Squareback vs round back alternator?

Electrical and Ignition

  1. jrc4y4

    jrc4y4 Well-Known Member

    Messages:
    459
    Likes Received:
    208
    Joined:
    Jun 8, 2012
    Location:
    Columbia
    Local Time:
    5:51 PM
    I rebuilt my 318 like 15 years ago and have put on 8k miles in that time. I replaced the alternator at the same time and recently the bearing went out on me. Seeing how alternators are relatively cheap I was just going to replace it. But when I started reading it looks like there is much against the newer (I assume mine is one, Oreilly) square backs but I don’t really understand the issue? Mine has always done well to keep a charge and I’ve ran it at night. Just wondering what I’m missing out on before I make a bad purchase.
     
  2. RustyRatRod

    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

    Messages:
    85,428
    Likes Received:
    67255
    Joined:
    Jun 7, 2010
    Location:
    Georgia
    Local Time:
    6:51 PM
    The square back is by far the better unit.
     
    • Like Like x 1
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

      Messages:
      54,166
      Likes Received:
      23935
      Joined:
      Oct 14, 2010
      Location:
      Idaho
      Local Time:
      3:51 PM
      Square back is a better design, and some amp ratings charge better at low rpm. 45amp I think. Something that seems to be prevalent with rebuilders is MISSING OR IMPROPERLY installed brush hardware/ insulators. BEFORE you wire it up, check between the two brushes (field terminals) which should show a low value of resistance. Then check each field terminal to the case and it should be "open" (infinity) resistance
       
      • Like Like x 1
      • Thanks! Thanks! x 1
      • Dana67Dart

        Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

        Messages:
        9,235
        Likes Received:
        6657
        Joined:
        Jul 16, 2017
        Location:
        Northern Colorado
        Local Time:
        4:51 PM
        What do you have now?

        Do you want to keep the oem look?

        I agree alternators are cheap, but round back alternators are few and far between ( I'm going through this right now)

        Alternators 101...

        Mopar had 4 alternators

        Round back single field wire
        alt_rear_bearing_dimpled-jpg.jpg

        Round back dual field wire
        70alt.jpg


        Square back wired as a single field wire (note green wire to one field wire)
        mopar-alternator-110-amp-satin-finish-22.jpeg
        This is also a square back wired as a one field wire (one of the terminals is internally grounded, note the tab is clipped off, this is what you will get from the parts store if you buy a "round back" alternator 99% of the time)
        1EE4CBC9-6AC8-49BB-93EB-7A312D936857.png


        Square back dual field wire.

        226778-300b52efdc799326e6169394f82969fd.jpg

        If you have the old style square voltage regulator
        Screenshot_20210402-212711.png

        you need a single field wire alt regardless of round or square

        If you have the newer rectangular VR with triangular shaped connector
        Screenshot_20210402-212730.png

        you need the dual field wire alternator regardless of round or square

        The square backs have a higher output than round BUT if you have oem electronics on your car there is no need for a higher output alt. Infact it can de detrimental.

        Alternators are relitivily easy to rebuild and parts are readily available.

        A press is the most complicated part of the process.

        The diameter of the pulley is a main contributer of poor charging at idle.

        I recently posted "diameter, diameter, diameter, alternator pulley" showing the ammeter bouncing with a 2.75 dia pulley vs a 2.5 dia pulley Diameter, diameter, diameter, alternator pulleys
         
        Last edited: Apr 2, 2021
        • Thanks! Thanks! x 3
        • Like Like x 2
        • pishta

          pishta I know I'm right....

          Messages:
          22,925
          Likes Received:
          12379
          Joined:
          Oct 13, 2004
          Location:
          Tustin, CA
          Local Time:
          3:51 PM
          what regulator are you running? round back single field used the old "in and out" regulator. The round back dual field only came in 2 years (70-71) then it went to the common dual field squareback. The dual field needs the electronic voltage regulator, or can be grounded on one of the fields to use the old style regulator.
           
        • 67Dart273

          67Dart273 FABO Gold Member FABO Gold Member

          Messages:
          54,166
          Likes Received:
          23935
          Joined:
          Oct 14, 2010
          Location:
          Idaho
          Local Time:
          3:51 PM
          Not entirely (stated) correct. you can ground either field terminal on either a round or square "isolated field" and use them with the old regulator. I'm sure you know that LOL
           
          • Thanks! Thanks! x 1
          • Dana67Dart

            Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

            Messages:
            9,235
            Likes Received:
            6657
            Joined:
            Jul 16, 2017
            Location:
            Northern Colorado
            Local Time:
            4:51 PM
            Re read what I wrote you and I are saying the same thing. I outlined the 4 mopar alts 2 round 2 square. One round and 1 square are 1 wire field.
            (Yes the square is a 2 field wire "isolated field" with one of the field wires grounded)
             
          • jrc4y4

            jrc4y4 Well-Known Member

            Messages:
            459
            Likes Received:
            208
            Joined:
            Jun 8, 2012
            Location:
            Columbia
            Local Time:
            5:51 PM
            I would like to keep the OEM look. I’ll yank it off when I get home Sunday to see what I have. I have a Mopar chrome box and I think an original black regulator. I’ll update. Thanks for the info guys!
             
          • Syleng1

            Syleng1 Karma is real and Life is short... FABO Gold Member

            Messages:
            2,520
            Likes Received:
            2215
            Joined:
            Jul 5, 2005
            Location:
            North Franklin, CT
            Local Time:
            6:51 PM
            Great info- even for us people who had them when all you got was a round back from the dealer. Ha!
             
            • Agree Agree x 1
            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

              Messages:
              14,100
              Likes Received:
              9719
              Joined:
              Feb 7, 2013
              Location:
              Phila. Pa
              Local Time:
              6:51 PM
              Chrysler never made a grounded field squareback.
              You can convert any isolated field into a grounded field.

              Now what the hell was the original question?

              Should you roll the dice with a parts store replacement or replace the bearing?
              Yes
               
            • Mike69cuda

              Mike69cuda 66 is the new 17 FABO Gold Member

              Messages:
              2,821
              Likes Received:
              2401
              Joined:
              Jan 2, 2018
              Location:
              Overland Park Kansas
              Local Time:
              5:51 PM
              From what I have seen the parts store alternators are all basically the same square backs. They just ground one of the brushes for the 69 back application as mentioned above.
               
              • Agree Agree x 2
              • jrc4y4

                jrc4y4 Well-Known Member

                Messages:
                459
                Likes Received:
                208
                Joined:
                Jun 8, 2012
                Location:
                Columbia
                Local Time:
                5:51 PM
                Turns out I have a dual field square back with triangular plug voltage regulator. I’ve ran it for 8k miles with no issues (except a bearing) and I’ll get one to replace it like it. Thanks guys! I learned a lot about different types of alternators from you guys. Who knew there were so many variations?

                5F3A6641-A3B9-4A95-9AD7-B19A0279AE5F.jpeg
                 
                • Like Like x 2
                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

                  Messages:
                  14,100
                  Likes Received:
                  9719
                  Joined:
                  Feb 7, 2013
                  Location:
                  Phila. Pa
                  Local Time:
                  6:51 PM
                  Thats one messed up alternator. Lucky it made it that far.
                  Next one you buy, try to get a regular squareback, not a revised one like you've got there.
                  The rear bearing should be flush or a little proud of the casting.
                  The output stud MUST have an insulator and MUST not be loose.

                  Identifying Chrysler Alternators (1960-1976)
                   
                  • Thanks! Thanks! x 1
                  • jrc4y4

                    jrc4y4 Well-Known Member

                    Messages:
                    459
                    Likes Received:
                    208
                    Joined:
                    Jun 8, 2012
                    Location:
                    Columbia
                    Local Time:
                    5:51 PM
                    good to know! I pulled the insulator off when I yanked it out, unsure if the new one would have one or not. I’ll check out the bearing when I pick up the new one this week. Thank you.
                     
                  • CLBER

                    CLBER Member

                    Messages:
                    23
                    Likes Received:
                    5
                    Joined:
                    Mar 14, 2022
                    Location:
                    Berlin, Germany
                    Local Time:
                    12:51 AM
                    Hello from Berlin, Germany! My name is Christian and I'm a mechanic usually working on European cars.
                    Just a helping a friend with repairs on his Plymouth Valiant V-200, L6, 170cid from 1960.
                    We're facing some issues with the alternator / regulator and we hope you can help us out. We're thinking about replacing alternator and regulator, preferably an electronic one if possible. Could you help us out which would be the right parts? We guess alternator and regulator don't match.

                    The voltage is fluctuating by checking at the Batterie +. Voltage went up till 18 Volts, so I checked the regulator air gap btw the armature and the magnet core at the hanger side which was found within specs and I bent the spring tension up because the voltage was found to be to high. Now its withing 13 and about 15 Volts but fluctuating very much, a bit less with all consumers on.

                    Regards, Christian.

                    Bild_2022-03-14_151406.png

                    IMG_20220314_120515.jpg

                    IMG_20220314_151544.jpg

                    IMG_20220314_151530.jpg

                    IMG_20220314_151601.jpg
                     
                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

                    Messages:
                    14,100
                    Likes Received:
                    9719
                    Joined:
                    Feb 7, 2013
                    Location:
                    Phila. Pa
                    Local Time:
                    6:51 PM
                    Christian.
                    I suggest looking through this thread first.
                    Identifying Chrysler Alternators (1960-1976)
                    From appearences your regulator and alternator match.

                    It will be easier for you to diagnose once you understand the functional differences.
                    In the UK and US the circuit arrangements are called different things. In Belrlin maybe something else?
                    Basically the difference is whether the field strength is controlled by switching the positive feed, or by the negative connection.

                    Now (2022) you can exchange that mechanical regulator for a positive controlling transistorized version. However I do not know if that will resolve the problem.

                    Here's one sold by FBO through E-bay. I've been using it, but not long enough to say whether it is any more durable than others.
                    upload_2020-5-31_12-29-39-png.png
                     
                    Last edited: Mar 14, 2022
                  • Ron816

                    Ron816 Mopar forever

                    Messages:
                    558
                    Likes Received:
                    684
                    Joined:
                    Nov 15, 2019
                    Location:
                    Quincy, MA
                    Local Time:
                    6:51 PM
                    I went with a powermaster round back for my 68 GTS
                     
                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

                    Messages:
                    14,100
                    Likes Received:
                    9719
                    Joined:
                    Feb 7, 2013
                    Location:
                    Phila. Pa
                    Local Time:
                    6:51 PM
                    I'm going to make two guesses about the cause:

                    One possibility is that only two legs of the regulator are working. This might result in a more on/off condition.
                    There is a 1966 Chrysler Master Technicians booklet that goes into detail about the regulator. Page 12 in particular about voltage regulation.
                    Find that here in html.
                    Alternators and Regulators (Session 228) from the 1966 Master Technician's Service Conference

                    Master Technician Service Conference Index - Chrysler's Training for Mechanics

                    or here in pdf
                    Browse MTSC by Model Year – 1966 – MyMopar
                     
                    Last edited: Mar 14, 2022
                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

                    Messages:
                    14,100
                    Likes Received:
                    9719
                    Joined:
                    Feb 7, 2013
                    Location:
                    Phila. Pa
                    Local Time:
                    6:51 PM
                    Second possible cause is in the wiring.

                    We see some modifications including that relay.
                    A relay can help work around some resistance in the run circuit. But there still can be power feed resistance problems, and with changes in load, there will be voltage drop with increased current.
                    The regulator will respond in an attempt to control the voltage it senses.

                    In this 1969 check, Chrysler wanted less than 0.4 Volt between the power sources (battery in this image) and the ignition and field.
                    Note the field is disconnected in this check. Later there's a check with it connected. That should be less than .55 Volts difference between the battery and the regulator terminal.
                    voltage-drop-jpg.jpg

                    Because the problem in this case is voltage regulation, it would be best to repeat the voltage drop measurement between the alternator output and the regulator input/sense terminal while the engine is running.

                    Originally the circuits looked like this.

                    upload_2022-3-14_13-5-54.png
                    This is a very simple arrangment.
                    When the alternator is generating power, current flows to the main splice through one connection.
                    Then to the key switch, and out to the ignition and voltage regulator.

                    However, if the R6 wire or connections are damaged, then there will be increasing voltage drop with increasing current flow.
                    Same goes for resistance or poor connections in the J1 wire, key switch, and Run wires (labelled J2).

                    Someone installed a relay, possibly to work around a poor connection.
                    We also often see accessories added to the battery. Perhaps the new fuses were added to the battery circuit. This is generally a poor location in older vehicles because power coming from the alternator does not go directly to the battery. Recharging the battery was a secondary function and a little electrical noise was not a concern.
                     
                    Last edited: Mar 14, 2022
                  • CLBER

                    CLBER Member

                    Messages:
                    23
                    Likes Received:
                    5
                    Joined:
                    Mar 14, 2022
                    Location:
                    Berlin, Germany
                    Local Time:
                    12:51 AM
                    Thank you all for your feedback and input, now we have something to digest and test.
                    I have found a transistorized regulator (like the one @Mattax showed) and to my surprise someone in Berlin sold it via ebay, it'll arrive very soon. But before we install it we need to draw a clean wiring diagram and eventually modify the wiring because it's all messed up. The original wiring is very simple but the past modifications (e.g. additional fuses, relais etc.) makes it more difficult to determin the fault(s). I'm gonna keep you updated and sure we have more questions to post soon.

                    Thanks again!
                    Christian
                     
                    • Thanks! Thanks! x 1
                    • Dana67Dart

                      Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

                      Messages:
                      9,235
                      Likes Received:
                      6657
                      Joined:
                      Jul 16, 2017
                      Location:
                      Northern Colorado
                      Local Time:
                      4:51 PM
                      I'm going to throw this out there. Maybe it is just fine and functioning as expected?

                      If you raise the engine RPM does the fluctuation level out?

                      Rebuilders are notorious for putting a 70mm dia or 76mm dia pulley on alternators that should have a 63.5mm dia pulley. The seemingly small dia change makes a huge difference in alternator shaft speed and the output at 1000 rpm shaft speed vs 1500 or 2000 rpm shaft speed can be the difference between charging and not charging.

                      Diameter, diameter, diameter, alternator pulleys

                      You mentioned with more accessories turned on it levels out.

                      I agree with Mattax. Get familiar with the workings of the old stuff before you attempt to make changes.

                      The master tech videos are really good at explaining how things work.

                      Mymopar.com has a lot of them

                      Don't get too hung up on the year and the car. Early 60s work the same as late 60s.

                      Welcome aboard and good luck to you.
                       
                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

                      Messages:
                      14,100
                      Likes Received:
                      9719
                      Joined:
                      Feb 7, 2013
                      Location:
                      Phila. Pa
                      Local Time:
                      6:51 PM
                      Ha!
                      I just looked at this screen shot again and see that slide does not show voltage drop measurement.
                      voltage-drop-jpg-jpg.jpg
                      Rather it shows voltage at the ignition connection. Subtracting that measurement from battery voltage will reveal voltage drop.
                      As described in the booklet, when using analog meters a more sensitive reading of voltage differences can be made by measuring between the battery positive and the ignition connection.
                      Also its taken from the ignition circuit test. The 0.4 Volts is with the field disconnected and the ignition points closed.

                      The following illustration is from the Field Circuit test.
                      upload_2022-3-14_15-55-29.png
                      In this test the engine isn't running and system voltage will be lower than the regulator's set point.
                      Therefore the regulator will allow maximum current through to the rotor.

                      When testing for voltage drop with the engine running, the test lead will have to be on the regulator's input terminal.
                      The other test lead should be used to measure the alternator's output voltage, and then also the voltage at the battery positive.
                      Be sure the battery has finished charging before measuring for voltage drop.

                      It looks to me like chrysler really wanted no more of 0.2 Volts lost when the alternator was running the engine and one accessory.
                      That's my interpretation of this 1960 test.
                      1960 Imperial and Chrysler Service Repair Book - Alternator Service
                      In it, the output is controlled by engine rpm. I'm not really thrilled with that idea.
                      I think it would be safer to leave the regulator connected and add a load to the system thats approximately 10 amps. For example, heater fan on medium speed, or lights on.
                      That's how I've been testing voltage drop. When I can I measure the amps with an inductive clamp.
                       
                      Last edited: Mar 14, 2022
                    • BillGrissom

                      BillGrissom Well-Known Member

                      Messages:
                      7,684
                      Likes Received:
                      526
                      Joined:
                      May 10, 2009
                      Location:
                      Sacramento
                      Local Time:
                      3:51 PM
                      A common problem with all combinations is that the voltage regulator (Vreg) doesn't have a solid ground. Chrysler relied on just that sheet-metal screw into the body as a ground. It never hurts to run a dedicated ground wire from the case of the Vreg to a good ground point on the car. Few people today still have the old electro-magnetic Vreg. As posted, you can buy a new electronic regulator for the older alternator (round-back) which has 1 field terminal (the other terminal grounded). Some look like the OE rectangular box, while others are a thin chrome box. That is termed "high-side switching". You can probably still buy new brushes with insulators for the alternators. Worst-case, you could switch to a later square-back alternator which has 2 field terminals. Just ground one terminal to use with the high-side Vreg, or you can use a later "low-side switch" Vreg (triangular connector) but would also have to run an IGN wire to the alternator (other terminal). The square-back alternator was used a long time, at least until 1982 (my Dodge Aries), so will likely be available for a long time.
                       
                    • CLBER

                      CLBER Member

                      Messages:
                      23
                      Likes Received:
                      5
                      Joined:
                      Mar 14, 2022
                      Location:
                      Berlin, Germany
                      Local Time:
                      12:51 AM
                      Hello everyone, we had fun to dive into the electrical system.
                      First we were trying to figure out and understand the functional differences in the electrical/ignition system on the car itself and the differences to the European (except early UK) systems. It's the first time I am working on a system like that, so it takes some time to reset the mind and don't follow the usual trouble shooting path.
                      What we don't understand is the difference between the field strengths is controlled by switching the positive feed, or by the negative connection.

                      What we checked and found so far:
                      the fuse box and wires are a mess, no infos what safes what.
                      but we searched and the red 10 Amps is going to the control relay. It's simple 40 Amps check relay that should close and open when current is applied ...
                      30 goes to the 10 amp fuse
                      85 comes from IGN2
                      86 goes to ground
                      87 goes to alt reg IGN

                      IMG_20220316_164516.jpg

                      initially the BAT wasn't charging and the red 10 Amp fuse was popped, I replaced it. Started the engine and another 30 Amps fuse in an extra box popped, the red 10 Amps is ok. You see that there are three cables are soldered together coming from the dash and going to the multi fuse box.

                      IMG_20220316_155618.jpg IMG_20220316_080934 (1).jpg

                      I made a simple wire diagram how it looks like here:

                      IMG_20220316_164438.jpg



                      bad to no ground on the alt reg housing, the screws used to hold the reg have a coating and a test revealed bad current flow/high resistance so I placed as a first step an extra cable and different screws to the bulkhead.
                      We didn't start the engine yet, first we want to be sure we're on the right path.


                      IMG_20220316_155007.jpg IMG_20220316_154926.jpg


                      Here's the question: can we just use this transistorized reg?:
                      Because here we have the right alt installed if I'm not mistaken the other thread Identifying Chrysler Alternators (1960-1976)

                      upload_2022-3-16_17-54-4.png
                      the actual grounded brush alt:
                      IMG_20220316_164842.jpg

                      The Valiant service manual from 1960 says this: IMG_20220316_150434.jpg


                      There is also no ignition ballast / IGN coil resistor installed in this car. But there should be regarding all wire drawings so far incl. the one from @Mattax which is from 1962:

                      upload_2022-3-14_13-5-54 (1).png
                       
                      Last edited: Mar 16, 2022
                    • CLBER

                      CLBER Member

                      Messages:
                      23
                      Likes Received:
                      5
                      Joined:
                      Mar 14, 2022
                      Location:
                      Berlin, Germany
                      Local Time:
                      12:51 AM
                      In the service manual:
                      IMG_20220316_180341.jpg

                      bad wire connection on the starter solenoid, it went loose my checking:

                      IMG_20220316_145057.jpg

                      The starter and ignition shows some very small resistance fluctuation while wiggling the key in the IGN1 and IGN2 position. Would like to replace but couldn't find so far the right one.
                      IMG_20220316_084300.jpg

                      I don't know how popular rockauto.com is in the US, but here people use it a lot for US cars.
                      They show only this starter / ignition switch:
                      There's an additional GRD contact. May it work the same way if I don't connect GRD or do we have the worng installed in the car!?
                      Maybe this gives also a hint to whether the field strengths is controlled by switching the positive feed, or by the negative connection ...?
                      # Ignition switch.PNG

                      The black wire is the one that goes from the starter switch IGN2 to the relay mentioned above, it's just connected "professionaly" to the wire:

                      The missing ignition ballast resistor should be connected in the engine area at this wire and the going to positive connection on the ign coil..

                      IMG_20220316_084151.jpg

                      Ah, I forget to say: Thank you all for welcoming me here and your support.
                      Christian
                       
                      • Thanks! Thanks! x 1
                      1. This site uses cookies to help personalize 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.