Introduction:
Lithium iron phosphate (LiFePO4) batteries are lithium-ion batteries that offer many advantages over other common lithium battery types. However, to get the best performance and longevity from your LiFePO4 battery, you must charge it properly and follow simple guidelines. This article will explain how to charge a LiFePO4 battery and what to avoid. We will also consider what to look for in a compatible charger and if you can charge a LiFePO4 battery with your regular chargers.
What is a LiFePO4 Battery?
A LiFePO4 battery is a lithium-ion battery that uses lithium iron phosphate as the cathode material and a graphite carbon electrode as the anode. The cathode is the positive side of the battery, and the anode is the negative side. The lithium ions move between the cathode and the anode during charging and discharging, creating an electric current.
LiFePO4 batteries have a nominal voltage of 3.2 volts per cell, meaning a 12-volt battery consists of four cells connected in series. The capacity of a LiFePO4 battery is measured in ampere-hours (Ah), which indicates how much current the battery can deliver for one hour. For example, a 100 Ah LiFePO4 battery can provide 100 amps for one hour or 50 amps for two hours.
LiFePO4 batteries have a lower energy density than other lithium battery types, such as lithium nickel manganese cobalt oxide (NMC) or lithium nickel cobalt aluminium oxide (NCA), which means they are larger and heavier for the same capacity. However, they have many other benefits that make them suitable for various applications, such as:
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Longer cycle life
LiFePO4 batteries can typically last for more than 3000 full charge and discharge cycles before they lose significant capacity, while other lithium batteries may only last for 500 to 1000 cycles.
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Higher safety
The LiFePO4 batteries are more stable and less prone to thermal runaway, a dangerous phenomenon where the battery overheats, catches fire or explodes due to internal short circuits or external damage. LiFePO4 batteries can also handle higher temperatures and do not decompose like other lithium chemistries.
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Lower cost
The LiFePO4 batteries are cheaper than other lithium batteries because they do not contain rare and expensive materials like nickel or cobalt, which have environmental and ethical issues associated with their mining and processing.
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Environmental friendliness
LiFePO4 batteries are more eco-friendly than other lithium batteries because they do not contain toxic or hazardous substances like lead, mercury, or cadmium.
How to Charge a LiFePO4 Battery?
To charge a LiFePO4 battery, you must use a compatible charger that can apply the constant current/constant voltage (CC/CV) charging technique with the correct voltage and current settings. The CC/CV charging technique consists of two stages:
1. Constant current stage
In this stage of charging LiFePO4 batteries, the charger delivers a constant current to the battery until the voltage reaches the maximum limit (usually around 3.6 to 3.8 volts per cell). This stage provides most of the charge to the battery and restores its capacity.
2. Constant voltage stage
In this stage, the charger maintains a constant voltage at the maximum limit while gradually reducing the current until it reaches a minimum level (usually around 5% of the rated capacity). This stage completes the charge and balances the cells.
The charging process is terminated when the current falls below the minimum level or a timer expires. Some chargers may also have a third stage called the float or maintenance stage, where the charger keeps a low voltage (usually around 3.3 to 3.5 volts per cell) to prevent self-discharge and keep the battery at full state of charge (SOC).
Steps to take in charging LiFePO4 battery properly
- Check that your charger is compatible with your battery’s specifications in terms of voltage and current. You can find this information on your battery’s label or datasheet. For example, if you have a 12-volt 100 Ah LiFePO4 battery, you need a charger that can deliver at least 14.6 volts (3.65 volts per cell) and preferably 10% to 30% of the rated capacity in amps (10 to 30 amps). You might ask, can you charge the LiFePO4 battery with a normal charger? Before using a normal charger, it is best to check the compatibility to ensure its usage.
- Connect your charger to your power source, either AC or DC, depending on your charger’s specifications. Make sure you connect the charger’s positive (+) terminal to the battery’s positive (+) terminal and its negative (-) terminal to the battery’s negative (-) terminal. You may also need to connect a temperature sensor or a communication cable if your charger has these features.
- Start charging by turning on the power source. Monitor the charging process using a multimeter or a battery monitor. You should see the voltage and current change according to the CC/CV charging technique. A fully charged LiFePO4 battery typically has around 3.6 to 3.8 volts per cell, depending on the manufacturer’s specifications.
- Disconnect the charger from the power source and the battery when the charging process is completed. You can store your battery at full SOC or use it immediately. If you will not use your battery for a long time, store it in a cool and dry place and check its voltage periodically. You may need to recharge it every few months to prevent capacity loss.
What to Avoid When Charging a LiFePO4 Battery?
1. Charging your battery with a charger that is not compatible with LiFePO4 batteries.
Using a charger designed for other lithium battery types or lead-acid batteries may overcharge, undercharge, or imbalance your battery, leading to reduced capacity, shortened cycle life, or safety hazards.
2. Charging your battery below 0°C / 32°F or above 45°C / 113°F.
Charging your battery at extreme temperatures may cause irreversible damage to the internal structure and chemistry of your battery, resulting in capacity loss, increased internal resistance, or thermal runaway. You should always charge your battery within the recommended temperature range specified by the manufacturer. When you follow this step, how long it takes to charge a LiFePO4 battery won’t be a significant concern. This is because charging at the right temperature makes it charge better.
3. Charging your battery when it is deeply discharged or over-discharged.
If your battery’s voltage drops below the minimum limit (usually around 2.5 volts per cell), recharge it as soon as possible to prevent further degradation. If your battery’s voltage drops below the cutoff limit (usually around 2 volts per cell), you may not be able to charge it at all, and you may need to replace it.
4. Charging your battery in series or parallel without proper protection or balancing.
Suppose you connect multiple batteries in series or parallel to increase the voltage or capacity. In that case, you must use a battery management system (BMS) or a balancer to monitor and control the individual cell voltages and currents. Otherwise, you may cause overcharging, undercharging, or imbalance among the cells, which can damage your battery or cause safety issues.
Conclusion:
LiFePO4 batteries are an excellent choice for many applications that require high performance, long life span, high safety, low cost, and environmental friendliness. However, to get the most out of your LiFePO4 battery, you need to know how to charge LiFePO4 batteries properly with a compatible charger that can deliver the correct voltage and current using the CC/CV charging technique. You won’t have to worry about how long to charge a LiFePO4 battery as proper precautions will be followed.