I bought four 6V AGMs. Evidently I'll be doing parallel + series to get to 12V, but I'm wondering if it makes any practical difference whether I wire each pair in series (to get a pair of 12V batteries, effectively) - and then wire those in parallel, or whether I should wire each pair in parallel (giving 6V pairs) and then wire those in series?I guess I'm wondering if it makes a difference in terms of balance, basically.Is there an ideal wiring diagram out there? The batteries are the type with offset terminals (i.e., terminals are in diagonally opposite corners).

That diagram is out of electrical balance.Use this:

smkettner wrote:That diagram is out of electrical balance.Use this: I am constantly amazed....although I probably shouldn't be, having done this forum thing for decades.......Your diagram is electrically identical to the previous one.What exactly do you think is "out of balance" about it ??Hint: NOTHING.

Vulcan Rider wrote:smkettner wrote:That diagram is out of electrical balance.Use this: I am constantly amazed....although I probably shouldn't be, having done this forum thing for decades.......Your diagram is electrically identical to the previous one.What exactly do you think is "out of balance" about it ??Hint: NOTHING.Depends on what you consider "out of balance".Do both supply 12 volt power? YesHowever, will both draw equally from BOTH sets of batteries, having equal lengths of wire? NOThe second is slightly better, as it pulls equally from both sets, thus "in balance".

Series/parallel is the way to achieve balanced draw from all batteries.That type of connection will also double the usable capacity, amp hours.

Parallel then series, or the other way around? | Good Sam Community

43 Replies

LScamper
Explorer
Aug 24, 2015
"You didn't doubt Kirchhoff, did ya?"

Kirchhoff is never wrong, but at my age my math is!
Salvo
Explorer
Aug 23, 2015
Cool.

You didn't doubt Kirchhoff, did ya?
LScamper
Explorer
Aug 23, 2015
Spice circuit simulation confirming Salvo's calculations. 105 Amp constant current load. Also tried to simulate Amp hours and state of charge vs time. The vertical scale should be Amp, Amp hours and percent state of charge not volts as is shown. The horizontal axis is in seconds. 3600 seconds is one hour. The colors may not show up very well, but I tried.

Amps

Amp hours

State of Charge
2oldman
Explorer II
Aug 23, 2015
Salvo wrote:
These are not readings, but calculations, based on Kirchhoff's circuit laws..
oh
time2roll
Nomad
Aug 23, 2015
Need to verify with a clamp-on ammeter.
Salvo
Explorer
Aug 23, 2015
These are not readings, but calculations, based on Kirchhoff's circuit laws.

I can imaging charging will give similar results. The good news, Bat4 will get the most attention.
2oldman
Explorer II
Aug 23, 2015
Interesting, thanks. I wonder how charging fares? And of course you also took readings after balancing the bank? :)
Salvo
Explorer
Aug 23, 2015
Got it at my fingertips...

Load current = 11.2A

Bat1 = 2.4A
Bat2 = 2.6A
Bat3 = 2.9A
Bat4 = 3.2A
2oldman
Explorer II
Aug 23, 2015
Salvo wrote:
The bank is loaded with 105A.
Did you ever do that same test with a much lower load?
Ductape
Explorer
Aug 23, 2015
I did mine in two separate banks; each one a series pair. Selector switch so I can do A or B or both. Makes it easy to stir the electrolyte if I hit just one bank with high charge current. You'll want to read all about that some day on the AGM charging threads. ;)

And balanced cable lengths too. Why not, after all?