Horizon BMS

Digital Battery Management System for electric vehicles.

...DOCUMENTATION IS STILL UNDER DEVELOPMENT...

History

Features

Non-distributed, Master-Slave/Autonomic topology. Distributed topology is also possible (under development)

Unlimited number of cells supported (each board supports up to 12 cells)

All types of cell chemistries (0.8..6.0V/cell) supported

CAN-bus serial link for full monitoring (option)

Undervoltage detection (BLDC controller control over CAN or dedicated line)

Overvoltage detection (charger control over CAN or dedicated line). Technically cells are never allowed to reach voltages

exceeding 4.2V. Electrochemical overvoltage state is located above this limit (4.235 V for Li-Po cells)

Balancing with accuracy better than 10 mV. For Li-Po cells charge is dumped once cell voltage exceed 4.15V.

Voltage measurement with accuracy 10 mV or better.

Current measurement (accuracy depends on range, option)

SOC calculation (option)

Each module is fully isolated (optical isolation for low voltage/overvoltage/communication lines)

Fully digital construction (BMS modules measure voltages using analog digital converter and report data using serial communication to master unit)

No current is drawn from cell if system is not powered.

Display terminal for cells' monitoring.

Horizon BMS is a digital balancer/protector/monitor/meter which falls under category of non-distributed Master-Slave devices.

Table copied from http://liionbms.com/php/bms_options.php to illustrate placement of Horizon BMS (marked green).

Assumptions and design principles

Horizon BMS has been designed as cost effective yet sophisticated and safe device. Its capabilities at present can be located between medium and advanced BMS systems. Below are listed operational features with descriptions.

• 1. Balancing modules (one module per cell) are not placed directly on cells as in many other BMS types. They are add-on boards placed in slots in units called 'mother boards'. Horizon BMS is meant to work with various cell types and in many cases placing units on cells is not possible (in Li-Po or many Li-Ion cells) or difficult. Especially in smallest EVs where battery compartment is to be as compact as possible.

  2. Each mother board hosts up to 12 modules. Mother boards may be linked together (with use of CAN bus) or work as independent devices.

  3. Excess energy from cells is dumped with use of external resistors. They may be placed in the same enclosure as mother board with BMS modules or put in separate enclosure and located elsewhere. Typical configurations might be as follow:

     1. 1. resistors in the same enclosure as mother board with units. Entire BMS is self contained within one casing.

        2. resistors are located inside separate enclosure/radiator.

        3. resistors are located inside vehicle frame which acts as radiator.

  4. Each mother board is capable of controlling charger and bldc driver via dedicated lines.

BMS module

The core BMS functionality namely protection and balancing is implemented as autonomous modules. Each module is powered by cell it monitors. Cell's voltage is allowed to vary between 0.8 to 6.0 Volts. Voltage measurement is realized with use of 10 bit analog digital converter which gives resolution approximately 4.9 mV/bit and with proper calibration (all devices are shipped calibrated) masurements should be accurate. Shipped modules are calibrated with use of Sanwa PC5000a digital multimeter.

By request modules may be shipped alone without mother boards. Each module has a clearly defined hardware interface and can be easily used in custom BMS projects. For example it can be used in a 'classical' manner being put on cell directly and controlling its own dedicated dump resistor. Use of mother boards simplify greatly implementation in the smallest (e-bikes/trikes, e-motorcycles) and small (e-quads, small e-cars) electric vehicles. By default Horizon BMS comes as a non-distributed system.

Each BMS module:

• • Is cell powered.

  • Draws only 1 mA from cell during normal operation.

  • Can be used autonomously (no need for master logic).

  • Requires no external power supply (except 5V activation signal)

  • Draws no current (0 mA) from cell when in deactivated state.

  • Cuts off automatically from cell if external activation signal is low.

  • Cut off is done with use of minirelay. It provides safe galvanic isolation in case of system failure.

  • Is completely optoisolated.

  • It provides control lines for:

  • Overvoltage state

  • Undervoltage state

  • Executive unit activation (for dumping excess charge)

  • It's equipped with 3 control LEDs.

  • It's equipped with 2 control (plus/mins) buttons for custom treshold calibration. User setting is stored in EEPROM.

Pictures below show (some) elements of the 2012 BMS architecture: