Replacing 12v FLA (450Ah) with 48v AGM (928 Ah) on my vessel

rwells36

CURRENT:
I have a pair of 8D parallel wired (450Ah) battery bank mated to a 2500 watt 12v 130A Inverter / Charger.

PROBLEM:
Amp hours are inadequate (supplies only about 1/2 of what is needed).

FUTURE:
I am taking delivery of eight (8) 116 Ah 12v AGM Group 31 FIREFY OASIS batteries that will replace the current inverter bank (above). These new batteries have a max charge rate of 250A (that's not a typo) they charge rapidly. Additionally, (3) new 315W 33.2Vmp, 9.5A 60 Cellsolar panels with MPPT 150/7012/24/48V-70A controller from Victorn will be installed.

VOLTAGE:
Using series wiring the new battery bank will be 48v with 232Ah mated to a new 2500 watt 48v Inverter / Charger.

QUESTION1: 
Would you recommend that the larger wiring for the 12v system be replaced?

QUESTION2: Given this set up should any steps be taken to mitigate or avoid uneven charging or discharging?

QUESTION3:
Did I leave out any bits of information needed to answer Question #1 or #2?

Comments from anyone with experience of either a) the Fire Fly batteries or b) moving from 12v to 48v is appreciated.

mike95490

So, this change is ONLY for the house battery and not the engine & marine electronics ?

While underway, how will the 48V bank be charged? 48V Alternator ?  12V engine system running inverter to power 48V charger ?

Your solar is completely inadequate  to recharge this large bank.  It will help maintain, but not much charge

I would not bother to change existing wire harness UNLESS it's showing corrosion damage.  Be sure to isolate the 48V system from the 12V system - don't try to be clever and tap your 12V loads off part of the bank, a couple months and you will be replacing the bank if you do that.

rwells36

Correct.

House 110v only (NOT marine electronics or pumps etc) that's serviced by an independent bank of 12v.

I have a 17kw generator aboard to charge beyond the solar. I can use my 24v alternator (D.C. - D.C. Converter) to augment the solar I suppose. My expectation was not much beyond maintenance

Estragon

Those batteries look interesting. A bit pricey, but if they stand up to deep discharges with good cycle like they claim, maybe they're worth it.

I would use beefy cables for interconnects (eg. 4/0) to minimize resistance, and take the 48v cable off diagonal (positive off the end of string 1, negative of string 2), or make the parallel connection with two short, beefy, equal length cables to a common point.

I'd also use the bigger 12v existing wire if it's in good shape. I would check for recommended breaker sizing for the new inverter though as the old one may be oversized.

Dave Angelini

Too many batteries in parallel but it is too late for that. As Estragon said on the 4/0 but if your AC loads are not much different than before you could go down to 2/0 if there is a 175 amp disco. There are ways to wire this that some might say are better but I would never do this unless long battery life did not matter.

AGM batteries are common to have high charge rates. They also are just about as efficient as flooded and do not have the ability to measure SG. Nice to not have maintenance as there is enough on a boat but a sanity check is not there with AGM.

Where are you going?

Estragon

If I'm understanding the setup correctly, it will be 2 parallel strings of 4x12v batteries in series for 48v. Two parallel strings should be ok?

If it was 8 parallel connections for 12v, that would be different. Potentially serious balance issue, need individual OCP devices, etc.

AGMs are nice on a boat for less gassing in a generally small enclosed space, and for low self-discharge if the boat is laid up in off season. That said, I'm about to replace mine with flooded.

Dave Angelini

It would have been better to use 6V batts in a single string but as Frank said, "that's life"
Also the thread is titled wrong, it really is a 232 AH bank @  48V