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  1. #1

    Lightbulb Single Engine OMC V8 Three Batteries and Isolator

    I have a 24 foot Bayliner that I would like to install three batteries in. One to start my engine, a second to run the stereo, and a third to run a 3000 watt inverter for a rope lights and a TV / DVD player. What would the best way to do this? One switch? Isolator? Can anyone provide a crude wire drawing or part recommendations?

    Thanks for your help!

    Marc Farmen

    Portland, OR

  2. #2
    Join Date
    Dec 2006
    Chaumont Bay, N.y., USA

    Default Re: Single Engine OMC V8 Three Batteries and Isolator

    Ayuh,... Run the 1 battery as the startin' battery, 'n the other 2 in paralleled for house batteries...

    1 switch, 2 circuits...
    Any Grease is Better,... Than No grease at All....

  3. #3

    Default Re: Single Engine OMC V8 Three Batteries and Isolator

    need to know altenator amperage output to provide the correct isolator size, to large will rob you of amperage. if you use a battery switch make sure it is for inboard applications, if out board style is used damage to the altenator will occure if selector switch is turned when engine is running.... if you would like to call a can explain wiring on the phone much easer 850-570-9393 p.s one switch on starten" battery wont help with charging. if house bank wired permently two problems will occure, shor power charging and isolator circuits cannot be properly wired...

  4. #4
    Join Date
    Mar 2009
    Portland, Oregon,

    Default Re: Single Engine OMC V8 Three Batteries and Isolator

    This is a rather old thread, and Marc has posted only one time. But for the sake of on-lookers, here's my two cents.

    The MBSS (main battery selector switch..... aka 1/ALL/2/OFF) poses no issues when selecting between battery banks while the engine is running.
    Passing through the "OFF" position is what may damage an alternator, if the MBSS does not provide "alternator field protection".
    Many today do not offer this!
    So yes..... whether we have an MBSS or a BS, we should not be passing through OFF during engine operation!
    Switching banks ONLY is a non-issue, as most of these MBSS's are "Make-before-Break" type contacts!

    Isolators are old school technology by today's standards!
    There will be an inherant .7 +/- voltage drop throuh an isolator.
    Instead, we should be using ACR's or VSR's in their place.
    Whe/if we use a multi-bank O/B Charger, the two bank charing (while on S/P or Generator) becomes a non-issue.
    ACR's or VSR's also help in this area.

    Ditto Bill re; two banks, rather than three, and in particular if an Inverter is to be used.
    Inverters are power hungry, and are not very efficient at what they do.
    No need for three banks, IMO.
    Keep your #2 HLBB as large as possible.
    This ensures that the % of discharge is less than that of a smaller bank would be, given the same load/duration.
    It will be the % of discharge, the duration left in this SOD, and how soon the bank is re-charged............, that makes or breaks battery longevity!
    Better yet, make the #2 HLBB (house load batt bank) 6 volt deep cycle batteries (in series/groups of two) and increase the Amp Hour capacity.

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

    Please... no PMs! Post your questions on the forum.

  5. #5
    Join Date
    Jul 2010
    Shores of Lake Erie

    Default Re: Single Engine OMC V8 Three Batteries and Isolator

    i HAVE A 1990 sEA RAY 350. pOWERED BY 2 7.4 ENGINES. Port is on a single battery. Starboard is on 2 in parallel. The 2nd being a house battery. When the house drains it then takes the starting battery. No gen set so i'd like to add another house to the existing one. Isolator to keep it from back feeding? Alt. is 70 amp I believe.

  6. #6
    Join Date
    May 2010
    DC Burbs/Maryland Eastern Shore

    Default Re: Single Engine OMC V8 Three Batteries and Isolator

    I can't answer your question with any certainty, but I can offer my educated guess...
    The Port side engine's alternator is charging the single start battery. This single start battery serves both engines. It is not connected to anything but the starter motors. The Stb. engine's alternator charges the two parallel batteries. There is probably a switch somewhere in there that allows you to connect the house bank (stbd) in parallel with the start bank (port) in case of emergency. It should not be set up in such a way that the start battery is ever used to power the house. The house should be able to start the engines, tho. Does that make sense?
    If it is set up properly then you don't need isolator as it is all already isolated.
    To add to the house, just add another battery in parallel to the two existing. This will give you extended reserve as well as greatly adding to battery life. I assume you are using deep cells for the house side. If not you should.
    If you spend a lot of time away from the dock (main charging source for all the batteries) and don't run the engines much, you can run down the house bank. That's OK cz you would still have a full start battery to get the engines going.
    There are plenty of ways to split up the charge pathways, add more capacity and increase alternator output. It all is expensive, so you really need to know how much battery and charging you need before diving in adding batteries willy nilly.
    Practicing the ancient art of ren-ching

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