My boat has two battery banks, one with two 6 volt deep discharge “golf cart” batteries, and the other a 12 volt cranking battery. RV’rs are used to this, house and starter batteries. But old boats are not, they are designed for a starter battery that runs gauges and a radio. So how does this work?
First, the only practical option for battery charging is the engine alternator. Panels have no where to go, and a generator quits working once it falls overboard or doused with salt water. In Ireland I saw river barges, like floating homes, with wind turbines. That could work on a slow-moving boat.
Then, alternators take power from the engine, which means fuel.
Another puzzle I could see was a battery master switch, and a battery selector switch which has the same function as a master switch. Why duplicate? When I dug into it I found a battery isolator, which kinda duplicates the function of the two switches. My first impression is that an idiot designed this mess, but then I realized there might be something to this design because it was so damned complicated.
After a day of tracing, diagramming, and testing I figured it out. The alternator is twice the rating of a regular unit. Almost everything on my engine is upgraded. The scheme with the isolator and two switches is actually a recommendation by the alternator manufacturer.
It works, but it has drawbacks: it can’t take the batteries to maximum charge, 100%. Nor can it “cook” the batteries to de-sulphate them. This means shorter battery life. Fuel goes in, batteries go out, the trick is optimizing this formula.
This wouldn’t be an issue if my motor knew about the modern digital gadgets, little pumps and motors that do things to help me out, things that were invented and added to old boats over the years.
Now that I have diagrams and numbers on paper, I have to go out and see how close I am.