Multiple Battery Banks

Big Windy · Dec 5, 2006

12v System

Can't answer all your questions, but you need a good boat electical book to show you the diagram you want. I doubt you have a big enough charger for what you want to charge. I just replaced my on board battery charger and was informed that you need the charger to have 10% output of the total amps put out by your batteries. My two 4Ds, put out 200 amps each, therefore I got a 40 amp charger. My batteries are wiring in parallel...your six volts should be wired in series...that way you'll double the voltage to make it 12.

Bill Roosa · Dec 5, 2006

Carger wiring

You have to check your charger. Take an ohm meter and measure the resistance between any two of the positive wires. If you get no circuit then you can indeed wire the battery banks separately. If however you get a circuit (most common case BTW) then you have to run all three (or splice a larger diameter wire in at the charger and run it )to the common terminal on the battery selector switch. If you really wanted to wire them separately and your charger will not support that then you could put a diode in the starter positive wire from the charger. This effectively makes it a separate circuit almost. If there are not separate circuits then you really only have one positive wire electrically.

Red · Dec 5, 2006

Many ways to skin a cat

Thyme, you probably can do that. One question is what is your energy budget? On the one hand, combining all four golf cart bats into one series/parallel bank will give you longer life because you will discharge the combined bank to a lower extent, and that gives the batteries longer life. OTOH, if your energy budget and charging allow you to recharge and alternate banks without going beyond a 30% discharge depth (for two batteries) then two banks gives you some redundancy. If you haven't bought the batteries yet, options to consider are just using 6 2.2v commercial cells, to make one industrial battery. Or, using two 12v batteries of larger size, if you can lift & stow them.<G>On wiring...I would expect you could use your existing battery switch for the two deep cycle banks (assuming that's how you want to go) and connect the SLI battery *just* to the starter and one charger lead--so it can only run the starter, and the charger charges it whenever the engine is running. That should be all you need to isolate and charge it.Instead of installing more complicated switches, etc., to allow your house bank to be used for emergency starting, you can buy a top-quality set of jumper cables and keep them stowed for that purpose, too. A bit more flexible.DO make sure those batteries are fused (not breakers) right on the battery, and the series/parallel bank is fused once for each series bank as well, preferably with a way to separate them reasonably quickly in case you find one bad battery (or one bad cell) trying to pull all four down. Cable quality, matching cable lengths, and clean connections all should be the rule for that kind of setup.

Stu Jackson · Dec 5, 2006

Your boat, your choice(s)

1. Most will agree with Fred that more than one house bank makes little sense, because the larger a bank is the less % drains out under any given daily load, and the bank simply lasts longer. Same number of batteries that last longer -- that's a no brainer. Calder has a very good description in his Boatowner's Manual. If you don't have the book, get it, read it and you'll have lots less questions like this.2. We use our 1-2-B switch for battery bank output only. We installed a PDP (positive distribution post) where all our charging sources go -- solar, alternator and charger. A combiner charges the start bank. Very simple. The combiner can be turned off if we're motoring a lot to avoid overcharging the start bank.3. Suggest you work up a wiring diagram or two of what you want to do before you start any wiring.4. A good explanation of a basic system is here, from the C34 Projects page on our website. It's one of many ways to do it, and I'v done mine differently. If you're a Catalina owner, read my Nov. 2006 Tech Notes in the C34 section for all the details of our setup. http://www.c34.org/projects/projects-electrical-system-upgrade-2.html

Fred Ficarra · Dec 5, 2006

makingthyme

I once found a flaw with Stu's work but I was wrong.

The red thing at the upper left of the bank is a fuse holder for our LectraSan disposal system. The other switch to the right is our selector switch wired like Stu's. I leave it in 'Both' normally. But I can turn off either the power to the control panel or the engine (for whatever reason). ABYC standards do not require a fuse or breaker for the starter motor system. (I have a long run so I use a giant cable and keep it separate from ALL other wires). But that might change. Blue Seas has a new series of breakers that I'm going to use to replace the fuse for my inverter feed cable. A smaller one would protect our starter motors. They don't pull near as much as an inverter can.As for using GCs for starting, the problem expressed by the 'experts' is that GCs are deep-cycle batteries and aren't designed to dump all their capacity instantly like a 'start' battery. Puuuuleeeese. My engine cranks so fast that if I leave it in gear with no fuel, we can still get to Seattle and back! (that's a slight exaggeration)Oh, each pair of batteries are wired in series to make 12 volts. (same amp hour capacity as one 6 volt) Then each pair are wired parallel for final capacity. It's in all the books. Easy to do.

Benny · Dec 5, 2006

Yes, it makes no sense to divide house bank.

plus it will simplify your installation. We have your same Truecharge and only use two charge leads. A friend of mine uses his third lead to charge the battery on a dedicated circuit for the windlass. In your two bank switch you have all you should need.

Multiple Battery Banks

Nereussailor

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Big Windy

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Bill Roosa

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Nereussailor

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Red

Stu Jackson

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Fred Ficarra

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Benny

Nereussailor

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