I've read Para 3.2 of the manual for the LIFePO4 Smart Lithium Batteries. I understand why it is OK to do a first charge of a group of batteries if they are in parallel.
I haven't figured out why the recommended charging rate for the group of batteries being charged for the first time, in parallel, is C/20, where C is the value for one of the batteries, not for the group of batteries. I think I know, but I'd like to know the official answer. :-)
The problem with this recommendation is the amount of time it will take to bring three 12.8V/300Ah Smart Lithium Batteries up to full charge, starting from their delivery State of Charge of 50% or less, and then hold it there for 'an absorption period of several hours at 14.2V', all at a charging output from a MultiPlus of no more than 15 amps! Can the Multi be reigned back like that? Perhaps the Cerbo can control it.
Please tell me if my maths is right:
300Ah x 3 = 900Ah x 50% = 450 Amps of charging for 1 hour to fill the three batteries, or
450Ah / 15A = 30 hours + 5 hours of absorption @14.2V for balancing of cells = 35 hours.
Do you agree that I need to allocate ~35 hours for the initial charging, done for the three batteries simultaneously, in parallel? To save time (and because we need to launch the boat and move it to a marina berth) this is likely to be done in two blocks of hours; first for five hours on the MultiPlus, then a break for an hour during launch, then motoring with the alternator's charge limited to 50 amps for up to 30 minutes. Then we'll recommence the MultiPlus charging, at 15A, until the batteries reach full charge and have their 'several' hours of balancing. All with me sitting on them like a mother hen.
I don't imagine the short period of throttled back alternator charging at three times the C/20 rate will do any damage, but do tell if you think differently.
I am keen to get these batteries off to a very good start. They cost a bomb!
