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Discussion in 'Technical Discussion' started by timvail, Aug 3, 2022.

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  1. timvail

    timvail Senior Member

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    georgian bay penetanguishene
    We have a 1990 sea ray 350 with twin 7.4litre Mercruisers located on GeorgianBay to get us into the skinny places we like. I left the dock a couple of days ago cruising at 1700Rpm when I noted the port engine came out of sync. The Volt meter had jumped to 16.5 volts on the port side. It lasted 15 seconds, then back to 13.5. Twenty minutes later, the same thing happened; this time, the starboard engine did the same thing. The volt meter read 16.5 volts. Ten seconds later, the port engine did it again. I throttled back to idle, and volt meters went down to 15 volts. On the run home, they ran at 14 volts without any change.
    New AGM batteries this year.
    I first thought the regulator was acting up, but on both engines at the same time?? Any ideas on where to start? Yes, it's intermittent.
  2. MBevins

    MBevins Senior Member

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    Windsor On. Canada
    My initial thought is to check the ground on your instruments, on that boat they'll be daisy chained so one bad connection can effect both sides of gauges.
  3. timvail

    timvail Senior Member

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    georgian bay penetanguishene
    Yes, it is one of the thoughts I had and will check when next at the boat. However, it first caught my attention when I could hear the port engine decrease in rmp slightly, which was confirmed by the sync gauge.
  4. Pascal

    Pascal Senior Member

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    Odd. Ground indeed would be the only common thing between the engines but do you have anything else in common? Any battery combiner or isolator? Did you have the generator running with the battery charger?
  5. timvail

    timvail Senior Member

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    No generator was running. There is an emergency start where the first bank and second bank are combined to start one or other engine if need be. I will have to have a better look in the engine compartment to see what else may be common to both.
    Tough when intermittent. Nothing obvious.
  6. Capt Ralph

    Capt Ralph Senior Member

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    Battery level normal and correct, Then goes a little higher and comes back down to normal.

    Gen-set and ships battery charger fighting the engines charging alternators can do this.
    Those fancy multi stage voltage regulators can do this.
    Bad connections, positive and negative leads may do this.

    New AGM batteries replacing standard flooded cell batteries? Charging profiles are pretty close and should not make a difference.

    Anybody below operating a head? Bilge pumps cycling? Heavy DCv lights?
    After a load, the voltage may rise to recover the battery and settle back to normal.
  7. timvail

    timvail Senior Member

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    Location:
    georgian bay penetanguishene
    All good ideas. Nothing 12 volt that I noticed in addition to usual items on I.e gps radio etc. The second time it happened I turned on my cell phone booster and both volt meters dropped from 16 to 14.5 volts.
    So will go through these suggestions tomorrow on the boat. Thank-you gents. Will try and eliminate what I can.
  8. Pascal

    Pascal Senior Member

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    Did you check that your dash voltmeter are accurate? Compare their readings to a direct reading at the battery terminals
  9. timvail

    timvail Senior Member

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    I will do it tomorrow. The plotter at the time also showed 16.5 volts as the meters did.