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Old 23-06-2014, 05:12   #1
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FLA sizing

My boats has built in battery storage of a specific size, currently smaller batteries are in their with wooden spacers taking up the slack. I have three 125 amp hour batteries in my house bank and that isn't enough, I need more capacity.

I am not prepared to go to a Lithium battery.

I want for a couple of reasons FLA batteries that I have to service

My battery boxes are 16" X 8.5" X 10.5". Is there a 6V golf cart battery that I could put two of them in this space? I don't logically know why, but I feel that 6V golf cart batteries are better than a 12V for deep cycle use, if nothing else, they would be easier on my back.

If that is not possible what is the largest capacity single 12V battery that would fit in that space (group size)?
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Old 23-06-2014, 06:00   #2
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Re: FLA sizing

Most of the battery makers publish specs on their websites... some of which are easier to find all compiled into one place than others. This one is Lifeline (not FLAs), but Trojan and so forth will have similar sizes for their FLAs since battery Group dimensions are intended to be reasonably standard.

Lifeline Batteries - Marine & RV Deep Cycle Batteries

-Chris
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Old 23-06-2014, 06:09   #3
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Re: FLA sizing

Right. You're going to have to tediously go through all the many battery sizes until you find a combination which will fit. I went through this a few years ago -- a PITA.

6v golf cart type batteries are the best bang for the buck in FLA -- many people swear by the Costco no-name ones. IF you can find a combination which will fit. Have a look also at Trojans -- Trojan Battery Company

I've had terrific luck with mine, and they weren't ridiculously expensive. I have a set of 8 of the 12 volt ones which are not as heavy duty as the 6 volt ones (they were the only ones which would fit my battery boxes). They are going on 3 years old and have very nearly same capacity as new, despite a very hard life on a non-shore powered mooring with me living aboard much of the year, and despite having been run down to stone dead on two different occasions and left for weeks.

Don't be tempted to fit "semi deep discharge" or "leisure" batts -- they don't hold up to serious house bank duty. Don't ask me how I know
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Old 23-06-2014, 07:40   #4
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Re: FLA sizing

I'm thinking the way to go is add a fourth battery so I can run two sets of T-105's or equivalent, the Sams club batteries I've used very successfully in an RV before.
Be a lot of wasted space in my current boxes and I'd have to add another to make it work, but probably be the best.

Stupid question and I'm pretty sure I know the answer, but a 200 amp 6V battery is equivalent to a 100 amp 12V correct?
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Old 23-06-2014, 09:18   #5
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Re: FLA sizing

Quote:
Originally Posted by a64pilot View Post
...I have three 125 amp hour batteries in my house bank...
My battery boxes are 16" X 8.5" X 10.5"...
Seems an odd size for a battery box. If you could remove the boxes, and consolidate the space, you'd have more options. 375 amp-hours is very low for your boat.

You must pair 6-volt batteries to get 12 volts; the pair providing one battery's total a/h. Using three 6-volt batteries is not an option.

Here are listed the common sizes. There are others.
List of Common Battery Case Sizes | BCI Group Numbers

TN's house bank consists of four 6-volt L16 batteries. Each has a rating 380 a/h, for a total of 760 a/h for the bank (at 12-volts).
http://www.trojanbatteryre.com/PDF/d...ata_Sheets.pdf
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Old 23-06-2014, 09:18   #6
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Re: FLA sizing

Quote:
Originally Posted by a64pilot View Post
I'm thinking the way to go is add a fourth battery so I can run two sets of T-105's or equivalent, the Sams club batteries I've used very successfully in an RV before.
Be a lot of wasted space in my current boxes and I'd have to add another to make it work, but probably be the best.

Stupid question and I'm pretty sure I know the answer, but a 200 amp 6V battery is equivalent to a 100 amp 12V correct?
Not exactly. In a battery bank you must keep the voltage. So you need two 6 v batteries in series to make 12 volt bank. Two 6 v 200 amp in series is 200 amp at 12 volts.
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Old 23-06-2014, 09:34   #7
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Re: FLA sizing

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Originally Posted by Zil View Post
Not exactly. In a battery bank you must keep the voltage. So you need two 6 v batteries in series to make 12 volt bank. Two 6 v 200 amp in series is 200 amp at 12 volts.

But given the question as posed , the OP is correct

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Old 23-06-2014, 09:43   #8
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Re: FLA sizing

Quote:
Originally Posted by a64pilot View Post
I'm thinking the way to go is add a fourth battery so I can run two sets of T-105's or equivalent, the Sams club batteries I've used very successfully in an RV before.
Be a lot of wasted space in my current boxes and I'd have to add another to make it work, but probably be the best.

Stupid question and I'm pretty sure I know the answer, but a 200 amp 6V battery is equivalent to a 100 amp 12V correct?
Yes.

Four T105's arranged series-parallel will give you nominal 500 amp/hours at 12v.

With battery capacity, more is almost always better -- I have 420 amp/hours at 24v -- but you could probably get by on that much capacity if your boat is not all that power-intensive.
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Old 23-06-2014, 11:35   #9
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Re: FLA sizing

Quote:
Originally Posted by a64pilot View Post

I'm thinking the way to go is add a fourth battery so I can run two sets of T-105's or equivalent, the Sams club batteries I've used very successfully in an RV before.
Be a lot of wasted space in my current boxes and I'd have to add another to make it work, but probably be the best.

If the current boxes are removable, might be useful to consider new boxes to maximize batteries in available space, too. There are a few threads around here about likely battery boxes...

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Old 23-06-2014, 12:38   #10
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Re: FLA sizing

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Originally Posted by ranger42c View Post
If the current boxes are removable, might be useful to consider new boxes to maximize batteries in available space, too. There are a few threads around here about likely battery boxes...

-Chris
They aren't, they are actually part of the settee, but the third battery is underneath in a plastic box, may have been added and there is at least room for one more.
So four 6V's is an option. Right now if you can believe the data on the battery itself I'm at 375 amp hours. Going to four 6V T-105's only gets me to 400 amp hours. Not much improvement, but as what I have is Walmart brand batteries, maybe that 125 amp hours per battery is a little optimistic.

To get where I want to be capacity wise I need at least 6, 6V T-105's.
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Old 23-06-2014, 12:51   #11
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Re: FLA sizing

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Originally Posted by a64pilot View Post
They aren't, they are actually part of the settee, but the third battery is underneath in a plastic box, may have been added and there is at least room for one more.
So four 6V's is an option. Right now if you can believe the data on the battery itself I'm at 375 amp hours. Going to four 6V T-105's only gets me to 400 amp hours. Not much improvement, but as what I have is Walmart brand batteries, maybe that 125 amp hours per battery is a little optimistic.

To get where I want to be capacity wise I need at least 6, 6V T-105's.

I'd have thought four T-105s in series/parallel would get you to ~450 Ah? More if you look at some of the taller versions (if you have space) that have the same WxD footprint...

Anyway, maybe that's only slightly better, but better is better. And certainly, six sounds even better-er.

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Old 23-06-2014, 13:13   #12
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Re: FLA sizing

T-105 Trojans are rated at 225 a/h. but I agree, 4 of them (450 a/h) doesn't make much of a bank for a boat like yours. Six would be OK.
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Old 23-06-2014, 13:20   #13
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Re: FLA sizing

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T-105 Trojans are rated at 225 a/h. but I agree, 4 of them (450 a/h) doesn't make much of a bank for a boat like yours. Six would be OK.
Yep, Mo money, Mo money
I'll just have to live with what I have for awhile, I ordered LED's from Marine Beam today, that should help ans I'll have to run the little Honda more than I want to for awhile.
For now I'm usually just weekending it so it's not critical, but before I go this and good solar is on the list.
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Old 23-06-2014, 14:36   #14
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Re: FLA sizing

I have used Sam's Club Golf Cart batteries for 20 years. Typically get 6 to 8 years out of a set, but my cruising style is not too rough on them.

Cbreeze is set up with 4 in the battery box and two in the fwd bilge. No starting battery but battery switches allow a set to be isolated.
The fwd bilge pair makes windlass and bow thruster power convenient.

I worried about the bilge location, but all switching and fusing is above the bilge area. Finally decided if I had water level in the bilge over the top of the batteries I had lot bigger problems.
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