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battery problems

Hi i have revently bought a 42ft narrow boat.It has two 110amp/hr batteries on itthe battery switch is on the negative side should this be on the+ side ?
It hasa dual voltage fridge which i am told will flatten the batteries if left running when the engine is off.
How can get this problem resolved and is there a web site that will explain how to fit a split charging system and seperate the engine start batterys and add some leisure batterys so that i do not get strande as i did last weekend

Asked by: edward Connolly  | 3.32pm, Monday 19 October

WW says:

The main battery isolator switch is generally on the positive side. Some of the reasons for this can be seen on www.smartgauge.co.uk/whereiso.html. If you are planning to modify your system, it would be a good idea to change the location at the same time.
Dual voltage fridges are designed principally for caravans where the 12-volt side is used when the fridge is connected to a towing vehicle on the move. The 230-volt side is used when the caravan gets to the site and is hooked up to the mains. These fridges work on the absorption principle which is much less efficient than compressor types. The best solution is therefore to fit a compressor fridge like the ones produced by Shoreline or Ranger. The latest models are very efficient, consuming around 24amp/hours in a 24 hour period.
There are two basic ways to separate the starter battery from the domestic bank, which usually contains three to five batteries depending on the anticipated load. The first is the relay which is a switch that connects the batteries together when the engine is running and isolates them when it is switched off. Second is the split diode which works like a non-return valve so that the charging current can enter the batteries but it cannot pass from battery bank to battery bank. Both systems have their advantages and disadvantages but diodes are probably the most commonly used these days.
Installing equipment that carries high currents is really a job for a qualified marine electrician who can check the rest of the system and recommend remedial action at the same time. Most areas of the system have people who specialise in this type of work. They can usually be found by chatting to local boaters or asking at boatyards or marinas.

Graham Booth  | 2.36PM, Thursday 22 October

Interestingly, all boats built in the USA, which have to conform to their equivelent of the RCD, must have the isolation switch in the common negative side, rather than the positive! They give alternative reasons for this, though I do prefer installations to have a positive isolator. You could fit both, of course...!

Mark Langley  | 1.17PM, Friday 23 October

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