Issue link: https://resources.mouser.com/i/1437660
6 ADI | Energy Storage Solutions By imaging a very old battery with a steep discharge curve, it is easier to calculate the state of charge of that battery by measuring the delta of the voltage drop in a small amount of time and knowing the absolute value of the battery voltage. For a new lithium-based battery, the accuracy required to make this measurement is orders of magnitude higher, since the voltage drop is much smaller in a given time frame. For the SOH, old batteries discharge in a faster and more predictable way: Their voltage discharge curve becomes even steeper and the target charging voltage cannot be reached. New lithium batteries will keep the same good behavior longer, but eventually can degrade with more exceptional behavior and rapidly change their impedance and discharge curve just when they are close to end of life or if they are damaged. Extra care must be taken for temperature measurements, ideally at every single cell, to integrate the SOC and SOH algorithms with this information to make them more accurate. Precise and reliable SOC and SOH calculations help extend battery lifetimes from 10 years to 20 years in the best case and generally result in a 30 percent lifetime improvement, which reduces the total cost of ownership of the energy storage system by greater than 30 percent after including maintenance costs. This, together with the higher accuracy of the SOC information, avoids overcharging or discharging conditions that can quickly drain a battery; minimizes the chance of short circuits, fire, and other risky situations; helps use all the energy in a battery; and enables charging batteries in the best, most efficient way possible. The LTC6813 battery management solution (BMS) proposed in this article can be used in healthcare devices such as portable ultrasound machines and in large scale (megawatt/hours) energy storage systems (for hospitals, factories, grid stabilization, electric vehicle charging infrastructure, and residential units), as well as in industrial robots and vehicles. LTC6813 application schematic in Figure 3 shows a typical BMS implementation for 18 cells battery module. The portability of ADI technology brings terrific advantages in reliability 3 LTC6813 application schematic. 4 LTC6813 isolated connection with an LTC6820.