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How to test a rectifier/regulator?

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  • How to test a rectifier/regulator?

    Hi, I am looking to test the new regulator/rectifier that I just installed on my 1987 Johnson 140 TXCLUA. The tachometer is not functioning. I have been testing voltage at the battery with the engine off and then after the engine runs for awhile..I get varied voltage. Anyone know how to test a regulator to see if it is working? I'm thinking I may have damaged it by getting the wiring wrong when I installed it.


  • #2
    Re: How to test a rectifier/regulator?

    Well you sould get varying voltages with the motor running or not.
    With the motor off a fully charged battery is 12.6 volts. With the motor on the voltage should be 13 or higher. 14.4 is the typical voltage to expect from an alternator. Outboards can vary a little more than this. What are the voltages that you are getting? The tachometer is a separate issue.

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    • #3
      Re: How to test a rectifier/regulator?

      Hi wifisher, thanks for the reply. The voltages I have read are varied. With the motor off I read 13.11V, 13.38V, 13.43V, 13.57V. With motor on I read 13.10V, 13.08V, 13.28V, 13.38V, 14.51V, 13.33V, 13.36V, 13.29V. These readings were with just the motor cables connected to the batteries, no accessories running at all. How does this sound to you?

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      • #4
        Re: How to test a rectifier/regulator?

        The "motor on" voltage should be fairly constant, like wifisher said around 14.4 volts. Your erratic readings point to a problem. Have you check all your connections? Faulty rectifier will cause problems with tach readings.

        You mentioned that you might have damaged the new one by hooking it up wrong. If the old one is still functioning, why don't you try hooking it back up and see if you get better reading and tach. If so, then the new one is damaged.
        "A life without risk is not a life." -unknown-

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        • #5
          Re: How to test a rectifier/regulator?

          Disable your ignition, put a voltmeter on your battery and crank the mtr over to run the battery down to about 12 volts. Don't do this all at one time to give your starter a rest. Then leave the volt meter on the battery and start the mtr up and run it long enough to see if your voltage goes up. If it does your charging system should be okay. Your posted numbers were to close together. The tach may be another matter.

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          • #6
            Re: How to test a rectifier/regulator?

            (Testing Tachometer With Water Cooled Regulator/Rectifier)
            (J. Reeves)

            A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

            A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

            However.... those water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

            The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

            NOTE: For the later models that DO NOT incorporate a wiring terminal strip, splicing into the "Yellow Wire" mentioned will be necessary.

            Remove that gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

            If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

            I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.
            Our Questions Require Answers... If You Refuse To Answer Our Questions... How Can We Answer Yours?

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            • #7
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              Re: How to test a rectifier/regulator?

              Originally posted by wifisher View Post
              Well you sould get varying voltages with the motor running or not.
              With the motor off a fully charged battery is 12.6 volts. With the motor on the voltage should be 13 or higher. 14.4 is the typical voltage to expect from an alternator. Outboards can vary a little more than this. What are the voltages that you are getting? The tachometer is a separate issue.
              This gent's reply is exactly correct.

              Bayprowler....you are splitting hairs. The measurements you have posted are way to "fine". 12v at rest, 14.5 or so when running. None of this tenths and hundredths stuff. It ain't that tight. Also, since you are reading essentially the same with the engine running AND off, your meter is not accurate. I suspect your meter's 13v is really 12v. Compare it to a known good voltage...like your car.

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