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Cascadia CM200 Inverter Installation
I replaced Scott Drive SD100 (See Blog below Scott Drive Failure) because the SD100 had a thermal breakdown. It is still not clear what caused the thermal breakdown except for the high temperatures on the day it happened. The SD100 is now non-functional. I got the CM200 to replace the SD100. The CM200 requires a Vehicle Control Unit (VCU) and a precharge circuit which were not used on the SD100. Those systems were built into the SD100. The VCU being used is the AEM VCU200. I provides all the CAN message to the CM200 for the motor control and performance based on various inputs like throttle and brake. It has a GUI for setup, calibration and control called AEMCal.
The only other signals the inverter gets are the encoder signals from the motor. This inverter rating is more than twice that of the SD100 which was 100kW. The CM200 is rated at 225kW. It's rated input is 750A at 450V! In my car, the battery pack cannot output that much current and voltage, limited to 600A at 340V. Even if the battery pack was capable, the peak current for the Siemens motor is 400A. The inverter in my application will therefore be limited to run at a lower power, but will be above what the SD100 was rated at. The most significant difference however, is that the CM200 can output the peak current for 30 seconds! The measured peak output of the Scott Drive was something closer to 3 seconds. Very underwhelming performance. The CM200 should greatly improve the driving experience.
Beginning of the CM200 installation.
Shown in this picture is the CM200 bolted to the inverter support frame. Since the CM200 is considerably smaller than the SD100 I had to cut some 1/4" aluminum plate to bridge the inverter support frame. I will use a couple of carbon fiber plates to cover the open areas in front and behind the inverter. The battery cables in the image are 2/0 gauge. That is the size of wire I used in my car to connect all the batteries to the drive electronics. The larger wire will require additional wire management and strain relief. You can see the CM200 uses specialized connectors for the cable to the inverter connections. The inverter comes with the larger wires and specialized connectors because of the high power rating.
The water lines still have to be connected to the inverter. That will happen after I change the water pump. For the higher power, the CM200 needs a higher cooling flow rate so a new, high capacity pump will be used.
AEM VCU200
Most of the car uses Ampseal connectors for the control signals. The VCU200 uses Molex connectors which will require a new wiring harness to connect the VCU200 to my cross-over box. The cross-over box was something I built for the car back in 2015. You can see the video here starting at 8:48 in the video. The cross-over box will require some modification for the VCU200 connection. All of the same signals are still used with a few new ones. The CM200 via the VCU200 has a lot more control functions than the SD100 every had. Eventually the VCU200 will be connected and control my BMS and an IMD (Insulation Monitoring Device) like this one from Isabellenhuette (link). An IMD will detect and help prevent what happened to the SD100 with the insulation break down short.
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Scott Drive Inverter Failure
Update 10/2/2026 (See Below)
Due to the success driving a total of 85 miles roundtrip for the BMW CCA Concours d'Elegance on 6/28/202 in Canton, MA, (link) I decided to go to some other car show events that were further than the ones I usually go to. Those are at most around 30 miles roundtrip. One of further distance shows was the BMW Day at Larz Anderson Auto Museum in Brookline, MA about a 75 mile roundtrip from my house. Nothing unusual that day other than the air temperature being in the mid to upper 80F. The car drove just fine down there, exhibiting the same 0.87 Ah/mile mileage as the trip to Canton did, six weeks prior. The problem was the parking of the car. The organizers of the event really did not have any people around to guide people to park. Cars were being parked in all kinds of locations. I had to park the car on a slight incline. With the hood open, the entire engine bay was directly in the sunshine, due to the incline. Normally this has not been a problem but the event was over two hours long. When it was time to leave the inverter showed 40C, just from sitting in the sun. I was not aware of the low temperature limit of the SD100, thinking it was the same as the Siemens motor, which is 85C. At the starting temperature the inverter was already too hot. The only safety in the firmware to protect against this issue was reduced current to the IGBT drive transistors. The car drove very irregularly, feeling like it was loosing power. Probably because of the high temperature. There were strange things happening too. The heater blower motor would intermittently turn on. The 12V voltmeter in the center console started show crazy numbers and then completely stop showing anything. On the drive home on the interstate the car actually turned off a couple of time, but started again each time. We made it back to my house. The temperature did not go above 45C, especially on the interstate where the radiator could help cool the cooling fluid. Later that day I moved the car out of the garage to do some work in the garage. When I was done the car drove just fine back into the garage. No hesitation or vibration.
The next day the car would turn on, however, the motor would not turn smooth with throttle application. It vibrated like it had the wrong U-V-W connection or the encoder connection was wrong. Since the car had just previously run and neither of those systems were modified there had to be something else going on. The contactors sequenced correctly. Bringing up the GUI for the inverter did not show any major problem or errors. It showed the correct battery HV. The only issue was the V Channel showed a noisy current value of tens of amps. That was strange. Opening the hood and it looked like the cover for the U-V-W channel output to the motor was discolored. Removing the cover I found the center channel to be burnt and the plastic around it was melted. That is shown in the image below.
I found the V channel was also shorted to chassis ground. That is because the heat must have melted through the cable jacket so that the braided mesh shielding was connecting to the case of the inverter. The V channel was so badly melted into the plastic cover that I had to chisel the burnt plastic to remove the cable. Once I removed all the cables I got the cover off the inverter and I found the images below.
PCAs were discolored but did not looked burnt and components had not reflowed off. The area below the top PCA showed the flux sensor was burned and melted. Removing the top PCA showed that the V channel driver board was also discolored but not burnt.
It looks like a lot of current went though the V channel. But why? Removing this driver PCA I could get to the contacts of the IGBTs. All three showed the exact same and correct diode voltage drop or resistance between the terminals. That would indicate the transistors were still functional and the junctions not shorted. Was the short to chassis ground in the V channel cable a result or the cause? Was resistance heating caused because of the high air temperature and high temperature of the inverter? A lot of current flowed through the V channel to cause that much damage. The current did not go into the motor but rather into the chassis of the car. The inverter output is a several hundred volt- kilohertz PWM signal. If that kind of signal was radiating out from the inverter it might have gotten induced into the +12V wiring and that is what caused the blower motor to turn on and why the 12V voltmeter in the center console died. No other 12V system or any of the other HV components in the car like the DC/DC converter or the charger were affected. But those systems have filtering to stop that kind of induced signal.
I cleaned everything up and installed a new flux sensor. I machined a piece of plexiglass to replace the melted plastic. Used some other cables I had with crimped on connectors to make the U-V-W cable connections. Below is the inverter installed in the car and connected to everything and energized with +12V and HV. The GUI showed the correct high voltage and the V-channel showed no current. But when the throttle was pressed the GUI would show a firmware fault and the motor would not turn. Some other component in the inverter apparently had failed. Without a schematic it is hard to tell what also failed. I was concerned that maybe a short in the motor led to the large current flow. To make sure the Siemens motor was still okay I checked the inductance of the motor windings. They were found to have an acceptable value and distribution and the motor was still isolated from chassis ground.
Update 10/2/2026
BMS Failures
Once I figured out what happened to the SD100 I started checking other systems in the car. Besides the 12V voltmeter in the center dash that failed on the ride home I found that all the BMS units were returning 0V on all cells on every BMS connected to a battery. I know nothing is wrong with the batteries because I could measure the SOC (State Of Charge) of each battery independently of the BMS and those are all within 0.5V of each other. I have seen channels drop out due to the issue in the BMS monitoring circuit on the batteries. See this blog post from 2023 when I first found the problem (link). That was something that changed slowly over time. I never saw where all the BMS connections in the battery would open circuit. I connected a spare BMS unit to one of the batteries in trunk and found all cells were measuring the correct cell voltage, with a small deviation between cells, similar to what has always been the case with these battery modules. I took one of the BMS units from the trunk battery box and put it on my test bench. This is the test bench with the 10 resistor series circuit that simulates the 10 cells in a battery (link) that I used the test all the BMS units prior to deployment. Precision resistors are used so the voltage drop is very similar for each resistor. The BMS unit reported 0xFFFF for every cell. The CAN BUS was working as I could see that data coming out of the BMS so it had nothing to do with data communication. It had to do with the BMS chip, the LTC6811-2. The main problem is that the test setup should only draw a little more than 3.1mA with 31V across the ten 1K resistors. The LTC6811-2 should only draw 0.005mA so the current to the chip should only be 3.105mA. This BMS current was 11.5mA! Clearly there is a short to ground somewhere. Putting the BMS on the solder station with the microscope I found most of the 100ohm resistors that make up the RC filter that is on each battery cell measurement to looked burnt. When I tried to de-solder and remove one of the resistors it broke in half. After that happened I started measuring the resistance of each resistor. Most were found to be open circuit. I also found some the capacitors that were connected to ground for the RC circuit had conductivities less than 1Mohm. I removed all resistors and capacitors on the input of the BMS IC. I have another test setup that has no resistors and no connection to the cell measuring inputs on the LTC6811-2. It only applies power to the V+ and GND pins of the LTC6811-2. That showed 11.5mA also so the LTC6811-2 is shorted internally. Returning 0xFFFF for the cells measurement is therefore because the LTC6811-2 has failed. I found the same problem on all the BMS units that were connected to the batteries the day the inverter failed. All showed more than 3.5mA on the V+ power test. On all the BMS PCAs, all the circuits on the DC +5V side of the PCA were working without any issue. The Arduino Nano Every was still functional and could communicate with SPI to the CAN BUS IC, which also was still working. That is because the DC input circuit from 12V is hardened against any spurious signals. The BMS reader, which was not connected to any HV was also fully functional. It was connected to +12V and the CAN BUS network. The reader has the same input hardening as the BMS units. The LTC6811-2 was connected on the DC side to the filtered input. But on the HV side it is connected to the battery on the V+ and GND. On the cell measurements it is connected with just the simple RC circuit between the LTC6811-2 and the battery cell on the BMS PCA circuit. If a transient reached the pack terminals it would go through the battery cells and then into the LTC6811-2. A fast pulse or a high frequency signal would conduct through the RC circuit to the LTC6811-2. The IC does have some internal filtering, but if the pulse was fast enough and powerful enough to damage the RC filter resistors and capacitors then it would also do something to the LTC6811-2.
I found when removing the resistors from the PCA that the PCB was damaged to the point where the component pad would lift, when removing the component. That means the PCB is damaged. So just replacing the LTC6811-2 on the failed BMS units will not work. The only option is replace all the units, with new PCBs and components. I have PCBs and the BOM so it is just a matter of ordering all the parts and the time to build all the PCAs. Once design upgrade that will be incorporated to the BMS will be a TVS (Transient Voltage Suppressor) component to the input, between the +V and GND of the LTC6811-2. That is the some type of component that is used in the DC hardening that worked to save components.
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Boston BMW CCA Concours d'Elegance 2026
I entered the 320E in the Boston BMW CCA Concours d'Elegance on 6/28/2026 in the Vintage class, which was the 1st and 2nd generation BMWs model years 1950's-1960's-1970's-1980's in the "Clean" presentation group and won 3rd place. They had both "Clean" and "Super Clean" presentation groups. For "Clean" neither the engine compartment or the trunk is looked at but everything else is. I probably could have been the the "Super Clean" group as my engine bay is as presentable and any of the Internal Combustion Engine (ICE) vehicles that where there. But the trunk has a battery box and the charger so I did not know how well that would be judged. All of the "Super Clean" vehicles took everything out of the trunk and laid it out on the ground behind the car.
Below is my 3rd place award and my entry page on the back of my car. Image below that is the line of cars that was in my group. My hood is open in the row of "Clean" Vintage. You can see the line of "Super Clean" that is the row of cars behind my row, all with the hoods open.
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Battery Box Covers
Here is what the smoke grey plexiglass battery box lids for the batteries in the rear seat look like. The box lids only cover the front and back of the battery boxes, to accommodate all the cables. I still had to make some extra cuts in the plastic to get all the cables covered. The covers should provide a nice support for the rear seat. The rear seat is not going to be used for passengers but it will support a couple bags of groceries. You can see the rear seat installed in the bottom image. The center of the seat sags because nothing is supporting it. I bought some more smoke grey plexiglass to make a cover for the fuse area to solve that problem.
Rear seat leather installed and all cleaned up.
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BMS Car Deployment 3
I mounted the four BMS units on black plexiglass plates and installed them into the rear seat with the batteries. You can see the three of BMS on the plates, installed in the rear seat below. The fourth is just off camera to the left. I had all the cables made up so it was just a task of connecting everything together. Just like in the BMS deployment in the trunk box everything is a tight fit in the rear seat area. The plexiglass mounting plates fit so tight behind the battery boxes that I did not need to bolt them to the rear seat platform. Every one of the battery cables with the DB25 connectors on the rear seat batteries had to have extensions cables made. The thinner grey wires are the temperature probe cables. It is not clear in the image, but one of the M12 cables goes to the trunk area to connect to the Interface box, that was detailed in the blog update 05-30-2026. The last step for the rear seat BMS deployment is to mount grey smoke plexiglass battery box lids that will support the rear seat. Those will be shown in a later update.
