I didn’t document this very well when I put it together so of course this is the thing that came back to bite me in the arse. OK, one of the things. Anyway, when I got it all hooked up in the car it didn’t work. So I had to take it all apart and try to remember what I had done. It was only two months ago but it might as well have been twenty years for all I could remember. A lot has happened in between!
The battery management system or BMS keeps an eye on your batteries during use and charging, as the name suggests, and handles things like balancing the cells to make sure they all remain in a similar state of charge. For this I’m using the SimpBMS code running on a Teensy 3.2. The maker of SimpBMS does offer dedicated hardware that I might well buy at some point, but for now my needs are limited.
The BMS primary interfaces with a load of secondary units attached to the battery modules themselves over CANBus. And it communicates with the other modules in the car over CANBus as well. This means you need to add to the Teensy a CAN transceiver. I’m using SN65HVD230 module. This connects to the Teensy via the following pins:
| Teensy | Transceiver |
| AGND | GND |
| 3v3 | 3v3 |
| CAN TX (Pin 3) | CTX |
| CAN RX (Pin 4) | CRX |
The CAN H and CAN L (CAN high/low) pins on the transceiver then go into your bus connections. In this case, there are three connections to be made here. There is the internal loom that connects to the five battery modules, and two external loom connections.
I decided to keep most of the connector on the internal loom because it had a standard 2.54mm pitch, which meant I could solder up a break-out board for it using standard dupont pins.
More to follow when I get this working again…