14 Aug Working hard on a new battery pack
Our last battery pack has gone through two races and almost two years of general abuse, so it’s time to build a new one for Apogee. Since Apogee is done racing, however, it’s hard to justify building a new pack using an old design. So instead, we’re building pack #1 for our new car as an opportunity to debug the design.
We’ve elected to go back to the 18650 cell. Why? While it’s more of a nuisance to package into a pack than prismatics, the cylindrical form factor is always the first to receive capacity and longevity upgrades. That means that as new cells become available, we can simply build a new battery pack without having to overhaul the design.
The new pack will have cells arranged into 36 series bricks of 13 cells each. This will give us a fairly high pack voltage and should allow for a fairly high top speed. Further, the bricks are designed to be as lightweight as possible, while still allowing the pack to be serviced at a brick level. Take a look:
Those collector plates are being made for us by our good friends out at Italix out of 1100 aluminum that will be tin plated so that we can solder on our nickel strip. They should be lighter than the copper alternative. You’ll see those in another post sometime in the next week or two.
Nathan, our resident mechanical wizard and team lead designed some nice plastic tabs that will help hold down the batteries. They’re designed to be laser-cut from any convenient plastic and glued into the bottom sandwich panel plate of our pack. A hook-and-loop strap wraps around the press-fit dowel pin and is used to hold the cells down. The tabs are cleverly designed to have a very subtle detent that will let you know when the battery brick is fully seated:
The cells we’re using are (almost certainly fake) A123 18650’s that we bought on Ebay. On the bright side, this will be a low-investment battery pack that we should teach us quite a bit.