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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 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.
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BMS Reader and Interface Box Deployment
Now that all the BMS units have been built up and the last ones are being installed, it was time to install the BMS Reader in the car. Shown in the first image below is where I mounted the BMS Reader in the trunk, in front of the trunk battery box. I installed the BMS Reader there because the 12V battery is in the trunk and the first BMS units to be deployed are in the trunk battery box. To be able to connect all the BMS units to the Reader and have +12V and GND connected to the BMS units I had to build the Interface Box. Below the image of the BMS Reader is the Interface Box. The connection design was detailed in a blog from 08/2023 when I first started designing the deployment of the BMS units (link). The actual layout of the BMS units is not like the drawing shown in the image. Instead of connecting each of the BMS units to the Interface Box, the BMS units are connected together in parallel with M12 tees and one connection to the Interface Box is made. Only one Interface box is used, with the two parallel strings of BMS units connecting to it.
The M12 tee connectors where first described in the blog on deploying the BMS units in the trunk battery box (link)and recently the blog on deploying the BMS units on the rear seat batteries (link). The image of the BMS connections from that blog showing the parallel connection is shown again here, below the Interface Box image (jump). That image is the way the BMS units will be arranged in the rear seat. The four rear seat BMS and the four trunk BMS units are connected together in parallel and each of those parallel strings are connected to the BMS Reader, via the Interface Box. They are all wired to create the correct topography for CAN BUS as detailed in this article (link). The topography diagram from that article is shown at the bottom of this blog. For the BMS interface the two BMS units at the end of each parallel string have the 120 ohm termination resistors soldered on the BMS PCA. Each node on my BMS system has a CAN Transceiver and Controller.
UPDATE: BMS measurements on 6-5-2026
BMS Reader deployment in the trunk.
Interface Box deployment in trunk.
The two cable connections on the top are from the the two sets of batteries and the cable connection on the right is to the BMS Reader. The box is switched because it is directly connected to the battery and the BMS Reader and BMS units do not need to be on at all times. The power for the box is fused. Nine BMS units plus the BMS Reader draw about 500mA at 13V. All the BMS units and the BMS reader individually draw about 50mA, so ten connected together draw 500mA. Eventually I will make a cable connection to the LEVID controller for the Instrument Cluster, so the battery voltages can be displayed on the 7-segment display.
Layout
BMS parallel connection using M12 tees.
CAN Topography Diagram
UPDATE: Above is the average cell voltage for 8 of the battery modules, measured recently with the new BMS system. Compare the plots shown in the blog from 5-3-2023. The batteries are at a different state of charge (SOC) but the cell voltage distribution is still just as small, less than +/- 2mV. No adjustment of the individual battery modules was done. This is after over three years of charge and discharge cycles since the data presented on 5-3-2023 and now is nearly 6 years of using the batteries without any adjustment.
One issue that has not been highlighted since I made the blog post about the problem, is that every battery, except one, has one or more cells not reading by the BMS. This is caused by a problem in the connection from the battery cells to the BMS connectors on the batteries, that was detailed in the blog from 10-27-2020. The images from that blog are shown below.
Unfortunately as detailed in that blog, the only way I found to fix this issue is to add wires to connect to the cells not reading by the BMS and that can only be done with the battery on a workbench. No way to accomplish that with the battery in the car. I found that it really is not clear where the problem lies. The soldering to the BMS PCB that connects the battery cells to the BMS connector look fine. It could be the PCB has some defect or the connector to the BMS on the end of the battery is defective. What is very strange is that the PCB does not have a conformal coating on it to protect the PCB. That is usually done on any automotive PCB because it protects the PCB from damage and corrosion.
Update 6/13/2026
Since I had all the hardware to test both the BMS units and batteries I thought would test the battery that has been sitting on my bench. Below is a screen shot of software I developed to test my BMS units (see blog 04-26-2026). The code graphically displays the battery voltage of each cell. The software does a lot of other calculations but what is most striking about this image is that cells 6 and 7 are measuring the wrong voltage. Cell 7 is not even measuring a voltage. This problem is exactly due to what I describe above - there is some broken connection in this battery between the battery cells and the BMS connection. The open connection also causes the next cell to read wrong because the cells are wired in series and the way the BMS IC circuit is designed. What is troubling is that this battery has never been in my car. It has been sitting on the bench for the past 6 years. This particular battery was found to have the first and second cell not returning the correct voltage, when it was first received and tested. I repaired those connections over 5 years ago. Now a new set of cell connections are broken. The battery has only been exposed to the temperature environment of the garage. But that temperature does not vary widely. The garage is heated in the winter and cooled in the summer. Not anywhere near the temperature variation a battery in a car parked outside would see.
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BMS Car Deployment 2
Update 5/2/2026 (See Below)
I built up and mounted four more BMS units in CINCH and Jameco enclosures. See the blog (BMS Ready for Deployment) to review the reason for the Jameco enclosures. These are to be installed in the rear seat with the batteries there. The CAN BUS data and power cables have been made. Still working on the temperature measurement cables. All of the enclosures will be attached to the deck of the rear seat. Unfortunately because of where the BMS units will be mounted in the rear seat all four of the DB25 cables on the batteries will need an extension cable.
Before deploying the BMS units I tested each of them with a program that tests the functionality of the BMS. It logs the 10 voltages measured by the BMS every 5 seconds and runs for 12 hours or more. For this test, code was developed to read the CAN BUS data from the BMS unit and send that out on the USB as serial data. It works very similar to my BMS Reader system, except only one BMS is under test and the data is sent out on the serial bus as text instead of writing to the SD card. The serial data is the HEX CAN BUS frame received from the BMS, converted into text. The HEX data is sent as text on the serial bus. The test program converts the HEX text data to digital and that is what is displayed in the screen shot of the LabView test code below with a GUI that shows the voltage of each cell as a graph. In the screen shot below the box highlighted in red is what one frame of CAN BUS data looks like as HEX data. The first number in the frame (0x61) is the frame number and the second number is the number of bytes in the frame (0x8). Each pair of bytes represent one voltage measurement. Since there are 8 bytes in a frame, four cell voltage measurements are represented in the frame. The first cell HEX data 0x77B1 is 30641 decimal, which when divided by 10,000 gives the cell voltage value. Four CAN BUS frames are required for all the BMS data. The first three frames are the voltage measurements and the fourth frame are the temperature measurements.
The voltages are created by a benchtop power supply and a resistor ladder. See image below. Each resistor is a precision 1K ohm resistor and 10 are are wired in series on the barrier strip to simulate the ten cells in the battery. Nearly the exact same voltage is dropped across each resistor. The difference in the cell readings shown in the screen shot above is do to the resistor precision. You can see from the screen shot that the Std Dev is less that 1mV and that is the variation of all 10 cells combined. This is the same method I used to test my BMS boards against the DC6620A BMS demo board (see BMS Bench Testing blog). For this testing, the CINCH enclosure labeled CAN BUS Reader is just a BMS PCA that has the Arduino Nano Every USB connected to the USB feedthrough so that the serial CAN BUS data could be read by the computer, running the LabView test program. I found looking at the BMS measurement variance in the 12 hour data that the benchtop power supply had more variation than any one BMS cell on any BMS unit. The tests showed all BMS units working very well and the measurements for any channel were very consistent.
Next steps are to finish all the cabling and mount the BMS units on the rear seat batteries. I will have to use a right-angle DB25 connector like the one shown below to connect to the batteries to give the battery cables a low profile to fit under the rear seat cushion. Link to this part.
I will also use these same 12mm tee connectors with the BMS units for the rear seat batteries, as I had for the trunk battery BMS units.
Here is the link for part number T58-A04-FMFR001 catalog page.
Update 5/2/2026
Below is what the layout of BMS units for the rear seat batteries looks like. The middle two Jameco enclosures will be further apart than shown in this image, which is why the data cable between them is longer. Before I can mount these in the rear seat I need to remove the rear seatbelt mounts. No one is going to sit in the rear seat now and the seatbelt mounts are bolted to the seat deck, in the same place the BMS units need to go. I will not need a separate mounting rail like I used in the trunk battery box. I can attach the BMS units directly to the metal of the seat deck. Before I do that I am going to mount some sound proofing underlament like I used under all the carpeting.
All of the DB25 extension cables for the battery connections have been assembled and tested. All of the temperature sensor cables have been assembled, but still need to attach the temperature sensor to those cables. I am using the same 1-wire sensors in a TO-92 case (link) that I used for the trunk box batteries. I found the heatsinks below (link) to mount the temperature sensors in to make good thermal contact to the battery case. They are small enough to slide between the batteries. Shown below the heatsink is how I electrically connected the sensors, using screw terminals with wires soldered to the pins. I will use some silver epoxy with the heatsinks to ensure good thermal contact to the 1-wire sensors.
