Originally Posted by chardis
Hmmm... sorry I'm really inexperienced when it comes to this type of thing. I'm confused by the last 3 posts.
It's easy to disconnect the battery from the engine... but then of course the alternator still needs to be connected to the battery in order to charge. But the alternator is grounded to the engine you are saying? So this then makes it an impossible situation as far as I ca tell, because as long as the battery is connected to the alternator then there is current flowing through the engine and into the hull
and causing electrolysis?
I don't understand... why can't use the remote battery switch on the positive line to engage/disengage a relay on the negative line, thereby isolating the engine from the battery that way?
Then if the alternator is grounded to the engine by design then I don't see what can be done to stop the current flowing through the boat..?
Right now I have a manual switch going from the battery to the engine on the positive line which can be set to 0 (off), 1 (engine battery) or ALL (house bank), and I have 2 remote battery switches which are net yet installed, and I plan on installing the relays on the negative, except I don't understand whether you're saying this is a good idea or not?
Sorry if I'm being stupid, but I'm still learning
all of this stuff, and I really appreciate all your help!
You cannot use a ground alternator. It has to be isolated. Generally the Yanmar
engine do have isolated alternators. They just have a wire from the negative terminal on the alternator to the engine ground. Remove this wire and the alternator is isolated.
On some alternators you cannot do this. The alternator case is permantly grounded, so where it bolts to the engine there is a ground conection. If you have this sort of alternator it needs replacing ( there are sometimes conversion kits that will change ground to isolated)
Yes a relay on the negative is needed
Yes you can use a remote battery switch on the positive line to engage/disengage a relay on the negative line.
But the relay only need a small switch carring a couple of amps to activate it so a large battery switch is not needed, just to activate the relay. You cannot disconect the positive to the alternator while the engine is running and there is little point disconecting the + to the starter motor because it's not connected to engine block or hull.
So a positive and negative connection is needed to the alternator when the engine is running. With an isolated alternator this is not connected to the engine ground. The positive lead also goes to the starter motor, but this is never electrically connected to the engine block or the hull. The negative to the starter motor is only connected by the relay during starting.
There is also a need to supply positive and negative to the senders and the engine panel when the engine is running. So the senders, like the alternator need to be isolated. This usually means purchasing
new senders for an aluminium boat.
The usual wiring is
start battery - battery switch-start motor- alternator- engine panel and senders.
start battery - battery switch-alternator- battery side of the relay-engine panel and senders
From the engine side of the relay starter motor
With this sort of wiring, an isolated alternator and senders there is no electrical
contact to the engine block or hull with either + or - wiring other than when starting.