Question for the electrical engineers.

A LONG time ago (early 90’s) I spent my summers down at the marina. Most of the boats were sail and trawlers. At the time (from what I remember) they all had giant house bank batteries and normal starting batteries. They were usually isolated by a perko switch. The switch would be in 1+2 when the engine was running.

So.... my question is;
How did the alternator charge the two drastically different battery banks? Seems like one would be under or over charged. I thought the stronger battery would get ruined trying to charge the weaker one?

Thanks.

In the real world, a typical alternator is not designed or intended to actually "recharge" a dead battery, not to mention, a large bank of batteries. So, its best to rely on shore charging, once the boat is back home.

With the engine running, the alternator is going to supply charge what ever bank, the main switch is turned to. So if on "1", then bank one, etc, if on "1+2", the alternator juice goes to both.

If you do connect a charged battery to a low battery, they will eventually equalize. The difference with running the engine with the switch on 1+2, is the positive flow of voltage into both banks, from the alternator. So it will not cause any damage to the batteries, to run with the switch in the 1+2 position, but if you have a very large house bank and you know youve run it down at the party cove, then it would not be a bad idea to just run with the switch on the main bank for a short trip back to the dock or ramp. Then, plug up your charger and let that replenish the house bank.

There are also some passive means for the alternator to supply both banks. Either a diode type isolator or a solid state voltage sensing relay. These allow the alternator to contribute to both banks, with no input from the captain.

Thanks, all of that makes sense.

I’m adding a second battery with the blue sea add-a-battery kit. I had the blue sea kit on my other Moomba and loved it. It had matching batteries and I didn’t give too much thought about any electrical imbalance.

The plan now is to keep the starting battery(only 1yr Old) and add a pair of golf cart batteries. We use the boat probably 75 to 25 ratio of surfing to just sitting. Hopefully the monster alternator on the 450 will keep all those batteries happy. And the 2 bank charger can finish the job back at the dock.

Thoughts?

Golf cart - what kind of tunes do you have going?

Nothing wild. But my boat is on a lift most of the summer without electricity. So I have to pull her out to charge the batteries. Eventually I plan on putting solar on the dock. Looking at the Costco interstate 6v batteries. I also figured the weight would be a side benefit!

MJHSupra, do you recommend a different set up? All opinions are welcome, thanks.

What size is that monster alt? I know Indmar moved up to a 230A alternator option on the Raptor, but then recalled them and changed back to the standard 90A (at least on some engines fitted in a different manufacturer, the new alt was the standard 90A).

If you have the standard 12A 2-bank, I would want to at least double that capacity. A pair of 6V could easily be north of 250 Ah.

Mine was one of the recalled ones. I thought they replaced it with another 230a.

Quote:

---

Originally Posted by The_Robo_Fighter

Eventually I plan on putting solar on the dock.

MJHSupra, do you recommend a different set up? All opinions are welcome, thanks.

---

Agree with MLA.

I figured you either had a monster stereo or something along the lines of no charger.

I see them on one of the local lake on the docks. Mostly powering the batteries for lifts. Good idea to get one.