Objective:
The Aux Battery needs to be also protected, as well as charged by the main battery while the car is operating on the main battery. Aux BMS will be powered by the aux battery itself.
Current State:
Currently, this board charges the Aux Battery. It doesn't do protection, that protection is handled by front power distribution. That's subject to change.
Protection:
- Over voltage
- Under voltage
- Over current
- Over temperature
Behaviour w.r.t Power Source:
| # | Main Power Source | Condition | What happens |
|---|---|---|---|
| 1 | Main | Aux battery is getting charged by the main battery and nears its full capacity (Overcharge condition) | The BMS must disconnect Aux from the main battery. |
| 2 | Aux | Aux battery is nearing under voltage. | BMS disconnects aux from the rest of the car. |
| 3 | Aux & Main | Too much current gets drawn from Aux. | BMS disconnects aux. |
| 4 | Aux | Aux temperature gets too high | BMS disconnects aux. |
Behaviour w.r.t Car State:
car state can be:
- Driving: Main battery is used. everything's powered.
- On: Car's turned on without pressing on brakes. Aux is powering the car.
- Off: Car's turned off, but Aux is being used to power some of the boards.
| # | Car State | Event/Condition | What should happen |
|---|---|---|---|
| 1 | Off | Over Voltage: We replace aux with another battery that's over charged. | Soon as Aux Battery gets connected to the Aux BMS, it should start discharging until it reaches the maximum allowed voltage. |
| 2 | Off | Over Current: why would we have this? 🤔 | |
| 3 | Off | Over Temperature: | Rest of the car is not powered. |
Questions:
| # | Question | Answer |
|---|---|---|
| 1 | When the car is turned off, how can we tell if the Aux Battery is faulty or not? | When the aux battery is not faulty, we power an LED. |
| 2 | Are we going to have fans to cool aux battery down in case it faults due to hotness? | |
| 3 | Could we have over current when car's off? |