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Battery Question

Discussion in 'Boat Electronics' started by Marc, Nov 19, 2005.

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  1. Marc

    Marc Guest

    I have a battery set up consisting of 4 group 24's divided into a
    house bank of 3 and a starting bank of 1, controlled by a 3 position,
    make before break, switch. The shore power charger is a Xantrex
    trucharge smart charger.

    The start battery has been running dry, while the house bank is
    normal. It turns out that the reefer, while switched at the breaker,
    draws from both banks simultaneously, and cannot be isolated to one
    bank or the other.

    My gut instinct is to sever the common connection. I believe that the
    the draw down of the starter battery is a greater percentage of its
    capacity than the house bank and thus the charger is frying the start

    My question: Is there any reson for the reefer to be connected in
    common to both batteries? What is common practice?
  2. Do all cells of the start battery require the same amount of water?
    If five cells need lots of water, and one very little, it is likely
    that the non-thirsty cell is shorted, and the battery should be
    replaced - in fact, I'd suggest that the battery should be replaced in
    any case. I have a Truecharge on my boat, and the batteries use very
    little water.
    This doesn't make sense - if the reefer draws from both banks, that
    would mean that the two banks are connected together, and _everything_
    will draw from both banks.
    Common practice would be to have the start battery powering only
    engine-related loads, with the house battery supplying everything
    else, including the reefer.

    Peter Bennett, VE7CEI
    peterbb4 (at)
    new newsgroup users info :
    GPS and NMEA info:
    Vancouver Power Squadron:
  3. David&Joan

    David&Joan Guest

    I think you have two problems, maybe not related: the starting battery
    boiling dry and a wiring problem. First the wiring problem.

    The prevalent wiring scheme for most boats straight from the factory is a
    starting battery wired to the "1" terminal of the 1/2/Both/Off switch and a
    house bank of one or more batteries wired to the "2" terminal of the switch.
    All house loads, starting and charging are wired to the common terminal of
    this switch. So, if the switch is in the Both position everthing is all
    hooked together in parallel.

    You wrote that the reefer, a house load, is independently wired to the
    starting and house banks- "draws from both banks simultaneously, and cannot
    be isolated to one
    bank or the other ". This is very weird, because it negates the switch and
    can allow the starting battery to be pulled down by the reefer load at
    anchor- not good. Or any other house load, like lights for example can do
    the same because the reefer connection always keeps everything in parallel.

    So, if it really is wired that way, then the simple solution is to wire the
    reefer load only to the common terminal.

    I doubt that this will solve your starting battery boiling dry, but it will
    at least give you the ability to do something about it. When set up like
    above, good batteries and chargers don't behave this way, particularly if
    they are all the same type of flooded cells, which they must be for you to
    see the electrolyte level. I suspect you have a bad starting battery.


  4. Larry

    Larry Guest

    If the reefer is connected to BOTH batteries, and all the grounds are
    connected together (negative terminals), then, all the batteries are
    perpetually connected together by the wires to the reefer. The reefer
    should not be connected to the starting all! Nothing should
    be connected to the starting battery except the engine, which is the heavy
    wire from the starting battery to the starter post. The only other
    connection from the starting battery is the heavy wire to the master
    switch, so the starting battery can be charged from the house circuit or
    the engine started from the house batteries..assuming you have one master

    Having just one charger to charge it all, frankly, sucks. Get a dual 10A
    charger and connect one output directly thru a 10A inline fuse to the
    starting battery. Connect the other 10A output to your house battery
    common point, again directly through an inline fuse. Are all 3 of these
    house batteries just hooked in parallel as I suspect? I'm not a great fan
    of that. I like to keep battery banks separately switched, so if one of
    them shorts or something, I can switch it out of the circuit in 15' waves
    offshore without a wrench. Screwing around with battery wires is a
    dockside exercise, not offshore rolling around. Switches could be as
    simple as those direct-to-the-post on-off switches on each one.

    Now, you need do nothing. Leave the 3 house batteries in parallel to their
    charger and leave the house switched to ONLY the house batteries, the
    normal position, say "A". Chance of losing all of them at once is near
    zero, but you could run them down. Starting battery is always connected to
    ONLY the starter and its separate 10A charger. You never need to switch it
    until something fails. If you only have one alternator on the engine, use
    a diode battery isolator to keep the batteries separate, charging through
    the isolator with the alternator output only hooked to the isolator's
    common post. Again, you start the engine and do nothing to charge it all
    from one alternator. Simple...always simple. The isolator connects
    directly to the battery posts, too, just like the AC charger.

    How are the batteries fused? If the starter shorts the starting battery,
    does a fusable link blow or do we just let it explode? If you're using #2
    cables to hook the battery to the starter and house battery switch, put a
    large fuse between battery MINUS terminal and "ground", negative common
    engine block. No circuit, including PRIMARY wiring to the batteries,
    should go unfused, like all the rest of the boats on your dock....damn
    them. Unlike the car, I can't just get out and walk if it catches fire.

  5. The Xantrex TrueCharge the OP mentioned has a built-in isolator, and
    has three outputs, so he should be able to connect one output to the
    house bank, and another output to the starting battery.

    Peter Bennett, VE7CEI
    peterbb4 (at)
    new newsgroup users info :
    GPS and NMEA info:
    Vancouver Power Squadron:
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