offGrid Systems website
Project duration: ~about 1 year
Projectvorm: Fixed price
Period: 2023
Activities: Idea, proof of concept, design electronics and firmware, prototyping, multiple improvements, production, support & warranty
Technologies: Cortex M0, software-based flyback, CAN-bus, C, high-current, LiFepo4 charging, Active Lipo balancing, BMS
Parts: M031TD2xx, STM32F105, SN65HVD234, MAX15062, LM3404, LTC4364, INA228, INA237

Description:

On another page we have described the development of an off-grid energy system monitoring and management solution. One of the key components of such system is the energy storage facility. This can be accomplished by means of old-school unmanaged and heavy lead-acid batteries, or with modern light-weight fully managed Lithium-Ion battery packs, or another lithium flavor such as lithium-polymer (LiPo), lithium-iron-phosphate (LiFePo4/LFP). This follow-up project is about the development of the battery management system (BMS) that resides in these new battery packs.

Active balancer module

Specifications:

  • Operating voltage 20-30VDC (nominal ~25.6V)
  • 105Ah or 280Ah LiFePO4 cells in 8S1P or 8S2P configurations
  • 200A Discharge and 100A charge paths, individual switchable, short-circuit proof
  • Current-loop 'bal.link' serial port for cell communication
  • Independent charge and discharge shunt resistors for current measurement and charge accumulation
  • State of Charge operating region 10% to 95%
  • Statistics-based balancing and advanced OCV-based end/top balancing
  • Heater output for cold climate operation (charge < 0°C, discharge < -20°C)
  • Battery statistics for delivered energy, saved energy, cell voltages and charge cycles
  • Event logging via CAN-bus
  • CAN-based OGS control® bus connects up to 48 batteries with the OGS control® Master
  • Optional front panel graphic display

Specifications balancer module:

  • Voltage 2-6VDC
  • Balancer current up to ~10A
  • Dual NTC sensors
  • Bi-color LED for status and fault indication
  • Current-loop 'bal.link' serial uplink/downlink
  • Pass-through for heater element connection

Active balancing:

The balancer modules have a integrated ~50W flyback converter that allows for removing charge from individual cells and to divert that energy to the cell stack or to a separate power resistor / heating element.

560Ah or 15kWh LFP battery pack

Application:

The controller is used to build custom hot-pluggable 105Ah or 560Ah LFP battery backs for the OGS control® based off-grid energy system. Multiple of these packs can be combined to create solutions with very large storage capacity. Currently, the design allows for 48 parallelled packs, thus a total installed capacity of almost 27kAh (~700kWh). Of course, that number or capacity can be expanded to greater numbers with modifucation of the CAN bus protocol implementation or with the addition of OGS CAN-bus repeater devices.

Scalability:

Using the same algorithms and electronics build with similar parts, we can build battery management systems with other configurations in excess of 100 cells. Contact us to discuss your requirements.

'OGS control' is a registered trademark of Reijneveld Machinebouw B.V.