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Charging LifePo4 batteries with an AC charger and Charge controller

harpo

Good at many things, master of none
Joined
Oct 1, 2019
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98
Location
PA, FL
Ok, I have read a number of discussions hear on charging parameters for Lithium Iron Phosphate but none really answer my questions. Hopefully, someone can succinctly answer them.
First, as I understand it, LifePO4 batteries should be charged at a constant voltage. No need for the three stage charging I have done with AGM. Is this correct?

Secondly, if that is the case and I want to charge my 12v LifePO4 battery pack to 90%, what voltage should my charging systems by set at? First the AC charger (if I can get a charger to charge at a constant voltage only) and secondly, my MPPT charge controller.

It seems universal that if one stays in a discharge range between 10 and 90% of SOC that battery life will be optimized. How is this best accomplished using both methods of charging indicated above?

Thanks in advance. Any links on the subject appreciated.
 
3 stage is indeed not needed. 2 stage will do.

You can use 3-stage, but you have to make sure the floating voltage isn't set too high to prevent overcharging.
Best practice with LFP is charge with CC/CV till 14.2-14.6V depending on your preferences, and stop charging once finished, no float (unlike lead-acid which loves to be topped-up at 100% all times, thus requiring float to maintain its high SOC)

What's the capacity of your bank? Meanwell provides nice and affordable chargers. The higher models can be switched to 2-stage charging as well.

For example the PB-600P is a 40A charger with 2-stage setting for <$200
It will charge at 14.4V. Float isn't used when selecting the 2-stage

Even bigger versions also allow adjusting the voltages, so you can set it to 14.2V (increasing its lifespan).
However, I personally won't make an issue of the battery life, 2000 or 4000 cycles... with normal usage (where you won't pull a full cycle daily) it will last 'forever', so I don't care if it's gonna be 8 or 10 years. Likely to upgrade (or sell my RV) before the cells are exeeding their rated cycles anyway.
Also, if not, in >10 years cells will be cheaper, higher capacity and smaller, so another argument to upgrade at that time.
2000 cycles is still 5.5 year when doing a full cycle every single day...

On another note: I did set my MPPT to 14.1, so generally the life is slightly higher anyway. The shore charger will be used only in emergencies (eg if there is no sun for days and the batteries go flat). Daily usage will be 14.1V as per recommendations for 'long life'.
Since I expect to have 70-90% of the time enough solar to keep them fully charged, I don't mind charging to 14.4 or even 14.6V occassionally.
 
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