When designing a battery pack it is useful to make a few series and parallel calculations. Hence one of the worksheets in our Battery Calculations Workbook is exactly that.
Cells that are in parallel have the positive terminals all connected together and the negative terminals all connected together.
When connecting cells in series the negative terminal of the first cell is connected to the positive terminal of the second cell. The negative terminal of the second cell is connected to the positive terminal of the third cell. This continues until we reach the total number of cells required in series.
The SeriesParallel worksheet looks like this. Note: all of the calculations are in the sheet and open to view, copy or use in a different way.
The worksheet is standalone from the other worksheets and just allows you to make simple calculations.
Enter the cell values in the top left cells.
Note: we use cells with a white background to indicate values that you can enter or modify.
Next enter the pack series and parallel values. Best to enter what you think are the target nominal values. The step size sets the values used up and down from the nominal series and parallel numbers.
The first chart top right gives the calculated pack voltages. As you can see, these are just against the number of cells in series as the number in parallel doesn’t alter these values at this level of calculation. The number of cells in parallel will effect the pack voltage under load, but that is a different calculation.
The graduated cells plotted versus series and parallel give the total pack size in kWh.
So, this chart gives you the energy (kWh) and the absolute maximum and minimum pack voltage.
The final two charts give:
The total mass of cells in kg against series and parallel.
The estimated pack mass uses the pack database and your selection of the “Pack Type” from the pulldown menu.
The pack type allows you to select which is the best fit and this then uses straightline coefficients to estimate pack mass from cell mass.
The coefficients for the different types of pack.
This selection will be improved as we get more data.
The SeriesParallel worksheet hopefully gives you a tool that allows you to understand how changing the configuration of a battery pack changes the voltage range, total energy and mass.
Battery Calculations Workbook
This can be purchased as a one off for $15 or get all updates for a year and access to the databases for $25.