House bank upgrade verification

[SailtheWind]

Call for verification
I have searched CF for answers but I have not been able to discover the one that I need. It seems like the threads I found only discuss even numbers of 6 or 12 v batteries, 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. I want to confirm that the drawing below will provide me with the desired outcome: 12 v at 720Ah
Yes all the batteries will be new and there is a separate 12v starter battery for the engine.

Battery A positive to load
Battery A positive to Battery B positive
Battery B positive to Battery C positive
Battery D positive to Battery A negative
Battery E positive to Battery B negative
Battery F positive to Battery C negative
Battery D negative to Battery E negative
Battery E negative to Battery F negative
Battery F negative to ground

Drawing.pdf

[tenchiki]

That looks good to me, you've followed the general principles just fine. How old are the existing batteries? Mixing new & old can be problematic.
My gut feel is to put the new ones in the middle to start with. Periodically physically rotating the batteries (so different ones are in the middle) might increase the longevity of your batteries.

[twinboat]

The drawing looks fine. You will have 12 volts from your 6 new batteries.

[SailtheWind]

Originally Posted by tenchiki

That looks good to me, you've followed the general principles just fine. How old are the existing batteries? Mixing new & old can be problematic.
My gut feel is to put the new ones in the middle to start with. Periodically physically rotating the batteries (so different ones are in the middle) might increase the longevity of your batteries.

Thank you for the tip of putting new batteries in the middle however I am planning to replace the existing four batteries with six new ones.

[guyrj33]

Looks correct to me, you've been careful to keep the cable paths the same length for each battery and each pair of batteries. Should work flawlessly.

[DeanMac]

Hi,
What size cables are you using to connect the batteries?
Thanks,
Dean

[rom]

I believe your diagram shows what's called a 3S3P configuration where you should probably use a 3P2S config. That is, *2 packs* of *3 batts in parallel* that are then connected in series. The idea is that you will then get only one serial connection instead of three which is admitted to be better as it makes it simplier to check proper balance and reduces the risk of toasting other batteries if one happens to fail.
There are at least 3 experts on the subject on this forum, you might want to wait a little bit for their confirmation.

[SailtheWind]

Originally Posted by DeanMac

Hi,
What size cables are you using to connect the batteries?
Thanks,
Dean

Your question raise a question mark for me. I had planned to use a heavier gauge either 3/0 or 4/0 for the long run positive and ground. The question I how have is can I use two different gauge. Gauge 2 for the short run between the batteries and the 3/0 or 4/0 for the long run. Can I mix various gauge or do I have to use the heavy gauge for the complete installation?
I am curious to hear the correct answer.

[seabreez]

The question I how have is can I use two different gauge. Gauge 2 for the short run between the batteries and the 3/0 or 4/0 for the long run. Can I mix various gauge or do I have to use the heavy gauge for the complete installation?

I usually go one step up in size and have the same size all over. I make my own cables. I solder mine. Use lugs of the proper size. Heat shrink at the ends. Coat with rubber paint to prevent corrosion.

[Stu Jackson]

Originally Posted by SailtheWind

Your question raise a question mark for me. I had planned to use a heavier gauge either 3/0 or 4/0 for the long run positive and ground.

What loads, distances and/or charging sources can you possibly have on a 38 foot boat that would require wires of that size for a house bank?

[smac999]

It seems like the threads I found only discuss even numbers of 6 or 12 v batteries, since my space only allow for the equivalent of three 12 v I want to make sure I end up with 12 v

I don't understand... 6 is an even number. and will take the space of 6 12v car batteries.

[smac999]

Originally Posted by Stu Jackson

What loads, distances and/or charging sources can you possibly have on a 38 foot boat that would require wires of that size for a house bank?

most 30-40' boats I wire are with 8 golf carts and either 2/0 or 4/0 main wiring. depending if running 2000 or 3000w inverters.


I normally run all jumpers in the same size. it's not like it's much more money when they are so short.


you can't run 2awg for all of them if you are running 4/0 off of it. some of the jumpers are running 2/3's the current. (2awg can't handle 2/3's of 4/0) and some are 1/3 the current.

[twinboat]

Originally Posted by rom

I believe your diagram shows what's called a 3S3P configuration where you should probably use a 3P2S config. That is, *2 packs* of *3 batts in parallel* that are then connected in series. The idea is that you will then get only one serial connection instead of three which is admitted to be better as it makes it simplier to check proper balance and reduces the risk of toasting other batteries if one happens to fail.
There are at least 3 experts on the subject on this forum, you might want to wait a little bit for their confirmation.

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 ?

[rom]

Originally Posted by twinboat

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 ?

Yes correct, except it's 9 jumpers instead of 7, not 5. But there is more at stake here than just a number of jumpers and one needs to understand the difference between one serial link versus 3. Here is a diagram that shows what it looks like. cheers.

Edit: the diagram proposes a permutation that simplifies the view and also shortens all jumpers. It might not suit that particular boat.

Edit 2: sorry just realized your Ah is incorrect. That's 2 packs of 720 Ah @ 6v !

[seabreez]

I have never heard of that configuration.

Anybody ?[/QUOTE]

The original drawing is ok