LiFePO4 does not store energy as a chemical reaction, it works like an ion capacitor. As such it does not need to spend time doing absorption, which is a time consuming reaction that is needed with lead acid and the like.
Once the charging target voltage is reached it is meaningless to continue (and can cause damage). Ideally the float voltage voltage is reduced to the battery rest voltage, which is 3.3V per cell.
The CC charge rate in my case is a function of solar power. So if I have 1A from the charger with full sun on PV and want to be able to save 4hr worth of that solar energy I need at least a 4Ahr sized battery, and that gives charge rate of C/4. I must also verify if the battery can take that charge rate, e.g. lead-acid is limited to about C/10, but LiFePO4 is often rated above 1C and some are 20C and over.
Half of a TPS3700 Window Comparator is used to set a latch when a cell gets to 3.65V that will hold the charger at the 6V6 rest voltage. The latch resets when the solar voltage drops.
The IO is true while each cell voltage is > 2.95V.
When the PV (10V) goes above 11V (yellow led) it will allow the latch to hold the reduced rest voltage.
These ideas are being explored for CC02
http://epccs.org/indexes/Board/CC02/
