More Batteries
With the new Sevcon controller's ability to handle up to 120v, it was time to expand the battery pack to 32 cells. The CALB 60Ah were discontinued and no longer available. I was able to locate 6 CALB CAM72 (72AH) cells. This new enhancement ended up motivating a complete rewire of the battery system. The boot(trunk) is now much cleaner but still could use a few more minutes of straightening up.
New BMS
The new ANT 32s 300A Bluetooth BMS from eBay is a nice upgrade from the previous serial port version. This meant the Arduino Uno that monitors the pack needed a HC-05 serial Bluetooth board which is a better answer since it isolates the Arduino from the high-voltage pack. The protocol (Github and Github) to monitor the Ant BMS over Bluetooth was straight forward and worked pretty much out of the box. The Uno drives a buzzer, red (IGN) warning indicator on the dashboard, and will disconnect the charger from the battery pack if an alarm occurs or the BMS is not communicating with the Uno over Bluetooth.
The battery pack is now divided into two 16 cell modules, which are easier to manage, than the previous 27 cell single module.
The Pack is 3.3v x 32 = 105v when charged, with a charge limit about 3.45 x 32 = 110v.
The new BMS is wired between the charger and the pack and is providing charge termination along with individual cell voltage monitoring.
The BMS also attempts to balance the cells after charging completes, which seems to be working since the cells are withing 5mv of each other after charging. While balancing, the BMS puts on a nice LED lightshow.
The ANT BMS Software is decent on an Android device and allows excellent customization. Here are the settings in the BMS:
New Charger
The original charger would only go to 99V even though its label indicated it could drive up to 110V. Attaching two 16s 58.4v LiFePO4 chargers in series worked out to be an easy solution and the lowest cost option for a 15A 115v charger. About $160 each versus a single 115v-15a charger which was closer to $500. The chargers are powered directly from the 220VAC power connection.
The chargers are self-terminating, shutting off the charge before any cell reaches 3.5V, which is where the BMS and Arduino are set to terminate the charge. This means there are three different systems monitoring the pack to assure cells are not over-charged. The Uno also monitors and provides an alarm if a cell drops too low, below 2.5V.
Bluetooth Configuration
The HC-05 need to be setup as a Master Serial device and binded to the Ant BMS. Here are the commands that setup the module. Once setup, it quickly connects to the ANT BMS when power is applied.
The required AT commands to set the configuration: Instructables
- AT+RMAAD (To clear any paired devices)
- AT+ROLE=1 (To set it as master)
- AT+CMODE=0 (To connect the module to the specified Bluetooth address and this Bluetooth address can be specified by the binding command)
- AT+BIND=32E3,2E,012345 (Note the commas instead of colons given by the slave module. This is the BT address of the BMS, discovered using a BT scanning app.
- AT+UART=38400,0,0 (To fix the baud rate at 38400)
The HC-05 is put into AT comms mode by holding the button at power-on and running at serial comms passthrough program on the Uno.
Results
The first few drives with the new pack indicate it is working as expected. The controller is driving higher RPMs without field-weakening (FW). In second gear, the acceleration is excellent and 3rd gear easily achieved 58MPH while the motor stayed fairly cool. More testing is still needed to see if the higher voltages results in better watt-hours/mile efficiency measurement. The added cells should add about 5 miles of range but that is still to be tested.
