More fun with 8D batteries

[Figment]

No, not beerguy again. His system is settled. It's insanely overcomplicated, and it my opinion he tore apart his boat for inconsequential gain, but whatever.

This time it's my father's boat. On with the rant.

I make a conscious effort to avoid sticking my head into his engine compartment, because it seems like I always get sucked in there for hours on end. For this reason, it was not until this past weekend that I learned of his 12V setup:

Twin diesel boat. Each engine has its own 8D battery. I know. Read on.

AC power is provided via shorepower, a 12KW generator, AND an inverter. The inverter has its own 8D battery.

That's THREE 8D batteries. Something like 200 amp-hours EACH, right?

The port engine's 8D is wired as the "house" battery for the boat's 12v system. Refrigeration, cabin lights, water pump, etc.
The average weekend-overnight drains this battery to the point that it cannot start the engine the next morning, requiring the use of a parallel-start device to make use of the stbd engine's battery, which has been sitting pretty all the while.

That's right.... the stbd 8D is used EXCLUSIVELY for engine starting. Never drained below 97%.

The inverter's 8D is enough to watch a movie on the tv/vcr and pop a bag of popcorn in the microwave, but that's about it. He's been thinking to add a FOURTH 8D because he's tired of needing to fire up the generator to run the battery charger.

Oh, by the by, the battery charger is not designed to support four batteries (the generator has its own group24 for starting), so it charges at least two if not three of these batteries via parallel wiring.

A total friggin mess. I didn't even know where to begin.
I ought to at least loan him my 12V Bible or some other chunk of my library, but I think I'd probably find myself down in the engine compartment for hours on end......

[Tim]

Sailboats: the solution to overcomplicated powerboats.

Good luck with that mess...even reading about it makes my head spin! Sadly, systems like that are more the rule than the exception. Electrical systems are complicated enough even when simple...and few onboard systems end up more Rube Goldberg-like in the end, usually because of patchwork solutions to one particular problem or another, rather than addressing the proper installation of the system as a whole.

[dasein668]

Geez, with all those 8Ds on board already, you sure could make a hell of a house bank... Pick up a couple starting batteries and wire all those 8Ds together....

[Figment]

That was my first thought, Nathan. Divorce the two systems. Let the engines have engine batteries, and separate them entirely from the "house" electrical system. Of course, the port engine then is left with a 200A alternator that isn't doing much, but I still think it's the way to go.

Bank two of those 8Ds together as the house battery. Let the 12v house circuits AND the inverter draw from that bank. When things need recharging, fire up the generator, which honestly is running most of the time anyway because he runs the air conditioning just to keep the bugs out of the cabin.

[Tim]

Of course dedicated starting batteries, and isolated house banks are always the best choice in an electrical system. In this case, it also seems to be one of the easier solutions to the issue.

[bcooke]

Do your really want to start a rewiring project at this time?...

How about just one starting battery for both engines? With a crossover to the house bank as a backup of course. Once the first engine was started would the one spinning alternator be enough to help out the engine battery for the second start?

I didn't even know where to begin

Britton's answer to all electrical nightmares:
A big pair of diagonal cutters.

Good luck!

-Britton

[Figment]

oh, no I'm not at all interested in engaging in any sort of rewiring project. I don't want to touch this one with a ten foot pole.
But when he asked if I thought he should buy that fourth 8D, or if he should splurge on one of those newfangled multistage battery chargers he's heard so much about.... I started asking questions, and in the end I had to talk him out of doing either.

Yeah, a new charger is a great idea, but fix the rest of that mess first.

"whadda you mean? what mess are you talking about?"

Two hours later, the only thing that got me out of that conversation was my cellphone ringing to tell me we had a frozen pipe back at the house...