Reusing 12 x SLA batteries in series/parallel - which way is best?

[Podgyguy]

I currently have 12 x SuperBatt DT120 SLA batteries in 12V parallel. I know it's not good practice, please don't troll me lol.

Now I'm upgrading to 24V, I'm wondering which is the best way to re-configure the 12 SLA batteries so I can re-use them more effectively.

I'm planning to connect the bank to the Victron Power In (which can take 4 separate lines in).

There's a good post here from coalfield that describes 6 x batteries in series/parallel with midpoint balancing (referencing the Victron wiring pdf).

But what about 12 batteries?

Is it best to just extend the example to 12 batteries and have a single line in to the Victron Power In?

Or is it better to have multiple banks to the Victron Power In (either 2 banks of 6 batteries with midpoint balancing, or 3 banks of 4 batteries without midpoint balancing) with the main leads to the Power In of equal length?

Or is there a better method?

(Batteries all same Ah/age/etc.)

 

[MichaelK]

If you are switching voltages anyway, why not just graduate up to 48V. Then you can wire your 12 batteries 4S3P, which is a much better configuration than 2S6P.

 

[Podgyguy]

good point and I agree. but i want to re-use my existing 12/24v Renogy 40A controller (in fact getting another one to double up) and I have a 24V inverter lying around, and will add a few more panels.

so sticking with 24v for now as its cheaper, and gives me a better bang for the buck. 48v will come in a year or two hopefully as part of a much bigger upgrade

i've seen a ton of YT vids by now. lots of vids on series vs parallel. but can't find decent vids on building a much larger lead-acid system.

what's best practice? serialise each set of 2 batteries into a 48V cell first, and then parallel them all? or parellel 2 banks of 6 batteries and then serialise?

or have multiple banks going into the Power In individually?

thx for commenting!

 

[MichaelK]

what's best practice? serialise each set of 2 batteries into a 48V cell first, and then parallel them all? or parellel 2 banks of 6 batteries and then serialise?

I would wire the individual strings for 48V, and the parallel three of them. If one individual string gets unbalanced, you can disconnect the others to charge up the misbehaver.

 

[Podgyguy]

I would wire the individual strings for 48V...

Thanks for that. btw I made a typo on my question above, i meant 24v not 48v but i get where you're coming from.

I did the two main options as a diagram and it's becoming clearer well a little anyway maybe ... seems both options are equal on pros/cons ... option 1 is more simple whereas option 2 has more cabling but allows me to isolate each bank with a breaker before they "parallel" on the Victron Power-In bus bar - (assume main leads to Power In all same size). I don't see any other difference in the balancing as option 1 has midpoint balancing, so as I understand it, both as as good as each other?

If one individual string gets unbalanced, you can disconnect the others to charge up the misbehaver.

I'm guessing you might be more in favour of option 2?

Appreciate the inputs! ?

 

[MichaelK]

I'm guessing you might be more in favor of option 2?

Yes. Keep in mind that for best balance, all the positive and negative leads coming out of the blue "Power In" box should be exactly the same length, so their resistances are the same.

 

[Podgyguy]

Thanks for that, great to get the thumbs up! I'll go with option 2 then

Not sure how to refer to this layout - I can wire it no probs, but I have yet to fully get to grips with the nomenclature (xSxP, xPxS, etc). If I understand correctly, it's read from 'right to left' referring to 'inside to outside'.

So option 2 would be described as a 3P2P2S? whoa hang on, that doesn't look right

 

[MichaelK]

So option 2 would be described as a 3P2P2S? whoa hang on, that doesn't look right

No. Just 2S6P. Each of the six parallel strings is equal to each other.

 

[Podgyguy]

Many thanks very helpful ?