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Old 29-03-2016, 06:39   #16
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Re: House bank upgrade verification

If ONE needs to understand the differnce, maybe you can explain.

I suppose some references would help in the explanation.

Yes, 720 AH, 7 jumpers. It was early and I was concentrating on the bigger issue.
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Old 29-03-2016, 07:44   #17
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Re: House bank upgrade verification

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Originally Posted by seabreez View Post
The original drawing is ok
yes I think it is. But do you think it's the best solution ? You seem to know what you're talking about so I would be happy to read your explanation. BTW, I was comparing 2S3P (and not 3S3P !) from OP's proposal and 3P2S, sorry for the confusion.
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Old 29-03-2016, 07:46   #18
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Re: House bank upgrade verification

I wired our boat battery bank a little differently, in a system that gives me more control, for safety if you get a dead/run-away battery; I can easily isolate any one or two of the 12v "batteries". I used 3 sets of 2 Trojan T105s, connected the (+) of one to the (-) of the next to make a 12v "battery, then connected the (+) each 12v "battery" to a on/off switch and then to a common bus bar. Then I connected that bus bar to another On/Off switch, then to the house fuse, and to the house load. If any single 6v (or the 12v "battery") develops a problem, a simple turn of that switch eliminates it from the bus bar (and the system)....but the house remains powered. And as long as all 6 are working correctly, I enjoy the higher amphr capacity of the entire bank. It's worked flawlessly now for 13 years. PS...I also monitor each battery via a pair of Xantrex Link 20 battery monitors....position #4 is for the isolated separate start battery.
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Old 29-03-2016, 08:11   #19
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Re: House bank upgrade verification

Quote:
Originally Posted by twinboat View Post
If ONE needs to understand the differnce, maybe you can explain.

I suppose some references would help in the explanation.

Yes, 720 AH, 7 jumpers. It was early and I was concentrating on the bigger issue.
As I said I am no expert, and I am suggesting the OP to wait for other respectable forum members to chime in.

In the meantime, the general idea is that when charging 2 (say 6V) batt in series, if one is "tired" and will not reach 7.2V but only say 6.4V then the other one will reach 14.4V minus 6.4V (say 14.4V is the charger's absorption setting) , which makes 8V. Because overall voltage is voltage of batt1 plus voltage of batt2. And here we go, 8V will toast the second battery.
As a result series connection should be avoided as much as possible and a 3P2S config should be prefered over a 2S3P because it only has 1 serial connection instead of 3, but still provides the exact same capacity (Ah) and voltage.
So what happens if one battery gets tired in 3P2S config ? You might expect the other 2 in the group to provide a good enough average voltage that prevents the other group from toasting. Also you might plug two cheap voltmeter (one on each group) to monitor the whole pack. Monitoring a 2S3P config would require 6 voltmeter.

As for references, you might as well just google 3P2S vs 2S3P as I don't have any.
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Old 29-03-2016, 13:56   #20
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Re: House bank upgrade verification

Just confirming A B battery located in one location C D battery second location E F battery in another location?
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Old 29-03-2016, 14:05   #21
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Re: House bank upgrade verification

Can you draw your set up I like to see drawing pictures better then words thank you
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Old 29-03-2016, 14:57   #22
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Re: House bank upgrade verification

Last time I was forced to use 6V batts to build a 24V bank, I used the method as in the lower image by #rom above (I used an array 4 batts wide while OP needs just two). This avoid an extra C+ cable as shown in OP first draft.

I am not 100% sure this is the right method but I gave it some thought and did not find any obvious problems.

b.
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Old 29-03-2016, 14:58   #23
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Re: House bank upgrade verification

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Originally Posted by smac999 View Post
I don't understand... 6 is an even number. and will take the space of 6 12v car batteries.
the reason I call it an odd number is because the set up I was using (please refer to post #1 drawing) is 3 sets of 2 6v batteries
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Old 29-03-2016, 15:03   #24
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Re: House bank upgrade verification

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Originally Posted by COLINFLTENG View Post
Can you draw your set up I like to see drawing pictures better then words thank you
there is a pdf drawing at the bottom of post #1
I am reposting it (hopefully this does not break CF rules)


Drawing.pdf
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Old 29-03-2016, 15:46   #25
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Re: House bank upgrade verification

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Originally Posted by SailtheWind View Post
since my space only allow for the equivalent of three 12 v I want to make sure I end up with 12 v not 18v.
My house bank currently has four 6v batteries (Trojan T125) connected in serial and parallel giving me 12V and 480AH of capacity. I would like to increase my capacity to 720 AH. This require a total of six 6v @ 240AH each wired in parallel and serial.

Perhaps I'm missing something, but... if you only have physical space for three 12V batteries, first how did you get four 6V batteries in there, and second, how will that space accommodate six 6V batteries?

I know our space where three 12V Group 31s fit is actually just slightly larger enough (than the 3x G31s) so that it will actually accommodate four golf cart batteries.

But six seems like pushing it...

Unless I'm just not able to interpret what you're meaning...

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Old 29-03-2016, 17:53   #26
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Re: House bank upgrade verification

Quote:
Originally Posted by rom View Post
As I said I am no expert, and I am suggesting the OP to wait for other respectable forum members to chime in.

In the meantime, the general idea is that when charging 2 (say 6V) batt in series, if one is "tired" and will not reach 7.2V but only say 6.4V then the other one will reach 14.4V minus 6.4V (say 14.4V is the charger's absorption setting) , which makes 8V. Because overall voltage is voltage of batt1 plus voltage of batt2. And here we go, 8V will toast the second battery.
As a result series connection should be avoided as much as possible and a 3P2S config should be prefered over a 2S3P because it only has 1 serial connection instead of 3, but still provides the exact same capacity (Ah) and voltage.
So what happens if one battery gets tired in 3P2S config ? You might expect the other 2 in the group to provide a good enough average voltage that prevents the other group from toasting. Also you might plug two cheap voltmeter (one on each group) to monitor the whole pack. Monitoring a 2S3P config would require 6 voltmeter.

As for references, you might as well just google 3P2S vs 2S3P as I don't have any.
What your describing is a situation where a cell is partially shorted or otherwise damaged. This can happen in a 12v battery just as well as two 6v batteries in series.
With three 6v batteries in parallel the low battery will drag the two good batteries down to the same low voltage condition preventing three batteries from being charged properly.
I've never seen anyone recommend 3p2s before and honestly can't see any advantage to it. Anytime you have multiple batteries (cells) connected together you will have cell balancing concerns, luckily flooded lead acid batteries are tolerant of some imbalance.
Lithium batteries are intolerant of cell mismatches and that's why charging lithium batteries is more exacting. But we're talking about golf cart batteries here.
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Old 29-03-2016, 18:57   #27
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Re: House bank upgrade verification

maybe using 8D 12V batteries would cut the connections by ?

8Ds are awful heavy but you can get at least 10 years out of gels, so it's not like you lift them very often.
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Old 29-03-2016, 19:48   #28
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Re: House bank upgrade verification

It just moves the connections into the interior of the battery.
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Old 29-03-2016, 20:45   #29
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Re: House bank upgrade verification

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It just moves the connections into the interior of the battery.
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Old 30-03-2016, 15:13   #30
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Re: House bank upgrade verification

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Originally Posted by twinboat View Post
You are proposing creating two, 3 battery, 6 volt 675 AH battery packs and connecting them in series with one single jumper ?

That would create the need for 9 jumpers instead of 5, if I got what you are saying.

I have never heard of that configuration.

Anybody ?
Actually I am proposing to create three, 2 battery, 12volt 240AH battery packs and connecting them in series for a 12volt 720 AH house bank. I was just asking if I built what the drawing (post#1) shows will I achieve my goal?
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