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  1. #1
    Join Date
    Dec 2016

    Default 12v electrics advice

    Just installed a NASA BM1 onto my sailboat.
    I have 2 battery’s, engine and in boat electrics.
    Isolator/changeover switch for batteries.
    Never had a issue till I fitted the BM1
    Common on switch is from alternator, aswell as the positive for wind turbine and positive for fuse board
    Battery 1 goes to boat electrics ( on battery )
    Battery 2 goes to engine starter ( on battery)
    After hooking up as per wiring diagram I get a drain on the battery
    When selected to either 1 or 2 no load as long as everything is off on board and engine
    When I select 1+2 I get a load of about 20a ( everything is off at board and engine ) I turn ignition and try to start the motor and engine struggles.
    I’ve never had this before until I fitted the BM1
    Does the configuration sound correct?
    Should the wind turbine and positive bar of fuse board be on the common of the battery isolator?
    I would have thought the wind turbine would have to be wired to battery for boat electrics?

    Any help would be appreciated

    2 x marine/leisure battery’s 80ah only 1 year old

  2. #2
    Join Date
    Oct 2016
    Currently Suffolk

    Default Re: 12v electrics advice

    The BM1 is a great piece of kit but is designed to work with only one battery or battery bank. How have you wired the shunt? It should be between the negatives of the engine and house batteries in order to work properly. I'll post a diagram if I can find it, but failing that I'm on my boat Friday and will send you a pic of my wiring set-up.
    "I thought my daffodils were yellow until I met Joe Kennedy."


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