Alternator and Voltage Regulator Questions

Discussion in 'Electrical and Ignition' started by stumblinhorse, May 15, 2018 at 12:57 PM.

  1. stumblinhorse

    stumblinhorse Well-Known Member

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    The electrical stuff is hard for me so I am hoping you experts can point me in the right direction. I think these are simple questions!

    Quick background. Original single field Alternator and mechanical Voltage regulator in 69 318. Alternator has been out and tested and got 15.1 volt output without a lot of noise etc. So Alternator is good, I think!

    I read the exact same 12.7V at the battery at any RPM. Recovers after being turned off a few minutes to 12.9V. Brand new battery.

    At the "BATT" connection on the alternator with the engine off I get the same 12.9V and with Running I get the same 12.7V.

    Questions:
    These equal readings tell me I have a good circuit from the Battery to the Alternator?

    The low voltage reading tells me that the Alternator is not sending power to the battery?

    The alternator test tells me the Alternator is working correctly?

    This tells me the VR is not working?

    A VR like this Mopar Performance Voltage Regulators P3690732 would most likely fix my problem?

    If it doesn't fix the problem, I can focus on the wiring from the FLD connection to the VR? Or I should just simply replace that with new when I replace the VR?

    Thanks for the help!
     
  2. skykeith

    skykeith Well-Known Member

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    Since your alternator has tested good, it is probably your regulator. Just go to your local auto parts store and get one. Don't bother with that Mopar performance one.
     
  3. stumblinhorse

    stumblinhorse Well-Known Member

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    My local parts store wants $61 for one. Not sure that it is worth it... hopefully the MoPar one will work as well.
     
  4. 67Dart273

    67Dart273 Well-Known Member

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    Test it ON THE CAR. Not that difficult Go to MyMopar and download a shop manual, and an aftermarket wiring diagram, There are also simplified diagrams there of the alternator / regulator

    I divide things "roughly" into

    1.....The charge circuit path, that is the alternator output, through the bulkhead, the harness, the ammeter, back out the bulkhead, to the battery

    2.....The field circuit.......from the igntion switch (branches off at the coil resistor)-----to the VR---------to the alternator field

    THE VR MUST BE GROUNDED. Unbolt the VR, scrape and clean around the mounting holes, and remount with star lock washers

    3.....The major components, IE the alternator and the regulator

    =============================================

    "Quick test"..........Done in the following manner, this will leave everything in the circuit EXCEPT the VR

    Unhook the VR wires, and jumper them together with a clip lead. Start the car while monitoring battery positive, and slowly bring up RPM. Your dash ammeter should move to the right, and the voltmeter should climb. If it does don't allow it above 16V

    If this is the case, check the VR grounding above, and if that is OK, replace the VR
     
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    • stumblinhorse

      stumblinhorse Well-Known Member

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      I have the FSM and see the wiring diagram.

      My ammeter is already bypassed. The charge circuit shows that I get the same voltage at the battery as I do at the "Batt" connector on the Alternator. So I think that tells me it is ok?

      The VR is grounded to the block at the head.

      So I can jumper the two connections, FLD and Ignition together? I would not have thought of that! I have a electronic ignition on the engine, any issue with that? My Alternator test said max output was 15.1V.

      What I don't understand is the role of the VR I guess. How does it tell the alternator to not allow power to get to the Battery?

      Thanks for the help!
       
    • 67Dart273

      67Dart273 Well-Known Member

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      OK an alternator output is always connected to the battery.........the main output stud.

      How it works........

      The ignition switch sends power to the VR off the same circuit that powers ignition. This IS ALSO THE SENSING wire that the VR uses to "figure out" what to do.

      The relay in the mechanical VR or the circuitry in the electronic one "shall we say" MODULATES the current going to the field connection. More field current= more output. As the VR senses the battery is low, it sends more field current to the alternator........higher output. As the battery "comes up" the voltage at the VR ignition terminal goes up and it "cuts back" and SHOULD normalize at nominal 14V

      By jumpering the wires, you are simulating "full field" "completely dead battery" so to speak.............Again, watch your meter and don't allow RPM to bring the voltage up past 16

      Your statement that the alternator will put out 15V does not mean much. An alternator that is DISCONNECTED from a load and that is spun up, with full field current can put out OVER A HUNDRED VOLTS!! (This is however hard on the alternator and diodes) IN FACT back "in the seventies" there use to be silly switchboxes sold that allegedly allowed you to get 110V (DC) out of your alternator. What this switchbox did was to.............disconnect the alternator from the VR and full field it............just like the test...........and also disconnected the alternator from the vehicle system........and connect it to a common outlet box!!!

      The point? ALTERNATOR OUTPUT voltage depends on the FIELD CURRENT and the LOAD THAT IS ON the alternator output. If you have a battery that is fully charged, and no loads in the car (no fans, no big stereo, no lights etc) and you "full field" the thing, the voltage can go WAY over normal, up over 20 -25V until it damages something.
       
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      • stumblinhorse

        stumblinhorse Well-Known Member

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        So I got my MoPar regulator and hooked it up. I am frustrated with this! I have 12.14v coming to the VR and I have nothing coming out of the regulator going to the field circuit. When I jumpered the field wire to the plug coming in it pretty much melted all the connectors in about 5 seconds, The time it took to start the the engine and walk to grab my multi meter. So no idea what to do next. Is it possible I got a another bad regulator?

        Help!
         
      • 67Dart273

        67Dart273 Well-Known Member

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        Oh SHEEET. What I get for giving you shortcuts, LIKELY what happened is the field wire is shorted to ground and burned up your old regulator. Either that or the field in the alternator is shorted. However, you said you had it tested and "good." So either the alternator is good, or the guy that tested it doesn't know what he's talking about.

        First thing the, is to disconnect the alternator field wire and check resistance of the field to ground there right at the alternator. Better yet pull it off the car so you can inspect.

        I hope you didn't do too much damage. Does "anything" still work? Lights?
         
      • jas0162

        jas0162 Well-Known Member

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        I tried to run the "single field" original system in my 68 a few years ago, but I didn't have any luck. Every single parts store voltage regulator I bought was a piece of junk. A new one from NAPA almost caught the car on fire. I switched to the solid state system and never looked back.
         
      • stumblinhorse

        stumblinhorse Well-Known Member

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        Yes, battery and everything is fine. No worries.

        Seems to me that having no voltage at the regulator on the post going to the field is the problem?
         
      • stumblinhorse

        stumblinhorse Well-Known Member

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        Can I just pick up a VR706 at the local auto parts store and hook it up? I have the single Field 69 alternator.
         
      • 67Dart273

        67Dart273 Well-Known Member

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        I'm trying to figure what caused things to burn up. DO NOT just buy another VR and hook it up you will likely burn it up too, ........unless you shorted something when you tried to jumper the wires

        Before you hook up the new one........and we can lead you through this........check the alternator field for shorts AND CURRENT DRAW, and unhook the VR field wire (green) at the VR and at the alternator. This will leave you with a green piece of wire hooked to "nothing." Now check resistance at one end to ground. It should be "open" or infinity.

        Take a jumper lead from the battery and hook in series with your meter in the AMPS position and the other end to the alternator field. It should not draw more than say, 6 amps max. Loosen the belt and turn the pulley. Should "average" some reading, post it back Refer to your shop manual. This procedure is in there
         
      • stumblinhorse

        stumblinhorse Well-Known Member

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        Pretty much a comedy of bad parts. The new VR AND Alternator were bad. Got both today. Works perfect.

        Simple tests that can be done. I will put them here to help others.

        Vehicle and key off.
        1. Test voltage at battery. Should be 12.7-12.9 volts. If not battery is low and needs charge or is bad.
        2. Test voltage at “batt” connection on alternator, should be pretty much same as battery. If not wiring through bulkhead, gauge, battery cables are bad.

        Key on vehicle off
        1. Test voltage at input plug on vr, should be similar to readings above. If not bad wiring through/from ignition.
        2. Test voltage at output on vr. Should be similar to input, If not bad VR
        3. Test voltage at “fld’ Lug on back of alternator. Should be similar to reading above. If not bad wiring from VR to alternator.

        Key on vehicle on.
        1. Test voltage at battery. Should be 13.5 or greater. If not alternator is bad.

        If tested in this order. It is simple to diagnose.

        Tests to do on new parts.
        Test new alternator in the store.
        Test VR in the store. Make pigtails to attach to a battery in the store. Input to positive terminal of 12v in store, ground to negative terminal and multimeter on output and neg battery terminal. Output should be similar to battery being tested on. Parts store stuff is junk. Test it before buying. Don’t waste your time.

        Thanks for all the help.
         
        Last edited: May 19, 2018 at 6:58 PM
      • 67Dart273

        67Dart273 Well-Known Member

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        If you knew all this why are you askin us?

        1...Seriously, though "parts store" test benches leave a lot to be desired. You CAN NOT really test an alternator without a full load and big enough motor to drive it to full load. The 1/4hp motor used on a typical test bench "ain't it"

        VR might be a different matter, but that doesn't mean the parts store tester is "correct."

        2....So far as your battery vs alternator stud test, this basically does not tell you much because it is not tested under load. There can be considerable resistance in the "charge path" from the alternator to the battery and you will get that reading WITH NO CURRENT going through that path

        3....As I mentioned before TEST IT ON THE CAR. If you do this correctly there will be little reason to doubt your findings. I have no idea, at this point.......why you got smoke from the harness........ You didn't say if or what you found. THIS MIGHT MEAN there is still an intermittent short and the "smoke" might return.

        4....YOU ARE NOT DONE YET!!!! You (the rest of us do/ did) likely have voltage drop in the ignition harness which will caust the VR to run over-voltage. Get the car warmed up and run long enough to get the battery "normalized." Check voltage at the battery running fast enough RPM to keep the alternator activated. If you read much over 14.2, you need to check the following:

        5....To check for harness drop, Turn the key to "run" with the engine stopped. Hook your meter to the closest point you can get (electrically) to the VR IGN terminal, and the other lead to battery PLUS

        What you are hoping for is a VERY low reading, the lower the better. Anything over about .3V (3/10 of one volt) you need to look into why

        Also be CERTAIN the VR is grounded properly with the mount, and that you have a proper jumper from the firewall/ VR or at least the front fender / rad support to the battery NEG. I like to add a no4 "starter" cable (eye to eye cable) from the rear of the drivers side head to the firewall, such as the master cylinder stud mount
         
      • stumblinhorse

        stumblinhorse Well-Known Member

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        I didn’t know all this when I started!
        I agree that the parts store bench is not a good test, but out of the box if the store says it’s bad, like one of them today, grab another one.

        Too crappy out to drive it on muddy roads today so i have to wait for a full run to determine over charging. No idea why jumper around the VR melted the wires. There was no resistance on the fld wire.

        Also the vr706 and a 2 field alternator hooked right up without any trouble. Just needed a 1/4” spade connection instead of the ring connector. No additional wiring needed. The MoPar above didn’t work right out of the box.