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MPP Solar LV 3kva 24 inverter/charger User Settings for 24 volt Lithium Ion batteries.

steelliberty

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Jan 18, 2021
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Does anyone have recommended user settings for the LiFePO4 Big Battery type 123 24 volt battery and the MPP Solar charge controller?

Bulk charging voltage 28.8 V (Suggested Charge Voltage) - but what about the float voltage value? 28.8 also ?

Low DC cutoff of 20 volts ?

Thank you.
 
Welcome to the forum.

8 cells for LFP 24V

28.8/8 = 3.6V - good.

Float must be at less than 3.4V/cell, or you run the risk of damaging the cells.

8*3.4V = 27.2V
 
Welcome to the forum.

8 cells for LFP 24V

28.8/8 = 3.6V - good.

Float must be at less than 3.4V/cell, or you run the risk of damaging the cells.

8*3.4V = 27.2V
I have a similiar scenario using 8s LiFePo4 batteries, solar charge controller and solar panels. My search for answers turned to this thread.

Can you elaborate when you say LiFePo4 float must be less than 3.4v /cell (8s would be 27.2v)? Can it be equal to or less? My charge controller has LiFePo4 setting but it's manual says its boost (bulk?) charge is 29.2v and float is 27.2v.

I don't want to damage my LiFePo4 batteries. I was looking at a video where someone was suggesting that the LiFePo4 battery with solar charge controller setup should have the controller set to float at 26.8v and the absorption (is this the bulk/boost?) set to same 26.8v since LiFePo4 doesn't drop charge like Lead acid, and resistance is much lower. Confusing for me to sort out.
I am waiting for the batteries to arrive and this is my first set up, so a total novice here. Will attach photos from manual. Please let me know if settings defined in manual are risky? Thanks!
 

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Sorry. Float must not exceed 3.4V/cell :)

27.2 is fine. Note that they will still take on charge at this level, but they will stop at about 95% SoC.
 
Sorry. Float must not exceed 3.4V/cell :)

27.2 is fine. Note that they will still take on charge at this level, but they will stop at about 95% SoC.
Thanks for the quick response. I suspect this complicates things, but I also was considering tweaking my BMS so the cells would not be charged fully as a way to extend the overall life. Perhaps somewhere between 3.5 and 3.55v as the top out voltage. Are there considerations or implications of doing this without also customizing the voltage settings of the MPPT ?
 
Bad idea. The BMS exists to protect the cells when something goes wrong. You don't want your BMS cutting the battery out of the circuit every time you charge your battery. You should manage the DESIRED voltage limits by changing the chargers/loads.

In your case, 28.0-28.4 would be your bulk/absorp setting on the charger for 3.5-3.55 peak voltage.
 
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