Charging system troubleshooting

Electrical and Ignition

  1. RBConvert

    RBConvert Well-Known Member

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    I want to start by thanking all the members here who have posted in the past answering charging system questions. I downloaded the comments and performed what I think is a comprehensive test and diagnosis of my low charging issue.
    The car is my 68 Dart with a Mopar 360 crate motor. Alternator is squareback and the wiring and VR have been updated to post 1971 style. Spark is controlled by a Mopar chrome box. I've owned the car for six years, the motor swap and charging system wiring were all performed by the PO. I've never had any wiring issues and no electrical components have been changed or updated during my ownership.
    Recently the ammeter has been showing slight discharge with no load, large discharge with the headlights on. RPM has no effect on charging. It's definitely discharging because the car will start and I can drive it around during the day with no load (other than brake lights) and the car will restart once; the second time it gets sluggish and by the 3rd time the battery doesn't have enough juice to turn the starter.
    With batt fully charged, engine off, Bat 12.45V; alternator stud is also 12.45V. Engine running at high idle (2000 rpm) the alternator puts out 12.07V; Batt is 12.2V. Engine running with headlights on the alternator drops to 11.53V; Bat is 12.0V. Is it normal for Bat + to be higher than Alt Bat?
    Ran two tests:
    With Key On, Eng Off the one FLD wire registered 11.37V. This could be one issue; expecting it to be closer to 12V. Reconnected it to the alternator, removed the other FLD wire and grounded the spade connector to the alternator. With engine running, charging voltage still 12.07V at alt Batt; ammeter still discharging.
    Second test, kept the first FLD grounded, disconnected the 11.37V FLD and jumpered over to the Batt +. No change in alternator output.
    So it should be the alternator, correct? Removed it and had it bench tested at O'Reillys. I stood next to the guy and watched the test, the alternator passed! Tried it twice.
    Can the alternator be functionally OK while diminishing output? Or should I dig deeper into why the FLD wire only registers 11.37?
     
  2. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    Only comment here is to think of it the other way. Battery is 12.2 Volts. Alternator stud is 12.07 V. Therefore current is flowing from battery.
    Probably 2 to 5 amps flowing out of the battery (as seen on the ammeter).
    That's not a terrible ammount of resistance. Around 10 to 15 amps flowing and less than a 1/2 Volt drop in the lines.
    Ideally yes it should be same as battery. Showing more resistance in the circuit from the main splice to the field wire than you saw with the power to the headlights. Key switch connector, bulkehad connectos, other? However it doesn't explain the lack of charging.
    If I interpret correctly the the blue field wire is the one you tested - the one spliced into the 'ignition' circuit.

    Grounding the spade terminal should have full fielded the alternator - and yes it should have started producing power.

    Interesting. (not in particularly good, but still interesting) What sort of test did it pass?

    Got a couple suggestions.
    I assume the alternator is still off. Measure the resistance between the field terminals. This just makes sure its not an open circuit.
    I'm going to assume you don't have a low current ammeter. So if you want to more on the bench, only things can do is check the brushes and then open it up, remove the stator and check it and the rectifiers. Pretty easy on the square backs. I posted a thread with some photos if you want to get a sense of that - just ignore the pulley removal stuff.

    Rig up test lamp you can splice in-line with the field circuit - one side could have a female terminal to slip on the alternator spade - the other an aligator clip.
    Run the engine with the test lamp in line. If the lamp lights up then current is going through the rotor and it should be making a magnetic field. based on what you've done and what you have available to check - that's the only thing I can think of.
     
  3. RBConvert

    RBConvert Well-Known Member

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    Both FLD wires at the alternator are green; the VR has a green and blue at the connector so somewhere there's a splice. All wire routes are heavily taped so I can't tell where. Only one wire had voltage some I assume that should be the blue wire.
    I have a pretty decent multimeter; it's HF but it's the $40 one not their cheapee giveaway unit.
    Setting it to 2ohms, there's .06 ohm across the FLD terminals. Between the two FLD wire connectors there's .56 Ohm.

    I have a test light. So if the lamp lights up with the engine running then does the culprit point to the VR?
     
  4. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    Yes.

    Were you back probing for voltage or had the wires disconnected?

    I'm asking because if the voltage was only at one field while back probing, then there is break inside the alternator. Could be a brush or could be in the windings.
     
  5. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    Assuming we're talking about just a non-powered lamp
    No. I would then suspect something related to the stator or rectifiers.
     
  6. RBConvert

    RBConvert Well-Known Member

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    I disconnected the wire and stabbed the probe into the connector.

    I reinstalled the alternator and just for S&G's I disconnected the VR connector and inserted two machine screws into the connector and jumpered between the two. Engine at 2000 rpm is putting out 11.9V at the alt stud. Down approx 0.17 V since yesterday.
     
  7. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    Not sure what you thought that does.

    Sometimes its helpful to look at the earlier system because its wiring is simpler.
    When voltage drops, electricity is permitted to flow through directly the regulator.
    When voltage starts to get too high, no electricity flows through.
    upload_2019-4-13_15-33-27-png.png

    When electic current is allowed through the regulator it goes to the positive field terminal, then through the carbon brush that rubs against the spinning copper ring. Electricity flowing through the rotor windings creates a spinning electro-magentic field.

    Two field terminals on the later alternators allow the later regulators to control the ground. In other words they open and close the connection to ground allowing or stopping the flow of electricity that creates the spinning magnetic field.

    Some people call the two field terminal versions, isolated field terminals. This means both are insulated from ground. This is a better way to understand it.

    This is a rough schematic of the regulator.
    Important thing is the regulator uses the system voltage measured at the feed wire (blue) to allow power through the rotor.
    If you jumpered the two wires together, then you created a short circuit to ground.
    upload_2019-7-14_16-20-2.png
     
  8. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    The test light in the circuit was just a way to determine if current was flowing through.
    upload_2019-7-14_16-27-28.png
     
  9. RBConvert

    RBConvert Well-Known Member

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    After reading your reply, i went back to the earlier threads and realized I missed a critical step in #6. After jumping the VR connector, then disconnect the blue ign wire from the alternator and ground the FLD. This will full field the alternator using the green wire and VR IGN terminal for source (direct from the thread). Wow! At 2000 rpm the Alt is putting out 20V and pegging the ammeter +. The test isolated the issue but I'm frustrated that I don't know what I'm seeing. I get that jumping the VR puts 12V on the green wire but i'm not connecting the dots on why grounding the IGN puts the alternator in full charge.
    I assume the issue is in the VR.
     
    Last edited: Jul 14, 2019
  10. Mattax

    Mattax Just the facts, ma'am FABO Gold Member

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    Lemme do this in drawings 'cause I'm a bit tired and may not be following clearly,
    The car has an early system with chrome box and of importance here, the ground contolling regulator.
    Schematically something like this.
    upload_2019-7-14_20-8-48.png

    and I think is what you just did as a test.
    upload_2019-7-14_20-16-22.png

    Which yes is pointing toward the regulator.
    But I don't understand why your earlier test didn't get the same result.
     
  11. kursplat

    kursplat FABO Gold Member FABO Gold Member

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    as an aside: thought you needed to run the replacement, "blue" electronic regulator, when staying with the single ballast and electronic ignition?
     
  12. RBConvert

    RBConvert Well-Known Member

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    Yes, the bottom schematic is the most recent test. And I was thinking the same thing; I'm going to repeat the earlier test and see if the results change. BTW, I used many of your earlier threads for reference and I really appreciate your patience.
     
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    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      This one
      Maybe I misunderstood. This is what I thought didn't work but should have had the same result (unless its a bad wire connection)
      upload_2019-7-14_20-23-59.png
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      Direct Connection used to advise using an electronic voltage regulator when using the electronic ignition.
      At the time, all they could offer for not rewiring and changing to 'dual field' alternators was to use their blue regulator. Supposedly the problem was the switching noise in the mechanical regulator. But now there other electronic regulators for that control the feed. So now I don't know if there actually is an advantage to ground controlling regulation over feed controlling. Could be something more subtle - an electronics person may know or be able to figure out more.
       
    • RBConvert

      RBConvert Well-Known Member

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      I'm not familiar the "blue" VR.
       
    • RBConvert

      RBConvert Well-Known Member

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      You got it. This schematic illustrates how I tested the VR yesterday. Bad wire connection - you mean with the jumper? I'm going to try to duplicate it again tonight.
       
    • RBConvert

      RBConvert Well-Known Member

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      The current VR on the car is a NAPA Echlin. Don't know if this makes a difference: the current VR has a smooth face; the two replacements I found (cheapo Chinese and an ACDelco) have a slight step-down on the face.
      [​IMG]
       
    • RBConvert

      RBConvert Well-Known Member

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      Found the blue VR on Mancini Racing. Constant 13.5V, "for drag racing use only"
      mopar-performance-voltage-regulator-31.gif

      This is their muscle car model:
      mopar-performance-voltage-regulator-37.gif
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      Maybe - I was thinking more like the splice or connection when the second wire was added (by previous owner).

      For example if either of these connections is loose.
      upload_2019-7-14_21-28-58.png
      Mopar Performance sold (sells?) blue painted electronic regulators. The one I mentioned was for alternators with one field terminal grounded. I'm pretty sure they also sold one for isolated brushed alternators like you have. Had the same triangular connector as a factory regulator.
      I haven't had to experiment with buying these. The most recent AC Delco item I bought was an alternator for my Wagoneer. QC was not there - would have flagged a major problem if this was a GM production item. parts store exhanged it and we got an older one that was fine. It's crap shoot out there.
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      There you go!

      I don't know what to suggest. If the black one comes with some sort of guarentee then it might be worth gambling at higher price.
      FBO has one (selling via ebay) for the single field wire that they are giving a 3 year guarentee. I figured that was worth a try.

      13.5 Volts is a little low on the set point. Maybe that's why its race only.
       
    • Mattax

      Mattax Just the facts, ma'am FABO Gold Member

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      Just looked - they dont have the newer style like your car has.
       
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      • RBConvert

        RBConvert Well-Known Member

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        The connector at the alternator is a little loose; looking at DelCity for some Packard 56 terminals.
         
      • RBConvert

        RBConvert Well-Known Member

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        Autozone and Oreillys sell a cheapo Chinese unit for around $14; the ACDelco unit is $45. Mancini is selling the black one for $27 + shipping. I'm calling them tomorrow to verify compatibility. Bought a lot of parts from Mancini over the years and never have had an issue.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        56 will work usually
        58 is closer to the original terminal. The connector for a 56 is sometimes loose on a 58. Del has posted that sometimes one won't fit in the other.
        upload_2019-7-15_6-57-7.png

        upload_2019-7-15_6-59-2.png
        Sources for Chrysler type wire terminals
         
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        • RedFish

          RedFish Well-Known Member

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          Pics above remind me of one from many years ago. All but 2 or 3 wire strands were broken.
           
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