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  1. #1
    Join Date
    Oct 2006
    Location
    Eliot, ME, USA
    Posts
    260

    Default Wiring help for single engine dual battery setup

    I have 2 batteries and one engine. I have a 1-2 both battery switch. I have a single wire alternator. Currently the alternator is connected to one battery. I have learned that this way it only charges both batteries when the battery switch is in the both position. Can I put the Alternator lead to the common on the battery switch? Will that then charge either battery or both depending what position the switch is in?

  2. #2
    Join Date
    Oct 2009
    Location
    Iles de la Madeleine, Quebec, Canada
    Posts
    23

    Default Re: Wiring help for single engine dual battery setup

    Yes you can but the best way to go is to buy a battery isolator that is good for 2 batteries, you then connect your alternator and the batteries to it and it will charge both batteries, if they need to be charged but if only one need to be charged it will select that one automaticaly and will not drain the current of the other battery when you are using one only. This way you can use one normal and a deep charge. The normal for the motor and the deep charge for the appliances when you are at dock or anchor. You will need to switch to the one that you want to use with the battery switch that you have now.

  3. #3
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    7,230

    Default Re: Wiring help for single engine dual battery setup

    Isolators are pretty much old school technology today. A better product would be an ACR (auto charge relay) or a VSR (voltage sensing relay).

    But let's back up for just a minute.
    Your 1-2 both battery switch can be thought of as an MBSS.... (main battery selector switch).
    If your single engine boat is set up correctly with the Engine Harness including the Alternator charge circuit, this alternator charge circuit will be a direct connection to the MBSS "Common" cable (generally terminating at the starter motor solenoid).

    This means that whichever battery bank has been selected, it will be supplying ALL 12 v power and will be receiving alternator charge.
    Now if you want to add an ACR/VSR, this divides the charge between the two banks regardless of MBSS selection.

    When the MBSS is managed correctly, most owners will crank on Bank #1 (a dedicated cranking battery) and will warm engine. This bank will be charging while warming engine.
    Then switch over to #2 (a bank of Deep Cycle batteries) and use accordingly, keeping #1 in Reserve until cranking again!
    (key point is in keeping #1 in reserve)


    There are a number of ways to configure a dual battery bank scenario.
    I suggest KIS.... keep it simple on smaller single engine boats!


    Here is a very simple schematic that is both KIS and yet works well for manual battery management.


    Click image for larger version. 

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    Note the Un-Interruptible bilge pump "float switch" circuit, and note the direct O/B Charger-to-MBSS connections.
    (schematically the same.... but with no Rat's Nest at batteries)

    The New House circuit and panel is optional, but not a bad idea, especially if you start adding GPS, DS, FF, etc. This takes the OEM hull harness out of the loop.

    .
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  4. #4
    Join Date
    Oct 2006
    Location
    Eliot, ME, USA
    Posts
    260

    Default Re: Wiring help for single engine dual battery setup

    Hi Rick Thanks, your diagram was excellent. It did bring up another question. On the house side you show a 6v battery in series with what appears to be a 12v battery. That means 18v for the house. Most equipment is 12v. Having 18 will not hurt anything? I'm still trying to correct all the wrongs in this wreck of a boat I have. Right now I have 2 12 volt batteries. One for starting and one for everything else. Not optimum but it works. There is no wringing harness for the engine it is very old. It is a 1964 Crusader CS280 which is an old Chevy 409. Runs great just a bear to get marine parts for it. I don't think they made to many of these. I've been slowly correcting the wiring issues and trying to enjoy going out now and then.

  5. #5
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    7,230

    Default Re: Wiring help for single engine dual battery setup

    Brian, perhaps I'll change that someday..... but I assure you, those would both be 6 volt GC Batteries.... equaling 12 volts total!
    The reason for the GC's, is greater ampacity..... i.e., Amp Hours.
    2 6 volt GC batteries (in series), typically equal more Amp Hours than 2 12 volt batteries (in parallel) will.
    Many of us have been using these for years!


    Even with no engine harness, you can make that schematic work.
    Just bring your alternator charge circuit over to the "common" cable connection, and you will be OK.
    Add the ACR or VSR, and you'll have less charging management to do.


    Also, it helps if we think of the battery banks as to their intended usage.
    #1 = Start load battery bank
    #2 = House Load battery bank
    Either being capable of powering all items on the boat, but the difference being that each type provides a better source of power for the intended load.
    IOW..... we'd not run house loads on a cranking battery..... and conversely, we'd not typically crank on a Deep Cycle (although there is more to this!)


    Make sense?

    .
    Last edited by RicardoMarine; 07-03-2011 at 01:23 PM.
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  6. #6
    Join Date
    Oct 2006
    Location
    Eliot, ME, USA
    Posts
    260

    Default Re: Wiring help for single engine dual battery setup

    Thanks again Rick, I'm going down tomorrow to run a new #8 wire from the alternator to the common post of the switch. I had my alternator rebuilt a couple of weeks ago and it's a 40 amp alternator. I'm thinking I should be ok with #8 wire it less then 10' of wire. It currently only has a #14 wire. Not sure how long it's been like that but I' think it's time to straighten it out.

  7. #7
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    7,230

    Default Re: Wiring help for single engine dual battery setup

    Quote Originally Posted by briang0 View Post
    Thanks again Rick, I'm going down tomorrow to run a new #8 wire from the alternator to the common post of the switch. I had my alternator rebuilt a couple of weeks ago and it's a 40 amp alternator. I'm thinking I should be ok with #8 wire it less then 10' of wire. It currently only has a #14 wire. Not sure how long it's been like that but I' think it's time to straighten it out.
    Yeah, #14 is way too small!

    There should be no need to run this #8 circuit to the MBSS common terminal.
    The MBSS "common" cable makes a connection at the starter motor.
    This would be the location for your Alternator Charge lead.
    It will keep the circuit short, and will use the common cable to take the charge to the battery bank that is being selected.

    Then if you want to include an ACR/VSR, you can.

    The only caveate to this would be a helm located ammeter, in which case this charge circuit must go to/from the helm and back. But in today's world, not too many use ammeters.... we use volt meters.

    For a more true House Load battery management system, look into a Xantrex LINK system. These systems track Amp Hours!
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

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