Originally Posted by The_Breeze
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.
12v deep cycler RV/Marine
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.