Delfin, I'm really intrigued by this.
Few questions please:
1) Which Lithionics batteries in what configuration do you have?
2) I gather the same AGM alternator regulator(s), and AGM battery charger(s) remain in place. Do they have settings for LFP also, or do their charge settings remain on AGM type batteries?
3) What model regulator(s) and charger(s) do you have?
2 X 300 amp 24vdc Lithionics
Lithionics battery management system
Balmar 624 regulator
Ample Power 130 amp 24vdc alternator, throttled to 100 amps via Balmar amp manager
Trace 4000 charger/inverter, 100 amps
Blue Seas battery combiner - no combine, auto combine and manual combine
Link 2000 battery monitor
My management of this bank is based on just one man's opinion on what seems to work well for us when cruising, and I suspect that as with anchors there will be other opinions on how I should be doing it. Be that as it may, the agonizing over chargers, regulators and alternators that are matched to the Li chemistry seems like a waste of time to me. This is because of the way the batteries charge, and the fact that they have so little internal resistance, so floating them as if they were a different chemistry can be harmful. When charging, and regardless of the state of discharge, the batts will accept a significant portion of their capacity in current while charging, so some folks increase the charging capacity of their vessels to take advantage of this. However, in our case, we use around 300 amps per day, so if I am recharging the batts with the alternator only, the job gets done in 3 hours or so. If we are staying put at anchor for a day or two, we'll run the genset and recharge in about the same amount of time, while doing laundry, making water, etc. If we want to recharge quickly and are going somewhere, we charge from both sources and they are full in an hour and a half, more or less. So, spending money and space on adding charging capacity doesn't seem like it has any pay off, at least for us.
I have both the Balmar and Trace charger set to output 28.8 volts for 4 hours. Why? Because I treat these batts like a fuel tank, not a Pb battery, meaning I put current to them until the acceptance rate drops to 5% or so of capacity, then disconnect them from the charging source via the BMS if we are underway, or turn off the genset if we are at anchor. When we start charging, the voltage rises very quickly to 27 - 27.1 volts, and stays there until the last 5 to 10 minutes of the charging cycle. During that period, the voltage rises quickly, as in .1 volts every few seconds. If I am asleep at the switch, the max current is 28.8 volts, which won't hurt them. If something goes wrong, the Lithionics BMS will shunt the current at 29.2 volts so no harm is done, and after 4 hours the regulator and genset charger drop the voltage output to 26.8 volts, which still isn't ideal for Li chemistry but isn't going to cause much harm either. However, you can set your watch on when the batteries will be full because if you throw 100 amps to them, they will accept 100 amps. Used 300 amps? 3 hours later, they are full, and you turn off the charging sources, just like you would close the nozzle when refueling and the tanks are full. Pretty simple.
The advantage of this chemistry is both in the flat and very high acceptance rate when charging, but also the flat voltage curve when discharging. You get 25.6 volts minimum right up until they are 80% discharged. Since I recharge at around 50% capacity, I never see less than 26 volts even under normal house loads. In fact, at 26.4 volts with no or very minimal load, you have no idea what state of charge the batteries are at. They could 20% discharged or 70% discharged, so their ability to deliver stable voltage through a good chunk of their capacity means you have to count amps to know where you're at, which we do with the Link 2000. I can't say it is completely accurate, but it seems in the ballpark.
When we return to shore power for weeks, I'll leave the batteries at around 65% charge, which they prefer.
Hope that helps.
