Engine battery problems......

[PetiteFleur]

Hi everyone, my friend has a problem with his engine battery circuit as follows. Boat launched 3 weeks ago, engine started OK. came back a fortnight later & battery completely flat. He assumed the battery was knackered as it was 4 years old. Fitted a new battery today and noticed that with everything turned off, a spark was spotted when connecting the 2nd terminal, and this is obviously what is flattening the battery.
Note - Service batteries not connected as they are a simple plug and socket separated from the engine charging circuit.
Has anyone any ideas on where to start?

 

[Searush]

Not much info to go on really. Do you have an isolator switch? What could be connected? Could something be wired before the isolator?

 

[PetiteFleur]

Hi searush, no isolator switch on the engine circuit, what other info would be useful? There are no other circuits in the engine wiring(that we know about!).

 

[rogerdog]

just wondering is the alternator ok -as if that is the only thing in line its (just) possible if diodes fail short circuit that they could discharge it .... but most likely is the idea of something not being disconnected when switched off -I think a day with a multimeter and tracing things would be the way forward before considering the less likely scenarios.

 

[Piers]

Sounds like a trace and find scenario with a meter. There shouldn't be a discharge if all it's connected to is the engine starter circuit. In any case, do add a battery isolator switch after you've found the problem.

 

[VicS]

I Agree with Piers.

Disconnect circuits one at a time while checking the current flow.

We must be looking for something in the order of 100mA so we are not chasing a few micro-amps. The alternator is an obvious first thing to check.

Also agree that a battery isolator should be fitted.

Engine instrument panel illumination?

 

[steve28]

do you have any wind or solar chargers, is there a stereo system fitted ?, also check to make sure charging light is off when engine is running

 

[moody1]

Does the circuit to engine have a full OFF switch that disconnects the alternator exciter as well as any connection to starter circuits etc. ? It's not uncommon on some boats where there is no ignition key to have exciter circuit on alternator live all time, unless battery isolator switch is used.
Hubby wired ours so that no power goes to exciter or push to start engine button unless a toggle switch is ON. This ensures that no power is wasted exciting a static alternator when battery power is on.

Just thoughts after we found similar.