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Old 15-09-2015, 11:46   #1
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Too many batteries?

I am switching out my house bank. I removed the 4 8d's and I can fit 12 Group 31 batteries in there place. Will charging them all be the issue? Charging will be from 400 watts of solar plus engine alternator 90

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Old 15-09-2015, 12:11   #2
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Re: Too many batteries?

Don't use 12V batteries unless they are AGM, use the 6V deep cycle battery, you'll get a longer life out of them.
To answer your question without knowing your daily usage and re-charge cycle would be difficult at best, I think. To a certain extent having excess battery capacity is a good thing for many reasons, it covers you when the unexpected occurs and by not discharging as deeply, you extend the battery life, but at some point it becomes self defeating, (if nothing else your wasting money and adding un-necessary weight) but I don't know what that point is, and without knowing your energy consumption, I don't think an intelligent answer can be given
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Old 15-09-2015, 15:02   #3
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Re: Too many batteries?

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Originally Posted by xeon_tsd View Post
I am switching out my house bank. I removed the 4 8d's and I can fit 12 Group 31 batteries in there place. Will charging them all be the issue? Charging will be from 400 watts of solar plus engine alternator 90

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Whats the total amp hour capacity of your new bank? Expected 24 hour usage in amp hours?
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Old 15-09-2015, 15:35   #4
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Re: Too many batteries?

I removed 5. 8ds. And replaced with Twelve 6 volt gc batteries. yes it is a lot of Amp hrs of batteries. but you only need to replace the amp hours that you use. I have 825 watts of solar panels that handles all my 12 volt needs. go with the 6 volt golf cart batteries they will serve you better as they are true deep cycle
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Old 15-09-2015, 15:45   #5
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Re: Too many batteries?

Hmmm . . . I take the OPs question (or at least the answer) to be a bit different.

Rather than being about amp hrs . . . . He has taken out 4 big batteries and put in 12 small ones. That's several times the number of jumper connectors, all of which are points of extra resistance and failure. And several times the number of individual cells, which create internal imbalance inefficiencies. So from an electrical efficiency and failure modes perspective it's a negative move. The only advantage I can see is that 8Ds are hard for one guy to haul around . . . But how often are they going to be moved?
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Old 15-09-2015, 16:53   #6
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Re: Too many batteries?

Well. maybe another answer in the 8D's are not true deep cycle batteries, and the golf cart batteries in fact are
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Old 15-09-2015, 17:36   #7
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Re: Too many batteries?

Deep cycle? That means you can take them way down and bring them up again... But why let them get so low? Monitor the batts and keep them charged.

I agree with Evan... too many connections and resistance and places for corrosion with a gaggle of smaller batts.
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Old 15-09-2015, 19:53   #8
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Re: Too many batteries?

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Well. maybe another answer in the 8D's are not true deep cycle batteries, and the golf cart batteries in fact are
8D is nothing more than a physical size specification. It has nothing to do with whether a battery is deep cycle or not.
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Old 15-09-2015, 20:40   #9
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Re: Too many batteries?

4 8ds on a 44 footer is crazy.

12 group 31s is even worse. With all that solar you would get on fine with 2 or 3 8Ds. 6 or 8 golf carts would also work.
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Old 16-09-2015, 05:48   #10
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Re: Too many batteries?

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Originally Posted by xeon_tsd View Post
I am switching out my house bank. I removed the 4 8d's and I can fit 12 Group 31 batteries in there place. Will charging them all be the issue? Charging will be from 400 watts of solar plus engine alternator 90

You might consider replacing with eight golf cart (GC-2) batteries; that'd give you almost the same capacity... with less weight and fewer connections. With the taller versions, if you have the vertical space available, you could even increase capacity.

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Old 16-09-2015, 06:47   #11
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Re: Too many batteries?

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8D is nothing more than a physical size specification. It has nothing to do with whether a battery is deep cycle or not.
That is correct, but it has been determined that there are no 12V deep cycle FLA batteries out there, regardless of what the label claims, deep cycle batteries have thicker plates and I believe may have more space between the bottom of the plates and the bottom of the battery case, they are made / designed for a long, slow discharge as opposed to a huge, but short duration discharge that a start type of battery is made for. Yes, there is more to it than that, that is just two differences.
The thicker plates are more tolerant of sulfation I believe, and the larger space under the plates gives more room for the material to build up before it shorts out the battery.
Of course there are many other types of deep cycle FLA batteries too, Forklift batteries and ones meant for Solar installations come to mind, but they are usually a lot more expensive per amp hour than the golf cart batteries are and aren't as readily available.
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Old 16-09-2015, 07:38   #12
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Re: Too many batteries?

Golf cart batteries was the path I chose. I am making two separate house banks of 6 batteries in each bank. With a new 4 way switch. I am running the starter to an individual switch.

The weight is not as big a deal on my old heavy boat, I am not racing. I also have pre-teen moving aboard full time and I will be working at anchor too.
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Old 16-09-2015, 08:20   #13
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Re: Too many batteries?

I think if I do the math correct that your going to have something like a 1,200 amp hour bank?
Note, I mess up math often.
But if the bank is that large, remember bank size isn't really what gives you usable capacity, the ability to re-charge it does, my belief is that your going to need a lot more than 400 W of Solar to effectively use that big a bank and even to properly maintain that expensive bank, but once you get enough Solar, you'll probably never have to worry about power.
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Old 16-09-2015, 10:04   #14
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Re: Too many batteries?

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That is correct, but it has been determined that there are no 12V deep cycle FLA batteries out there, regardless of what the label claims, deep cycle batteries have thicker plates and I believe may have more space between the bottom of the plates and the bottom of the battery case, they are made / designed for a long, slow discharge as opposed to a huge, but short duration discharge that a start type of battery is made for. Yes, there is more to it than that, that is just two differences.
The thicker plates are more tolerant of sulfation I believe, and the larger space under the plates gives more room for the material to build up before it shorts out the battery.
...
Determined by who? Reference for that?

Rolls Surrette for example makes 8D size FLA batteties, which indeed have thicker plates and very high quality construction. Since high quality deep cycle batteries are their claim to fame, I strongly suspect they would disagree with the above.
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Old 16-09-2015, 18:24   #15
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Re: Too many batteries?

A good rule of thumb is to have charging sources available that are rated (in amps) at 20-25% of the amp-hour capacity of the battery bank - even if you do not intend to deep cycle the batteries. If you have 1000Ah of batteries (whether AGM or FLA) you should have an alternator, or solar, or genset+AC charger that are rated at 200A, and, if it is an alternator it would need to be a very good one to put out that much juice for the time it would have to run. I won't go in to all the reasons why this is a good rule of thumb. It has been discussed/debated ad nauseum in many threads on here.

High quality deep cycle AGM batteries are readily available in the US, both locally and from a variety of vendors, and even online with good prices (including shipping).High quality FLA batteries are also available but shipping can be expensive if you order remote. "Golf cart" batteries are a size and type (deep cycle) and not a quality. GC-2 is the "small" 6-volt golf cart battery size and is the one most commonly used on boats. There is a higher capacity and taller GC2H "golf cart" battery, but the GC-2 is usually what people think of. Rolls and Surrettes are VERY high quality deep cycle FLA batteries and are available in most common sizes, including GC-2 "golf cart". You generally pay for quality.

Four 8D batteries on a 44' boat is an unusually large bank and would require serious charging sources, which you may or may not have on the boat. If you can't keep them charged right you might as well just plan on replacing them often. I have three older AGM 8D's (756Ah) on my 42' boat and plan to downsize to either two 8D's (510Ah), four GC-2 golf carts (440Ah @ 12v), or four GC-2H taller golf carts (600Ah @ 12v). I am leaning towards the GC-2H batts. But total volume/weight is pretty proportional to the Amp-hour capacity so you really can't fudge on that. You do have to have air space between whatever batteries you get, along with room for the cabling, so a lot of smaller batteries will generally need more room for the same amp-hour total.

If it were me, I would not go with a lot of Group 31 batteries.

But what you really should do is to calculate your "battery budget" to determine what you think you need in battery capacity - all the uses. Most all the books on boat electrical systems will show you how to do that. Then you can evaluate what you need and compare it to how you will charge it all.
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