Swapping Out Trojan T105 House Bank for FireFly L15+ Bank

[Boatcrazy]

Following. We're currently using 6 T105s for a house bank, and like you, we need to keep them in the current compartment.

 

[rolomart3]

I'm swapping out my existing 12v house bank (six Trojan GC2s in 3P2S) for six FireFly L15+s in either (12v) 6S2P or 2P6S configuration.

Background: FF L15+s are interesting in that each battery consists of 2 x 450Ah/2v cells that can be set up in either series or parallel configuration. This allows using the same six L15+s to set up either a 12v/900Ah or 24v/450Ah bank.

I'm looking for input here first on which 12v FF configuration (6S2P or 2P6S) to set up before I confirm with the factory, Schwab, etc. The 6S2P (see drawing of Old Bank and New Bank together) is much neater than 2P6S config (see Alternate configuration drawing), but maybe the 2P6S is better for some reason?

The batteries must go in the box as shown for the old T105 and new FF L15+ footprints to match.

If I interpreted your diagrams correctly, there seems to be no problem. The confusion arises because inside each rectangle you are referencing two separate 2-volt batteries.

 

[eheffa]

I put a set of 6 12V firefly batteries into our Nordic Tug 37 a year ago for 660 Ah total.

So far they have worked very well. They have a flatter voltage curve than the previous AGM’s ( I.e. dropping to 12.7 V pretty quickly but then staying there a good while) They tolerate draws down to 40% capacity without any difficulty keeping voltages north of 12.2V.

With Solar charging and a desire to keep generator runs to a shorter duration, the Fireflies (in theory) allow one to get back to 90% SOC and not be damaging the bank.

So far I'm very pleased and have not seen a degradation in performance but I will need a few more years before I can be definite.

-evan


Here's a link to the Wiring Diagram and Pic of installation

https://eheffa.zenfolio.com/p513003349/ea11ea0ee
https://eheffa.zenfolio.com/p513003349/e9f13d85c

 

[Wil]

Each FF L15+ battery indeed does consist of 2 x 2v cells that can be wired in series or parallel.

The confusion arises because inside each rectangle you are referencing two separate 2-volt batteries.

 

[Wil]

Thanks for the example, nice to hear they're providing good service to date. Your six FF G31s are 12v each, you paralleled them all up. My six FF L15+s are a max of 4v each, so require a series-parallel setup. Actually could go with the six 2v version (2P6S), but the 6S2P version has the advantage imo.

I put a set of 6 12V firefly batteries into our Nordic Tug 37 a year ago for 660 Ah total.

So far they have worked very well. They have a flatter voltage curve than the previous AGM’s ( I.e. dropping to 12.7 V pretty quickly but then staying there a good while) They tolerate draws down to 40% capacity without any difficulty keeping voltages north of 12.2V.

With Solar charging and a desire to keep generator runs to a shorter duration, the Fireflies (in theory) allow one to get back to 90% SOC and not be damaging the bank.

So far I'm very pleased and have not seen a degradation in performance but I will need a few more years before I can be definite.

-evan


Here's a link to the Wiring Diagram and Pic of installation

https://eheffa.zenfolio.com/p513003349/ea11ea0ee
https://eheffa.zenfolio.com/p513003349/e9f13d85c