So it was finally my turn to drive the MX-5 for a week. It turned out to be five days, because my wife needed the larger car I left at Weber's place. Logistics.
I got to use "Mexy" as a real car - getting the groceries and hardware supplies, driving my daughter to school, and parking half way between where I live and where I work; there is no free parking handy to buses closer than that.
Early in my stewardship, the car was mostly good. I recall one drive from one shopping centre to another (hey - why not?) I had the top down. I was slipping past four wheel drives twice the height of the MX-5 with the wind in my hair - I felt like a rock star! But alas it didn't last, and "bad Mexy came out".
As Weber mentioned above, she would get jerky at certain rev ranges. Fortunately there was a work-around - use a higher gear. I formulated the idea that it was motor temperature causing the problem - when the temperature reached a certain level, it seemed to play up. The controller does monitor motor temperature, and does cut back the power level when a certain temperature is reached. This seemed to explain the "memory effect" - why when it started going bad, it usually stayed that way, at least for some hours. This was the first of many theories!
On the first work day, she was good when I drove my daughter to school. This was her first drive in an electric car, so I was very pleased that it went well. She was impressed, and learned the term "EV grin"
But soon after it went bad again. Bad enough, that I decided it was worth driving back via Weber's place, even though it's quite a detour. This was because we hadn't planned ahead, and had left the Olimex programmer with Weber (this is needed to update the Driver Controls Units (DCUs) that do miscellaneous jobs like sending pedal information to the motor controller, and driving the instruments. There were some instrument changes I particularly wanted. We also wanted to sort out some issues with the CAN-ethernet bridge that we use for data logging. To cut a long story short, someone at Tritium had made a change to suit their network, and we overlooked a checkbox that would have quickly restored it. Things like that can burn up time. On the way back from Weber's house, there is some 100 km/h freeway driving (in retrospect, I probably should have avoided this and taken another route). At above around 90 km/h, the jerkiness was so bad that I could occasionally hear the tailshaft hitting something metallic, probably a battery box. But by staying only a little above 90 km/h and staying in fifth gear, I could avoid the worst of it.
Fortunately for the rest of the time, I didn't need high speed. After the first minute or so after a charge, there would be a transition from "reasonable Mexy" to "bad Mexy". The motor temperature theory was discarded because the temperature limit before limiting power is 140C, and we never got near that figure. We know the temperature sensor isn't way off, because motor temperature is logged.
One of the instrumentation improvements was the addition of a voltmeter, displayed as one of 5 "virtual instruments" (well, one real and 4 virtual) on the tachometer. I noticed that at times the pack voltage would drop some 8 volts in a single update. Despite our battery management system, I thought somehow the pack must have a weak cell or two, and some weird communications problem must be preventing the BMS from telling us about it, and limiting motor power. Or maybe it was limiting power but in a jerky way, somehow without displaying abnormal stress on our "stress-o-meter" (we have the battery stress or discomfort displayed on what used to be the oil pressure gauge). But besides being unthinkable, it just didn't fit the facts that well.
Wednesday, my last day with Mexy, was not a great one for me. I managed to lock my keys in the MX-5, and the only other key was with Weber. By a comical sequence of errors, I managed to get my key back, the rescue EV almost ran out of charge, but it all came good in the end. Weber ended up driving Mexy to his home, and it was basically bad all the way.
As luck would have it, Mrs Weber needed the other EV that night, but part of the comedy of errors found it at my place charging. So despite an alternative ICE being available, and knowing the problems, she chose to drive Mexy, and again Mexy was bad all the way.
We had to find a solution to this problem!
Stay tuned for the next instalment!
[ Edit: some minor edits for clarity. Shipping past -> slipping past. ]
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.