from chemistry to pack
How should you connect battery cells together: Parallel then Series or Series then Parallel? What are the benefits and what are the issues with each approach? Series and Parallel The operating voltage of the pack is fundamentally determined by the cell chemistry and the number of cells joined in series. The ampere-hour capacity of the … Read more
How can we go about maximising pack energy density? What can we look at to reduce the mass and volume? Where are the opportunities given a defined cell? A great example of shrinking the size of a battery pack is the Mercedes Vision EQXX research car. The advantage they had was a much more energy … Read more
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: Plotting continuous power versus system nominal voltage it is possible to see the voltage/power/current design points. Typically electric … Read more
Often it is difficult to estimate the battery pack volume, hence here is an approximation based on data fitting. Hence a first approximation is that the battery pack volume will be 5x the total energy in kWh. A 100kWh battery would have a volume of 500 litres. If this was a design optimised for volume … Read more
It is possible to use the battery pack database to estimate the pack mass from cell density. The key relationship we have is between cell and pack gravimetric energy density. This graph has been pulled together by scouring the internet for cell and battery data. The ratio of cell density to pack density is 0.6235 … Read more
For many applications contactor mass doesn’t matter, but for aviation every gram counts and hence we wanted to look for a trend. Contactor mass plotted versus continuous current rating. Not very much data with just 23 parts, but it appears that we are seeing distinct masses based on frame size. Hence a relationship to continuous … Read more
Peak vs continuous power is a recurring question across the electrification space. We need to deliver a repeatable amount of power for the user to have confidence in the machine and we need high power numbers to deliver the brochure wow factor. The transient peak power works well for a number of vehicle applications. However, … Read more
Obviously Cell Capacity and Pack Size are linked. The total energy content in a battery pack in it’s simplest terms is: Energy (Wh) = S x P x Ah x Vnom Hence the simple diagram showing cells connected together in series and parallel. What about flexibility in pack size? There are very good reasons for … Read more
When the battery pack contactors are closed onto a motor and inverter there will be an inrush of current into the inverter capacitor. This very high current is at a minimum likely to age the contactors, it could permanently damage the contactors. Therefore, when we closed the contactors on the battery pack we do this … Read more