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4788 Charging system and Batteries-gctid814705

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    4788 Charging system and Batteries-gctid814705

    When I pulled the Shrink wrap off the boat this spring, I found that my engine starter batteries were dry. I had the boat plugged in all winter to keep the batteries charged so they wouldn't discharge and freeze. I also found that my house batteries had a surface charge, but when I put a bit of a test load on them ( 2- 6V golf cart batteries in series) that there was very little capacity. I also found my gen set battery a little low on charge. I have always wondered how the charging system works, as in what charges what and how. The wiring diagrams that came with the boat manuals are of no real help as it shows only one engine starter battery and I have two and it doesn't show the invertor at all. I decided that the regulator on the charger must has failed to sense the voltage of the batteries correctly resulting in over charging causing dry batteries.

    The starter batteries were in the boat when I bought it 9 years ago, so I felt that they were due for replacement and the house batteries were 5 tears old and were not holding a good charge last season. The Gen set battery was replaced last year and was revived with a good charge.

    I was concerned about the state of my batteries and the charging system. I didn't want to replace the batteries without figuring out what was going on with the charging system. I decided to replace the chargers so this didn't re-occur. Well before I started wholesale swapping of components, spent many hours on my belly in the engine room, at the battery boxes and behind the main battery switch panel inside the salon door on the left. My research involved physically tracing wires through harnesses as well as using my ohm meter to verify findings.

    So this is what I learned

    The two engine starter batteries are charged by the corresponding engine alternators as expected as well as the battery charger that sits on the shelf beside the port engine transmission. It is under the invertor that is hanging from the salon floor.

    The invertor has a dual function in that it charges the house battery as well as doing the invertor function when there is no 120 volt supply. The charge function is automatic when there is a 120 Volt supply either by shore power or gen set.

    There is a large gauge wire from the Starboard engine alternator going directly to the House battery. So when you are under engine power, your S. B. engine alternator is charging your house battery.

    The Gen Set Battery has no charger other that it's own alternator.

    I decided to buy a new multi charger that charges and maintains 3 Batteries. I connected it to charge the two engine batteries and the Gen set battery. I have checked out the invertor charging function of the house batteries and it seems to be functioning as it should.

    I will rethink my recharging of the house batteries while 'on the hook'. If I run the Gen set, the house batteries will charge at an unknown amperage probably 10 to 30 amps at 14.2 volts. If I runs the S.B. engine at 1000 RPM the house batteries should receive a significantly higher charge via the S. B. alternator. I am going to see if I can borrow a clamp on Amp meter to get a better reading of both methods of charging. I feel running the S.B. Engine would give a faster charge but at more fuel consumption as well as running the engine at low load is not advisable.

    Any thoughts or discussion?

    I might actually go boating soon rather than working on the boat. The Admiral is giving me direction that boats are to be used not just worked on!



    Hi Carlos,

    A few comments that might help. First, if you still had the original pro mariner analog battery charger that Bayliner installed, that is known to fry batteries and shorten their life and definitely should be replaced with a smart three stage charger. Sounds like you did that. Second, I am not sure what kind of cruising you do but if it is anything like what we do on the west coast, we anchor a lot, don't run air conditioning all the time, and therefore only run the generator 2-3 times a day to run high amperage loads (stove, water heater, etc.) and charge the house bank at the same time. To do this you need a much larger house bank - typical 6-8 6V batteries. Your 2 6V house sounds very much undersized.

    Regarding charging g the house bank, I am not sure what size your inverter is (?), but if or example, the 2500W Trace inverter we had on our 4788 had a 120amp smart 3-stage charger, and would charge much faster than the starboard engine. The alternators have an analog voltage regulator and may put out 60-70 amps to start with but will quickly drop to less than that. Your engine alternator should be the last choice for house bank charging.

    If you do need and install a larger house bank, then a shunt type battery monitor like a link unit is a must. It will tell you the exact state (amp hours used) of your house bank as well as the exact amp load going into or out of the bank.
    "Allante I" Rayburn 75
    Previous: '97 4788


      Hi Carlo. Not sure whether you can do this, but my neighbour has a relatively new Xantrax inverter/charger and had issues with boiling his batteries on his 580. He managed to recover his 8 new AGM for the moment (24v system) with copious quantities of demineralised water, he backed of the charging volts to the minimum and installed a temperature sensor of the side of one of the batteries so if they do overheat again, the charger will respond or switch off accordingly.i

      You could check out whether a thermal sensor switch is included or available for your model inverter.

      John H
      Brisbane QLD Aust

      2000 - 4788/Cummins 370's



        Our boating similar to yours. we tend to travel 1 to 2 hours a day to different anchorages in a day.

        The invertor in the boat is the original one I believe installed at manufacture.

        I will see how the system performs this season. As suggested, I may have to increase my house battery capacity.




          Instead of the direct connection from the stbd alternator to the house battery, I would assume the stbd alternator feeds an isolator and the isolator outputs go to the stbd engine battery and house battery.

          Look at the inverter setup settings to be sure the final "float" voltage is not too high (to slow down the loss of water).
          1997 4788 with Cummins 5.9 (315 hp)
          12 ft Rendova with 40 hp Merc 4 cycle
          Pacific NW


            My 47 sits 7 months all winter with zero charge on stsrt and gen set batteries with zero issues. How much current does your inverter produce in the chg mod?. In the winter I set it to max chg of 5 amps so if I lose power when it comes back on, ie blow shore breaker. In summer I set inverter chg to 100 to 130 amps depending on how hot it is outside, ie hotter I set to less current max. I tie my house and inverter batteries as one bank with four 8 Ds,or about 8 big golf cart batteries equivalent. If you are using up watter in batteries, they are not being chd with a smart chg to just pulse them when needed. I fill my batteries once per year and use about a gallon of water for 4 house/ interter and one 8d start battery, or less than a quart per battery per year.
            Started boating 1965
            Bayliners owned: 26 Victoria, 28 Bounty, 32, 38, and 47 since 1996