Odd voltage regulator issue

Electrical & Ignition

  1. hunt2elk

    hunt2elk FBBO Gold Member FBBO Gold Member

    Messages:
    7,716
    Likes Received:
    6806
    Joined:
    Jul 15, 2009
    Location:
    WI
    Local Time:
    3:55 PM
    Got this car put back together 4 years ago. Everything in the electrical system is new except the ignition switch. Car is a 1970 and using this style alternator.
    During restoration I installed a brand new USA made MP 3438150 voltage regulator. It was working great for 200 miles and then I noticed the operating voltage had dropped from 14.2 to 13.2. Had the alternator checked and it was fine. Called Summit and they sent me another Mopar regulator under warranty. While I was waiting for that, I bought a couple of Standard VR125's (made in China). I put one of those on and everything was fine again. Last summer I noticed the volt meter was running over 15, but chalked it up to cheap gauges. Finally got around to replacing them with some good Autometers. I now have 5000 miles on the car. Same high voltage as before, and this time I verified it with a multimeter. Was running at 15.5 volts. So I dug out the warranty replacement MP that Summit sent me years ago. Installed that and the voltage was right at 14.2. Life was good for a week, but now the voltage has dropped to 13. Dug out the second Standard VR125 I bought previously. This one is putting out 15.4 volts. So I have 2 Mopar 3438150's that both started out good and then went to regulating around 13 volts. 2 Standard VR125's. One ran for quite awhile ok and then over regulates at 15.5, and the second one is 15.4 out of the box. All 4 of these units were bought at the same time. Anybody else ever had a crazy situation like this? Are there better regulators I could try?

    20210913_182420.jpg 20210909_141058.jpg 20210909_141230.jpg 20210913_165726.jpg
     
  2. pnora

    pnora FBBO Gold Member FBBO Gold Member

    Messages:
    1,241
    Likes Received:
    1203
    Joined:
    Apr 21, 2020
    Location:
    Ishpeming, Mi.
    Local Time:
    4:55 PM
    You could have a problem with the plug. If there is a poor connection that could be your problem.
     
    • Thanks! Thanks! x 1
    • Agree Agree x 1
    • RJRENTON

      RJRENTON FBBO Gold Member FBBO Gold Member

      Messages:
      1,924
      Likes Received:
      1762
      Joined:
      Jul 1, 2015
      Location:
      South Shores area of Decatur, Illinois
      Local Time:
      3:55 PM
      First of all, the origional alternator was a round back style, depending on origional accessories, it was either a 37 amp or 42 amp either single or dual sheave drive. Most aftermarket replacement alternators are the square back alternator design shown. Their capacity very depending what the origional unit came from. The regulator you show is correct for either styles of alternators. Internally, they have components that vary the alternators field voltage to provide a nominal 14.5 system voltage. There is an internal voltage divider network, inside the regulator, that also provides temperature compensation to allow for cold weather, allowing higher system voltage and lower voltage in hot weather. Because of the origin of these internal items, the ×/- tolerances on these components are likely causing the disparities. In addition, insure that the case is securely grounded to the engine block with its own wire. The field current is low, 5-6 amps, at maximum charge rate, a 14 AWG wire is sufficient. I'm sure others will have their own ideas and suggestions.
      BOB RENTON
       
      • Like Like x 2
      • Thanks! Thanks! x 1
      • hunt2elk

        hunt2elk FBBO Gold Member FBBO Gold Member

        Messages:
        7,716
        Likes Received:
        6806
        Joined:
        Jul 15, 2009
        Location:
        WI
        Local Time:
        3:55 PM
        The harness was a new M&H when I built the car. Terminals look good but I will ohm them out tomorrow. Just remembered that a guy gave me this meter years ago. Oddly, both Mopar regs test good and both Standards test bad.

        20210913_194134.jpg
         
      • hunt2elk

        hunt2elk FBBO Gold Member FBBO Gold Member

        Messages:
        7,716
        Likes Received:
        6806
        Joined:
        Jul 15, 2009
        Location:
        WI
        Local Time:
        3:55 PM
        When I had the alternator rebuilt, they replaced the 37 amp internals with a 60 amp version, I don't think that has anything to do with my problems though. I do have a seperate ground wire from the mounting bolt to the battery. It is probably only a 16 gauge wire. I think I am going to redo that with a 14.
         
      • steve340

        steve340 Well-Known Member

        Messages:
        793
        Likes Received:
        636
        Joined:
        Jul 7, 2018
        Location:
        New Zealand
        Local Time:
        8:55 AM
        As previously stated the Mopar voltage regulators need to be earthed to work properly.
        Might pay to check yours - paint can get in the way.
         
        • Agree Agree x 1
        • Nacho-RT74

          Nacho-RT74 Well-Known Member

          Messages:
          4,842
          Likes Received:
          1667
          Joined:
          Oct 8, 2012
          Location:
          Valencia, España
          Local Time:
          10:55 PM
          stock fields wiring is actually 18 gauge.

          No need for a ground wire between alt to the batt, as far the mounting bolt area is clean and the ground wire between block and batt is also tight and clean.

          Sure I'd check the ground between reg and firewall. Not saying is that but worths checking that.
           
        • 440 PHIXX

          440 PHIXX Well-Known Member

          Messages:
          215
          Likes Received:
          286
          Joined:
          May 6, 2011
          Location:
          Phillytown
          Local Time:
          3:55 PM
          My brother had a ‘70 Challenger back in the 80’s that constantly drained the battery. He had it to several garage’s and even an electronics specialist. They gave up. I found it to be the ground on the voltage regulator.
           
        • hunt2elk

          hunt2elk FBBO Gold Member FBBO Gold Member

          Messages:
          7,716
          Likes Received:
          6806
          Joined:
          Jul 15, 2009
          Location:
          WI
          Local Time:
          3:55 PM
          Yeah, I have the paint scraped off where the bolt head rides. I'll stick a star washer there as well.
           
          • Like Like x 1
          • 451Mopar

            451Mopar Well-Known Member

            Messages:
            2,644
            Likes Received:
            1955
            Joined:
            Oct 25, 2011
            Location:
            Aurora, CO
            Local Time:
            2:55 PM
            The 14.2 to 13.2 might be the temperature compensation if the 13.2 was with a hot engine compartment?
            I have been using the Transpo C8313 adjustable regulator in the '71 Charger with a 136 Amp Denso alternator.
             
            • Like Like x 1
            • hunt2elk

              hunt2elk FBBO Gold Member FBBO Gold Member

              Messages:
              7,716
              Likes Received:
              6806
              Joined:
              Jul 15, 2009
              Location:
              WI
              Local Time:
              3:55 PM
              Learned something new today. I didn't realize that the output voltage is supposed to drop as the regulator heats up. Guess that's what Bob was referring to in an earlier post. So my 13.2 is no doubt ok after I have the car heated up. I feel better about that than the 15.5 volts put out by the Standard vr125's. It still seems weird that the Mopar ones will put out 14.2 all the time for a couple hundred miles, and then drop after being in service. I will check out that regulator you mentioned.

              20210914_085930.jpg
               
              • Like Like x 3
              • RJRENTON

                RJRENTON FBBO Gold Member FBBO Gold Member

                Messages:
                1,924
                Likes Received:
                1762
                Joined:
                Jul 1, 2015
                Location:
                South Shores area of Decatur, Illinois
                Local Time:
                3:55 PM
                YES....THIS IS EXACTLY what I was referring to. Car batteries require a slightly higher charging voltage when cold than they do when hot, hence the ambient compensation (temperature change) afforded by the voltage regulator. This is accomplished by positive temperature compensation (PTC) resistors as part of the internal voltage divider network of the voltage regulator which controls the transistor that is switching the alternators field current and ultimately alternator's output voltage.
                BOB RENTON
                 
                • Like Like x 1
                • Thanks! Thanks! x 1
                • Agree Agree x 1
                • 451Mopar

                  451Mopar Well-Known Member

                  Messages:
                  2,644
                  Likes Received:
                  1955
                  Joined:
                  Oct 25, 2011
                  Location:
                  Aurora, CO
                  Local Time:
                  2:55 PM
                  The temperature compensation is so you don't overheat a hot battery and boil the electrolyte.
                  Many newer cars have a temperature sensor in/under the battery tray to better monitor the batteries temperature.
                  Also the regulator senses the battery voltage closer to the battery. The battery sense, the regulator power in our regulator version, can be an issue with trunk mounted batteries. You can mount the regulator near the battery and power the regulator from the battery through a relay, just need a longer field wire from regulator to alternator.
                   
                  • Like Like x 1
                  • Thanks! Thanks! x 1
                  • 72RoadrunnerGTX

                    72RoadrunnerGTX FBBO Gold Member FBBO Gold Member

                    Messages:
                    1,414
                    Likes Received:
                    952
                    Joined:
                    Jan 14, 2009
                    Location:
                    Shoreline, Washington
                    Local Time:
                    1:55 PM
                    Have you checked for voltage drop between the battery positive post and the ignition 1 terminal (regulator reference) at the regulator while under running load? Any resistance at any connection in between will cause a higher-than-normal charge voltage measured at the battery. Beginning in 1970, column mounted ignition switch, the Molex connection at the bottom of the column has been a problem since very early on. Bulkhead connections, specifically Ignition 1 and battery charge terminals have contributed to high voltage drop.
                     
                    • Like Like x 1
                    • hunt2elk

                      hunt2elk FBBO Gold Member FBBO Gold Member

                      Messages:
                      7,716
                      Likes Received:
                      6806
                      Joined:
                      Jul 15, 2009
                      Location:
                      WI
                      Local Time:
                      3:55 PM
                      I'll do those tests next time I am out in the garage. I am thinking everything is ok basically because only the Standard regulators are passing high voltage. The Mopar ones are more inline with spec, although may be a tad low.
                       
                      • Like Like x 1
                      • Gold Rush

                        Gold Rush Well-Known Member

                        Messages:
                        129
                        Likes Received:
                        107
                        Joined:
                        Nov 29, 2017
                        Location:
                        San Angelo TX
                        Local Time:
                        3:55 PM
                        I replaced my '74 voltage regulator when reinstalling the engine a few years ago. Didn't think to check charge rate until one of the many charging issue threads popped up here. Found I was actually at 15.3 volts. After chasing the problem a while I discovered the ignition switch itself was causing "ignition 1" voltage drop which in turn told the regulator it needed higher charge rate. Replaced the ignition switch and the charge rate dropped to 14.7. Since the '74 is still in restoration mode I didn't worry about that slightly high voltage at the time.

                        Now that we are closer to being on the road I readdressed the issue a couple weeks ago. With aid of a very understanding auto parts store, I bought a new (different brand) regulator and my cold charge rate is now 14.3 volts.

                        SPECIAL NOTE: While chasing the voltage drop start at the regulator connector while still connected to regulator; then go to the bulkhead connector (outside and inside). Don't stop there. check both input and output side of that ignition switch!!
                         
                        • Thanks! Thanks! x 1
                        • 72RoadrunnerGTX

                          72RoadrunnerGTX FBBO Gold Member FBBO Gold Member

                          Messages:
                          1,414
                          Likes Received:
                          952
                          Joined:
                          Jan 14, 2009
                          Location:
                          Shoreline, Washington
                          Local Time:
                          1:55 PM
                          Yes, excessive internal ignition switch contact resistance contributes to the total voltage drop measured. After correcting any voltage drop issues found, still don’t like the charging voltage at the battery, there is a good quality adjustable regulator available from the aftermarket that can be used to dial in the desired voltage at the battery.

                          regulator.jpg
                           
                        • 383man

                          383man Well-Known Member

                          Messages:
                          4,690
                          Likes Received:
                          3514
                          Joined:
                          Jul 19, 2008
                          Location:
                          Md
                          Local Time:
                          3:55 PM
                          One good thing to do to our older Mopars is put a relay in to power the voltage regulator battery sense circuit. Later Mopar did this on some cars and called it a field loads relay. Basically to take the 12 volt key run wire to the reg and run that to a relay coil and then ground the relay coil. It will only power when the key is in the run mode. Then wire the relay right from the battery to the voltage reg volts sense circuit. It works great because you eliminate the ign switch and any bad connection between the ign switch and reg. You get battery volts right to the reg. It will let the reg see a much more accurate battery volts.
                          As for the volts changing yes all factory voltage regulators sense ambient temps as it raises the set voltage in colder weather. But that said when its 80 degrees out it may charge at 13.6 and when its 20 degrees it may be at 15. But I have never seen any change a full volt from underhood temps as eng warms up. Yes they sense ambient outside temps and adjust the voltage setting accordingly. But as I said I have not seen any change much if any just by the eng underhood temps. In the summer my volts is around 14.2 and it stays at 14.2 from a cold eng to 190 degrees in the eng. I may be wrong but I believe they only sense the volts at key on and keep that setting until the next start. Good luck with it. Ron
                           
                          • Thanks! Thanks! x 1
                          • Nacho-RT74

                            Nacho-RT74 Well-Known Member

                            Messages:
                            4,842
                            Likes Received:
                            1667
                            Joined:
                            Oct 8, 2012
                            Location:
                            Valencia, España
                            Local Time:
                            10:55 PM
                            The field load relay function used on later models is ( as far I recall ) to activate the field circuit JUST when in run and not cranking due the low voltage the field circuit gets while cranking throught the ballast saving the regulator from sensing that low voltage and trying to compensate
                             
                            • Thanks! Thanks! x 1
                            1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
                              By continuing to use this site, you are consenting to our use of cookies.