Battery Management Systems Overview 250

active cell balancing

A cell load balancing method in which energy from higher-voltage cells is transferred to lower-voltage cells until the voltages match. Active cell balancing saves more energy that passive balancing but is more expensive to implement.

alternating current

AC. Current that continuously reverses the direction of flow of electrons. Alternating current is converted to direct current (DC) to charge EV batteries.

amperage

A measurement of the amount of current flowing in a circuit. Amperage is measured in amperes (A).

ampere-hours

Ah. A unit used to measure electrical energy output over time. One ampere-hour indicates that a battery can supply one ampere of electricity for one hour.

anode

An electrode with a negative charge. In a battery, the anode sends current to the cathode.

battery management systems

BMSs. A computer that monitors, regulates, and coordinates the operations of a battery pack. The battery management system helps to prevent overheating and thermal runaway.

battery monitoring unit

BMU. A printed circuit board assembly in a battery management system to which battery cells are wired. The battery monitoring unit processes data from battery cells and sends the data to a control unit.

battery pack

A group of battery cells connected together to produce large amounts of electrical energy. Battery packs may also include components such as sensors and battery management systems.

BMS

Battery management system. A computer that monitors, regulates, and coordinates the operations of a battery pack. The BMS helps to prevent overheating and thermal runaway.

BMU

Battery monitoring unit. A printed circuit board assembly in a battery management system to which battery cells are wired. The BMU processes data from battery cells and sends the data to a control unit.

cathode

An electrode with a positive charge. In a battery, the cathode recieves current from the anode.

cell load balancing

The automated process of adjusting the energy levels of individual cells in a battery pack to eliminate variation across the cells. Cell load balancing ensures that all cells continuously operate at the same voltage levels during charging and discharging.

cells

A single unit of a battery. A cell contains a cathode, an anode, and an electrolyte solution.

centralized battery management system

A battery management system in which all cells are wired to a single battery monitoring unit connected to a single control unit. A centralized battery management system uses a single primary control unit that receives data from the battery monitoring unit.

charge capacities

The maximum amount of voltage a battery cell can safely recieve from a charging session. Charge capacities of cells reduce over time at slightly different rates.

comparator

A type of electronic circuit or device that can compare an input to a reference value and produce an output based on the comparison. Comparators used in battery management systems may include analog or digital types.

continuous discharge current

The maximum amperage that a battery can safely output continuously during operation. Continuous discharge current is typically measured in ampere-hours (Ah) or kilowatt-hours (kWh) and displayed on battery packs and battery management system components.

control unit

A component of a computer's central processing system that directs its operation. Control units in a BMS receive data from the battery monitoring unit (BMU) to direct tasks, such as thermal management and load balancing.

controller area network

CAN. A communication protocol designed to allow electronic control and transceiver devices to send data in a reliable way. The controller area network protocol was designed for the automotive industry and is based on the ISO 11898 standard.

cooling systems

A group of components that remove heat from an electrical system in order to regulate temperature using air, liquid, or other methods. Cooling systems for lithium-ion battery packs typically use liquid cooling methods.

current sensors

A device that detects the flow of electricity from an electrical component, such as a battery, and outputs an electrical signal in response. Current sensors in a battery management system help prevent overcurrent and undercurrent.

cycle life

The total number of times a secondary cell battery can be discharged and recharged before it must be replaced. Cycle life depends on the battery's design, materials, and operating conditions.

DC Fast Charging

A method of charging electric vehicles that converts large amounts of AC from the electric grid to DC within the external charging components, then transfers it directly to the battery engine. DC Fast Charging, which is sometimes called Level 3 Charging, provides much faster charging speeds since it converts much higher AC voltages, ranging from 480V to 1000V.

direct current

DC. Current that travels in one direction. Direct current does not reverse the direction of flow.

discharge speed

The rate at which a battery cell's energy is reduced to the minimum safe voltage level during oepration. Discharge speeds of cells reduce over time at slightly different rates.

distributed battery management system

A battery management system in which individual cells or small cell groups are wired to designated battery monitoring units at the cells' locations. A distributed battery management system uses multiple PCBAs and a single primary control unit.

earth fault

A short circuit fault that creates an unintended path to the ground. Earth faults, or ground faults, are usually caused by worn insulation and can create overcurrent conditions.

earth leakage

Current from an electrical circuit that travels to the ground circuit. Some earth leakage, or ground leakage, is normal, but excessive earth leakage indicates a hazardous condition.

electric vehicle supply equipment

EVSE. Technology used to connect electric vehicles to the electric grid for charging purposes. Electric vehicle supply equipment includes charging stands, wall boxes, cables, connectors, adapters, and other devices.

electric vehicles

EVs. A vehicle that is propelled by an electric motor that draws its power from a battery. Electric vehicles, including hybrid electric vehicles, require high energy, lightweight, rechargeable batteries.

electrolyte

A conductive solution containing an acid, an alkaline, or a salt. The electrolyte in a battery connects the two electrodes.

EV

EVs. A vehicle that is propelled by an electric motor that draws its power from a battery. Electric vehicles, including hybrid electric vehicles, require high energy, lightweight, rechargeable batteries.

fault codes

The digital information output by a computing device that corresponds to a malfunction in a mechanical or electrical system. Fault codes are used to identify the type of malfunction and help facilitate troubleshooting processes.

fuses

A safety device that opens a circuit when it detects excess current. Fuses often have a component that melts to open the circuit.

ground

A source of zero electrical potential, such as the earth or another large conducting body. A ground absorbs electrical currents and is typically the negative terminal of an EV battery pack.

ground fault

A short circuit fault that creates an unintended path to the ground. Ground faults, or earth faults, are usually caused by worn insulation and can create overcurrent conditions.

ground leakage

Current from an electrical circuit that travels to the ground circuit. Some ground leakage, or earth leakage, is normal, but excessive earth leakage indicates a hazardous condition.

grounded

Using a source that absorbs stray electrical charge. Grounded items may use the earth or another large conducting body, such as a motor housing, that serves as a source of zero electrical potential.

housing

A protective cover designed to contain the cells, modules, and all the circuitry and sensors required for a rechargeable battery to function. A battery housing can be rigid metal or plastic.

IEC 61851

A standard for electric vehicle charging that defines physical layer and communication layer connection requirements. IEC 61851 specifies pulse width modulation (PWM) as a requirement to control AC charging communication.

integrated battery management system

A battery management system in which control units and battery monitoring units are part of the battery pack itself. Integrated battery management system components are typically enclosed within battery modules or other enclosures within the battery pack.

integrated circuits

ICs. A complete, miniaturized electronic circuit that contains a variety of components on a single piece of semiconductor wafer. Integrated circuits, also known as microchips or chips, include components like transistors, resistors, capacitors, and diodes.

internal resistance

The opposition to current flow within a battery. Internal resistance is measured in ohms and increases as a battery ages.

ISO 15118

A digital communication standard for data communication protocols between electric vehicle software and charging equipment. ISO 15118 outlines communication methods required for DC Fast Charging stations, which must communicate directly with a vehicle's battery management system.

isolation resistance

A measure of the degree of separation between high-voltage currents, which can be monitored to detect ground leakage and current leakage. Isolation resistance is measured in ohms and can be calculated based on internal resistance in a battery pack.

isolation resistance

IR. A measure of the degree of separation between high-voltage currents, which can be monitored to detect ground leakage and current leakage. Isolation resistance is measured in ohms and can be calculated based on internal resistance in a battery pack.

kilowatt-hours

kWh. A unit used to measure electrical energy usage or delivery over time. One kilowatt-hour indicates that a battery can supply 1,000 watts of electricity for one hour.

lead-acid

A type of secondary cell battery that uses lead dioxide as a cathode and lead as an anode. Lead-acid batteries are very cheap to produce and therefore widely used despite their lower energy, power, and cycle life.

Li-ion

Lithium-ion. A type of secondary cell battery that uses a lithium compound as a cathode and, usually, graphite or carbon as an anode. Li-ion batteries are widely used in portable electronics and electric vehicles.

lithium-ion

Li-ion. A type of secondary cell battery that uses a lithium compound as a cathode and carbon, usually in the form of graphite, as an anode. Lithium-ion batteries are widely used in portable electronics and electric vehicles.

load

A component in a circuit that converts electricity into light, heat, or mechanical motion. Loads are used in battery circuits by BMSs for passive cell balancing.

memory chips

A type of integrated circuit designed to store electronic data. Memory chips typically store data as binary digits.

microchips

A complete, miniaturized electronic circuit that contains a variety of components on a single piece of semiconductor wafer. Microchips, also known as chips or integrated circuits (ICs), include components like transistors, resistors, capacitors, and diodes.

microprocessors

A type of integrated circuit containing a central processing unit (CPU) that is wired to separate memory chips and input and output devices that perform electronic functions. Microprocessors send processed data outputs to external control devices.

modular battery management system

A battery management system in which individual cells are wired to a battery monitoring unit that connects to two or more control units. A modular battery management system contains a primary control unit and one or more secondary control units.

modules

A unit that contains several battery cells connected in either series or parallel. Modules in EV battery packs also contain fuses, sensors, and cooling mechanisms.

National Highway Traffic Safety Administration

NHTSA. An organization under the United States Department of Transportation that governs and standardizes transportation requirements in the U.S. The National Highway Traffic Safety Administration specified the CFR 571.305 standard outlining isolation resistance requirements for electric vehicles in the annual Code of Federal Regulations.

nickel-metal hydride

NiMH . A type of secondary cell battery that uses nickel hydroxide as a cathode and a hydrogen alloy as an anode. Nickel-metal hydride batteries are cheaper than lithium-ion batteries and are used in some hybrid electric vehicles.

ohms

A unit of measurement for electrical resistance. Ohms indicate the amount of resistance in a circuit.

onboard charger

A device installed in an electric vehicle that converts stored alternating current supplied by a power source into direct current to power the electric motor. Onboard chargers are used in fully electric and plug-in hybrid vehicles, but not fully hybrid electric vehicles.

onboard diagnostic

OBD. A vehicle's self-diagnostic and reporting capability. Onboard diagnostics data stored in electric vehicles can be accessed using onboard diagnostic type 2 (OBDII) scanning tools.

overcurrent

A condition in which the flow of electricity exceeds the maximum amount specified for a battery or electronic component. Overcurrent can damage battery cells and lead to overheating.

overcurrent

A state in which the flow of electricity exceeds the maximum amount specified for a battery or electronic component. Overcurrent can damage battery cells and lead to overheating.

overvoltage

A condition in which the electrical force of a battery cell or other electrical power source exceeds the specified maximum operating voltage. Overvoltage can cause dangerous power surges that can damage battery cells and create hazardous conditions.

passive cell balancing

A cell load balancing method in which cells with higher voltage are discharged to match the lowest cell voltages in a battery pack. Passive cell balancing results in some energy loss due to heat transfer when discharging high-voltage cells.

PCBA

Printed circuit board assemblies. A layered construction of conductive and nonconductive material with various electronic components soldered to it. PCBAs can be found in almost all electronic devices.

power

The rate at which a device converts energy from one form to another, such as converting electrical energy into light or movement. Power is measured in watts (W).

printed circuit board assemblies

PCBAs. A layered construction of conductive and nonconductive material with various electronic components soldered to it. Printed circuit board assemblies can be found in almost all electronic devices.

radio frequency integrated circuit

RFIC. A type of integrated circuit that includes antennas, amplifiers, modulators, and other devices that enable wireless communication. Radio frequency integrated circuits transmit and receive data using radio frequency (RF) signals.

range estimation

The calculated distance an electric vehicle can travel on one full charge. Range estimation is determined by the state of charge and state of health of a battery, along with other factors.

resistance

R. The opposition to current flow, which can be measured by a BMS. Resistance within a battery cell is known as internal resistance.

secondary cell batteries

A battery that can be recharged. Secondary cell batteries are charged by running electrical current back through them to restore their chemical energy.

SoC

State of charge. The amount of energy currently contained in a battery. SoC is usually given as a percentage, with 100% meaning that the battery is fully charged.

state of charge

SoC. The amount of energy currently contained in a battery. State of charge is usually given as a percentage, with 100% meaning that the battery is fully charged.

state of health

SoH. A measurement of a battery's condition or performance compared to its original specifications that is based on voltage, internal resistance, and other conditions. State of health decreases over time due to several factors, including charge and discharge cycles, operating temperature, and damage to the battery.

temperature sensors

A device that detects thermal energy from a component and outputs an electrical signal in response. Temperature sensors in a battery management system help prevent overheating and help maintain ideal operating temperatures.

thermal runaway

The process of a defective or damaged battery cell overheating and damaging nearby cells, causing them to also overheat. Thermal runaway can cause fires or explosions if not detected and stopped.

thermal sensors

A device that detects temperature changes in and around other devices. Thermal sensors are used to help maintain safe operating temperatures in electric vehicles.

topologies

The configuration or physical pattern of parts and components within a working system, such as a controller area network. Common BMS topologies include centralized, distributed, and modular BMS architectures.

undervoltage

A condition in which a battery cell or other electrical power source operates below the specified minimum voltage. Undervoltage can cause battery cells to overcompensate for power loss, leading to overheating.

voltage

The electrical force or pressure that causes current to flow in a circuit. Voltage is measured in volts (V).

voltage sensors

A device that detects the charge level of an electrical component, such as a battery, and outputs an electrical signal in response. Voltage sensors in a battery management system help prevent overvoltage and undervoltage.

volts

V. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. Volts measure voltage, which is also known as electromotive force.

WiFi

A type of wireless network that enables communication between devices at a single geographical location. WiFi networks are typically established by connecting a wireless access point to a wired internet device.

wire harness

A collection of wires organized and bundled according to function. A wire harness, also known as a wire harness assembly, facilitates easy installation and saves space.

wireless battery management systems

WBMS. A battery management system (BMS) that uses wireless communication between internal BMS components. Wireless battery management systems transmit data from cells to wireless sensors, monitoring, and control units.

Zigbee

A cost-efficient wireless communication technology commonly used for automating manufacturing processes. Zigbee networks use a network coordinator device that manages all wireless communication on the network.