Home Forum Ask A Member 1983 50 hp Johnson Rectifier test results

Viewing 10 posts - 1 through 10 (of 12 total)
  • Author
    Posts
  • #4385
    seahuntboater
    Participant

      Just asking for a little help here to determine if rectifier is bad. I see no change testing battery voltage (12.2)with engine off or running and revving.

      My rectifier has 4 wires. All wires were disconnected for the test. Used the Diode/beep setting on digital volt ohm meter.

      Test Reading with leads in one direction

      Ground to : Red .95
      Yellow 1 .52
      Yellow2 .53
      Yellow3 .52
      Reading with leads reversed was 0 on all wires

      Test Red to : Yellow1 .53
      Yellow2 .53
      Yellow3 .52
      Reading with leads reversed was 0 on all wires

      I know it is good that I get 0 in one direction and pretty consistant readings the other. But is the Ground to red supposed to be almost twice as high as the other readings? Is this rectifier ok?

      Thanks.

      Ralph

      #37323
      Anonymous

        This rang two bells… One where I had been working to "reverse engineer" an airguide tachometer transmitter and I had done resistance measurements on what turned out to be a (germanium) diode (rectifier) bridge: Some measurements will send current through two diodes, so you get twice the voltage drop (resistance).

        The other was reading about car alternators being three-phase, and having six diodes:
        http://www.allaboutcircuits.com/textboo … lternator/

        I wonder/suspect the three yellow wires are from three different coils in the alternator?

        #37324
        frankr
        Participant

          US MEMBER PAY BY CHECK

          I’m not finding fault in whatever it was that you did. But start over and do it the right way.

          There are 6 diodes in that rectifier. You need to test each and every one of them separately.

          1. Ground to yellow #1 and reverse leads. Continuity in one direction only.
          Repeat ground to each of the remaining yellow leads.

          2. Red to yellow #1. Continuity in one direction only
          Repeat red to each of the remaining yellow leads.

          That is 12 tests and it needs to pass each and every one.

          Forget about additional tests that I have not spelled out here, and forget about the doubling, etc. That only confuses things.

          #37325
          frankr
          Participant

            US MEMBER PAY BY CHECK

            Diode connections (3-Phase)


            print screen windows 7

            #37326
            seahuntboater
            Participant

              Frank. My tests seem to incorporate what you said Actually there were 14 tests in the above. Is the ground to red supposed to show anything? mine is double the rest of the readings.
              thanks.

              #37329
              frankr
              Participant

                US MEMBER PAY BY CHECK

                Ground to red is meaningless. Well, maybe if you want to do some math… Anyhoo, you would be testing all six at the same time. But suppose one was open? Look at the diagram above.There are 3 pairs of two diodes in series. Suppose the upper left one is open. That would be the same as taking it right out of the picture and leaving a gap where it was. The two right columns would still pass current in one direction and block it in the other direction (as they should). But the remaining good one in the left column would not be doing anything either way because current can’t even get to it through the open gap.

                So the rectifier would seemingly pass (passing current in only one direction), but in fact it has that bad diode.

                Make sense?

                #37348
                fleetwin
                Participant

                  US Member

                  Ralph-
                  When you said "0", did you really mean infinity? These terms get confusing and cause confusion….
                  In any event, you will probably need to test the resistance on a fairly high scale, using the low scale would show an open (infinite resistance) in both directions when testing each diode. You later mention using the "diode test function" and beeping.
                  In any event, like Frank says, there are six diodes that each have to be checked in two directions.
                  Test three of the diodes by checking between each yellow rectifier lead and the red rectifier lead. You should see infinite resistance in one direction, and less than infinite resistance in the other direction.
                  Test the other three diodes by grounding one lead of your ohm meter to the block or rectifier case (if you have removed it), then connecting the other ohm meter lead to each of the yellow leads one at a time. Again, you should see infinite resistance, then less than infinite when you reverse ohm meter leads on each of these three diodes.
                  So, you are checking six diodes in total, but doing twelve resistance tests because you are reversing ohm meter polarity on each diode…
                  Keep in mind that this is only a four amp charging system, so you will not see much of any voltmeter deflection at low speeds, especially if you are running other accessories. You probably won’t see much over 13 volts when you run at high speeds. Keep in mind that a bad battery, poor connections, inaccurate voltmeter can affect what you are seeing even though the charging system is working as designed.
                  You could connect an ammeter in series between the rectifier red lead and the red/hot lead it is connected to on the terminal board. You need a fairly sensitive ammeter that can show low amp readings clearly. You would connect the positive lead of the ammeter to the red rectifier lead, the negative ammeter lead would be connected to the red/hot battery lead on the terminal board. Please be very careful not to let these hot leads touch ground. Again, you wouldn’t see much at lower speeds, but should see 2-3 amps once you get the RPM up.
                  It might be simpler to just connect the ammeter between the engine’s positive battery lead, and the positive battery post. I know, I know, usually it is a no no to pull the positive engine battery lead off the battery when it is running. But, it won’t hurt anything to do it on this charging system.
                  Needless to say, you must start the engine first. PLEASE do not connect the ammeter between the engine positive lead and battery positive post then try to crank the engine, your ammeter won’t like trying to get a hundred amps squeezed through it while trying to run the starter motor!
                  So, again, start the engine, then remove the engine positive lead from the battery while the engine is running. Now connect the positive ammeter lead to the engine’s positive battery cable, the negative ammeter lead to the positive battery post, then check output at higher RPM.
                  Let us know if you don’t see alternator output, then we can go on to check the alternator windings and connections….
                  PS- are you sure you have the yellow leads properly matched up between the rectifier and alternator windings?
                  There are three yellow leads that have to be matched properly, oftentimes hard to see…
                  Yellow (no tracer)
                  Yellow with a grey tracer
                  Yellow with a blue tracer
                  Again, these tracers can be hard to see, make sure the yellow leads are properly connected between the rectifier and alternator leads….

                  #37350
                  billw
                  Participant

                    US Member

                    For what it’s worth, I also agree that your test is showing a good rectifier. The diode/beep test is actually a voltage drop test, which shows a half-volt drop across each one, in one direction only. That’s right. What’s not right is 12.2 volts. A fully charged battery should just sit on the floor and have 12.6 to 12.8 volts ready to go. 12.2 is pretty low. How old is the battery? If it’s older than three or four years, I would can it without a second thought, ESPECIALLY if it’s an Exide. You literally could not GIVE me an Exide, after what those things have put me through, even in my old Ranger. (The only time my Ranger failed to start in TWENTY YEARS of ownership, was when a TWO-year-old Exide failed.) Like Don said, those charging systems only put out a few amps max; and a failing battery will take all of those amps, without getting to charge voltage. A battery can be capable of starting a little 50 hp outboard and still be failing internally…..

                    Long live American manufacturing!

                    #37352
                    seahuntboater
                    Participant

                      thanks . I will recharge that battery and check to get it around 12.6 if possible.

                      #37353
                      seahuntboater
                      Participant

                        fleetwin. my endine does not have an alternator . I do see yellow with blue tracer and grey tracer. The rectifier (aftermarket) only has yellow wires and I believe it does not matter which yellow rectifier lead goes to which ones on terminal block. Other then the red on the terminal block there is one grey wire attached to yellow from rectifier and the yellow grey coming from stator is that proper? thanks

                      Viewing 10 posts - 1 through 10 (of 12 total)
                      • You must be logged in to reply to this topic.