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Old 01-13-2021, 09:44 PM   #1
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Two Strings of 12v - Battery Question

A few moons ago, we were discussing battery configurations when I came upon a post where it was stated that two strings of 2-12v batteries wired in parallel and brought together at a common junction point was more effective than wiring all 4 in parallel. I believe that post came from Chance and sincerely apologize if that's incorrect and hoping it may help you recall it too.

I searched '2 strings' and 'two strings', quotes included, and be it far from me to locate that post again.

Reason I ask: my parents had their RV in for service. I commissioned the shop to replace their small two-battery battery box with two new boxes that hold 2-12v GR27DC wet cells (4 batts in all). The RV is a combination horse trailer/RV (Sundowner Cherokee). All of their camping is equine and they almost exclusively dry camp. Their getting up there in years and loading their 5kw generator in the back of their truck is becoming a little taxing, though depending on the length of their stay may still be unavoidable. Solar is in my head but that may be a next step. I have to see if they like this and use it before taking them down that road.

The new boxes are mounted externally in an over and under configuration to accommodate a 4-12v parallel design if what I remembered was wrong. I also had them install a 1000w inverter and a battery monitor. They installed a 4-way switch - string A, string B both and off. This is all intended as an introduction to more independence from their generator. If they like it and use it, I'll introduce them to solar.

Can someone resurrect that post and/or answer the following question:

If they use only one string at a time, they're limited to 105ah of consumable energy if they follow the rules. If they use 'both' does it still give them the 210ah or is that negated by the 2 string design? My recommendation to them, based on what I remember. would be to set the switch to 'both'. In addition, if they need the generator, I believe the switch would have to be in the 'both' position to charge the entire bank (the way it's wired).

If I left out a critical piece of info, please let me know. I will get it.

TIA

Simple specs:
12v deep cycler RV/Marine
Wet cell
105ah per (420 total, 210 usable)

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Old 01-13-2021, 10:08 PM   #2
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Quote:
Originally Posted by The_Breeze View Post
A few moons ago, we were discussing battery configurations when I came upon a post where it was stated that two strings of 2-12v batteries wired in parallel and brought together at a common junction point was more effective than wiring all 4 in parallel. I believe that post came from Chance and sincerely apologize if that's incorrect and hoping it may help you recall it too.

I searched '2 strings' and 'two strings', quotes included, and be it far from me to locate that post again.

Reason I ask: my parents had their RV in for service. I commissioned the shop to replace their small two-battery battery box with two new boxes that hold 2-12v GR27DC wet cells (4 batts in all). The RV is a combination horse trailer/RV (Sundowner Cherokee). All of their camping is equine and they almost exclusively dry camp. Their getting up there in years and loading their 5kw generator in the back of their truck is becoming a little taxing, though depending on the length of their stay may still be unavoidable. Solar is in my head but that may be a next step. I have to see if they like this and use it before taking them down that road.

The new boxes are mounted externally in an over and under configuration to accommodate a 4-12v parallel design if what I remembered was wrong. I also had them install a 1000w inverter and a battery monitor. They installed a 4-way switch - string A, string B both and off. This is all intended as an introduction to more independence from their generator. If they like it and use it, I'll introduce them to solar.

Can someone resurrect that post and/or answer the following question:

If they use only one string at a time, they're limited to 105ah of consumable energy if they follow the rules. If they use 'both' does it still give them the 210ah or is that negated by the 2 string design? My recommendation to them, based on what I remember. would be to set the switch to 'both'. In addition, if they need the generator, I believe the switch would have to be in the 'both' position to charge the entire bank (the way it's wired).

If I left out a critical piece of info, please let me know. I will get it.

TIA

Simple specs:
12v deep cycler RV/Marine
Wet cell
105ah per (420 total, 210 usable)
The only thing the two string theory does is split the 4 parallel batteries into two banks of 2 parallel batteries. The total available AHs don't change and depending on the cable lengths, it may actually be less efficient due to the resistance losses in the cable.

But you have the operation of your switch correct and it does give you some redundancy in 12 VDC power supply and a better handle on remaining AHs left by using it to split the banks when dry camping.
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Old 01-13-2021, 10:11 PM   #3
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The attached image shows various ways

To get a balanced load charging the upper left hand if the best way and simplest
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Old 01-13-2021, 10:27 PM   #4
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Originally Posted by The_Breeze View Post
A few moons ago, we were discussing battery configurations when I came upon a post where it was stated that two strings of 2-12v batteries wired in parallel and brought together at a common junction point was more effective than wiring all 4 in parallel. I believe that post came from Chance and sincerely apologize if that's incorrect and hoping it may help you recall it too.

......cut.....

That is not what I said. I said most experts do not recommend wiring 4 X 12-Volt lead-based batteries in parallel when you have other options.

What you describe above solves nothing it is still four 12-Volt batteries in parallel.

If I recall correctly, I added that lithium batteries are an exception. Four are commonly wired in parallel.
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Old 01-14-2021, 12:24 AM   #5
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And as usual, the brains in this outfit prevail. I'm sure JamieGeek will come online later

Thank you VERY much!
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Old 01-14-2021, 12:26 AM   #6
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Originally Posted by lwmcguire View Post
The attached image shows various ways

To get a balanced load charging the upper left hand if the best way and simplest
Love it. TY
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Old 01-14-2021, 12:29 AM   #7
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Quote:
Originally Posted by Chance View Post
That is not what I said. I said most experts do not recommend wiring 4 X 12-Volt lead-based batteries in parallel when you have other options.

What you describe above solves nothing it is still four 12-Volt batteries in parallel.

If I recall correctly, I added that lithium batteries are an exception. Four are commonly wired in parallel.
And why I reposed the question. I doubted my interpretation and called myself into question. Thanks for the clarification. I wish I could have found the original citation but alas.
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Old 01-14-2021, 04:00 PM   #8
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Quote:
Originally Posted by Chance View Post
That is not what I said. I said most experts do not recommend wiring 4 X 12-Volt lead-based batteries in parallel when you have other options.

What you describe above solves nothing it is still four 12-Volt batteries in parallel.

If I recall correctly, I added that lithium batteries are an exception. Four are commonly wired in parallel.
Found that thread. Bookmarked. You indeed call out three types - 6v, 12v and lithium as well as the string design.
https://www.thorforums.com/forums/sh...7&postcount=11
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Old 01-14-2021, 05:52 PM   #9
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Thank you. I understand the 4x6v. But Im ignorant about parallel vs. series. Im assuming the wiring for the 4x6v is as per lwmcguires diagram above? (Pictures are a big help for me. Thanks again)
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Old 01-14-2021, 06:02 PM   #10
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Originally Posted by droregon View Post
Thank you. I understand the 4x6v. But I’m ignorant about parallel vs. series. I’m assuming the wiring for the 4x6v is as per lwmcguire’s diagram above? (Pictures are a big help for me. Thanks again)
Before repeating everything that's been said before, try referencing the above URL in the previous post. Most of the brain trust on this site weighed in to answer my questions and they provided a wealth of information.

If you still have questions after that, circle back and I'm sure folks out here will be more than happy to clarify.

Quickly put: series doubles volts, parallel doubles amp hours. That previous post goes into much greater detail and I honestly think it should help.

Let us know how you make out.

p.s. LMC's diagram is your best bet for a wiring diagram. It shows proper wiring and the best setups for equal charging.
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