1989 300WE Batteries & Charging

Discussion in 'Classic Sea Rays' started by schwarz633, Nov 2, 2019.

  1. schwarz633

    schwarz633 New Member

    Oct 1, 2019
    1989 Weekender
    Mercruiser 5.7 Inboard Straight Drive
    I looking for some clarification on the batteries and charging system on my recently purchased 1989 300WE. The owner's manual has a bilge layout diagram which correctly shows 3 batteries in a row between the engines. I'm assuming that there are 2 engine batteries and 1 house battery. There's also a diagram of the emergency start system, which I have, but it only shows 2 batteries, each having an on/off battery switch. I have 2 battery switches, a 1/2/1+2/off and an on/off. I'm thinking that the 1/2/1+2/off is for the 2 engine batteries and the on/off is for the house battery.

    There's a 120VAC powered Chargemaster 12/25-3 charger with 3 outputs connected to the 3 batteries. The manual also has small section on the crossover charging system, but it only mentions 2 batteries. Reading between the lines, it sounds like either engine alternator can charge either engine battery. Does that mean that the house battery is only charged when plugged in at the dock?

    I need to spend some time tracing wires and get this sketched up as I haven't been able to locate a wiring diagram for the boat.
  2. boatmailster

    boatmailster Active Member

    May 13, 2007
    none to share
    none to share
    If you have dedicated emergency switch then I believe system is wired that way:
    Dual battery switch 1/2/1+2/OFF is for one engine and house battery. Second ON/OF switch is for second engine battery and being charged on its own. Emergency (parallel) switch allow you to start either engine assuming that other battery is good. It should be easy to figure it out if Im correct. Turn Off dual battery switch and leave single battery switch On. Try to start either engine. One should start. Turn of engine, turn off single battery switch. Turn on dual battery switch to position 1. Try to start engine. If not start, turn to position 2. Correctly wired should start on one of positions. Now position which motor didnt start should be your house battery. Check if in bilge you have battery isolator installed. Follow wire from alternator and check if there is device what split charging wire to two batteries (engine and house). If you have battery isolator installed then you dont have to worry about charging. Your house battery is always being charge when that engine is running. If you dont have isolator installed then you need to have switch on position 1+2 to have both batteries charged when engine is running. Also if isolator is installed then dual battery switch could be only for engine batteries and house battery has own switch. Combination like that wont work without battery isolator.
  3. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor GOLD Sponsor

    Apr 21, 2009
    At over 30 years old and who knows how many previous owners, I wouldn't assume anything written in a manual is still correct.

    Best thing to do is to follow the various cables and make a sketch of everthing.

    "Logically", two of the batteries would be tied together to make "bank #1" (in parallel with each other... + & - tied together) and the other battery is "bank #2". Bank #1 would start one of the engines and ALSO be the house bank. Bank #2 would simply start the other engine.

    Unless you have a generator... then the third battery is for the genny.

    Note... "Logic" and "previous owners" don't always go together! Follow the wires.
  4. Rdelaespriella

    Rdelaespriella New Member

    Nov 24, 2015
    Redondo beach
    1989 Sea Ray weekender 300
    350 mercruiser inboards
    When the battery selector and battery on/off switches are off, all the batteries are independent, bank 1 engine 1 , bank 2 engine 2, and house.
    That is how it should be when charging at the dock.
    When you turn the switch on/off, you connect the house battery to whatever battery bank you chose with the battery selector.
    Engines running.
    You select bank 1 on the selector and switch on, bank one’s alternator is charging that house battery
    If you select bank 2, switch on, then bank’s 2 is charging the house battery.
    The only time you would select ”all” in the battery selector is for emergency start, or an alternator goes bad.the emergency start on the dash uses a solenoid to momentarily join B1 and B2 batteries
  5. Rdelaespriella

    Rdelaespriella New Member

    Nov 24, 2015
    Redondo beach
    1989 Sea Ray weekender 300
    350 mercruiser inboards
    A piece of advise
    Whenever doing any type of electrical repair, make sure you are doing it with good quality MARINE GRADE cables, connectors, and components.
    I know that going to the parts store and buying those cheap assortments that are not even automotive grade is tempting.

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