For anyone interested......
Last year my lead acid batteries died, so decided to spend big on Lithium, or LiFePo to be exact, this flavour of chemistry seems the safest and most forgiving of them all. $4500 later, they arrived.
First problem was the placement. Like me, these things dont like low temperatures, we are talking minus something, so I placed them inside the hovel to keep them warm. The generator shed being 30 feet away gave voltage drop issues with the 100 or so amps charging current. This caused havoc with the alternators seeing over 18 volts at their output terminals.
I cured this by running independent sense wires, directly from the battery terminals back to the power shed, allowing the over voltage regulator to work correctly, it now reads the actual battery voltage and not the alternator output.
The maximum terminal charge voltage of the batteries is 14.7 volts, anything higher will damage the chemistry.
Here I simply designed a high voltage cutoff using a LM311 voltage comparator that switches off the alternator field current when the battery voltage reaches 14 volts... plenty, as the Lister is only used as the backup when the solar fails..
The main charging voltage comes from 800 watts of solar panels. The MPPT controller will switch of at 14.6 volts, this means the bank is full.
Here is the schematic of the car alternator control when I remember how to do this picture posting thing.....
These old car alternators are modified by removing the internal regulator and connecting one brush to ground, the other to a wire into the controller.
I then wondered about these Battery Management Systems built into these Lithium packs.
After reverse engineering one sample, I could not see how they can "balance" each cell with just a 100 milliamp draw, when each cell has a capacity of 600 amp hours..... it would have zero effect.
Firstly, I decided to establish if these Lithium cells actually do get out of whack with each other, they cannot be equalised as a lead acid bank can, this would overcook the highest cell. Is this an actual problem, or just an internet theory, steeped in myth and confusion.
I removed the BMS.
After nearly a year, the cells are within 3/10ths of a volt, highest to lowest, so unless I am extremely lucky, very unlikely, the balancing thing appears not to be the issue its made out to be. So, to simplify matters, we leave out the BMS.
It it also important not to discharge these LiFePos to less than aound 10.7 volts. This apparently causes permanent damage.
This requirement is easily met , almost all inverters will automatically disconnect at around 11 volts.
The difference with Lithium to lead acid is night and day, with a charge absorption efficiency approaching 95 percent, no sulphation or gassing..... no watering, no stress, just set and forget.