using AGM and Lithium in separate banks on a sailboat

[Joe Delaney]

I have 2kw of rigid solar permanently installed and an additional 1kw of flex panels attached to a canvas that can be rolled out at anchor
2 midnite solar classic 150's MPPT's
6x 2v Blueriver 1150ah AGM's in series for a 12v bank

the system has run flawlessly for two years now since I first programmed everything and installed the AGM,s they ran me a little over 4k but they're really heavy for a sailboat. I am going to move them from the current location aft to just forward of the mast, which should help
thy rarely go below 70% and reach float on most days, running induction cooktops, electric convection oven, electric water heater, tv's fridge freezer etc. I'm pretty happy with it.
to run the AC I either need shorepower or to run the genset, 8kw diesel, can run everything and top up batteries after a few gloomy days.


But I want to run an air conditioning, I'm in Florida, So I've ordered 4 x 3.2v 400ah prismatic cellsto give me a 400ah lithium bank, as I understand it, it's best to keep these isolated from the AGM's
Here's my question: what is the best way to charge these two systems,
I could dedicate a Midnite solar to each bank and write a separate charge profile for the lithium and divide the solar
I could run all solar to one bank and charge the second bank from the first using a dc to dc programmable charger, in which case, which should be the primary bank?
my first thought is that as lithium accepts charge faster , it should be primary, even though it a lot smaller than the agm bank

I'd appreciate any opinions/input

it's my first post so go easy on me.

 

[Dauntless]

What the draw for you A/C?
How many hours do you expect a 400 AH bank can run it?

 

[RCinFLA]

I assume you have one of the Midnites on the 1KW array and other on 2K array.

I would not tie the AGM and LiFePO4 together, as I would not count on BMS current limit tolerance value, so I would probably just put 150A/15v capable A-Off-B switches on outputs of each Midnite. Some of the high current marine battery A-B switches are only designed for short duty cycle at high current for engine starting application so double check what you are buying.

Should avoid switching during high current so if you must switch during high current production you probably should open the PV panel line breakers into Midnite first, assuming they are running with much less line current.

 

[SVAvocet]

We are keeping our lithium house bank 12v 360ah and our one AGM 12v g31 starter battery separated and charge our Lithium bank through a 60a dc to dc charger. All our renewables have lithium science built in but I didn't want to have to replace our balmar alt regulator and our AC shore Battery charger. So Charging our lithiums is only from our two renogy mppt controllers with 200watt each of solar, and the DC to DC charger taking from our AGM starter battery and suppling the Lithium through 60a limit.
With your AC pulling so much power you might need something that can give more juice to the batteries other than a DC to DC charger. But keeping the 2 systems separated is not only cost efficient, but also keeps the batteries safe from accidentally overcharging since when Lithium are done charging they are DONE charging, unlike floating a L.A.
The last reason I did our system this way is that if we come into a third world country and say our Balmar Regulator stopped working, its much more common to be able to get a AGM, L.A. version vs a newer and more expensive Lithium compatible version, same for the AC Shore Battery charger.

 

[grizzzman]

Perhaps a Hybrid LFP/AGM system is in order. Look below if intrusted.

 

[Dauntless]

Avocet, I'm not clear why you did not reprogram your regulator.

 

[Dauntless]

Avocet, I'm not clear why you did not reprogram your regulator.

 

[SVAvocet]

Avocet, I'm not clear why you did not reprogram your regulator.

Didn't reprogram the alternator reg because it only has flooded and gel cell profiles. Not lithium compatible.

 

[Dauntless]

It's older than an ars 5?
I used the advanced program mode which allows one to set charging parameters in my ars-5.
Works great. In fact, more consistent than my mpp solar inverter charger.

Important for me, for when I'm cruising, I like moving every other day.