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Add a second battery and dual switch - can it harm alternator?-gctid464811

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    #16
    malayphred wrote:
    I didn't read 'captharv's' article on charging, but his post is right on the money. I hope it gets the attention it deserves in this discussion. Thank you cap'.

    What you just stated makes no sense at all and is how all these crazy electrical theories are kept going. By "burn up the alternator" I am guessing you mean it could be overloaded and subsequently overheat and (maybe) catch fire? As captharv correctly points out, that can't happen.

    The mechanic is NOT 'partly right'. He is not even 'remotely' right. I give him credit for taking the time to suggest advice to the OP, but he is out of his element.
    I did read CaptHarvs article about batteries & charging & I said nothing to conflict it. I am not an electric engineer. I have had an alternator catch fire. They get so hot that they melt the insulation & short out. The original poster did not say what year his 3.0 Mercury is. Some of the older ones had the alternator built in under the harmonic balancer without the cooling fan. The man that rebuilt mine told me it is a low RPM problem.
    Ernie
    1986 3270
    Volvo 305s


    MMSI 338130047
    Lake Michigan

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      #17
      CaptUgly wrote:
      The original poster did not say what year his 3.0 Mercury is. Some of the older ones had the alternator built in under the harmonic balancer without the cooling fan.
      That would have been Merc's rather unique 470 3.7L charging system.
      Rick E. Gresham, Oregon
      2850 Bounty Sedan Flybridge model
      Twin 280 HP 5.7's w/ Closed Cooling
      Volvo Penta DuoProp Drives
      Kohler 4 CZ Gen Set

      Comment


        #18
        2850Bounty wrote:
        That would have been Merc's rather unique 470 3.7L charging system.
        1978 470 is what I had catch on fire. Water cooled voltage regulator.

        You can't compare our marine alternators on a gas engine with the alternators on a diesel truck. They are definately huge & designed to do the job.
        Ernie
        1986 3270
        Volvo 305s


        MMSI 338130047
        Lake Michigan

        Comment


          #19
          CaptUgly wrote:


          You can't compare our marine alternators on a gas engine with the alternators on a diesel truck. They are definately huge & designed to do the job.
          I'll certainly agree if we are talking about smaller Amp out-put Marine alternators.

          .
          Rick E. Gresham, Oregon
          2850 Bounty Sedan Flybridge model
          Twin 280 HP 5.7's w/ Closed Cooling
          Volvo Penta DuoProp Drives
          Kohler 4 CZ Gen Set

          Comment


            #20
            Being a retired engineer, who has designed consumer electronics, we play a role of "What IF?)" with other engineers, the marketing guys, and sometimes the company legal dorks. We try to allow for possible problems which the loose nut that operates the item can cause.. In engineering circles we call this human engineering.

            The local CG ATON team (Aid to navigation ) when placing atons on the ICW, try to put the aid 50-70' into the channel so if someone passes it on the wrong side, hes still safe if he passes it close. ( And they still get sued)

            Boats are so much more prone to the operators suing manufacturers, and in most cases, over an opertor caused problem. Thats because its a "recreational item" and operators usually are not trained or ediucated in its proper operation.

            Boats are offered from the factory with dual batteries and a MBSS ( master battery selector switch). The switch has 1-2-both-off positions. So its entirely probable that it will be run on the "both" position to charge both. (DUH!) The alternators are the same with the dual batt option or without.

            An alternator is a regulated voltage device and has a current limit by the design of the wiring. A 55 amp a;ternator will start out at about 55 amps, and taper toward 0 as the battery charges up. This is regardless of number and capacity of the batteries. If the alternator was capible of 65 amps, don't you think the alternator factory would sell it as a 65 amp and charge more money?

            The only problem they have not designed out is if you have a completely dead battery (read: sulfated) and the jumpers are connected backward, it will blow the crap out of the diodes.

            I still stand by my statement in my first post Re: the mechanic's competance.....

            .
            Captharv 2001 2452
            "When the draft of your boat exceeds the depth of water, you are aground"

            Comment


              #21
              Thanks all for such thorough replies. New to BOC but a returning member after a 5 year absence. Old boat was Ciera 2655, new boat is a 2008 Bayliner 185 with 3.0L, a nice little runabout now they we actually live on a lake. No longer need the sleep aboard. Only wanted the second battery and switch in emergencies and as a back-up... insurance if you will. Sounds like no worries installing the Perko switch and second battery provided I follow all the recommended precautions. Again, many thanks for your advice and time!

              One last dumb question if you can reply. When running in the number 1 position, is only the number 1 battery being charged then conversely number two position and number 2 battery. Seems like a no brainer, but it does not stipulate on installation instructions with Perko switch. If true, then all I have to do is alternate boat rides between number 1 and number 2 to keep both batteries charged without fear of alternator overload that may occur running on "both" selection. Is this a true assumption?

              Happy boating!

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                #22
                biloxi54 wrote:
                • 1 wrote:
                • When running in the number 1 position, is only the number 1 battery being charged then conversely number two position and number 2 battery.
                • If true, then all I have to do is alternate boat rides between number 1 and number 2 to keep both batteries charged
                • without fear of alternator overload that may occur running on "both" selection. Is this a true assumption?



                • 1 wrote:
                • This would be true if you do not have an ACR (or similar) in the loop.

                  In other words.... while #1 bank only is selected, it becomes your "source", and it becomes your charge "destination".

                  Likewise when selecting #2 bank only.
                • Cranking a quick firing engine requires less Amp Hours than what many of us think it to be.

                  During your engine warm-up, most of the AH's are charged to the cranking battery.

                  Let's say that your starter motor draws 200 amps, and that the cranking duration is 5 seconds.

                  There's 3,600 seconds in one hour.

                  Do the math for total amp draw X's cranking duration, and you'll see your Amp Hours used.

                  Now do the math with your average alternator charge rate.
                • I prefer to allow the charging system to sense each bank individually by avoiding the ALL/BOTH selection.

                  However, doing this should not harm your alternator.



                Rick E. Gresham, Oregon
                2850 Bounty Sedan Flybridge model
                Twin 280 HP 5.7's w/ Closed Cooling
                Volvo Penta DuoProp Drives
                Kohler 4 CZ Gen Set

                Comment


                  #23
                  Awesome, thanks!!!!

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