Charging Nissan leaf cells with LiFePO4 Charger
I have recently added Nissan leaf cells to an ERIDER 8000W scooter. I am using a ZEVA BMS to monitor charging of 10 Nissan leaf batteries (20 cells x 4.2V = 84V HVC) using a charger designed for 24 x 3.65V = 87.6V HVC Lithium Iron Phosphate cells. The charger constantly charges at 20A or C/3 for the 60 AH Nissan cells until the end of charge signal from the BMS trips the relay and stops the charger. Is it OK to charge at full current right up to the 4.2V high voltage cutoff ?. Most lithium battery chargers appear to reduce current for the last 10-15% of the charging process. I am limiting the cells to 4.1V at present until I get this sorted out but would like to get the last 10-15% of battery capacity.
As you already noted your LiFePO4 charger would switch from CC to CV stage when the batteriy reaches 87.6V. But with the 10 Leaf modules you can never reach that voltage as your BMS shuts off charging when the battery reaches only 84V. Your charger would have to be tuned down to 84V for it to switch to CV stage, if that is possible at all...
Apparently when in the Nissan Leaf, the cells are only charged to 4.1V to maximise battery life. I don't know if this is with CC and then CV charging but I suspect it is. This is about 90% of full charge.
When I charge at CC to 4.1V am I achieving 90% of full charge. I suspect not as I have CC charged a couple of times to 4.15V and this gives 10% extra capacity. My question is if I CC charge to 4.2V will the batteries still be not fully charged and likely to last longer?. My charger is not adjustible so I can't reduce HVC.
you do lose a little capacity charging CC to 4.1v as opposed to cc-cv to 4.1v
you could get around that by just doing cc to 4.15v, or accepting the slightly lower capacity
when the highest cell reaches 4.1v, what's the lowest cell voltage?
When highest cell reaches 4.1 volts lowest cell is close say 4.07-4.08.
I have hacked the charger as detailed in the post:
and managed to reduce HVC to about 84V. Excellent.