Lithium Iron Phosphate batteries are charged in two stages: First, the current is kept constant, or with solar PV that generally means that we try and send as much current into the batteries as available from the sun. The Voltage will slowly rise during this time, until it reaches the ‘absorb’ Voltage, 14.6V in the graph above. Once absorb is reached the battery is about 90% full, and to fill it the rest of the way the Voltage is kept constant while the current slowly tapers off. Once the current drops to around 5% – 10% of the Ah rating of the battery it is at 100% State-Of-Charge.
You can refer to the above charging curve for a typical 12.8V LiFeP04 battery pack.
Follow the below points to set your charge controller for charging LiFePO4:
1. Bulk/ Absorb Charge:
You can set the charge controller bulk/absorb setting in between 14.2 and 14.6 Volt will work great for the LiFePO4 battery.
2. Float Charge:
For lead-acid batteries, float charging is required because of its high rate of self-discharge that it makes sense to keep trickling in more charge to keep them always charged. But at the same time, LiFePO4 doesn’t require float charging, so if your charge controller cannot disable float, just set it to a low enough Voltage that no actual charging will happen. Any Voltage of 13.6 Volt or less will do the job.
3. Equalize Charge:
No equalize charge is required for the LiFePO4 battery. If equalize stage cannot be disabled from your charge controller, set it to 14.6V or less, so it becomes just a regular absorb charge cycle.
LiFePO4 batteries do not need temperature compensation! So, you have to switch this off from your charge controller.
Note: If you don’t have adequate experience with battery charging, I will highly recommend buying a good charge controller ( EPEVER TRIROn Series ) which has features to charging LiFePO4 battery.
If you are making the battery pack for other than solar applications, then buy a good charger from Aliexpress or Amazon. The rating of the charger shall be as per the battery charging-discharging rate which is found in the datasheet. In general, a 0.5C or half of the Ah capacity charger is safe for charging the battery pack.
Example: For a 42Ah battery, the charging current is 21 Amps.
Hope you enjoyed reading about my project as much as I have enjoyed building it. If you’re thinking about making your own I would encourage you to do so, you will learn a lot. If you have any suggestions for improvements, please comment below.