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landyacht318's avatar
landyacht318
Explorer
Oct 18, 2015

Theoretical vehicle Voltage regulator manipulation, update

My Alternator's voltage regulator in inside my Engine computer.

I am not always happy with the maximum voltage it chooses to allow.

My Field wires, One sees Z1 voltage( mopar) basically 13.7 to 14.9v vehicle system voltage, the other goes right to my Engine computer, both are 14 awg wiring..

Now I figure if I wanted to raise voltage I could put a resistor somewhere on this circuit.

If I wanted to reduce voltage, well, I suspect I'd have to somehow increase voltage on this field circuit.

The current voltage range allowed is 13.7 to 14.9v. Often it chooses 13.7v when the battery is still depleted, other times it chooses 14.9v when the battery is bursting full.

If the ECM voltage regulator is bypassed, the check engine light illuminates.

I'd love to be able to easily bypass it without setting off the Check engine light, and use an adjustable voltage regulator instead.

Nothing would make me happier than a dashboard mounted potentiometer with a 14.7 and 13.6 clearly delineated and a voltage regulator which obeys my desires.

Right now the full range I need is perhaps 14.5v to 13.5v.

My AGM battery recommends 14.46 ABSv at 77f, but it gets 14.7 to 14.9v often when driving. It 'seems' Ok with this. I cannot detect any capacity loss in nearly 200 50% Deep cycles over the last 23 months.

I am considering not getting a house battery at all. This AGM can so easily start my engine depleted to 30% SOC, and can handle such obscene charge currents, I think I can get away with just a feel good 12AH Asian jumper AGM which comes in most jumper packs to parallel if I ever cannot start my engine.

It Should also be stated I am not stressing this. Nothing is broke and going to Leave me stranded. I am only willing to go so far in my Quest for Ideal. More important is to not fry the engine computer trying to trick it/ bypass it entirely when trying to pick my maximum allowed voltage manually.

Honestly I get more irritated seeing 13.7v on a discharged battery when more amps are available, than I do seeing 14.9v on a fully charged one. At 14.9v and fully charged my Ammeter reads +0.0 amps.

Really hoping to better grasp externally regulated alternator Voltage regulation and entice discussion along these lines, as my knowledge is cloudy and lacking in this area. If you are the type you cannot be bothered with any manual approach along these lines, then click the back button and move on to some other thread, please.

On a related note, My recently replaced reman'd lifetime warranty alternator can produce 20 more amps at hot idle than my previous one could, but does not seem to produce as much as the previous at higher rpm, even with a battery depleted enough to still be well below absorption voltage. I've not gotten it above about 78 amps where as my previous one, when still healthy, could do almost 110amps into a depleted battery at ~3150rpm cold.

66 Replies

  • Don't ever connect a digital voltmeter to a MoPar ECU controlled charging system.

    The LED numerical segments change voltage readings three times a second and it would't be long before they stressed from fatigue and fall to the bottom of the meter. Ever see over-fatigued LED segments laying in a pile at the bottom of a meter? It ain't pretty.

    The OEM analog meter reads 5-volts with the key on.

    Ummmm Baby! This be some topnotch quality Dee Troit designing and quality control. Pretty soon Somalia will be building better cars than we do.
  • The OP is trying to weasel out of the promised 40 page thread on the care and feeding of a T-1275! :(
  • A couple thoughts:

    1. Do you think factory wiring between alternator output and battery could be improved to any significant degree?

    2. Did the truck have a dual alternator option? Maybe you can set up something as your second alternator to do what you want. Either add charge rate to existing battery or split off the new alternator into a dedicated house battery (if system doesn't tolerate what you're after). I can say on my class C, running the solar panels at 14.4 volt and feeding that to Ford's chassis system, I don't get any check engine lights.
  • landyacht318 wrote:

    I am not always happy with the maximum voltage it chooses to allow.


    I think you need to find something else to be unhappy about.
    The odds are that IT knows what is best better than you do.

    Even if that is not true and the batteries actually need a higher charge occasionally, that would be MUCH better achieved with an external device.
  • Steel yourself for a sadly too high odds of ******* the ECU off and having it render the whole program into limp home mode (check engine light). MoPar crafted an ECU menu that compares field voltage to battery voltage and if one of the two differentials exceeds a pre-determimed point, the ECU takes its ball and goes home.

    It won't damage anything. But it may disappoint. Not even a dummy ballast an artificial field load will "outsmart" the ECU. A volt gauge warning would have been too easy. An alternator failure demands gross pollution and a 20% loss of economy and top gear.

    More dope-smoking engineering hard at work.
  • Well, Mexwanderer, with his extensive knowledge and experience with alternators would be the "go-to" guy on implementing an external regulator for your system. He has posted about various off-the-shelf devices.

    My concern would be about heat effecting the chassis alternator and possible failure. I had an alternator fail suddenly a couple of months ago and even though only 6 miles from home, it involved a lot of logistics and falderal to get the vehicle back home. Replacement was another circus and I never did get the equivalent alternator as a replacement.

    That ordeal sensitized me to how I want to treat my alternator in the future. There's no way I'd put an excessive draw on it.

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