Hi! Some quick background… My name is Juha. I am working on my first eFoil, sourcing the parts and so on. I have ordered my board from Noahark. It is the 48" CF variant. The setup will be 14S, FSESC75200, FS65161 120kv, Gong Curve MT foil, etc. My first DIY battery was for an esk8. It was, or is, a 12S4P Molicel P42A pack with FlexiBMS battery management system.
eFoil batteries are quite a bit more expensive than esk8 batteries, because they typically have much more cells in them. That got me thinking about battery optimization. I wanted to figure out the cell that would yield the best Wh/cost for me, based on my desired total pack Wh. Thanks to Mooch, we nowadays have actual discharge capacity characteristics available for most common battery cells.
Selecting cells for a battery pack is challenging. Manufacturers often state optimistic cell performance characteristics. Therefore, battery cells should be chosen based on actual test data. An additional challenge comes from the fact that the actual discharge capacity of the cells depends on discharge rate, so the relationship between cell count and total pack discharge capacity is not self evident. Doubling cell count more than doubles the pack discharge capacity.
This calculator solves optimum parallel cell count based on actual cell discharge characteristics (from Mooch!). Two input data points are required to resolve the capacity-discharge rate dependency, and they should be as close as possible to actual discharge rate, if possible. While two points aren’t scientifically optimal, they are probably good enough. Inputs are desired pack Series count, target discharge capacity, continuous and maximum pack current. Continuous current is used in the pack capacity calculation, and optimum P config is resolved from that. The calculator also considers max current capability of the pack, and selects a P config that fulfills both requirements (capacity + max current). The sheet also resolves total cost of suggested packs, and value of cells (Wh/cost) in resulting pack config, as well as the energy density of the resulting packs.
It is best to do your own math before making a buying decision. This calculator should only be used as guidance. I do not take any responsibility for inaccurate data, math errors or any other issue whatsoever
I would suggest to download the excel and refresh the cost data yourself before deciding which cells to buy. The prices are checked occasionally, but as they change constantly, its hard to keep up. The EU prices include VAT, the US prices do not.
- v0.1 Internal development version
- v0.2 First release to public
- v0.3 Added weight calculation, thanks Brycej for the suggestion. Also refactored the excel to contain cell data in one sheet and actual calculations and results in another sheet
- v0.4 Calculate required P count based on Wh and required max discharge, instead of only target Wh. Max discharge headroom is configurable. Lower headroom stresses the pack more.