Scott Drive Installation
Although I was part of the group that originally developed the GEVCU to use with the DMOC so many years ago, I recently removed the GEVCU and DMOC and replaced them with a new inverter/controller called a Scott Drive. Even though I have been driving the 320e for nearly two years with the new tires and suspension I have had several problems with the GEVCU. The GEVCU would just suddenly fail to control. The symptom was all the calibration data was lost so the throttle and brake inputs would not register and thereby the car would not move. Also the contactors sequencing was lost so when the car was turned on so all the contactors would close causing one to fuse closed because of the high inrush current. I had to build another contactor system and placed that in the trunk. It ran independently of the GEVCU and used an Arduino Uno to control the sequencing and the timing of the contactors. I also had to jumper around my original contactor box. The GEVCU failure happened twice over the past two years and when it happened again recently I decided to replace the whole system. I emailed several other GEVCU users and some had seen similar failures. The consensus is that the EEPROM was failing – that is where the calibration and setup data is stored. That is very weird because the EEPROM is on the isolated side of the GEVCU board with the CortexM3 processor and no one saw a processor failure. It could be that I just got a bad group of EEPROM ICs. All the GEVCU boards I had were fabricated around the same time. But that does not seem like it could be the issue since others have experienced GEVCUs that were not built by me. All of the failures I experienced happened when the car was first turned on – I never experienced a failure while driving. Fortunately I was never stranded anywhere, the failures all occurred in my driveway or garage. The GEVCU failing was not the biggest issue, however. The fusing of the contactor was a serious problem because when the car was turned off it really was not off. The battery pack was still connected and that caused the battery pack to over discharge. This now made the third time the CALB batteries were discharged below 2.5V (see blog Driving soon???). Once I recovered the batteries I found several that would charge to the upper voltage limit faster than other batteries, even though they were all bottom balanced to the same voltage. That became a problem because the pack charging would have to stop and I would have less than 60AH charge in the pack. I tested several of the high voltage batteries on the battery cycling system I have and they only showed a small decrease in capacity, anywhere from 5 to 8 AH. But I was seeing batteries max out and limit the total pack charge to 45AH.
I had purchased the Scott Drive SD100 from EV West more than 5 years ago thinking at some point I would do the upgrade. Of course the Scott Drive upgrade was not without problems. The wiring harness had to be changed for the throttle and brake and the Scott Drive has a completely different connector that had to be assembled. When I first tried to turn the Scott Drive the motor would not turn smoothly. I discovered a bent pin in the Siemens motor connector that was one of the motor phase control pins. The pin must have been bent when I installed the new control cable for the Scott Drive. Once I fixed that I then found the motor would spin smoothly, but only in reverse. The Scott Drive has a great GUI for setup, calibration and control of the inverter. But what I discovered next was that the firmware in my Scott Drive was several revs old so the controlling GUI would not work, specifically to change the direction of the motor rotation. That required a firmware upgrade via an AnyDesk session with Scott Osborn, the maker of the Scott Drive, who lives in New Zealand. It took a couple of weeks to arrange the upgrade. I hope for any future upgrades I will be able to carry out the process because Scott charges for the upgrade and the time difference makes it challenging to communicate. One feature of the Scott Drive that I don’t remember setting a limit for in the GEVCU was the maximum output current. My original 60AH CALB batteries are capable of discharging at 10C. That would mean a max current rate of 600A. The Scott Driver 100 that I have is limited to 400A. The inverter is also limited to 150kW peak, which is more than the DMOC was rated for. With 400A and my pack voltage of 375V I would get to the 150kW peak, at least for a short time during acceleration. It is hard to say if the limit changed the acceleration capability of the car. I never really measured it by anything more precise than the seat of my pants. I had always planned to take the car to a dynamometer. Unfortunately the closest shop to me that had a dynamometer closed last year and all the others were far away. Driving a long distance to one is really not an option as the pack is discharged, the voltage drops, so the output power drops. But the real problem is just having the range to go there and back. With a pack charge of 45AH that means just under 50 total miles driving range. Probably the range would be way under 50 miles because some of the battery capacity would be used on the dynamometer.
The last upgrade I did was not really planned. During one of the times that the GEVCU failed I was moving the car in and out of the garage with an electric wench. To pull it out I would attach the wench to a tree at the end of the driveway and then to pull it back into the garage I have a bolt screwed into the concrete to attach the wench. Pulling out was no problem because the 320e has a tow hook on the rear of the car. But on the front there is none so I was pulling on the main cross-over. I think what happened when I was straightening the car the tow band slipped off the cross-over and slipped onto the steering rack, thereby pulling on the tie-rod connection. That must have pulled something out of alignment in the steering rack as the steering was locked, I could not turn the wheels. Because the car was not pointed straight I had the jack the front of the car with a floor jack and slowly pull it back into the garage. I ended up having to replace the steering rack. Fortunately remanufactured racks are still available for my car. The upgrade was the mounting bushings that mount the rack to the car. I upgraded to polyurethane bushings that should give the car more precise steering. Also fortunately there are several YouTube videos on how to install the steering rack on mine and similar model BMWs. But seeing how it was done and doing it turned out to be very far apart. I hope I will never have to do that again!
A video of all these upgrades can be seen here.