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    Alternator / Electrical Challenges

    Afternoon all,

    I wonder if you can help me out with some challenges I've got with a car I'm trying to sort out for someone.

    Early Mk1.5 car - 21xxx series Commission number. Mk1 wiring loom.

    The alternator died in the car, low voltage on the dash and also struggling to hold a charge. The power steering houses had leakage and it looks like it soaked the alternator in storage and took it out.

    Put a new 18ACR Mk2 altrernator into the car and also noted that some cables had suffered from heat exposure onto the manifold, some blistering so at the same time I also renewed the battery to bulkhead cable and also bulkhead to alternator cable. Used good thick cable, battery thickness cable from battery bulkhead and equivalent gauge into the alternator. I used a two into one splitter to connect the two 'big' connectors to the alternator and spliced in a new connector for the ignition warning light.

    The car had a Mk1 wiring loom in it btw, and had a mk2 alternator fitted at some time, so some wires looped up but the wiring diagram confirm all colours not required for a mk2 alternator.

    I charged the battery and took the car for a drive, the voltage was good and it was running well, then around 35 miles in the voltage started dropping.

    I've checked the voltages on the battery lead to bulkhead, alternator to splice point, alternator splice point to bulkhead, across the battery. All correspond within 0.01v on my meter.

    I pulled the connector off the alternator, replaced that and put in new live cables from the alternator back to the splice point.

    With the engine running, the alternator is producing no voltage, when I connect that splice it all reads square.

    If I sit on the voltmeter and let the car run, the volts in the system drops gradually over time, revving the engine doesn't do anything.

    Any help greatly welcomed ? Have I just got a dud alternator - I'm not au fait enough to know if they effectively 'shut' down when not connected into the main wiring...

    Thanks !

    Matt


    #2
    Is the ignition light working? i.e. does it come on when you turn the ignition on before starting the car? And then does it go out after the car is started?

    The alternator needs current through the ignition light to get an initial magnetic field going in order to start generating, generally speaking, no ignition light, no output from the alternator.

    Roger
    White TV8 BW35 no mods and now a Dolly Sprint to keep it company
    So many cars, so little time!

    Comment


      #3
      I hadn't connected that back up on this iteration, I'll give it a go tomorrow morning and see.

      I don't recall any issues with the ignition light - it was on, then when revved / warmed, it was out again.

      Definitely didn't come on when driving it and voltage dropped.

      Thanks for suggestion !

      Comment


        #4
        So...

        I put that ignition light lead back on this morning - made no difference.Still draining the batter on tickover.

        Thinking that the only changes we had made to the systerm was the alternator (new) and some cables, I thought since the cables had all been changed the maybe that alternator had popped / died on that c80-90 mi drive.

        So. Jacked it up, swapped the alternator for another new one I just happened to have (long story why I had two new alternators!). Started the car, revved the car, 15v off the alternator.

        Wired it back together. Gave it rev, loom at the bulkhead / battery now reading 14v+.

        All I can think is - bad alternator. I'll get it stripped and refurbed by a trusted service specialists and put away as a spare. Never know a new alternator pop like that though.

        Thanks for advice - always welcomed !

        Comment


          #5
          Originally posted by marshman View Post
          Is the ignition light working? i.e. does it come on when you turn the ignition on before starting the car? And then does it go out after the car is started?

          The alternator needs current through the ignition light to get an initial magnetic field going in order to start generating, generally speaking, no ignition light, no output from the alternator.

          Roger
          I see that people often refer to the ignition warning light as being necessary for the excitation of the magnetic field for the alternator on a Mk1. To me, this is not true, and I am sure Lucas did not fall into such a design trap. Having a simple warning bulb cause your alternator fail to output because it blew would be poor design.

          In reality there is a Resistor externally mounted on the back of the 16RA (between R and C2) that is precisely for this purpose. Of course, I stand to be corrected on this....

          Dave

          Comment


            #6
            Originally posted by Bakdraft007 View Post

            I see that people often refer to the ignition warning light as being necessary for the excitation of the magnetic field for the alternator on a Mk1. To me, this is not true, and I am sure Lucas did not fall into such a design trap. Having a simple warning bulb cause your alternator fail to output because it blew would be poor design.

            In reality there is a Resistor externally mounted on the back of the 16RA (between R and C2) that is precisely for this purpose. Of course, I stand to be corrected on this....

            Dave
            Yes I agree BUT the O.P. said Alternator was a MK2 and wiring had been changed to suit. Most alternators will "self excite" if revved high enough so the current to the field coils supplied via the ignition warning light is not strictly necessary BUT it does mean that the alternator starts generating a meaningful output much sooner and means you don't have to rev the nuts off a cold engine as soon as it starts. I believe that a variation in the amount of current flowing through the ignition warning light is why some cars have to be revved more than others for the light to go out. Possibly because the warning light has been replaced at some point with the wrong wattage lamp.

            Roger
            Last edited by marshman; 28 October 2020, 18:48.
            White TV8 BW35 no mods and now a Dolly Sprint to keep it company
            So many cars, so little time!

            Comment


              #7
              Sounds as if you worked out the replacement was duff?
              infuriating.
              would only get worse if the second one was too.
              I had that pain!
              There are 2 secrets to staying on top :- 1. Don't give everything away.
              2.

              Comment


                #8
                All,

                Apologies for delay in response. A few work challenges and other chores to do, so working on the car has been spit / spat stuff.

                I've got it sorted in the end - and as suggested by some of you, and frankly confusing to me, the alternator looks to have been the fault. I checked the feed lines into the alternator, but no impact and then put the meter across the cables from the alternator when they were off the loom and gave the car a good sustained rev and still didn't get any real juice off the alternator.

                So swapped, the unit out with another one a mate had knocking around (fortunately its so common!) and then guess what...a nice little rev up and boom 14v.

                Thanks for your help all and apologies again for delayed response. Close to driving this one now !

                Matt

                Comment

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