Battery Pack Design Criteria and Selection 45 Maximum Continuous Discharge In order to calculate the maximum continuous discharge current that the system can provide, you need to multiply the number of cells in parallel (N p ) times the cell current (I c ) multiplied by the maximum C-rate (C Max ) to get the maximum discharge current (I Max Continuous ) in amperes. The other method for this is to use the maximum discharge current that is supplied by the cell manufacturer on their data sheet multiplied by the number of cells in parallel to get a close estimation of the maximum discharge current.
N p Ч I c Ч C Max = I Max Continuous or 1 ( cell in parallel ) Ч 90A Ч 5C = 450AMax Continuous Discharge This same formula can be used to determine the maximum continuous charge current that is available; simply replace the C-rate or the current with the maximum continuous charge current or maximum continuous charge C-rate that is supplied by the manufacturer. Calculating Charge Voltages Maximum charging voltage is simply equal to the total number of cells in series multiplied by the cell’s maximum voltage as defined by the cell manufacturer. 96 cell Ч 4 . 2Vmax = 403 V Maximum Minimum is calculated in the same manner:
number of cells in series multiplied by the cell’s minimum voltage as defined by the cell manufacturer. 96 cells Ч 2 . 7V = 259 V Minimum Converting Customer Requirements into Pack Designs Now that we have a basic understanding of the types of formulas that are needed in putting together a basic lithium-ion pack concept, we should talk briefly about customer requirement documents. Customer requirement documents can range from hundreds of pages for the more sophisticated customers to extremely simple one line descriptions for companies that are less familiar with battery technologies.
But in either case the most important thing that should be done prior to beginning to develop your battery design and concept is to sit with the customer to discuss what the requirements mean and what the most important characteristics of the requirements are. When you meet with the customer you will get a better understanding of what they are trying to achieve with the battery, which will drive your specification development. You may find that the inverter and the motor have different voltage ranges than were indicated in the