Firefly L16 Bank Configuration

My house bank (six T-105+) died, so looking at six Firefly L15/L16 2v-900Ah/4v-450Ah batteries to replace it. Change the regulator and inverter/charger from FLA to AGM, good to go. They'll fit in the battery box nicely (height is Ok), and upgrade charge/discharge/PSOC/AmpHr performance. Spendy though.

These batteries are interesting in that each one can be changed to 2v/900Ah (parallel) or 4v/450Ah (series) configuration. This would allow change to a 24v system with only strap changes, something to do down the road. Attached is a top view of one in 4v series configuration (though missing one strap).

I'm still learning wrt configuring a battery bank, came up with two ways to do these (see pdf). Example 1 would be a 6S2P configuration, Example 2 would be a 2P6S configuration.

Questions:
1) Did I get the terminology right for those configurations?
2) Are those two configurations electrically correct?
3) Is one configuration better than the other for best charge/discharge distribution?
4) I believe both configurations result in a 12v/900Ah bank?
5) Is there another configuration that would be better?

Example 2 is correct, and is 2P6S, or in long hand 2 parallel batteries, then 6 of those in series.


Example 1 is shorted out all over the place. See marked up attachment.

twistedtree said:

Example 2 is correct, and is 2P6S, or in long hand 2 parallel batteries, then 6 of those in series.


Example 1 is shorted out all over the place. See marked up attachment.

Click to expand...

I thought the better wiring diagram (from your note) was to take the power off the center of the parallel wiring system. I don't recall where I read it, but they said optimal would be parallel with center loading. is my memory failing me?

On example 2, it makes a difference which way you turn the batteries. If the cells in each are left and right, it is correct. If the cells in each are up and down, half of them will be charged and discharged slightly less than the others.

In a parallel arrangement you want to wire it such that equal current flows through all the cells, taking into account possible voltage drops in the connections. There are numerous explanations of this in the literature. Take the positive from on side of the parallel structure, and the negative from the other side.

Have you asked Bruce Schwab for his feedback?

TT, thank you, I see where my 'series' thinking went awry. Better shorted-out on paper. Attached is the revised drawing.

twistedtree said:

Example 2 is correct, and is 2P6S, or in long hand 2 parallel batteries, then 6 of those in series.

Example 1 is shorted out all over the place. See marked up attachment.

Click to expand...

Wil said:

TT, thank you, I see where my 'series' thinking went awry. Better shorted-out on paper. Attached is the revised drawing.

Click to expand...

Much better.

The cells are oriented 'up & down', not 'left & right' when looking down at the top of the cell. It doesn't look to me that circuit would work at all if the cells were oriented 'left & right'.

DDW said:

On example 2, it makes a difference which way you turn the batteries. If the cells in each are left and right, it is correct. If the cells in each are up and down, half of them will be charged and discharged slightly less than the others.

Click to expand...

I've been doing my reading and understand the concept of spreading the charge/discharge current equally over all batteries. What I'm still figuring out is just how to do that using the 2P6S drawing in my last msg.

DDW said:

In a parallel arrangement you want to wire it such that equal current flows through all the cells, taking into account possible voltage drops in the connections. There are numerous explanations of this in the literature. Take the positive from on side of the parallel structure, and the negative from the other side.

Click to expand...

I don't want to waste busy professionals like Mr. Schwab's time educating me on basic concepts. That's where forums like TF are valuable--to give the beginner a big headstart, if they're willing to read and ask hopefully intelligent questions.

Moonfish said:

Have you asked Bruce Schwab for his feedback?

Click to expand...

After studying the two (now correct, thanks) 6S2P & 2P6S drawings, it seems to me that the 6S2P configuration is more desirable because the connections are simpler, and the charge/discharge current is more evenly spread through the batteries. Negative is at one end, and positive is at the other end of the bank.

The 2P6S configuration is looking a bit Heath Robinson, due to all the extra connections. ....And I still haven't quite figured out how charge is distributed through this configuration of bank...

Does that make sense?

View attachment 12v Firefly Connection Possibilities Revised.pdf

I'd agree. An easy way to check if your battery wiring is reasonably balanced is to count the number of connections current has to flow through for each battery. If they are the same or close, you are in good shape. Also, keep the positive/negative supply cable lengths similar, not the way you have drawn them.

Wil said:

I don't want to waste busy professionals like Mr. Schwab's time educating me on basic concepts. That's where forums like TF are valuable--to give the beginner a big headstart, if they're willing to read and ask hopefully intelligent questions.

Click to expand...

Excellent point, and wise use of the knowledge here!

Good tip, thanks. I am aware of cable lengths in assuring charge balance.

gsholz said:

I'd agree. An easy way to check if your battery wiring is reasonably balanced is to count the number of connections current has to flow through for each battery. If they are the same or close, you are in good shape. Also, keep the positive/negative supply cable lengths similar, not the way you have drawn them.

Click to expand...

Thanks!

Moonfish said:

Excellent point, and wise use of the knowledge here!

Click to expand...