

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    Perhaps. But you'd have to operate it at constant speed and constant volts .

    I don't see it as practical.

    What is it you are trying to power ?

    Since you seem handy enough to have re-assembled your alternator, consider this experiment:

    A 1964 thru 1969 Chrysler electromechanical voltage regulator is about the simplest i know of. It acts like variable resistance to ground.
    Actually it's old "Dancing Contact" design, 1930's era Pulse Width Modulation if you will.
    Anyhow, one terminal senses battery voltage after ignition switch and the other provides 'ground" for field.


    '63 and '62 work almost same except they provide +12 to field brush instead of ground. You'd ground the other brush instead of tying it to diode trio.

    since i don't know what it is you're up to, i just mention this as a way to get your alternator going for about ten bucks.
    Last edited: Aug 5, 2017
  5. Aug 6, 2017 #4


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    Why not use a constant current (electronic)_ regulator (After the Voltage regulator, that is)? That sort of regulation would be less trouble than using a (mechanical based) speed regulator. 2A is a pretty light load to be dealing with.
  6. Aug 6, 2017 #5
    I drew up a schematic of what I think should work. Starting with a 10k resistor should do something I assume the higher the resistor value the lower the output but a low value resistor will give more power but will need to be high watts otherwise will get hot and burn out. I am using this on a tractor running an auger and it only runs at 800 rpm.

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  7. Aug 6, 2017 #6

    jim hardy

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    I think 10K will give a disappointing result. You'll need more field current .
    I'd go to auto parts store and buy a taillight socket then try various size bulbs in it. 1157 bulb has two filaments which gives you four resistances to play with - bright filament, dim filament, both in parallel, both in series. It won't burn full brightness so should last a good while.

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