1st Test Drive!
The last item on the punch list for the first drive was calibrate the brake pressure sensor. I had spent a lot of time and effort in getting that sensor mounted near the rear brakes that I detailed in an blog from last year named Almost Rolling. The pressure sensor is used to indicate braking which will signal to the GEVCU to command the DMOC/Siemens into regen to slow the car. Because the regen torque can be set to a very high level almost no brakes are required. But the transducer has to signal the brakes are being applied and the brake lights come on. The calibration procedure is very simple, just take a reading with the brakes off and then with the brake pedal pressed. Unfortunately when I press the brake pedal the pedal went to the floor with no resistance. Somehow air had gotten into the brake line and the brakes would need to be pressure bled again. Previously I had a real problem pressure bleeding the rear brakes. I could not get a good flow of brake fluid to remove all the air in the line. Something was preventing the flow. Besides the master cylinder the only other component in the brake line is the proportionating valve that is used the regulate the pressure in the rear brakes so they don't lock up. These types of valves were used before ABS was developed. I was concerned I might have to replace that valve because of the rear disk brakes I had installed. They would brake stronger than the drum brakes that the car came with and might lock-up with hard braking. But I also increased the braking strength of the front brakes too with new rotors and pads. I thought I could just see how the brakes would work without changing it. With the brake bleeding problem it became necessary to replace the valve. I installed an adjustable valve from Wilwood brakes. That solved the brake bleeding problem but I still could not get a good brake pedal. The only thing left to check were the rear brake calipers. I had read online that some new calipers need to be bench bled. Before going to that effort I unbolted the caliper from the hub, with the flexible brake line still attached, I rotated the caliper so the bleed nipple was straight up. Using the pressure bleeder I found both calipers had a lot of air in them, especially the right rear. By moving and rotating the caliper I was able to get all the air out. Once I was able to do that and bleed the rest of the brake system once more I got a good stiff brake pedal and I was able to calibrate the brake sensor.
Just when I was in the process of getting the car ready for the first test drive I discovered the GEVCU was not sequencing the high voltage contactors correctly and the DMOC would not spin the motor. It seems the GEVCU lost some of its configuration data. When I was trying to figure out what was going on I discovered the contactors were fused because I could measure high voltage at the buss bar when the car was off. That means they do not switch the high voltage and are permanently shorted. They can be damaged when a high current pulse happens. The DMOC has a large capacitor bank and when not charged looks like a dead short and will take a large current pulse from the battery pack if not controlled. In my design I use a precharge resistor to limit the current inrush. But that only works if the contactors sequence correctly. With the GECVU loosing configuration data it must have caused the contactors to fail because I had bench tested the contactor box many, many times. I even found a problem with the GEVCU MOSFETS that would have lead to this problem. But I fixed that circuit issue on the GEVCU I am using and had tested it extensively. Unfortunately the contactors are not easily replaced in my build. They will have to be replaced but since they are fused they should conduct enough current to move the car. To get my first test drive I built another precharge/contactor circuit that runs off an Arduino Uno processor and relay shield. Once I installed that and verified it was working I was ready for the test drive.
Finally I was able to get the car off the jack stands and back it out of the garage under EV power. That is the first time the car has been out of the garage since January 2014 when I pushed the car out of the garage and pressure washed the engine compartment after the internal combustion engine (ICE) was removed. I drove the car out of the garage this time to finish painting inside the engine bay and the area where the hood is mounted. After the painting was completed I had to drive the car back into the garage and wait for the paint to dry a couple of days so I could mount hood. I mounted up several GoPro cameras around the inside and outside of the car. After that I went on the first test drive. The car drove great! Very smooth and responsive! I did not drive it further than around the block a couple of times because of the fused contactors. Before going on the test drive I weighed the car. On this website in my design section I showed after all the ICE components were removed the car weight was just 1776 lbs. Now with all the electric vehicle components the car weight is 2860 lbs and the weight is nearly 50/50 front to rear (48/52). If the rule of thumb for energy use holds then the 320i should use no more than 286W/mile. My Leaf used to do better than that and the Leaf was a heavier car. The Chevy Volt I have now is a much heavier car but because it has such low coefficient of drag I have seen energy use as low as 250 W/mile. Obviously the lower the number the further the car will go on a given battery capacity. So with my total capacity at 3.5V charge being 26.6KW the 320i should be able to go 97 miles - almost the full 100 mile design goal! Of course how far the car will drive on a charge is dependent on so many factors, the most of which are how aggressive I drive the car and how fast I drive on the interstate. The Volt does so well because of its aerodynamic shape, but the 320i is a bit of a brick so it will consume a lot more energy at highway speeds.
I still have to finish the carpet installation and install the passenger seat. I still don't know what I am going to do with the rear seat. There really is not much room in that car for the rear seat so maybe just a platform that protects the battery boxes would be good. Something will have to be done with the contactor box. I might just jumper over the failed contactors and continue to use the new contactor box in the trunk. I also need to fix the BMS board and find out why the instrument cluster is not working. I tested that before I mounted it in the dash so all the cabling should be correct. For the test drive I used my Samsung tablet to display the embedded website so I could monitor all the drive functions. Once all these issues are resolved I plan to fully charge the battery pack and take the car for a long drive to see what the energy use will be.
But there still is a lot to do before the car can become a daily driver. I have some BMW badges that need mounting along with the "Electric" badges I got. Have to make sure all the lights are working and then the car needs to be inspected. I need to have the registration changed to show it is electric drive now, although on old cars like this they do not do an emissions test. Mostly just mechanical and lights but that will put the car in the registry database and I will be able to get an EV license plate, if I want.
A video of the first drive and some of these other fun issues can be found here.
Or you can check out the prequel video to the first drive here.