That Last Twenty Percent

​Hey Electrified Miata team, here's the latest update in the never ending quest to go faster, have fun, and be safe! For those of you following along, last week, we were going to manually charge the pack using a variac and careful monitoring and find a way to drill holes in the bus bars so we can finish assembling our first battery pack.  I was really hoping to be able to put the covers on the battery pack, but for lack of the right parts, fell short. We did make quite a bit of progress in other areas.   We'll discuss the bus bars first, as they were frustrating us with a number of drill bits shattered.

The lack of drilled bus bars were holding up battery assembly, so I concentrated my efforts here. We had managed to finish one hole in test bus bar of the size I wanted (.060"), so I tried to solder it to see how it would work while attaching to the pack. I couldn't solder to this bar!  Joe and Ed were pretty adamant that soldering to the bar would be tough but somethings I just have to check out for myself.  The larger soldering iron is pretty good, but the heat sinking capabilities of the larger copper bar far exceeded my soldering iron's output.  I just couldn't solder to the bar!  I might have been able to heat the bar up, and put all the wires on, and then attach it to the battery after it cooled, but this seemed like way too much work, especially given we had a tough time drilling small holes.   While I'm fully confident Ed could have done it, it was much easier to drill a larger hole and use the standard screw and terminal method. (see pic)  Drilling the bus bars was actually anti-climatic *after* Ed thoroughly clamped the bar down and purposely dulled some bits.  Thanks to Ed for the shop time.

​Now that the bus bars were drilled, it was time to add them into the pack.    The new method of connecting went quite a bit smoother than I thought, other than the fact I initially soldered to the wrong side of the pack, sigh.   There was a moment of  excitement when a copper bus bar fell onto the pack creating sparks.  I got to test my 'do something quick' neurons; they were still working just fine, thank you! I'm glad the bar didn't contact the wall as I removed it from its sparking position on the pack in a big hurry.   The pack seemed to be ok, but I'm sure I tested
some of the cells beyond their normal limits.   I also managed to get sparks while using a crimping tool to attach the ring terminals.   I'll be so glad to put the cover on the pack.

To finish the pack, I needed to connect the BMS connections, which monitor every 'cell' (10 cells in parallel for this pack).   Each cell needs a set of wires attached to it.  This both powers the BMS board and provides a way to see how much voltage is present in  each cell. I thought I ordered the right pieces, but when they arrived, I was pretty sure they were not correct.  Quite frustrating, but in any first time venture, some mistakes are expected.   When we met as a team, Joe verified that I had got the wrong part and help me get the correct parts.  They should be here in plenty of time for me to finish the pack for next week.   I also charged the pack using the variac, a timer, one of Dad's old amp meters, and my meter for voltage.

​​While the batteries are critical to our project, they aren't the only place where progress was being made.

Our crimping tool arrived so when we need to assemble our power control box with the fuse and big contactors,  we'll be ready.

Bruce and Eric now have the motor mounted on the go-kart, brakes bled and brake rotor shimmed.   The kart will be ready for adding a battery and controller for testing next week.  Great work guys!  Joe decided to help us organize and plan.   He produced great documentation for the BMS system.  Now I need to do the same for some of the other parts of the system.  After we get the go-kart spinning, I intend to take some time to organize, plan and document our next steps.

When we met this week, Joe showed me how to use the 'git' tool.  This will allow me to integrate my code and documentation with the rest of the project. Thank you Joe.  I'm happy learning new things and 'git' has been on my list to learn for a while.  The purpose of this weeks meeting was to verify all the sub-projects that had to come together before we can get our go-kart running.  Since our display technology is not ready, Ed is lending some portable volt meters we can place on the battery packs to monitor them as we test.  

Plans for this coming week are for test assembly and integration.   We'll need to program the kart controller, finish one battery pack, finish mounting and wiring the power control box, make the Pi portable using the mini-battery pack and write some software to control the power. Hope I get the right parts soon!  Also there are plans in the  future to test some cells beyond their stated limits so we know what to expect when trying to get that last bit of speed.  What is racing, but taking everything to the limit one more time? Stay tuned and thanks again for reading. It's not too late to join us for the fun - contact me (using this link if you don't have my number)