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

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  • Guest's Avatar
    Guest replied
    Awesome, thanks!!!!

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  • 2850Bounty
    replied
    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.



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  • Guest's Avatar
    Guest replied
    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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  • captharv
    replied
    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.....

    .

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  • 2850Bounty
    replied
    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.

    .

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  • CaptUgly
    replied
    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.

    Leave a comment:


  • 2850Bounty
    replied
    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.

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  • CaptUgly
    replied
    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.

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  • FISHIN00
    replied
    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.

    Leave a comment:


  • 2850Bounty
    replied
    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.

    .

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  • Guest's Avatar
    Guest replied
    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.

    Leave a comment:


  • CaptUgly
    replied
    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.

    Leave a comment:


  • captharv
    replied
    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.

    Leave a comment:


  • Guest's Avatar
    Guest replied
    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.

    Leave a comment:


  • Guest's Avatar
    Guest replied
    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.

    Leave a comment:

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