1974 Johnson 70 over charging to 15.3 volts

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  • Txgunslinger

    US Member - 1 Year
    Replies: 7
    Topics: 2
    #271507

    1974 70ESL7 saw the old stator dripping rubber and decided to replace it and the rectifier. I replaced the old with a CDI stator and a Chinese rectifier. Took it out and ran it , putting out 15.3v

    came home and ordered an oem rectifier ,  got it today and installed it. Same malarkey. Over 15v at 3800 revs. Scratching head. Battery is showing 12.4 v when I turn on the key. I verified it with an ohm meter. Even went to Napa and checked the battery . 660 cca battery , teats 580cca. Scratching head.  I called CDI thinking output too high but called too late.
    I’ve ordered a oem johnson service manual but it won’t be here until Jan 30th so until then I thought id ask for input.


    dave-bernard

    US Member - 2 Years
    Replies: 1939
    Topics: 29
    #271510

    If it has no regulator, then that would be normal. I am not a OMC guy but that was normal for older merc’s.


    frankr

    US Member - 1 Year
    Replies: 6414
    Topics: 50
    #271512

    Agreed.  It is normal.  Thousands of them out there running around like that, including mine.  Expect it might go even a bit higher.


    DAN UMBARGER

    US Member - 2 Years
    Replies: 197
    Topics: 25
    #271513

    I was always under the impression that the OEM alternators were only 7 amps and COULD’NT put out that kind of voltage thus they only had a small rectifier. Not sure what amperage the CDI stators are but can’t be that much bigger can they? Have you tried a different volt meter?


    crosbyman

    Canada Member - 2 Years
    Replies: 2991
    Topics: 287
    #271514

    Voltage and amps are two different things…

    you  coud can always install  a rectifier regular for a flat  voltage.     that way  some  eqpt like depth sounders won’t turn off due to  high voltage

    peaks

     

    Joining AOMCI has priviledges 🙂


    frankr

    US Member - 1 Year
    Replies: 6414
    Topics: 50
    #271515

    The rectifier that came with those motors did not provide any voltage regulation.  However, CDI now makes a REGULATED RECTIFIER for people that just stand to see 16V as normal.  BTW, the factory service manual says to just turn on some lights.


    Txgunslinger

    US Member - 1 Year
    Replies: 7
    Topics: 2
    #271517

    Well when I had it in the water last week, the voltage display on my Garmin 740s read the same as the dash bolt meter. Today I checked the voltage at the motor and the battery and both were the same as the dash 15.3. My concern is I’ll dry the battery and have a meltdown while out fishing.
    I’ll call CDI Monday


    Txgunslinger

    US Member - 1 Year
    Replies: 7
    Topics: 2
    #271518

    Won’t it dry the battery?


    crosbyman

    Canada Member - 2 Years
    Replies: 2991
    Topics: 287
    #271523

    millions of motors work the same  and no issues. ….

    Joining AOMCI has priviledges 🙂


    billw

    US Member - 2 Years
    Replies: 1961
    Topics: 63
    #271526

    I had an old 1971,125 hp Johnson, that used to do the same thing. Back then, there WAS no optional regulator.So, I used to watch the voltage and run the power tilt in the down direction, occasionally to knock the voltage back down. You just need to add some more fishing equipment and lighting, to get it under control. You probably only need to find about five more amps. (You have the opposite problem from the Apollo 13 crew!)

    Long live American manufacturing!


    Txgunslinger

    US Member - 1 Year
    Replies: 7
    Topics: 2
    #271629

    Well I spoke to CDI and like some of you said he wouldn’t really worried about 15.3 V. But if it was concerning they had a regulated rectifier that would hold it down somewhere around 14 14 1/2 V. So that’s what I did I order the CDI regulated rectifier.

    This seems foreign to me because I’ve had boats all my life and I could always look at the voltmeter on my Suzuki’s, or my mercury. Verrado’s end they’ve always held a voltage about 13.2 volts . I guess that’s the difference between old old motors, and the new motors that are being produced in the last 20 years. Thank you all for your replies.


    crosbyman

    Canada Member - 2 Years
    Replies: 2991
    Topics: 287
    #271633

    happy ending 🙂

    Joining AOMCI has priviledges 🙂


    billw

    US Member - 2 Years
    Replies: 1961
    Topics: 63
    #271649

    13.8 used to be sort of the accepted “ideal,” but these days, I see 14 to 14.5 on new engines all the time. I personally don’t like 15 and above, either. If I had a boat with that reading, I would be trying to find out why.

    Long live American manufacturing!


    Txgunslinger

    US Member - 1 Year
    Replies: 7
    Topics: 2
    #271657

    Yeah the 15.3 kind of freaked me out a bit. I replaced all the electrical components and the wife wanted to go boating so we went and dropped it in the water and everything was “normal “ until I looked down and saw 15.3 on my volt meter and then checked my garmin 740s and it verified the voltage. I’ll install the regulator/rectifier this evening and check the timing and then give it a try.

    Update; Worked like a charm.


    billw

    US Member - 2 Years
    Replies: 1961
    Topics: 63
    #271681

    Funny, usually the Garmins on our boats under-rate the actual voltage entering the unit by 1/2 to one full volt. It makes for some semi-hetaed discussions between the electronics techs and the engine techs at the boatyard. Like, say there is 12.5 at the back of the unit. The display might say 11.5, which leads the electronics guys to tell us a reported electronics problem is a problem with the boat, not the electronics……

    Long live American manufacturing!

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