Battery bank question

[Tnflakbait]

I am redoing the electrical system on my 33 ft catamaran. I plan on using 4 100 amp hr batteries. I have an outboard with electric start. I am wondering if there is any good reason to have seperate banks or just one main bank. The outboard starts by hand easily. I have a small freezer that draws about 2 amps. Any thoughts or opinions? Thanks!

[btrayfors]

In general, it's preferable to have one large battery bank rather than two or more smaller ones. This is because each battery in a large bank is likely to be worked less (smaller amperage draw and less deep discharge) that it would be in a separate smaller bank. Perhaps more importantly, a large bank can be charged faster than a small one without damage to the batteries, providing that you have an adequate charging source.

I think your planned 400AH bank will be more than sufficient, given the info you've provided. However, a real concern would be with charging: how are you going to charge that bank? Assuming you're talking about flooded batteries (not AGMs or gelled batteries), a charge capacity of 50-80 amps would be ideal, controlled by a smart regulator. Don't know how you're gonna do that with an outboard. Some folks use small Honda generators. If that's your plan, the Honda 2000EU would be appropriate, as it has enough power to drive a sizeable battery charger with ease.

At dockside, you'll also need a charging source.

Just a few thoughts...

Bill

[Pblais]

Bill brings up some good points. It's a total package not just the batteries. batteries tnd to give up early in life when they never get fully recharged on a regualr basis. I would assume you are talkintg about deep cycle batteries.

400 amps is a good size for running small stuff and a fridge. Iahd about that on my last and current boat and it's a good size you can last a while with and be able to recharge it. The dedicated starting battery with an isolator is often used just incase you forget to switch off some things and kill the bank. You really don't want the bank drained more than 50%. That also shortens it's lifespan when done too often.

[cal40john]

First of all I agree that one large house bank makes the most sense to me, but 2 equal banks seems to be common from a while ago. Both my boat and my friends boat had equal sized banks in them when they were purchased, and I've seen other boats set up that way. I thought that it was one of those things where people have figured out that another way is better, but I have Charlie Wing's Boatowner's illustrated Handbook of Wiring, 1993, and he still is promoting equal banks. His explanation was very confusing to me until I drove out of my head my own faulty preconception that he did not mean two equal banks and a starting battery. He does not discuss unequal size banks at all. So of course the argument he presents of not leaving the switch in the both position is to not leave you stuck with no way to start the engine makes sense. He also says it allows you to monitor the performance of the battery bank that has had a rest period without using an electronic device.

Is there another reason people were so set on equal sized banks? Since Wing did not discuss the unequal bank possibility at all, he of course doesn't present an argument for or against that system.

John

[Tnflakbait]

Thanks for the great responses. I guess it seems like one bank of 4 would be best? As far as charging goes, I am trying to avoid a generator. I don't like the noise/smell and gas required. I have started aquiring solar panels and I want to get enough to keep the batteries at a good level. I was thinking about 8 amps max output, not sure though. I still need a charger for the dock however. Any ideas on what would be good? I don't want to spend a ridiculous amount on it and weight is an issue as well.

[btrayfors]

Re: chargers for dockside (or generator) use, it's hard to beat the Iota chargers, with IQ-4 smart controllers. They are very robust, virtually RFI free, use pulse-width modulation technology, have automatic equalization capability, and are relatively inexpensive. They come in 15, 30, 45, 55, 75, and 90A versions. For a 400AH battery bank, a 55A or 75A would be appropriate. Be sure to get the IQ-4 option ($35). You can find them on eBay and through various marine suppliers.

Re: solar panels, the more the merrier. How many and how much capacity would depend on your intended use (cruising practices) and location.

Re: batteries, many sailors prefer to use 6V golf-cart batteries in a series/parallel arrangement. Four of these would give you 450AH capacity. This is probably one of the most economical ways to get that kind of capacity in a true deep-cycle battery bank.

Re: the question on one large bank vs. two or more banks, yes, it's true that this is a fairly recent accepted practice. Many older boats, including mine, were wired with two banks through a 1-2-both switch. I'm convinced that many were done this way just because they didn't know what to do with the switch if you didn't have two banks :-)

One large bank is preferable for the reasons cited above. If you like, you can set up two banks (equal or unequal capacity...it doesn't matter so long as the battery types are the same), and use them mostly as one large bank by leaving the house battery switch in the "both" position. This is how it's done on my boat, and it works well so long as you use BIG battery cables, have really good connections, and have a robust battery switch.

Re: a separate starting battery, yes, that's almost always the most desirable thing to do. Keep the starting battery completely separate, and charge it using a device like an EchoCharger which senses a charge on the house batteries and bleeds off enough to keep the starting battery fully charged. EXCEPTION: if the motor is just an outboard and is easily started by hand -- as in the case of the original poster here -- then it might be economical to simply use the house bank for engine starting and not have a separate starting battery setup.

Bill
S/V Born Free

[Kapena]

I have 2 separate 225AH house banks and also a starting battery. Allows me to run to 50% discharge and flip the switch to the other position without having to start my engine to charge things up. Xantrex recommends this operation.

Another cruiser runs both battey banks in parallel...his batteries have lasted for 10 years...I'm lucky to go 2 years. I'm going to try running them this way this season and see how it works out.

[btrayfors]

Kapena,

Yes, that's the right way to go. A single large bank will put less load on each battery in the bank. This has several beneficial effects, including more available amp hours (Peukert's equation: a battery's usable amp hours is inversely proportional to its load), faster charging (assuming you have adequate charging capacity), and shallower cycling (which extends battery life).

However, if you're only getting 2 years out of your batteries this suggests another problem: your batteries are likely becoming sulfated from lack of full and complete charging.

How are you charging your batteries?

Bill

[senormechanico]

I doubt you would really need a shorepower charger if you're not living aboard. If the boat's used in southern California with mostly good weather, you ought to do fine with 8 amps worth of solar and a regulator. Af full time liveaboard situation would be different.

I live just north of Seattle, have my 33' Dragonfly at my dock with only 3 amps worth of solar (at best in the summer). The only time I bother with running a shorepower cord is in the dead of winter so I can plug in a heater to save my plumbing from freezing.

[Strygaldwir]

The nice thing about having a charger while you are on shore power is you don't cycle the batteries down. Batteries have a finite number of charge discharge cycles. The deeper the discharge, the few cycles. If you are discharging the batteries at night and recharging them with solar during the day, you are using some of their useful life. Now, if you are not aboard and you have no load on the batteries, solar charging makes absolute sense. Otherwise, they are getting so affordable now a days, it makes a large degree of sense, if you can swing it.

The other point is, you will/should periodically equalize your batteries. This is impossible? on solar. My equalization phase has always taking twenty-four hours of continuous charge to equalize. Can't really do that with solar.

Cheers, and good sailing

Keith

[senormechanico]

Keith,
You're right about equalizing the batteries if you only have a little bit of solar. It can be done with a bigger array and bypassing the regulator, you just need to monitor the process.

BTW, my 4 Trojan T105's are still going strong after 12 years with less than a month per year's shorepower use.