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Sizing Starting battery charger

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Section - I have a 1979 Cruise-A-Home I just bought. It has a pair of OMC 350 ...
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  1. #1
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    Member Since : Oct 2018
    Home Port : OR
    Cruise-A-Home Corsair
    Posts : 7

    Default Sizing Starting battery charger

    I have a 1979 Cruise-A-Home I just bought. It has a pair of OMC 350 engines. The current configuration of the battery system has a house bank of 4 Trojan 105 batteries for 12 v and 450 Amps and a pair of group 24 batteries for cranking. The house bank is charged from the starboard alternator and a Freedom 25 invertor/charger.
    The starting batteries are paralleled and are charged from the port alternator and, currently, an auto grade charger - yes, dangerous.

    I have a few of questions:
    1. Is there a good reason to split the starting batteries and charge them from a dual-output charger?
    2. How are chargers for starter batteries sized? All I have is the CCA on the batteries and no Amp Hours.
    3. If the batteries are split for starting how to charge the batteries with a single alternator underway but a two output shore charger when on shore power?
    4. A salesman recommended a ProSport 8 Amp charger and a Blue Sea 7610 ACR and trigger the AC to disable the combination when on shore power. Is this a good idea?

    Any help would be appreciated.

  2. #2
    Roger's Avatar
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    Member Since : May 2011
    Home Port : Maple Ridge, BC, Canada
    Boat's Name : Sweet "P" II
    1979 Tollycraft 30 Sedan
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    Welcome David. Those Cruise-A-Homes are pretty slick. I pass a marina with one all the time. Unfortunately it hasn't moved in years.

    If it were me I would keep the configuration just as it is now (minus the automotive charger). This is also really similar to the way that I set up our boat.

    I would keep the group 24's paralleled to give the starters the benefit of the extra amps. I agree that an 8 amp charger probably would be fine as the start batteries typically don't need much charging. The alternator replaces what the starters use up pretty quickly.

    I wouldn't worry about the ACR but would consider adding an emergency crossover switch to combine the battery banks in case of a failure.

  3. #3
    Cap'n Ray's Avatar
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    Member Since : Sep 2011
    Home Port : SW Florida
    Boat's Name : Bali Ha’i
    1988 Carver 3207
    Posts : 1,845

    Default Sizing Starting battery charger

    Hi David;

    If you haven’t yet, check out the articles “Batteries and the maze”, and “Sizing your house battery banks” here on the site- lots of good info, maybe some ideas as well! I’m with Lotus on leaving it how it is though(minus the automotive charger)- a good marine charger is a bit more expensive, but a lot safer, and more likely to survive the environment.

    Let us know what you decide to do, and share photos of the boat & systems you work on. We all love progress!
    Last edited by Cap'n Ray; October 9th, 2018 at 20:39.

  4. #4
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    Member Since : Oct 2018
    Home Port : OR
    Cruise-A-Home Corsair
    Posts : 7


    Thanks for the suggestions. I decided to go simple and keep the dual 24s. I would like to be able to parallel with the house bank but the house bank is at the other end of the boat (was like this when I got it). I think I will pick up an extra group 24 or 27 and keep it on 1 bank of a dual bank shore charger (a marine one that knows how to steer current). Then put in a switch between the backup starter and the parallel starter bank. More battery than I need but probably easier than running a high current line from the house bank to the back. Still thinking about this one.

    The engines are getting major service and new hoses next week. Ouch... Been a long time since it was done but luckily it runs well.

    This cruise-a-home is going to be out and about. I did not buy it to live on but to be on the river with (Columbia).

    I will post pictures as I go. New DC and AC panels are on the way as well as a SmartPlug, Galvonic Isolator, and ProMariner ProNautic 1210P. The current Shore power is hardwired through the boat skin to the AC panel. Lots of fun...

    Thanks again for the thoughts.
    Roger likes this.

  5. #5
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    Member Since : Oct 2018
    Home Port : OR
    Cruise-A-Home Corsair
    Posts : 7


    Oh. The House bank is 4 Trojan T105 for 450AH. It drives a 2.5KW Freedom inverter/charger as well.

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