Operation

The SuperBMS has 3 modes: Idle, Charge/Balance/Discharge, and Emergency Low Power.

Idle

When the BMS is in idle mode, it will constantly monitor the cell voltages and board temperatures. If anything goes wrong, an alarm will be triggered, and a reason for the alarm will be printed to the serial console whether or not verbosity is turned on.

The BMS will not be able to charge/balance/discharge the battery at any time while in idle mode. The mode must be externally changed in order for the BMS to be able to charge/balance/discharge.

Charge/Balance/Discharge

In this mode, the BMS will either charge, balance, or discharge the battery depending on what the target voltage is.

In order for charging to work, an external battery charger must be connected. (see Connections)

If the battery is balanced and at the target voltage, the BMS mode will automatically switch back to idle, and 2 chirps will be played by the buzzer.

Emergency Low Power

In the event that the battery is at a critically low charge, the BMS will switch to this mode.

In this mode, the BMS will try to save as much power as possible by doing the following:

  • Deactivate ICs
  • Important operations like temperature regulation and alarms will not be enabled
  • Discontinue providing power to P+ and P- terminals
  • Turn off charger relay

The UART will remain enabled and active, although if the device communicating with the BMS was being powered by the BMS, it will no longer function.

If you want to charge the battery, the reset button must be pressed once a charger is connected. After the board resets, the BMS will enter charge/balance/discharge mode and will disregard the low charge error. Once the battery has recovered from the low charge state, the BMS will return to normal operation.

If the BMS fails to recover the battery, this likely means the battery is damaged or that the battery’s charge was too low to recover from. (see Recovering From Low Charge)

Furthermore, a very low battery could damage the BMS, or prevent it from functioning properly. Monitoring the BMS with the built-in USB port and your favorite serial monitor is highly recommended.

Error State

In the event that an unrecoverable error occurred, resulting in an exception being raised in CircuitPython, the buzzer will play a long tone to indicate an error and the BMS will put all ADCs to sleep, disconnect all discharging resistors, disconnect the charger, turn on the fan until the board is cool, and then exit.

At this point, the BMS will need a power cycle or the reset button to be pressed.

Please create an issue on this repository if an error occurs.

Connections

The SuperBMS has 8 connections.

  • Main Battery Port
  • B+ C+ P+
  • B- C- P-
  • UART

Main Battery Port

The Main Battery Port is where the individual cells are connected to the BMS.

This port also supplies power to the BMS.

B+ C+ P+

The battery, charger, and load positives. All connected together.

Current flow between these pads is unregulated.

B- C- P-

The battery, charger, and load negatives.

A relay is between B- and C- for controlling whether the charger is connected or not.

A MOSFET is between B- and P- for controlling whether the load is connected or not.

UART

The serial communications port. (see Interfacing with the BMS)

Code

Only modify the code if you know what you are doing.

In the main script, modules are imported, pins defined, objects are initialized, and the main loop is run.

The BMS object is where most of the stuff gets done, it also contains all of the important variables.

Configuring the ADCs

Information on the ADCs (ADS1248IPWR) can be found here:

Changing variables

Here are the variables that can be changed:

mode

Controls the mode the BMS is in, being:

  • 0 - Idle
  • 1 - Charge/Balance/Discharge
  • 2 - Emergency Low Power

cellCount

The number of cells connected to the BMS.

maxTemp

The maximum allowed temperature for balancing/discharging.

fanTrigger

The temperature in which the fan will be turned on.

minVoltage

The minimum cell voltage before alarm.

maxVoltage

The maximum cell voltage before alarm.

targetVoltage

The voltage the BMS will try to achieve during Charge/Balance/Discharge.

warningVoltage

If a cell drops below this voltage, the BMS will set the corresponding index of the status summary to True when a device requests it.

shutdownVoltage

If a cell drops below this voltage, the BMS will switch to Emergency Low Power mode.

dV

The target maximum cell voltage difference for balancing.

balTime

The duration of the charge/balance/discharge cycle.

errorDetect

The change in voltage per cell between measurements to trigger a Measurement Error.

verbose

Activates lots of print statements for the built-in USB console.