So I thought I was well on my way to completing my 4th battery for my 1968 1600-2 restoversion. Unfortunately, on closer investigation using the foam core mock-up I had built, we realized that the freshly installed rebuilt brake booster and master cylinder created a not-so-insignificant interference. The photos below show the basic idea of the front battery pack sitting under the hood, above the motor and transmission. When we previously checked this position, the brake booster was not installed... doh!
After drowning my sorrows for an evening, I started playing "what if" scenarios with the LG lithium-ion battery sub-modules. We realized it was really the width of the complete battery pack that was the problem, but we had some room to grow vertically if I could come up with another workable configuration. Part of my challenge in this new configuration was self-imposed. I am proud of the fact that I had managed to thermally couple the heat sinks on the cell module to the aluminum base plate of the previous battery design, thus using the entire aluminum enclosure as a heat sink for the battery pack, which would improve performance, reduce thermal gradients, and extend the life of this passively air-cooled battery. With a 90 degree rotation of the cell module, I'd need a new thermal sinking strategy. With more red wine (or a nice West Coast IPA - can't remember), one quickly emerged. I would rotate the modules 90 degrees on their long side and create vertical aluminum heat sink plates inside the pack to achieve the same thing as the top and bottom plates of the "short box" design.
Before we set off down this path, we smartly modified our mock-up to ensure this new configuration, which cut about 5 inches from the overall width, would work. And... it did! We gained room in all the prior interference concerns and were even able to drop the pack overall a bit.
With that confirmed, I set about designing and building the new enclosure...
Since there would be less pressure on the heat sinks compared to using gravity to press them to the thermal plate, I decided to use a thermal gap pad in the interface to ensure good thermal conductivity between the cell module and this plate. It's the bluish-purple pad below. This made tolerancing my box build a bit trickier and in the end, I used some spacers between two of the cell modules to take up some gap and maintain pressure against the sink plates.
Here's a shot of the final configuration. The one section of 80/20 that runs down the pack creates a nice 20mm gap that allows me to run the BMS and CANbus cabling from front to back as these cell modules have voltage sense connectors on both ends as they use double-ended cell terminals.
The cell monitoring boards mount to the back of the cell modules and are more accessible through the back cover over the short box design should they need servicing in the future. Quick check was done hooking up 12Vdc and CAN to the master BMS and checking on the display and laptop that we've got good communication with all the cells and thermistors. All good!
The completed "tall box" battery. The handles will help for installation. They can be left in place or removed once I've got the pack installed. Haven't decided on that detail yet. I also paid extra attention to sealing this enclosure during the final assembly as it will live under the hood. All of the panels have silicone "gaskets" and the connectors are fully sealed. Should water eventually find a way in, the terminals are coated with dielectric grease and power terminals covered with moisture sealing mastic.
Here's a comparison between the tall box and short box batteries. The tall box was a bit fussier to build, but is a bit more efficient in use of space and materials. In the end, it's helpful to now have a couple of different battery configurations for future builds and various space constraints we are likely to run into.
I promise my next blog post will have more "car stuff" than batteries...Onward! Thanks for reading.