Charging oddity - starter batteries not charged when isolator off

[PaulRainbow]

Okay, a bit of an update on this. Had some technicians on the boat this week, had the same problem that the engine start batteries were so low that the engines were reluctant to start. So leaving the engine isolator breaker on has made no difference to the state of charge. Had the batteries tested today, and the tests have shown that the batteries are end of life. New batteries being fitted this afternoon. Hopefully this will end this problem once and for all.

I'm down there next week, I'm going to investigate where the charger is feeding into the batteries, so at least I know whether the isolator is helpful or unhelpful in this scenario.

Any emergency provision if the engine batteries won't start the engines ?

How are yours wired, i have a pair of batteries that start both engines and a set of batteries (now LifePO4) for domestics. There was no way to start the engines from the domestics when we bought the boat, but i've corrected that with a remote solenoid that parallels the load side of the main isolators.

 

[Sticky Fingers]

Jump lead between the isolators was the tactical fix.

There is one pair of batteries dedicated to engine start, and a second pair of batteries for domestic. These two separate banks are each charged by a dedicated feed from the Victron charger. There is no current interconnection between the battery banks to allow for emergency use. I agree, a more professional way of jumping them would be useful. Press and hold maybe, so eliminate the 1-2-both problems of old.

Additionally, there is a third pair of batteries in the bow for the bow thruster, which are charged using a Victron Orion unit fed from the engine start batteries; this only operates when the isolator is not off.

Finally, a single 12 V battery for a generator start, this is charged separately by a small CTEK charger.

 

[PaulRainbow]

Jump lead between the isolators was the tactical fix. But I agree, a more professional way of jumping them would be useful. Press and hold maybe, so eliminate the old 1-2-both problems of old

Press and hold is one solution for a quick jump start, often seen on Sealines and Fairlines. Something that does not address is a dead or faulty battery.

I routinely fit a 3rd isolator switch (on boats with manual switches). Connect the switch terminals to the load side of the main isolator switches. Low engine battery, turn the switch on, start the engines, turn it off.

If the engine battery is totally dead or faulty (shorted cell, battery exploded etc) you'll want to keep that isolated. In this instance the press and hold switch is useless. With the above arrangement you isolate the dead engine battery, turn the emergency switch on and the engines start and run from the domestics to get you home. Same procedure for a failed domestic battery. As a safety measure the switches are fitted with removable keys to prevent accidental paralleling of the batteries.

My boat has key operated solenoid isolators, so i fitted an additional solenoid, wired as above, with a 3rd key switch, with a warning light, in the electrical cabinet.

 

[Sticky Fingers]

Right, thank you, Paul, that's very informative indeed. I'll add this to the ever increasing list of jobs!