Having been referred to your web site from Canal Junction I was wondering if you could help on the basis of your excellent advice and assistance service you offer. I have just purchased a fairly old (1986) and basic 60ft narrow boat. It has 2 domestic batteries and 1 starter battery. There are three isolator switches in a white box next to the batteries with negative leads entering the box. approximately 12″ x 8″. One switch is marked domestic, one engine and one link. The boat was described as “split charging”. On purchase the owner had all three switches turned on. What are the simple steps I should follow to understand what charging system I have and how should the switches normally be set.
Please make sure that you put a subject on your emails. Luckily I had a look through my spam bin and found yours.
First of all visit the www.TB-Training.co.uk website and study the charging system section of the Electrical Course Notes. That should give you some idea of what split charging systems are all about.
Without checking the boat I would say that during normal use the engine and domestic switch should be turned on and the link switch off.
I would expect the link switch would only be used when the engine battery was flat and it would then form a sort of “Jump lead” circuit so the engine started from the domestic battery. This will not be good for the domestic batteries, but will do little harm now and again.
Unfortunately the term “split charge system” has no definition, so the above assumes some form of automatic battery “linking” system when the alternator is charging – either a split charge diode or split charge relay system. This, however may not be so. That link switch may be the means of charge splitting, so you need to do a test.
Set the switches as outlined above and measure the voltage across both battery banks (expect over 12v on each). Start the engine and give it a bit of a rev to make sure the alternator has energised and remeasure each battery bank voltage. Both should have risen and be virtually identical. If so you have some form of “automatic” charge splitter in use.If not, turn the link switch on. You should then find both banks give the same voltage reading. If this is the case the link switch should be turned off as soon as the engine is stopped for the day and on as soon as it is started in the morning.
Please be aware that master switches in the negative side of the batteries may cause a fire under certain conditions IF YOU HAVE ANY EQUIPMENT THAT REQUIRES A PERMANENT FEED – typically a car radio, automatic bilge pump or security system. If nothing is permanently fed I am sure it will be OK.
