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Battery for Start/Emergency House use

Discussion in 'Musings With Maine Sail' started by Ward H, Feb 1, 2019. Add this thread to a FAQ

  1. 907Juice


    Joined Apr 7, 2016
    131 posts, 45 likes
    Beneteau First 305
    US Seward, Alaska
    For the price of nice jumper cables, I wired an emergency parallel switch. And I don’t have to monkey with battery banks in separate rooms and 8ft apart.

    Sailm8 likes this.
  2. jssailem


    Joined Oct 22, 2014
    8,110 posts, 3,330 likes
    CAL 35 Cruiser
    US Salem, Moored Port Everett WA
    I have carried an automotive Group 24 pseudo (Deep Cycle) battery on board. I plan to connect it to an ACR this spring while I work on phase 2 of my electrical upgrades. I have not needed to use it and hope it will eventually die with out use. That really is what a “Back up” is all about. If I had experienced an emergency I could have wired the pattern into the system and used it to start the Perkins. Phase 2 will mean I can just flip a switch... Faster and easier.

    Ward H likes this.
  3. sailcrazy1


    Joined Sep 29, 2012
    7 posts, 1 likes
    Taswell 43 Center Cockpit
    US currently the eastern Carrib
    We use a setup that follows what the batteries were designed for. We use 6- T105s(deep cycle) for the house bank, and then a car start battery for the engine starting-both the prime engine and the genset. As was explained to me, the thinner plates of the starting battery provide the bigger (but short term) energy for the engine starter, but are not designed for the long-term use of a deep cycle. Both are isolated from the other. the engine alternator recharges then house bank, and the start battery is recharged via the genset alternator and a Balmar Duo-Charge from the house bank. I do, also, have a parallel switch so I could connect the 2 banks if I ever needed to....have never used it! The system has worked perfectly now for10+ years, thru Asia, the Medd, and now the Caribb.

  4. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,824 posts, 633 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME
    A deep cycle battery can certainly be used to start these motors. They not only last longer, because they are constructed better, but they can also be called upon for emergency use and not destroyed as easily as a start batttery would be by cycling it. They are also serviceable, a key factor on a boat.

    "Trojan Battery:
    Can I use my deep-cycle battery as a starting battery?
    Deep-cycle batteries can be used for engine starting but starting batteries should not be used for deep-cycle applications. A deep-cycle battery may have less cranking amps per pound than a starting battery, but in most cases a deep-cycle battery is still more than adequate for the purpose of starting an engine."

    Tom J likes this.
  5. CarlN


    Joined Jan 4, 2009
    388 posts, 36 likes
    Ketch 55
    US Bristol, RI
    A fact of boat life is that "Every switch will eventually be left in the wrong position".

    The best installation I ever had was a small (33ah) Optima starting battery with no switches. The battery was so small that it is mounted right beside the engine in an open tray keeping battery cables short. It was fused. It's only purpose was to start the engine which it did briskly. It probably would have cranked the engine until the starter overheated. The battery could be turned "off" for storage by disconnecting the cable from the positive battery terminal.

    The start battery was charged by a voltage sensitive relay from the house bank. All charging sources went to the house bank. There was no "parallel" function. Instead, a short piece of battery cable with appropriate terminal fittings was wire-tied beside the start battery that could be installed in an emergency to connect the house to start batteries. It was never needed. The house bank's 14.4v absorption and 13.6v float voltages were well within the Optima's specs when charging via the VSR.

    Putting the start battery beside the engine, freed up space in the house bank locker for more house battery - which helped tremendously. The Victron battery monitor was wired to both the house and start bank and alarmed if either falls dangerously low.

    This setup always worked for the eight years I owned that boat.

    Last edited: Feb 11, 2019
  6. Garbonzo


    Joined Dec 4, 2018
    4 posts, 1 likes
    Balboa 27
    NA US Denver
    My back up is the hand crank on my BMW D7.

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