Parallel then Series or Series then Parallel

Parallel or Series connection of battery cells

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

Continuous Current Rating

Continuous power versus battery nominal voltage graph

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

Pack Mass from Cell Density

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

Contactor Mass

Schaltbau contactors

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

Rolls-Royce Spirit of Innovation

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

Cell Capacity and Pack Size

Size of battery packs vs cell capacity

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