LiFePO4 battery is becoming more and more popular. Since about 2018, LiFePO4 batteries have entered the attention of battery enthusiasts on a large scale, and their relatively excellent performance and reassuring safety are unforgettable. Of course, there are also many battery beginners who have entered the field of LiFePO4 battery. For beginners, it is especially important to learn some of the terminology involved in the LiFePO4 battery.
Current is the physical quantity of the average directional movement of electric charge, which refers to the electric charge passing through a certain section of the power carrier per unit time. The unit used is “A”. In LiFePO4 batteries, the current is generally reflected in parts such as load current/maximum cut-off current.
Voltage is the potential difference between two points, and to use a simple analogy is the force that pushes an electric charge. The unit of voltage is “V”. The nominal voltage of the LiFePO4 battery is 3.2V. Of course, this voltage is not constant and will vary with the state of the battery.
The internal resistance of the LiFePO4 battery refers to the resistance that current flows through the battery when the battery is working. It includes ohmic internal resistance and polarization internal resistance. Resistance represents the degree of resistance of a circuit element to current transmission. The physical unit is “Ω”. The size of the internal resistance will affect the size of the voltage and current, which will cause some performance fluctuations for the LiFePO4 battery.
This is one of the most important parameters of LiFePO4 batteries and one that is directly linked to your money. The size of the battery capacity indicates the amount of effective power that the battery can hold. Generally speaking, a battery with a larger capacity will last longer. Usually “Ah” is used as the physical unit.
The energy of a LiFePO4 battery indicates how much energy can be released from the electricity stored in the battery. At present, the most mainstream is to use the physical unit “KWh” to express. The calculation method is very simple, battery capacity * battery voltage = battery energy. When considering energy backup for your device, the first consideration should be the energy of the LiFePO4 battery.
Series & Parallel
Series/parallel connection is a very important battery connection method. All high-capacity battery devices are composed of many batteries connected in series and in parallel. It is worth mentioning that it is not recommended to mix batteries. If you must mix batteries, please choose batteries with the same chemical properties and use them in parallel.
Series connection (S): A battery connection method in which the positive pole of one battery is connected to the negative pole of another battery. After the connection is completed, the voltage of the battery pack will become 3.2V*2=6.4V. But the capacity remains the same.
Parallel (P): A battery connection method in which the positive pole of one battery is connected to the positive pole of another battery. After the connection is completed, the capacity of the battery pack will become the sum of the two batteries. But the voltage remains the same.
For large-scale LiFePO4 battery equipment, it is impossible to use only series or parallel connections, and most LiFePO4 batteries use series + parallel connections. Generally, *S*P or *P*S will be used to represent, for example, a 24V battery pack composed of 16 LiFePO4 batteries will be represented by 8S2P or 2P8S.
DOD is the depth of discharge, which is the percentage of the battery’s discharge to the battery’s rated capacity. Generally, the recommended DOD of LiFePO4 batteries is 80%, but there are also many LiFePO4 batteries that can achieve a DOD discharge of 90% to 100%.
SOC is the remaining power ratio of the battery. For example, 50% SOC means that the battery has only 50% energy left. LiFePO4 batteries are lithium-ion batteries and are generally not recommended for long-term storage at full SOC. 50% SOC is the best storage state.
The battery terminal is the part where the battery is connected to other devices, and power is also output or input through this interface. The battery terminals of LiFePO4 batteries are generally divided into 4 parts: stud/nut/washer/busbar.
Overcharge and Over-discharge
Overcharge and over-discharge are one of the most noteworthy parts of LiFePO4 batteries. Overcharging and over-discharging can cause great damage to the battery. However, this situation basically does not occur when the BMS is installed. The BMS can help the battery avoid problems such as overcharge, over-discharge and over-current, and can also monitor the temperature of the LiFePO4 battery.
There are currently 3 popular LiFePO4 battery shapes, cylindrical, prismatic, and pouch. All 3 battery shapes will have some impact on the properties of the battery, and there is no such thing as a better one. But currently more popular are the prismatic LiFePO4 battery cells, which are widely used in electric vehicles, RVs, home energy storage, and battery DIY projects.
After a brief understanding of the relevant terms of LiFePO4 battery, it will be of great help to refer to other people’s DIY equipment and design battery packs in the future. After knowing the basics, you can slowly carry out deep learning and eventually become an expert of LiFePO4 batteries.