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

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

    Have a bowrider with 3.0L Mercruiser. Always had dual battery systems on my bigger boats so I bought a dual switch but when I went to buy a second battery to hook it up I was warned by a mechanic that I could burn up my alternator by trying to charge two batteries. Of course with this small boat there is no onboard battery charger or shore power. Has anyone tried this or is this a fool's errand?

    Thanks!

    #2
    i have a dual battery and basic perko switch, never had a problem so far...just dont turn the switch to "off" or pass thru "off" with the engine running.....

    Comment


      #3
      if both batteries are at the rock bottom of discharge it may overload the alternator but I really doubt it. If one is full, the other one empty the alternator will not see a difference.

      Having said this, in my small boat all I want is a jump start box. I have one and never needed it to start my boat despite running an electric trolling motor from the one and only battery (deep cycle starter battery group 27 Wally World). And a portable battery is really useful for camping.

      Comment


        #4
        I installed a combiner when I added my second battery and selector switch. I was going to install an isolator but was told the isolator generated heat and used power. The combiner is electronic, doesn't generate heat and doesn't draw any power. It is also small.

        It keeps both batteries charged, and doesn't let a low battery draw a good battery down.

        You can ruin the diodes of an alternator by switching the battery switch when the engine's running, depending on the battery switch and the alternator. Some switches have built in protection. Some alternators are protected on their own. I was going to add a Zap Stop to my circuit to prevent diode damage and then found out the my alternator didn't require one.

        I alternate which battery I use, sometime using #1 all day, next time use #2.
        1998 Capri 1950CL
        3 Liter MerCruiser
        Furuno 1622 Radar, Garmin echoMAP44dv, Garmin 300 AIS receiver, Uniden Cl 2 VHF with Hailer,
        2 batteries with Combiner, Joystick Wakeboard Tower

        Comment


          #5
          wgander wrote:
          You can ruin the diodes of an alternator by switching the battery switch when the engine's running, depending on the battery switch and the alternator. Some switches have built in protection. Some alternators are protected on their own.
          Most all MBSS's are equipped with what we call "make-before-break" contactors, meaning that while switching from one bank to another, and/or through ALL/BOTH, there is never a "NO Current" scenario.

          However, while switching "to" or "through" the OFF positon, it may damage an alternator if the MBSS is not equipped with field protection.

          .
          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


            #6
            unless it's one with AFD (= 2 diodes). They cost a few cents more...... Guest 2110A is a decent one for smaller loads.

            Comment


              #7
              You can charge both banks without harm. I have been doing it for years.

              The only time you will harm your alternator is if you completely disconnect the batteries while the engine is running. Like moving your battery switch to off. You can move from all to 1 or 2 in any combo as long as you don't hit off.

              Like Rick says the battery switch is a make before break switch which means it goes to the intended position before releasing from the previous one.

              Doug
              Started boating 1955
              Number of boats owned 32
              Bayliners
              2655
              2755
              2850
              3870 presently owned
              Favorite boat. Toss up. 46' Chris Craft, 3870 Bayliner

              Comment


                #8
                dmcb wrote:
                ................ which means it goes to the intended position before releasing from the previous one.
                Much better said than I!
                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


                  #9
                  biloxi54 wrote:
                  Have a bowrider with 3.0L Mercruiser. Always had dual battery systems on my bigger boats so I bought a dual switch but when I went to buy a second battery to hook it up I was warned by a mechanic that I could burn up my alternator by trying to charge two batteries. Of course with this small boat there is no onboard battery charger or shore power. Has anyone tried this or is this a fool's errand?

                  Thanks!
                  I'm an electrical engineer, and I can say with certainty that there is "technically" no justification for your mechanics' warning.

                  However, having said that, let me also say that 'automotive' devices (and marine - you know what I mean) are often designed and constructed to be as inexpensive as possible, unlike their 'industrial' cousins. (I hope that makes sense). If this is the case with your alternator, there is some remote possibility that overloading it could be unadvisable.

                  I think your mechanic is talking through his hat.

                  To cause damage, the device will have to produce an output higher than it's design (or rating), and this is unlikely.

                  Comment


                    #10
                    A great item to look into is an automatic charging relay. Relay remaines open till the start battery hits about 14.4 volts than closes to charge second (house) battery. Also with this system, run house loads on second battery and never worry about draining your start battery.

                    Comment


                      #11
                      biloxi54 wrote:
                      Have a bowrider with 3.0L Mercruiser. Always had dual battery systems on my bigger boats so I bought a dual switch but when I went to buy a second battery to hook it up I was warned by a mechanic that I could burn up my alternator by trying to charge two batteries. Of course with this small boat there is no onboard battery charger or shore power. Has anyone tried this or is this a fool's errand?

                      Thanks!
                      As far as the alternator is concerned, it pputs out a regulated voltage and is current limited intermally. The only thing of concern is the charging will take longer with two batteries. However, if the alternator is OK, it will be fine.

                      IMHO, I think you need a new mechanic. He obviously doesnot understand electrical systems and charging.

                      Read rhis:

                      http://www.baylinerownersclub.org/fo...s-and-Charging

                      I am a retired engineer with battery and charger experience. I wrote the article to answer these type of questions.

                      Moreover, my own boat has a starting and house bank. The house bank is 2 6V golf cart batteries @ 220 A/H in series to give a 12V 220 AH battery. The alternator which is the stock merc (mando) one is 12 years old and still ticking.

                      Another FAQ is: " putting a discharged battery in parallel with a charged one will damage the charged one. BULL!

                      The automatic charging relays mentioned in other posts do exactly this. It waits until the starting battery is fully charged and puts the house battery across it.

                      If you want a device designed to create the need for a new battery, buy an automobile trickle charger, and leave it connected all the time.

                      BTW, welcome to the zoo. 1st post and all.
                      Captharv 2001 2452
                      "When the draft of your boat exceeds the depth of water, you are aground"

                      Comment


                        #12
                        I think your mechanic is partly right! It depends on how you run it. If both batteries are low on charge & you are just ideling the engine ( trolling) it may burn up the alternator. If you get the RPM up a little it wil probably be fine. I would keep one charged up & turned off for a reserve.
                        Ernie
                        1986 3270
                        Volvo 305s


                        MMSI 338130047
                        Lake Michigan

                        Comment


                          #13
                          CaptUgly wrote:
                          I think your mechanic is partly right! It depends on how you run it. If both batteries are low on charge & you are just ideling the engine ( trolling) it may burn up the alternator. If you get the RPM up a little it wil probably be fine. I would keep one charged up & turned off for a reserve.
                          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.

                          Comment


                            #14
                            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.
                            [SIZE]3 wrote:
                            + 1 [/SIZE]

                            If an alternator was prone to severe damage (in this, or a similar scenario), then perhaps explain why a car/truck (with a dead battery), can be successfully jump started, and then left to operate while the alternator is bringing the battery back up to a good SOC!

                            Or use an example of a diesel truck with dual batteries.

                            .
                            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


                              #15
                              I have 2 batteries on my boat,with a phase charger....which means...after the starting battery is recharged the phaze charger opens up the 2nd circuit and charges the 2nd battery. Mine is a unit from BassPro,MinnKota and Blue Sea are two other units on the market for around $100. The unit also prevents current being back drawn into the starting battery. Easy to install,everything is done automatically....I have had no issues.

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