Hello Electrified Miata fans! This will be another short article. Much of the work I'm doing is monotonous. This status is much the same as last time; waiting on the
coupler, building batteries, and working on the BMS system. We have one small battery, weight 37.1 pounds, waiting for side panels and BMS boards and plastic
coverings. I could tell you about the parts that I ordered online that wasn't what I ordered, or the laborious process of double nutting 100+ studs so they can be driven in the battery containers, but these are repetitive task items that happen in any project, especially prototypes.
There have been a few hiccups along the way since my last blog. When stringing multiple BMS boards together, Joe discovered a problem with the communication signal between boards degrading. In fact, so much degradation that it doesn't work after stringing three boards at 9600 baud.
After much investigation and consulting one of Joe's friends, (thank you Jon Guy), we evaluated options to fix this. The short version is we chose the cheap, 'boost the signal with a Mosfet' option. This option seemed the least of all the evils with regards to more power consumption, more cost, more complexity, or reduced reliability. A BMS board revision will be required.
Joe received the BMS test fixture boards which are different from the boards
above. These are used to install BMS firmware and verify functionality of the boards. He is finding multiple first run issues with the test fixture boards and getting the board to be functional. :)
Another hiccup a battery broke when I went to move it from the floor to the
It may be easier and cheaper to assemble the batteries using 4 x 6 panels but they don't hold together as well the 2x2.
I reassembled the pack using the 2x2 and assembled the battery to the point where it can be fitted for top and bottom plastics.
The goal for next week is finish the second small battery and hope to get notification that the coupler is shipping. Two complete small battery packs will pave the way to start testing these batteries and the BMS software on our go-kart. Then we can have finally have fun while waiting for parts or making more batteries.