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Old 10-09-2010, 11:20   #1
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Eight Golf Cart Batteries in One Bank ?

Ok, here's what I want to do, what's the best way to do it?

I have 8 220ah 6v golf cart batteries (Costco) for my house bank. I want to wire them such that I have a house bank of 880ah at 12v.

I'm thinking two 880ah banks at 6v in parallel then the two 6v banks wired in series to bring the voltage to 12v, but what's the best way to accomplish this? I find myself getting a little lost being that I'm not a razzmatazz boat electrical guru, ya' know?

Much thanks,

Thomas
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Old 10-09-2010, 11:35   #2
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Hmm, I think the way most would wire it would be as 4 12v sets (2 6v together in series and 4 for these in parrallel). Doing that would be positive on one battery would be positive, Negative of that battery would be connected to positive of the second. The negative of the second is now negative at 12V, the possitive of the first is possitve at 12V. Do that 4 times with your 8 batteries and connect all the 12v possitives and all the 12v negatives together and you have your amp hrs at 12v.
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Old 10-09-2010, 11:50   #3
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Thomas, this warrants a read about wiring up multiple batteries.

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

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Old 10-09-2010, 13:04   #4
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Thomas, Pete's link is right on for what you need to do. Just treat each PAIR of your 6 volts as a single battery on the diagrams. Chuck
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Old 10-09-2010, 13:48   #5
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Conrad G is right just keep in mind you will have some balancing issues with the series parallel banks.
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Old 10-09-2010, 14:09   #6
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here is what I did on my 1350AH bank

12 6v AGM's

works great
Attached Files
File Type: doc battery layout.doc (35.0 KB, 381 views)
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Old 10-09-2010, 14:19   #7
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Quote:
I have 8 220ah 6v golf cart batteries (Costco) for my house bank. I want to wire them such that I have a house bank of 880ah at 12v.
The historical approach is not to put too many flood batteries in one bank. If you take just one battery it has individual cells that combine to produce the desired voltage and amp hour capacity. When any charging system looks at a battery bank it sees one battery. One cell might be dead thus lower the overall voltage of the battery as it appears. The end result is the charging system over charges the battery and it eventually gets damaged and dies a premature death. Maybe not in a day but over time it give out sooner than it should because of your failure to notice it.

If you were to make multiple banks you could then discharge one bank at a time and recharge them as you were able and thus fully recharge them. Doing as full a recharge after a 50% discharge is the most economical way to use batteries. You get the most bang for the buck. flood batteries have the lowest absorption rate and while cheaper take more engine power to recharge them. It's the math of operation not the cost of the batteries at CostCo.

In the end it's about managing the risk of your already spent money. So how cheap are you? Buying Costco batteries on the cheap and then trashing them won't save you any money and cost you more if you last a long time owning a boat. If you don't last long with a boat you wasted so much money the batteries won't really count. There is the cost you buy them at but how soon is the cost to replace them? It's the bigger picture totally.

Splitting them into banks allows you the opportunity to detect a problem and switch out the bank until you find the offending battery cell gone south. Since banks should be of equal age if you replace the one battery after the initial period of maybe it was a defective battery soon it may not matter. At a 50% lifespan if one cell went bad, you really wouldn't add back just one new battery to a whole bank. It shifts the performance of the bank and suddenly the charging profile is slightly undercharging! It the other way you get hurt in the wallet.

You can lose on either end of the charging profile. Keeping flood banks of manageable size means you'll not risk the whole bunch for one failed battery.

Your best most economical approach is never buy more batteries than you need. Too many batteries always fails because you have to recharge them soon or pay the price later. The ones sitting on the store shelf are always brand new. If you want to pinch pennies, it's the very first thing you do. Don't buy extra batteries! Buy only what you can afford and are able to fully recharge.

Not recharging fully is a pretty severe penalty. Large flood banks always recharge the last 10% dog slow. Not fully recharging 100% costs you a penalty over time. 50% discharge then 100% recharge is the sweet spot with batteries. LiFePo batteries is another story but on a budget, they are not in sight with binoculars.

Look at it from the money point of view not the I want a big bank point of view. You can size any bank based on that approach and save money. After two weeks out the extra dead batteries are a burden not a benefit.
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Old 10-09-2010, 14:26   #8
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You are on the right track. Doing it as one large bank rather than small ones allows you to have approx 440 Ahrs of useable battery. That should run your boat for a couple of days assuming you draw current like most full time cruisers. What you need to be sensitive to is having a large enough charging system to insure you do not let the plates sulfate. So having a 200 amp alternator and 100+ amp a/c charge are requirements. Also you will need to equalize periodically.

Ask me how I know.. I have an 840 Ahr primary bank and my biggest issue when not living aboard and drawing it down is not allowing it to sulfate.
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Old 10-09-2010, 14:56   #9
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make them pairs and divide them into banks for house using toggle switches for each one instead of perk gonna break switches. goodluck. they are easier to handle in smaller sets--2 banks should do well in a charging situation --otherwise takes forever to charge and is hard to handle.
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Old 10-09-2010, 15:53   #10
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There is a good diagram in the Trojan Battery co. users guide, section 2.4.3, Series/Parallel Connections.

http://www.trojanbattery.com/pdf/UsersGuide_English.pdf
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Old 10-09-2010, 16:03   #11
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Whoa...there!

The above posts provide conflicting information, re: whether single bank or multiple banks should be used, and the (alleged) benefits of each.

The OP said he had eight golf-cart batteries and wanted to make a single 880AH 12V house battery bank. That's a perfectly good thing to do. IMHO, the advice to treat this as four 12-volt batteries in parallel (using 4 pairs of 6volt golf-cart batteries wired in series) also makes good sense. That's how I'd do it.

I would NOT split this bank into smaller ones. Somebody didn't do the math when they advised the split. You get the best efficiency...both in usage and in charging....when you have a single large bank, not two or more smaller ones.

Why?

1. In a larger bank there is a smaller load on each battery. Mr. Peukert comes into the equation and provides more usable AH.

2. In a larger bank each battery is discharged to a lesser degree than it would be in a smaller bank.

3. There is no need to tend to battery switching.

4. Charging a larger bank is more efficient, because the bank will take more charging current than will a smaller bank. This is particularly important with flooded batteries (which is what the OP has...not AGMs), since they'll only take about 20% of their rated capacity in charging current.

IMHO, the bit about bad cells is WAY overblown. Yes, it can happen in any kind of battery. But, if you start with new batteries and treat them right, it's unlikely to happen in the 5-7 year lifespan of the flooded golf cart batteries.

And, if it does happen, no big deal. Identify the culprit, and remove that PAIR from the bank by undoing one positive wire (resulting in a 660AH house battery bank). Then, decide what to do....replace the bad battery, etc.

Bottom line for house batteries:

single bank: GOOD
multiple banks: NOT SO MUCH

Bill
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Old 10-09-2010, 16:09   #12
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G'day, mate. Give the insights that Pblais outlines above significant consideration. Try to get a handle on what your average daily amphour demand is if you don't already. Remember, what goes out has to go back in eventually. The charging system needs to be thought out as well when you going to have to put 440 amphours (at 50% discharge) or even 220 amphours (25% discharge) back in. Cheers.
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Old 10-09-2010, 16:11   #13
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LOL I love it when you get a bunch of folks in the room that are smarter than me and have them solve a problem....you learn so much.

Thanks,

Thomas
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Old 10-09-2010, 16:27   #14
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Well it's complicated because I will soon be adding a wind generator and solar panels. I'm also going to add some refrigeration which will be a power drain as well. At some point in the near future a auto pilot, so it all adds up hence my desire to have a slightly larger bank. Of course, the debate rages on whether this should be one large bank, or several smaller ones that I switch between.

Thanks,

Thomas
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Old 10-09-2010, 16:29   #15
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Well, I know what I would do, and that is exactly as Bill Trayfors points out. I have in the past wasted way to much time and energy with multiple banks when it would have simplified things to have the batteries in one large bank. Bill points out some valid and important items about one large bank vs. two smaller ones. The major one IMO is charging and usage efficiency.
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