10-cell BMS using TI bq76930
ntosme2
Posts: 38
BMS Build Log: vehicle edition
So far I've converted, or helped convert several electric vehicles but I haven't actually built a proper battery monitoring/balancing system. That changes now!
Design requirements:
* Isolated modules - target pack voltage is 330V, 100-series LiFePo4
* Multi-drop bus - CANBUS because it's the ubiquitous industry standard in most vehicles
* Very low quiescent power draw - the BMS shouldn't be the cause of significant cell imbalance
* Balancing - extra energy in weaker cells is dumped near 100% SOC to correct for drift between cells
Version 1 has a couple major flaws, but I'm able to interact with the bq76930, read cell voltages, and enable the balancing circuits. RevB will fix some missing traces and rearrange how the Propeller and CAN transciever are powered.
I'm going to go ahead and make this an open-source, open-hardware project.
https://gitlab.com/ntosme2/bms_pcb
https://gitlab.com/ntosme2/bms_firmware
So far I've converted, or helped convert several electric vehicles but I haven't actually built a proper battery monitoring/balancing system. That changes now!
Design requirements:
* Isolated modules - target pack voltage is 330V, 100-series LiFePo4
* Multi-drop bus - CANBUS because it's the ubiquitous industry standard in most vehicles
* Very low quiescent power draw - the BMS shouldn't be the cause of significant cell imbalance
* Balancing - extra energy in weaker cells is dumped near 100% SOC to correct for drift between cells
Version 1 has a couple major flaws, but I'm able to interact with the bq76930, read cell voltages, and enable the balancing circuits. RevB will fix some missing traces and rearrange how the Propeller and CAN transciever are powered.
I'm going to go ahead and make this an open-source, open-hardware project.
https://gitlab.com/ntosme2/bms_pcb
https://gitlab.com/ntosme2/bms_firmware
Comments
Some of us do not know what is a bq76930.
I had a look at the TI website and find that it is a very advanced battery monitor, covering a wide range of pack sizes. I attach a snippet below for others.
This is a very useful, practical project. My own interest is remote 48V solar power systems. I will follow your development with interest.
BQ76930 snippet from TI website;
The bq769x0 family of robust analog front-end (AFE) devices serves as part of a complete pack monitoring and protection solution for next-generation, high-power systems, such as light electric vehicles, power tools, and uninterruptible power supplies. The bq769x0 is designed with low power in mind: Sub-blocks within the IC may be enabled or disabled to control the overall chip current consumption, and a SHIP mode provides a simple way to put the pack into an ultra-low power state.
The bq76920 device supports up to 5-series cells or typical 18-V packs, the bq76930 handles up to 10-series cells or typical 36-V packs, and the bq76940 works for up to 15-series cells or typical 48-V packs. A variety of battery chemistries may be managed with these AFEs, including Lithium Ion, Lithium iron phosphate, and more. Through I2C, a host controller can use the bq769x0 to implement many battery pack management functions, such as monitoring (cell voltages, pack current, pack temperatures), protection (controlling charge/discharge FETs), and balancing. Integrated A/D converters enable a purely digital readout of critical system parameters, with calibration handled in TI’s manufacturing process.
Features
AFE monitoring features
Pure digital interface
Internal ADC measures cell voltage, die temperature, and external thermistor
A separate, internal ADC measures pack current (coulomb counter)
Directly supports up to three thermistors (103AT)
Hardware protection features
Overcurrent in Discharge (OCD)
Short Circuit in Discharge (SCD)
Overvoltage (OV)
Undervoltage (UV)
Secondary protector fault detection
Additional features
Integrated cell balancing FETs
Charge, discharge low-side NCH FET drivers
Alert interrupt to host microcontroller
2.5-V or 3.3-V output voltage regulator
No EEPROM programming necessary
High supply voltage absolute maximum (up to 108 V)
Simple I2C compatible interface (CRC option)
Random cell connection tolerant