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Posted: Wed Dec 06, 2017 12:28pm

Post Subject: batteries

Dear Tony, my daughter lives on a widebeam boat, moored in a marina.The boat's domestic batteries are connected to mains electricity.However it seems that the starter moter battery isn't so on the odd occasion when she needs to move the boat she has to use jump leads from the domestic or service batteries to the starter battery.Is there a better probably safer solution to this problem? Also do you recommend the use of a galvanic isolater if your boat spends long periods moored in a marina with other boats.Thank you in advance for any advice you can offer. Yours sincerely, Robin Adair


Posted: Wed Dec 06, 2017 1:29pm

Post Subject: batteries

Your question implies the use of a battery charger and most of the cheaper and non-marine offerings only have one set of outputs so it is connected to the battery that needs most charging - the domestic bank. When running the engine the engine charging system should be wired to charge both battery banks. From what you say she may well have destroyed her engine battery by long term under charging but only time will tell. Assuming the boat is conventionally wired the quickest and cheapest way is to pop a jump lead between the domestic and engine battery positive terminals while charging and remove it when charging is stopped. Just take care not to cause a short circuit with the lad or clips to any negative terminal or metal. A longer term solution would be to fit a twin output marine charge so it charges both banks. If you think she may want to fit solar charging in the near future then fitting a voltage sensitive relay will automatically join both banks when charging and disconnect then when not. If you want more information about this please email because I will need to send you a wiring diagram. Any boat that is correctly wired for safety and spends long periods connected to a shoreline is at danger of excess hull corrosion because the mains earth wire completes a circuit between boat, water, bank/pontoon, and back to the boat via the mains earth line so to combat this a galvanic isolator or isolation transformer should ideally be fitted. A galvanic isolator may fail in an unsafe way so needs regular monitoring. If your daughter is daunted by this an isolation transformer might be a better bet but many Galvanic isolators have a meter or monitoring LEDs built in so it only takes a glance. Some now plug in between the shoreline and the boat's shoreline socket.

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