File this under “typing myself smart”. Or “smaaaht” as we say in Boston. Anyway, I’m trying to work out the maths on the lipo cells I looked at here. Now, after reading a bit more closely, it seems like to get a good model I should go with the Turnigy single cells at 40C. This is just for the sake of crunching some numbers, and the Turnigy are a pretty good, standard cell.
So, here are the specs for those cells.
- Cell voltage: 3.7 (nominal)
- Cell capacity: 5Ah
- C rating: 20C
(note: Chris mentioned a 40C rating on the ES thread, which he said was 20C real-world, so I’m going with that.)
Total current per cell: 100A
For 200V we need to run 54 cells in series. Let’s say we want around 40Ah and see what that gives us. 8 cells paralleled? So 8 x 100A? 800A? Can this be right? If it is, it’s crayzeeeeee, so let’s dial it down to 400A, or 4 cells in parallel, because 400A at 200V = 80kW. Or 5 cells. Sorry, coffee needs to kick in.
So we have a 100kW pack. It’s made up as 54s5p, or 270 cells. Each cell weighs 130g, so 270 of them is about 35kg, or 77lbs.
Now, here’s the thing. That’s 100kW peak for the pack, but 100kW continuous for the motor (I have to check that to confirm.) This pack is crazy light, so let’s add some to get some more juice. If we go to 6 cells, we have 600A at 200V, so about 120kW. That’s enough buffer, I think, and now the pack has 324 cells and weighs 93lbs.
Also, we can re-configure this for higher voltage, which, I believe will give me better performance out of the Rinehart. Let’s go with 108S and drop it down to 3p. Now we have 400V at 300A.
This all adds up to a 15Ah pack running at 400V, which gives us a 6kWh pack and weighs 100lbs.
Funny. Wasn’t that just about the size Chris was talking about?
The price? $2000.
Guess what. You know that pack configurator calculator thing I thought should exist? Well I made one. My skills are weak in this regard, but if you want to play with it, here it is: pack-config