When we use lithium iron phosphate batteries, we are often confused about how it is discharged. This can affect the way we use the battery. Therefore, there are many details about the discharge you need to learn.
What is 12V LiFePO4 discharge curve?
The full charge OCV of a 12.8V battery is around 13.8. The battery will only be damaged if the applied charge voltage is significantly higher than the battery's full charge voltage.
This means that in stage 2, the Li-ion battery should be kept below 14.7V and the battery should be kept below 15V when charging. Based on this, the charging voltage range between 13.8V and 14.7V is sufficient to charge any battery without causing damage. When selecting a charger for any chemical, it is important to select a charger that will stay between the limits listed above.
Aolithium 12V100Ah lithium iron phosphate battery charging parameters
Charging voltage: 14.2-14.6V
Floating voltage: 13.6V (or disabled)
Maximum voltage: 14.6V
Minimum voltage: 10V
Nominal voltage: 12V or 12.8V
What is the self discharge rate of LiFePO4 battery?
LiFePO4 batteries have a very low self-discharge rate of 2% per month. This means that when LiFePO4 batteries are stored, they lose 2% of their charge capacity each month. To prevent higher rates of discharge, we recommend disconnecting all power from the battery. When storing LiFePO4 batteries, be sure to store them at 50% or higher state of charge (SOC). For long term storage, a higher state of charge is recommended. If you want the battery to maintain a good charge at the end of its storage period, charge it to 100% and store it in a fully charged state.
Can you over discharge a LiFePO4 battery?
LiFePO4 batteries can undergo more than 4000 deep cycles. LiFePO4 batteries can be continuously discharged to 100% DOD with no long-term effects. However, we recommend that you only discharge to 80% to extend battery life.
For lead-acid batteries, we give a different recommendation. Most lead-acid batteries will have a significantly shorter cycle life if discharged below 50% DOD.
Can LiFePO4 charge and discharge at the same time?
The battery cannot be charged or discharged at the same time. However, it may happen that the charger is connected to the battery when the battery is connected to the load.
Let the charging current be Ic . The current flowing into or out of the battery is Ib and the current flowing through the load is IL.
Note that the current that charges the battery is proportional to its discharge. In other words, the internal resistance of the battery is lower when it is highly discharged, and higher when it is not so discharged. The load resistance and current Il are constant. The current through the charger Ic = Ib + IL according to Kirchhoff's current law (assuming negligible internal resistance of the charger). So you see that the battery is charging, but the connected load draws current from the charger instead of the battery.
If the battery is fully charged, there will not be any charging current into the battery. In that case, the battery will also be discharged through the load. il = Ic + Ib. The ratio of Ib to Ic will depend on the internal resistance of the charger and the battery.
Back to your question, the battery cannot be charged or discharged at the same time. If the load is connected to the battery while charging, the charger will power the load while charging the battery. When the battery is fully charged, the charging current drops to zero. After that, the current through the battery is reversed and discharged through the load. This causes the battery to discharge so that it can be charged from the charger. In effect, the system stops at a point of balance that does not involve battery current. As long as it is connected, the charger will supply power to the load and the battery will not be drained or charged.
Correct ways to charge LiFePO4 batteries
Check the charger
Before using the LiFePO4 charger, check that the charger cable is insulated and not broken. The charger terminal connectors should be clean and properly matched to the battery terminals to ensure a good connection and optimal conductivity.
Aolithium LiFePO4 batteries can be safely charged between 0°C and 45°C (32°F and 113°F). Lithium iron phosphate batteries do not require temperature compensation for voltage when charging at high or low temperatures. All Aolithium LiFePO4 batteries are equipped with an internal BMS that protects the battery from low and high temperatures. If the BMS is disconnected due to low temperatures, the battery must be warmed up so that the BMS can reconnect and receive charging current. If the BMS is disconnected due to high temperatures, the battery will need to cool before the BMS will accept to charge the battery. Refer to the data sheet for your specific battery for BMS low and high temperature cutoffs and reconnection values.
Charging LiFePO4 in parallel
When charging LiFePO4 cells in parallel, make sure that each cell is within 0.1V of each other before putting them into service, this will minimize the chance of imbalance between cells. If you are charging 12V LiFePO4 cells, the charge voltage should be between 14V - 14.2V. When charging 24V cells in parallel, the charge voltage should be 28V - 28.4V. Charging 36V LiFePO4 cells in parallel requires a voltage of 42V - 42.6V. Finally, charging a 48V LiFePO4 battery requires a voltage parameter of 56V - 56.8V.
Charging LiFePO4 in series
When connecting cells in series, make sure that each cell is within 50mV (0.05V) of each other before putting them into use. This will minimize the possibility of imbalance between cells. If your cells are out of balance and the voltage of any cell is >50mV (0.05V) to the voltage of another cell in the group, you should charge each cell individually to rebalance. You can periodically charge each cell individually to avoid imbalance. When charging LiFePO4 cells in series, it is best to use multiple chargers to charge each cell individually to ensure that the cells remain balanced.