![]() ![]() The dynamic voltage information can effectively simulate the behavior of the lithium battery and determine its SOC, but this method cannot estimate the battery capacity (mAh). This method estimates the incremental or decremental change in SOC based on the difference between the battery voltage and its open circuit voltage. The dynamic voltage algorithm battery meter calculates the state of charge (SOC) of a lithium battery based solely on its voltage. The figure below shows that the same battery voltage under charging and discharging has a significant difference in the state of charge obtained through the open circuit voltage method.įigure 11 Error trends when full charge capacity is overestimated and underestimatedĢ.4 Dynamic Voltage Algorithm Battery Meter In other words, if the state of charge is estimated only by checking the table, the error will be very large. Therefore, a fixed open circuit voltage table cannot completely represent the state of charge, and the state of charge cannot be estimated solely by checking the table. Under different loads, temperatures, and battery aging conditions, the battery voltage curve will also be different. The assumption for the open circuit voltage is the battery terminal voltage when the battery is at rest for more than 30 minutes. Another method is the dynamic voltage algorithm designed by RICHTEK.įor a fuel gauge that uses the open circuit voltage method, the implementation method is relatively easy, and the corresponding state of charge can be obtained by checking the table based on the open circuit voltage. There are two typical methods for estimating battery SOC: the open circuit voltage method (OCV) and the Coulomb counting method. Its basic functions are to monitor voltage, charge/discharge current, and battery temperature, and estimate the state of charge (SOC) and the fully charged capacity (FCC) of the battery. In battery management, the fuel gauge is responsible for estimating the battery capacity. Usually, after 500 charge and discharge cycles, the fully charged battery capacity will decrease by about 10% to 20%.įigure 4 Performance of self-discharge rate of lithium battery at different temperatures 02-Introduction to Battery Fuel Gaugeīattery management can be seen as a part of power management. Each time the accumulated discharge capacity equals the design capacity, one cycle is counted. Generally, the larger the C-rate, the smaller the available capacity.Ĭycle life is the number of complete charge and discharge cycles that a battery can go through and can be estimated by the actual discharge capacity and design capacity. Different charging or discharging rates can result in different available capacities. For example, if a 1C discharge is used for one hour, ideally, the battery will be fully discharged. The C-rate is a measure of the charging or discharging current relative to the battery capacity. When the battery voltage is less than or equal to the minimum discharge voltage, it can be called fully discharged. This voltage value is not fixed but varies with load, temperature, aging, or other factors. The minimum discharge voltage can be defined as the cutoff discharge voltage, which is usually the voltage when the charge state is at 0%. The battery capacity also decreases at low temperatures.įigure 2: Charging characteristic curve of lithium battery The higher the discharge rate, the lower the battery capacity. The following figure shows the relationship between voltage and battery capacity at different discharge rates. The absolute state of charge for a brand new fully charged battery is 100%, but for an aged battery, even if fully charged, it cannot reach 100% under different charging and discharging conditions. The absolute state of charge, on the other hand, is a reference value calculated based on the fixed capacity value designed when the battery is manufactured. Typically, the range of relative state of charge is from 0% to 100%, where 100% represents a fully charged battery and 0% represents a fully discharged battery. Since the available energy can vary due to charging and discharging currents, temperature, and aging, the definition of the state of charge is also divided into two types: the absolute state of charge (ASOC) and the relative state of charge (RSOC). The state of charge can be defined as the available energy state of a battery, usually expressed as a percentage. 01 - Introduction to lithium-ion batteries ![]()
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