Battery charge question

[Shiver Metimbers]

At present the boats charge system for start and auxiliary batteries can be isolated both positive and negative at the battery isolating switches. Would it have any adverse effect with electrolysis etc if I kept the charge side of things non isolating? My train of thought is, if the switches accidentally get turned off while the engine is running the batteries will still charge, thus saving the alternator from damage.

 

[pappaecho]

Depends if you are using shore power, where double isolation is needed. Perhaps you could compromise and have one bank fully isolated with the other not so, when say shore power was not in use. The alternative may be a cheapo 12 volts sounder from Maplin or similar, wired to sound when both banks are fully isolated and the ignition is on

 

[saltwater_gypsy]

If the negative side is isolated you will not get the continuity to charge the batteries and the alternator voltage will rise to about 18V and possibly damage the diodes..
There is a scheme where you have a low resistance (about1ohm) which is switched across the alternator whenever the batteries are disconnected but I don't have details and don't want the responsibility!!!! You can also consider having some bit of equipment permanently connected across the alternator

 

[Dave_Seager]

You need some means of breaking the circuit from the batteries so that they can be isolated in case of a fault such as a short circuit. This must include the charging circuit in case that circuit has the fault. Therefore, the risk of breaking the charging circuit while the engine is running will still exist.

You can get diodes to protect the alternator called ZapStop but they do not seem to be available outside the USA.

For what it's worth, I have accidentally turned my batteries off while running without any lasting damage. I considered fitting a ZapStop but never got around to it and have never made that mistake again. After all, there are so many other mistakes that one can make when boating and we just have to learn and establish our own procedures to avoid them.