Smart Battery Management System with KiCad

“ GreenBMS is an open-source smart BMS power management system that supports Bluetooth communication. “

Overview

Smart BMS is an open-source battery management system for lithium battery packs (LiFePO4, lithium-ion, NCM, etc.).

Author’s Statement:

Why Choose Green BMS?

A year ago, I bought an electric motorcycle for my daughter and replaced the exhausted PB-gel battery with a lithium battery pack (LiFePO4).

To manage the lithium battery, I couldn’t find an intelligent, affordable, and easy-to-configure product on the market. So I decided to make one myself!

After a lot of work, when I saw it working well, I decided to share the Green BMS project with the world, giving others the opportunity to use it and even improve it.

My daughter’s scooter has traveled hundreds of kilometers, but this project is not only suitable for electric devices but can also be used for solar storage systems and any application powered by lithium batteries.

I am glad to contribute my little effort to the environment and a sustainable future through my project!

Hardware Features

A lithium battery pack requires a BMS (Battery Management System).

The main functions of the BMS are:

• Prevent battery voltage from being too high
• Prevent battery voltage from being too low
• Protect the cells when the temperature exceeds the range
• Balance the battery cells

The smart BMS also has the following features:

• Monitor the battery pack
• Monitor each battery cell
• Control parameter settings

Green BMS includes four main components:

1. Battery Module

2. Control Unit

3. Limiter

4. Android Application

The voltage and temperature values of each battery are obtained by the corresponding battery module (Attiny) and sent to the control unit (Arduino Mega) via a serial I2C line.

The control unit starts or stops charging through the limiter (which includes a power relay for opening or closing the charging circuit) (via output relays). The control unit can also start or stop discharging through output relays.

Balancing current: maximum 1.2 A (adjustable via parameters).

When balancing only one battery in the pack, the control unit activates the current limiting function inside the limiter (charging current limited to 1A).

The control unit can connect to smartphones via the Green BMS application (Bluetooth)!

Battery Pack Module

The battery module connects directly to the battery and is powered by the battery itself

The battery module microcontroller (Attiny84) receives the battery voltage, battery terminal temperature, and balancing resistor temperature signals and executes the following functions using the logic included in its software:

– Communicate with the main control unit via I2C serial protocol

– Send values of battery voltage, battery positive and negative terminal temperatures, and balancing resistor temperature to the BMS control unit

– Perform battery balancing according to the instructions from the control unit (via mosfet).

The battery module communicates in parallel with the control unit via an isolated 4-wire I2C bus.

The user can program the I2C address of each cell module using buttons and check the ten and unit values through the flashing of two indicator lights. The settable address range is from 1 to 99.

The module address is independent of the module’s connection on the I2C bus. The address is stored in the Attiny EEPROM.

Another important function of the battery module is the voltage compensation calibration using the button on the circuit board.

The average current consumption of the battery module is 15 mA.

Battery Pack Module Hardware

The above image shows the main components of the battery module. When connecting the 7-pin programming connector, the microcontroller gets power from the battery; when the connector is not connected, the microcontroller is isolated from the battery: in this case, the software can be loaded by connecting an “Arduino as ISP” cable.

The software in the Attiny84 microcontroller is developed using the open-source Arduino IDE application.

The software is loaded using the “Arduino as ISP” tool, which is a special configuration that uses the Arduino Uno controller as a programmer for the Attiny microcontroller.

Limiter Unit

The BMS battery management system limiter unit starts or stops charging according to the instructions from the control unit.

When the BMS is only balancing one battery in the pack, the control unit commands the current limiting relay to force the charging current down to 1A to stop charging the battery that has reached the balanced voltage (being balanced) while continuing to charge the other batteries.

The current limiting circuit includes a Mosfet IRFZ44N, an NPN transistor BD139, and a 0.68-ohm power resistor, which generate high temperatures, so a metal current limiting box must be selected for heat dissipation, and a dedicated insulation kit must be used to secure the above components.

In addition, the limiter is equipped with a safety thermostat that opens the circuit when the critical temperature is reached.

Honeywell 2455R 82-195 L70C

The Green BMS limiter uses a 12vdc power relay, and it is recommended that the charging current does not exceed 20A.

The Green BMS limiter is suitable for 16s Lifepo4 48v: it can be used for charging at higher voltages, but the voltage between the “IN” and “OUT” terminals must not exceed 10V, and in any case, caution must be exercised to ensure the system is safe!

Green BMS APP

For the Green BMS App, you can refer to:https://hackaday.io/project/181453-green-bms/log/198377-green-bms-android-app

Using the APP, various configuration and monitoring operations can be completed:

License

The Green BMS has been certified as open-source hardware by the Open Source Hardware Association, UID: IT000007.

License: Creative Commons Attribution-ShareAlike 4.0 International License

Repository & Download

The open-source repository can be found on Github:

https://github.com/Green-bms/SmartBMS

Baidu Download:

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