Charging LiFePO4 batteries, algorithms
![DSC_1927b](https://lygte-info.dk/pic/BatteryLiFePO4charge/DSC_1927b.png)
Chargers use slightly different methods to charge LiFePO4 batteries, do this change how much energy is stuffed into the battery?
I am working on a computer controlled charger for testing and for one of the tests I decided to check this.
The methods
- CC/CV voltage with 3.4 to 3.8 volt as target and a very low current termination
- CC/CV voltage with 3.6 volt as target and a high termination current.
- Voltage charge, i.e. check battery voltage with current off.
Easy to test when you have a charger where these parameters can be adjusted.
The tests
All test are done as a charging, followed by a discharging and capacity measured at both operations.
![Charge-18650-LiFePO4-CCCV-1.0%203.4%2010m](https://lygte-info.dk/pic/BatteryLiFePO4charge/18650-LiFePO4/Charge-18650-LiFePO4-CCCV-1.0%203.4%2010m.png)
The first test to 3.4V, this is only slightly above the full cell voltage.
![Charge-18650-LiFePO4-CCCV-1.0%203.6%2010ma](https://lygte-info.dk/pic/BatteryLiFePO4charge/18650-LiFePO4/Charge-18650-LiFePO4-CCCV-1.0%203.6%2010ma.png)
The usually voltage used for charging LiFePO4 is 3.6V or 3.65V.
![Charge-18650-LiFePO4-CCCV-1.0%203.8%2010m](https://lygte-info.dk/pic/BatteryLiFePO4charge/18650-LiFePO4/Charge-18650-LiFePO4-CCCV-1.0%203.8%2010m.png)
A 3.8V charging voltage is rather high, but it do not stuff more capacity into the cell. A slight temperature increase is present when the voltage goes high.
![Charge-18650-LiFePO4-CCCV-1.0%203.6%20200m](https://lygte-info.dk/pic/BatteryLiFePO4charge/18650-LiFePO4/Charge-18650-LiFePO4-CCCV-1.0%203.6%20200m.png)
Using a faster termination, i.e. higher termination current.
![Charge-18650-LiFePO4-VOLTAGE-1.0%203.6](https://lygte-info.dk/pic/BatteryLiFePO4charge/18650-LiFePO4/Charge-18650-LiFePO4-VOLTAGE-1.0%203.6.png)
Using pulsing current and measuring the voltage when current is off, this is a fast charge method, but as can be seen above it is not faster than the other methods.
![Result](https://lygte-info.dk/pic/BatteryLiFePO4charge/Result.png)
capacity is in mAh, TC is Termination Current in mA
The capacity difference between the charge voltages is very small, but using a low voltage (3.4V) means slower charging. The higher termination current do not have much influence on the charge time, but may affect capacity.
![Charge-18650-LiFePO4-CCCV-1.0%203.6%2010ma%20pct](https://lygte-info.dk/pic/BatteryLiFePO4charge/18650-LiFePO4/Charge-18650-LiFePO4-CCCV-1.0%203.6%2010ma%20pct.png)
How much can a faster termination affect the end result? The current start dropping at 97.2% or 1119mAh charged, this means that even a charge without any CV (Constant voltage) phase will be within about 3% of full capacity.
Conclusion
This is just a simple and fast test, but it shows that the different charge methods only has a small influence on the final charge on a LiFePO4 battery.