Over Voltage with New Battery Disconnect Switch

Discussion in 'Electrical and Ignition' started by gradedcatfood, Oct 6, 2018.

  1. gradedcatfood

    gradedcatfood 1972 Plymouth Duster 440

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    Hey everyone,

    I recently just installed a new battery disconnect switch in my car and to conform to NHRA rules I also hooked my alternator charge wire to the disconnect switch. Ever since then the car has been getting too much voltage (about 16v) and is causing my fuel pump to scream like a demon monkey.

    If I disconnect my new charge wire that goes from my alternator to my disconnect switch and reconnect the old wire to the alternator the voltage goes back to its normal 14.5v and life is good.

    I had a spare voltage regulator and swapped that and I still have the issue. I also made sure the voltage regulator has a good ground.

    I feel like I may have bypassed a voltage regulator circuit? The field wires from the alternator are still going to the voltage regulator though so I'm not sure where I messed up but I'm certain it has to do with my wiring considering when I put it back to stock everything is fine.

    The wiring does "work" in the sense that when I disconnect my master disconnect my car does shut off even if the car was running.

    Here is the alternator I am using: Alternator - Dual Field-440 Source

    The photo is what I went off of for wiring in this thread: Pics on battery cutoff switch

    Thanks for all the advice and help.

    5951863-2postfullcutoff.jpg
     
    Last edited: Oct 6, 2018
  2. Dana67Dart

    Dana67Dart Most undignified way to get to Colorado!

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    Seems to me that you are bypassing the V reg by applying 12V to the field wire. The diagram in your post would only disconnect the starter from the battery.

    What is the intended purpose of the disconnect switch?
     
  3. 67Dart273

    67Dart273 Well-Known Member

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    This is caused by voltage drop. The VR MUST SEE battery voltage ACCURATELY. This includes the ground path which is a real possibility. Your VR power path (functional) is from battery +, through the switch, cable, up front, through whatever connects it to factory wiring, through whatever path goes to the ignition switch, through the switch, out the bulkhead connector, and to the VR IGN terminal.

    "Rig" a wire long enough to reach to the front of the car. This can be anything from no22 scrap ethernet wire to no14 or larger.

    Clip that to battery POS, run up front, and connect to one probe of your meter.

    Turn key to "run." Engine stopped. Measure as close as you can get to the VR IGN terminal. This might be the blue field wire at the alternator. Do NOT disconnect anything to measure. You want the reading "under load" with "circuit normal."

    THAT READING is the voltage drop in the harness. Let's say your read 1.8V. THAT will be ADDED to the proper 14V or so charging setpoint of your VR, and you will then see 14+ 1.8= 15.8V charging running

    Then you'll have to chase through all wiring terminals, switches, etc until you find the drop

    GROUND. In your case since you say it becomes normal when you change the wiring, grounding is likely not the problem but you should take steps to make it "right" anyhow:

    HOW is your battery grounded? Are you using the body? You need a BIG ground jumper from the engine block to the body, an no1 starter (ring to ring) at least

    VR.........remove, scrape around the bolt holes of both body and VR, and remount using star lock washers. VR MUST be grounded to "same as battery" neg post.
     
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    • 67Dart273

      67Dart273 Well-Known Member

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      By the way I DO NOT CARE for the separate charge wire bit from battery to alternator. When you pull the disconnect, yes the engine dies, but THIS LEAVES A LARGE gauge wire "hot" all the way to the front. Think about that if you are upside down, gas streaming everywhere, and the track guys have "pulled the switch"
       
    • gradedcatfood

      gradedcatfood 1972 Plymouth Duster 440

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      What should the field wires be? There is a blue and a green going to the alternator and not sure what they are supposed to be measured at...

      The purpose is to pass NHRA tech so that the disconnect switch shuts off the car while running. The diagram isn't perfect as that power wire running to the starter also runs to a positive post in the front of the car which goes to the starer relay, other ignition stuff etc..
       
    • gradedcatfood

      gradedcatfood 1972 Plymouth Duster 440

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      Appreciate the write up and will try some of this tomorrow but I don't understand a couple things.

      1) To test voltage drop, am I measure DC voltage in parallel with positive side of battery to a field wire off the alternator?

      2) I don't understand how bypassing the original charge wire and just running my own straight to the cut off would cause voltage drop and if it did I don't see a way to resolve that considering that is the only wire I change in the charge circuit.
       
    • 67Dart273

      67Dart273 Well-Known Member

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      1...You are measuring the DIFFERENCE in voltage from the battery to the VR which shows the amount of drop. You want one probe on the battery positive post (hence the long test wire) and the other probe "as close as you can get" to the VR ign post. If you disconnect the VR to measure this at the VR connector, you have just removed the load and the drop will decrease, causing inaccuracy

      2....I don't know off hand, but you obviously did something. You did not bypass the VR by the description of what wiring you changed
       
    • Dana67Dart

      Dana67Dart Most undignified way to get to Colorado!

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      My assumption is that you are using a single pole disconnect switch between the battery and the rest of the car. Somehow you are trying to also disconnect one of the field wires to the alt to stop it from generating electricity

      Is this correct?
       
    • 67Dart273

      67Dart273 Well-Known Member

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      The "popular" voltage drop problem WITH FACTORY wiring can be anywhere in the circuit path from the battery PLUS to the VR terminal

      In a stock car, this includes the following terminal points and components:

      Battery to FUSE LINK, through the RED BULKHEAD CONNECTOR terminal, to the AMMETER and through the AMMETER, out the ammeter on BLACK to the under dash WELDED SPLICE, and branch off to feed the IGNITION SWITCH CONNECTOR, through the SWITCH, back out the SWITCH CONNECTOR on "ignition run" blue, back out the BULKHEAD CONNECTOR on blue, and BRANCH OFF to feed various circuits, ignition, choke heater, smog doo dads, and the VR IGNITION TERMINAL in the CONNECTOR

      Every single thing in bold type is subject to a problem, including bad connections within the factory ammeter wire ends, or the ammeter itself.
       
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      • 67Dart273

        67Dart273 Well-Known Member

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        GROUND......The way to check the ground circuit for this problem is to warm up the engine (VR is voltage sensitive to temperature, or compensated) and run the engine at a "low to medium" cruise RPM, run this test first with all loads off, and gain with all you can power on, radio, heater, lights, etc

        Hook one meter probe to battery NEG right at the post. "Stab" the other terminal into the VR mounting flange, being sure to get through chrome, paint, rust. You are hoping for the lowest reading possible, zero volts would be perfect

        As in the first harness test, ANY voltage being read here is ADDED to the normal setpoint of the VR. For example, if you read .4V, that is added to a properly working VR, so if it is 13.8, + the .4 will be 14.2. That does not sound bad, except all drops add up, so if you have a ground drop AND a hot side harness drop, you can easily come up with a couple volts!!!!
         
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        • gradedcatfood

          gradedcatfood 1972 Plymouth Duster 440

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          I have this single pole switch: Flaming River Big Switch and Lever Kits FR1003-2

          yes I am using that to disconnect the battery to the car. I also have the charge wire (largest black wire) from the alternator to the battery side of the disconnect switch so that when the switch is off the alternator is cutoff from the car circuit and the car will die.

          My understanding is that the field wires are the 2 smaller wires connected to the alternator (blue and green I think) but I have not disconnected those are modified them.
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          This is what Im asking about "I also hooked my alternator charge wire to the disconnect switch" How did you do this"?
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          Got it. So you are bypassing the standard charge path that 67DArt273 posted, correct?
           
        • gradedcatfood

          gradedcatfood 1972 Plymouth Duster 440

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          I disconnected the original black wire connected to the alternator and then connected a 6GA wire to that post on the alternator and ran it to the back of the car and connected it to the side of the switch where the battery is connected to. Very similar to the photo in the first post

          Yes. I am bypassing that original black wire as I just disconnected it and tapped it off. I assume that's what the photo in the first post's photo meant when it said "disconnect fatory wiring"
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          how is the car getting power from the battery? into stock wiring? Where?
           
        • gradedcatfood

          gradedcatfood 1972 Plymouth Duster 440

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          Please see photo.

          The top positive post has a large 1GA red that comes from the battery disconnect switch. Then from that post I have that red wire going down to the starter relay

          IMG_5301.jpg
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          Sorry but the photo is not helping me. You said that you disconnected the black Charge wire from the alt and ran a new wire from the alt back to the batt side of the disconnect switch.

          My question is from the disconnect switch how does that wire get back to the front ? AND where is it attached in the schmatic
           
        • gradedcatfood

          gradedcatfood 1972 Plymouth Duster 440

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          With that new 6GA wire that is from the alt to the batt side disconnect switch I dont believe it needs anything to get back to the front of the car considering there already is a wire running from the other side of the switch to that positive post in the front of the car.

          My understanding is that once that new 6ga wire is attached to the + side of the car circuit it's good to go.

          In that schematic in the first photo, the wire that runs from the cut off switch to the starter is how that charge wire gets back to the front of the car. That wire in the schematic that runs to the starter also runs to that battery positive post in post #16 photo
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          VERY simplified charging system

          upload_2018-10-6_21-58-19.png


          VERY simplified on how I think you are wiring your car

          upload_2018-10-6_22-0-17.png
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          I think by putting the alt charging directly on the battery rather than following the stock route through the ammeter etc as 67Dart273 stated is the cause of your issues.
           
        • gradedcatfood

          gradedcatfood 1972 Plymouth Duster 440

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          Thank you for the diagram as I think you are correct on how I am currently doing things but I don't see the difference on that diagram (how i'm doing it) and the photo in the 1st post.

          Whole reason why I ran that 6Ga wire to the battery side of the switch was to pass NHRA regulations. Previously without that wire the car would still stay on when you disconnected the switch as the car would run off the power coming from the alternator.

          It ultimately sounds like I may need to try to find a new way of disconnecting the alternator as I thought the first photo would accomplish that with no issues.
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          found flaw in my diagram. Deleted it so as to not lead anyone down the wrong path.
           
          Last edited: Oct 7, 2018
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          The relay could interrupt the field cir instead and the alt will cut out.

          You could even wire a switch to cut out the alt while on a run ASSUMING your battery can provide enough power for all your needs while on a run. gain a few HP?
           
        • gradedcatfood

          gradedcatfood 1972 Plymouth Duster 440

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          Ooo this looks like it could work. Could you please describe the wires for this relay as I don't fully understand how to hook it up.

          What would be the "activator" wire? Probably just any wire that connected to ignition considering I could wire it so when I disconnect the master switch it would engage the relay and then what field wire would I be "engaging/disengaging"? The blue or the green on the alternator?
           
        • Dana67Dart

          Dana67Dart Most undignified way to get to Colorado!

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          You would wire it the same as the diagram I posted but instead of interrupting the charge wire you would interrupt either of the field wires. (SOMEONE ELSE NEEDS TO JUMP IN HERE AS I DON'T HAVE EXPERIENCE WITH A TWO WIRE FIELD ALT BUT.... as understand one of the wires provides voltage to the field and the other provides ground to the field DON'T QUOTE ME ON THAT!)

          You could test out my theory by disconnecting one of the field wires while the engine is running and the alt is hooked up in stock fashion if the car voltage goes from 14 ish to 12 ish indicating no charging, also the amp meter should read large discharge.

          as in the diagram it would be from the source after the disconnect switch but before the car stock wiring