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Old 10-12-2016, 02:19 PM   #1
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Capacity of 2 6-volt Batteries?

Just before selling me the boat, the PO installed a new house bank--6 6-volt golf cart-style batteries wired to make a bank of 3 12-volt batteries.

The 6-volt batteries are each rated at 230 Amp Hours.

I'm trying to determine/estimate the AH capacity of each 12-volt set. I have googled this and gotten widely varying answers.

1. Some say the combined capacity of 2 6-volt 230 AH batteries is still just 230 AH.

2. Some say it doubles to about 460 AH.

3. Some say it almost doubles, but with about a 25% loss, to maybe 345 or 350 AH.

Anybody actually know what the answer might be?

Thanks!
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Old 10-12-2016, 02:24 PM   #2
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1. is the correct answer.

Two 6v in series for 12v, Ah rating stays 230.

Gang six up so each pair is paralleled, and three pairs are in series, and you get 12v and 3 x 230 for 690Ah
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Old 10-12-2016, 02:35 PM   #3
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When you wire in series voltage increases, but Ah capacity stays the same. Two 6V 230Ah batteries wired in series = 230Ah @ 12V

When you wire in parallel Ah capacity increases and voltage stays the same. Four 6V 230Ah batteries wired in series/parallel = 460Ah @ 12V.

You have a series/parallel bank of: 690Ah
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Old 10-12-2016, 02:45 PM   #4
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Originally Posted by Ski in NC View Post
1. is the correct answer.

Two 6v in series for 12v, Ah rating stays 230.

Gang six up so each pair is paralleled, and three pairs are in series, and you get 12v and 3 x 230 for 690Ah
Correct. Maybe this thread will stay under 20 posts.
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Old 10-12-2016, 02:50 PM   #5
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Correct. Maybe this thread will stay under 20 posts.
LOL, yeah , I don't agree with any of the other posters.
Due to internal resistance of all those different cells in the banks, you do not get all those amp hours, you always get less that you think you should get, and it varies depending on cell construction and internal battery resistances.
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Old 10-12-2016, 03:58 PM   #6
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LOL, yeah , I don't agree with any of the other posters.
Due to internal resistance of all those different cells in the banks, you do not get all those amp hours, you always get less that you think you should get, and it varies depending on cell construction and internal battery resistances.
A 12 volt battery consists of six 2 volt cells wired in series. A six volt battery consists of three 2 volt cells wired in series.

Two six volt batteries wired in series consists of six 2 volt cells wired in series. The only difference between this and a 12 volt battery is that there are two separate cases.

The result is the same.
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Old 10-12-2016, 04:48 PM   #7
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To add my 2 cents, theoritically it is 690Ah. Considering that you should not use your battery at more than 50% discharge, you have in reality 345Ah available which in 12v will represent 4140wh of energy.
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Old 10-12-2016, 04:53 PM   #8
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Greetings,
Ya, but what about the anchor?

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Old 10-12-2016, 06:55 PM   #9
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Greetings,
Ya, but what about the anchor?

Hope this won`t end with multi meters fired at 20 paces. You electrical guys should get together and agree on something. People are just getting confused.
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Old 10-12-2016, 08:13 PM   #10
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Originally Posted by Oldersalt View Post
The 6-volt batteries are each rated at 230 Amp Hours.
So you have 6 1.4 kW*h batteries, 8.4 kW*h total, no matter how you wire them.
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Old 10-12-2016, 08:14 PM   #11
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Considering that you should not use your battery at more than 50% discharge
Why not 80%?
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Old 10-12-2016, 08:30 PM   #12
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Why not 80%?
Why 80%?

Good deep cycle golf cart batteries can often go below 50% and still have decent cycle spans...
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Old 10-12-2016, 08:34 PM   #13
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Why 80%?

Good deep cycle golf cart batteries can often go below 50% and still have decent cycle spans...
Modern batteries, such as Odyssey, can be discharged to 20% of rated capacity without shortening their life span. State of the art batteries can be discharged even deeper.
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Old 10-12-2016, 08:40 PM   #14
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Modern batteries, such as Odyssey, can be discharged to 20% of rated capacity without shortening their life span. State of the art batteries can be discharged even deeper.
OK.... I agree...just wasn't sure what you really meant.

The OP did say golf cart style batteries...my bet is flooded otherwise most people do state the more modern labels.
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Old 10-12-2016, 08:46 PM   #15
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OK.... I agree...just wasn't sure what you really meant.

The OP did say golf cart style batteries...my bet is flooded otherwise most people do state the more modern labels.
Right. Besides, the question was, how many electrons I can squeeze out of the box. Not what will happen to the box afterwards.
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Old 10-12-2016, 10:52 PM   #16
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Greetings,
Ya, but what about the anchor?

IMHO ... there are better anchors than 6 volt golf cart batteries.
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Old 10-13-2016, 07:04 AM   #17
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IMHO ... there are better anchors than 6 volt golf cart batteries.

Which ones do you mean?

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Old 10-13-2016, 07:09 AM   #18
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Originally Posted by sdowney717 View Post
LOL, yeah , I don't agree with any of the other posters.
Due to internal resistance of all those different cells in the banks, you do not get all those amp hours, you always get less that you think you should get, and it varies depending on cell construction and internal battery resistances.
This is a good point but not for the reasons many may think. The "sticker rating" is just that, a quasi meaningless sticker/guide. It is nothing more than a suggested Ah capacity. It is often based on testing similar batteries from lots or production runs many, many years earlier. Some manufacturers even extrapolate or attempt to calculate Ah capacity from a 25A RC test, a shorter and less costly test, and you will only rarely get the rated Ah capacity from the battery especially if a proper break in & cycle-up is not done..

Batteries, especially deep cycle flooded batteries, also need to cycle-up to their capacity rating. This can take as many as 50-150 cycles before attaining the stickers Ah rating. Sadly many boaters abuse batteries to the point where they never get to cycle-up to their rated Ah capacity and large numbers of boaters totally destroy their batteries well before a full break in of 150 cycles can even occur.

AGM and GEL batteries cycle up to capacity faster, AGM in 3-7 cycles, and GEL in about 7-15 cycles but most flooded deep cycles need at least 25-50+ deep cycles to attain their Ah capacity rating and some as many as 150. Of course if you start PSOC cycling right off the bat, before the batteries break in & cycle-up, you'll never see rated Ah capacity..

If you know the capacity of each battery in the bank, and then wire them in parallel or series/parallel, as a bank, and apply a C/20 discharge rate at 77F you will get the total capacity of all batteries, but you need to know the actual capacity of each individual battery first...

Using a sticker rating is almost always misleading and inaccurate.

For round numbers most boaters & publications simply use the "sticker rating" which can certainly be extremely misleading and quite often inaccurate by as much as 5-25% off what the sticker suggests.
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Old 10-13-2016, 09:03 AM   #19
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Quote:
Originally Posted by CMS View Post
When you wire in series voltage increases, but Ah capacity stays the same. Two 6V 230Ah batteries wired in series = 230Ah @ 12V

When you wire in parallel Ah capacity increases and voltage stays the same. Four 6V 230Ah batteries wired in series/parallel = 460Ah @ 12V.

You have a series/parallel bank of: 690Ah

Thanks for clear and precise explanation.
Then if Ah capacity stays the same what is the good of having 6 x 6v batteries wired in series (actually my service battery bank) instead of 3 x 12v batteries wired in parallel?
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Old 10-13-2016, 09:15 AM   #20
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what is the good of having 6 x 6v batteries wired in series (actually my service battery bank) instead of 3 x 12v batteries wired in parallel?
Cost and weight. The 6 volt batteries will each weigh much less (not quite half, but close) to what an equivalent 12 volt battery would weigh. Makes them easier to move around. Also, at least here in Florida, because of the huge market for 6 volt golf cart batteries, it is cheaper to get two 6 volt batteries than it is to get one, larger, 12 volt battery.

As to the series/parallel thing. I used to shop at a PAC-n-SAV store. You know, one of those warehouse stores kind of similar to Costco or Sam's Club. So I just remember pac-n-sav: Parallel Adds Current-n-Series Adds Voltage.
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