Wednesday, June 18

I'm writing this after the fact, so I don't quite recall what got done on this day. Making more cell carriers I imagine. Also spent some time thinking about battery boxes.

I no longer have my own miata in a place where I can take a photo of her in profile, so I did a bit of searching on Google images and stole this:

My idea is to have three battery boxes. A big one in the rear between the firewall that's directly behind the seats and the trunk, and two (together they have the same capacity as the rear box) up front on either side of the motor.

There are two conflicting issues that I'll need to deal with. The BB600 cells are known to vent (spit out H2 and O2 and some of their electrolyte) during charging. This means that the cells need to be placed somewhere where it is convenient to get to them for adding distilled water. Generally that means they should be near the top surface of the car. On the other hand they're pretty heavy. That would mean there's an advantage to mounting them as low as possible (keep the car's center of gravity close to the road). The picture above is the "convenient watering" version. Here's where they would go for a "low CG" version.

I want to experiment with two different configurations. A straight series pack of 150 cells, and a pair of parallel strings of 100 cells each. By adding some foam spacers I should be able to achieve either configuration using the same boxes. Here are some scale drawings of the rear box in both configurations: