Chevy Bolt Batteries
To get more driving range and because many of my original CALIB batteries had degraded, the batteries were upgraded in late 2020. The upgrade batteries that were acquired new are the Chevy Bolt 5.94kW-h module shown in the picture below. These modules are made by LG Electronics and are NCM (Lithium Nickel Cobalt Manganese Oxide) chemistry. Each module has a 180AH capacity and the 9 modules that will be used gives a 53kW-h battery capacity. For a 85% discharge that provides 45kW-h of driving capacity. At the measured power consumption of 292W/mile by the vehicle that capacity should provide just about 155 miles driving range. Although the new batteries are bigger and weigh more than the CALAB cells the new batteries will only increase the weight of the car 100 lbs but increase the driving range by 2 times! A great feature of these modules is that they are already wired for a Battery Maintenance System (BMS). Each module has 10 cells wired in series and there are connections to each cell on the module so the individual battery voltages can be measured. The connections are a pair of multi-pin connectors at one end of the module. The Chevy Bolt uses a central processing unit for the battery maintenance so in the Bolt each battery module has a pair of cables that runs back to the central controller. For my build each battery module will have its own BMS controller. This is easier than running wires from each module up to the engine compartment. Although between the wires from one module the most voltage would be 41V (full charged battery) the wires will have the full pack voltage, with respect to ground. Local BMS control will be safer at this point in the 320e build. I was able to order the Chevy Bolt battery wiring harness on Chevy Parts Online. By taking the wiring harness apart I could build several cables with the corresponding connectors already attached and used them to connect to the local BMS controlling circuit. The connectors already had the correct number of wires. Each side of the battery is different so the connectors have to match the battery connection. A BMS demo board, the DC2259A made by Analog Devices was initially tested to use for the module BMS. The connections to the battery module and a BMS demo board are shown in the second and third photos below.
BMS connection on battery module. These connectors were obtain from a Chevy Bolt battery wiring harness that was purchased online. The connectors are keyed and lockable. If I could not get the Chevy Bolt battery wiring harness I would have had to find the connectors, find the pins for the connector and the crimp tool for the pins. The premade connectors was the only way to go.
I did not have a wiring diagram of the BMS connections on the Bolt battery module. I assembled a couple of barrier strips and broke out all the wires from each connector to determine which wires were the pairs for each battery cell in the module. I highlighted the connections for the first cell. Using this method allowed me to make a connector to connect the BMS demo board. However, the wiring order had to change for connection to the BMS demo board. True that in the image M11 to M21 is the first cell. For the BMS demo that M21 wire has to be next to the M11 wire (green and cyan). By alternating the wires from each connector the battery voltage steps up for each connection, relative to the battery (-) connection because the cells are all wired in series. The image also shows why the BMS connectors are unique to each side. One side has 5 wires and the other has 6. They are not interchangeable.
A DB25 connector is used for the wires coming from the battery module to make connection the BMS demo board because the demo board is only supplied with screw connectors. The DB25 was installed on all the modules to enable the test of all the batteries with one DC2259A Demo board. You will notice a green/yellow wire coming out of the battery on the right side and a cyan wire coming out of the left side. Those were installed to fix a problem that I found with the Bolt battery modules. Scroll down to the bottom of this page for the link to the update for the Bolt batteries.
Pictured below the DC2259A BMS demo board that demonstrates the LTC6811-1 BMS integrated circuit. It is the 48-pin integrated circuit at the center of the board. The other components on the board are a set of transistors and resistors for trimming the battery cell voltages and a group of circuits for data communication with Isolated SPI.
Below is a plot of the average of the ten cells in each battery module that was measured with one DC2259A BMS demo board on 12-21-2020. This measurement is of the as-received modules from the factory. For effectively 90 cells the cell voltage variance is only +/- 2.5mV. If the two modules that show the largest difference we adjusted to match the other modules the variance would drop to +/- 1mV!
UPDATE: Below is the average cell voltage for 8 of the battery modules, measured recently. The batteries are at a different state of charge (SOC) but the cell voltage distribution is even tighter, less than +/- 1mV. The 9th battery module was not included because it is being used as a bench test platform and the battery box to house the module has not been built yet, so it is not in the car connected to the other battery modules. No adjustment of the individual battery modules was done. This is after nearly three years of charge and discharge cycles.
Read an update on the Bolt Batteries here.