Protection and limitation
There are two ways how the BMS can protect the battery:
- Turn off the BMS ports
- Limitation - send a CAN message and ask the connected device to reduce the current
Limitation
The limitation concept is, that the connected device is listening to the BMS and reducing the current if the BMS asks for it. If the device listens to the BMS, the BMS is not forced to turn off the ports. This results in a better user experience, because the user can still use the device, but with reduced power.
The BMS can send a CAN message with a limitation request. This message is implemented on the application level - the BMS must send the message and the controller must react to it, otherwise, the BMS will turn off the ports and the limitation concept will not work.
| Variable | Description |
|---|---|
/driver/totalLimitPos | Avaliable relative current in positive direction |
/driver/totalLimitNeg | Avaliable relative current in positive direction |
Both variables have a range from 0 - 1. If the value is 0, it means, that there is 0 current available. If the value is 1, it means, that the full current is available.
If there is any limitation active, the BMS will indicate what is causing the limitation with state /driver/limit. Use the wtf command to see the reason for the limitation and check "Limiter state" section. More about diagnostic
limit dec value | Description |
|---|---|
| 0 | No limitation |
| 1 | BMS temperature too high |
| 2 | Battery temperature too low |
| 4 | Battery temperature too high |
| 8 | Not used |
| 16 | Cell voltage too low |
| 32 | Cell voltage too high |
| 64 | DSC current too high |
| 128 | CHG current too high |
*limit is a bitwise state.
Protection - turn off the BMS ports
Turning the ports off is always the last resort. If the BMS turns off the ports, the user must turn them back on. The BMS will not turn the ports back on automatically.
If the ports are turned off due to the protection of the battery and BMS, the BMS will enter PROTECT state.. Use the wtf command to see the reason for the protection. More about diagnostic