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  • Charging issue

    1987 Yamaha 70 hp was charging fine until a post in battery got loose. Noticed output voltage on my depth finder was down to 12.6 instead of usual 16 volts plus. I changed battery and does not seem to be charging. I checked rectifier using technique in service manual and it seems to check out. Where to next?

  • #2
    Check voltage at battery when motor is running. What is it? With a meter....

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    • #3
      I'd obviously check that connection that was loose on the old battery. Was the new battery fully charged before you installed it? The output of that motor would not be high and if the battery was significantly discharged charging may take a while to show up as higher voltage. A current meter inserted in series would show the actual charging current.

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      • #4
        it was 12.6 at battery with engine running and reving it slightly with fast idle lever. i did not take it out in the water. same as with battery voltage before i connected to engine. did charge at 16 volts or better consistently. engine ran maybe 16 minutes with the lower voltage/short in battery terminal to get me back to dock.

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        • #5
          is it likely the bad battery would have messed up the coil?

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          • #6
            Originally posted by medicineman View Post
            it was 12.6 at battery with engine running and reving it slightly with fast idle lever. i did not take it out in the water. same as with battery voltage before i connected to engine. did charge at 16 volts or better consistently. engine ran maybe 16 minutes with the lower voltage/short in battery terminal to get me back to dock.
            You are saying a short in battery terminal? Does that mean the lead was "+" and actually touched earth or "-"? If that is the case you may have damaged the regulator or lighting coil or wires in between. As advised, make sure both terminals have clean, tight good connections and check output voltage with engine running ( don't forget water).

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            • #7
              the positive did not short out with the negative. the positive bolt made in battery became loose in the battery so it was not making good connection----same result as if cable had been loose. but it never actually shorted out with negative or earth.

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              • #8
                Originally posted by medicineman View Post
                the positive did not short out with the negative. the positive bolt made in battery became loose in the battery so it was not making good connection----same result as if cable had been loose. but it never actually shorted out with negative or earth.
                Auto parts store will test the battery. Start there.

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                • #9
                  i have replaced the battery with a known good one.

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                  • #10
                    is it just to simple to test the lighting coil output then the rectifier output and be done ?

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                    • #11
                      I will see if I can locate the procedure for that

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                      • #12
                        Originally posted by medicineman View Post
                        is it likely the bad battery would have messed up the coil?
                        No. Battery voltage should not be able to make its way back to the lighting coil.
                        Last edited by boscoe99; 05-17-2018, 09:34 AM.

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                        • #13
                          Originally posted by rodbolt17 View Post
                          is it just to simple to test the lighting coil output then the rectifier output and be done ?
                          Awwww, that is so much work.

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                          • #14
                            Disconnect the connector between the lighting coil and the rectifier/regulator. Should be two green wire leads. Measure the resistance between the two connectors at the end of the green wires. Should be ~ .45 ohms at 68* F. Before making the test, hold the two multi-meter leads together. Note the reading. Add that amount to the 0.45 ohms test specification.

                            Test each lighting coil output lead for continuity to ground. Should not be any.

                            Start and run the motor at a fast idle. Using a voltmeter, measure the AC output voltage from the lighting coil. Should be more or less about 25 AC volts at 1500 RPM. If so, the lighting coil appears to be acceptable.

                            Reconnect the lighting coil to the R/R. Measure the battery voltage. Should be ~ 12.7 volts if the battery is fully charged. Start and run the motor at a fast idle. If the battery voltage rises to 13.0 or more volts the R/R is good.

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                            • #15
                              16 volts is a bit high isn't it???
                              Scott
                              1997 Angler 204 CC, 2006 F150 TXR

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