Cell layout
The LiFePO4 cells selected for the 356 Speedster are manufactured in a large prismatic form factor measuring 71 x 182 x 279mm. Terminals and vent caps are on top of the cell (279mm height) and therefore restrict possible layouts to some combination of 71 x 182mm blocks. In addition, terminal connections must all be plus-to-minus in series.
Revised design improves terminal connections
The front pack contains 16 cells. The most negative terminal (indicated by the B- in the diagram) of the entire 36-cell pack is located in the front, while the most positive terminal is in the rear.
The positive connection of the front pack is routed to a safety cutoff switch located behind the driver's seat in the cockpit.
After some experimentation, the most efficient design places both external connection terminals in the middle of the front pack.
This layout reduces cable length and eliminates wiring clutter.
Sixteen-cell front battery box modified to fit into former spare tire hold with optimized connection points
The Cars
Porsche 356 Speedster
The iconic Porsche Speedster proved to be an excellent EV conversion candidate due to its low weight, relatively simple design, and ample front/rear compartments for mounting pristmatic lithium battery cells. Weight distribution was improved over the original rear engine configuration with better acceleration and overall performance.
Saab Sonett
The unusual fiberglass Sonett, originally powered by a Ford V4 engine, combines a low center of gravity and front wheel drive, optimal for our high performance EV conversion. Without the need to accomodate a long drive train, the space behind the two seats was used for additional batteries. The original four-speed transmission remains intact along with the braking system.