At some point in the development of a battery pack design you need to consider the continuous current rating. Do this for charge and discharge as this then gives you one for the fundamental requirements to determine:
- cell to cell busbars
- HV joint requirements
- HV distribution busbar cross-sectional areas
- contactor sizing
- fuse sizing
- connector sizing
Plotting continuous power versus system nominal voltage it is possible to see the voltage/power/current design points.
Typically electric vehicles have been sized around a 300A continuous rating, hence giving ~120kW continuous power rating at 400V. However, with a move to greater charging power capability this has brought a shift to 800V systems as seen with the Porsche Taycan. Thus allowing the continuous current to be kept below 400A and allowing ~300kW continuous for fast charging.
We should also consider what is continuous. For a cell a time greater than 30s is considered continuous. In battery pack design continuous is normally considered as the power rating over the complete usable window. Very high continuous power ratings might result in quite a short total charge discharge. Hence the heat capacity of the battery pack should also be considered when looking at the cooling system requirements.
A look at the approach for sizing a battery pack. From usable and total energy through to cooling system options.