Additional further vocabulary (for intermediate/ expert users)
Battery Profile: term used to represent a collection of settings implemented in a BMS to manage several situations. Typically the profile includes informations such as maximum and minimum voltage settings, total cell capacity and current limitations.
Cell balancing: part of the battery management process. Balance a pack refers to the act of matching cell voltage. Since a pack is only as strong as its weakest cell, it’s important that all cells are balanced to get the highest pack capacity. There are two types of balancing methods:
• Passive balancing: this method uses a restive load to burn off excess energy from batteries with a higher voltage (higher SoC) and bring them down to the voltage of the lower cells. This method is the most widespread and the most cost effective one.
• Active balancing: this method involves charging the lower voltage cells using the energy taken directly from the higher voltage cells. This can significantly increase the cost of the system but the energy efficiency is higher since the energy is recycled.
CANBUS: the Common Area Network BUS is a high speed differential mode digital communication network protocol. The protocol is specified up to 1 Mbps and has built-in error checking and negotiation for a high reliability.
CANdapter: module to convert CANBUS data protocol to USB protocol. It’s designed to convert the CANBUS traffic into data that an ordinary computer can understand.
Baud Rate: refers to the speed at which data is transmitted on a network. This is typically expressed in kilobits-per-second (kbps). To select the wrong baud-rate can cause issues on the network. Baud-rates are for instance: 125 kbps, 250 kbps, 500 kbps (the standard for automotive) and it’s possible to go up to 1000 kbps (also written 1 Mbps).
Current sensor: device that is used in order to measure how much electric current is flowing through a given wire. This is very important to calculate the State of Charge as well as to keep the battery into its safety current limits. A current sensor has a given current range, for instance from -100 amps to 100 amps. The current sensor should be sized properly to maximize accuracy and reliability.
Charge Current Limit: (CCL for short) maximum charge current allowed by the battery pack without damaging or exceeding system ratings. This value can change due to a number of reasons including temperature, voltage, internal resistance and age.
Discharge Current Limit: (DCL for short) maximum discharge current drawn from the battery pack without damaging or exceeding system ratings. This value can change due to a number of reasons including temperature, voltage, internal resistance and age. This is the rated current.
Charger Safety Relay: (SFTY for short) signal line from the BMS to a battery charger that, when driven low, allows a battery charger to charge the battery pack. When this line floats high, the battery charger is responsible for shutting itself off immediately to prevent damaging the battery pack. The use of this relay is strongly advised at least as a backup measure to ensure that the battery charger terminates properly to prevent damage to the battery pack.
Coulomb counting: technique used to track the State of Charge of a battery pack. It works by integrating the active flowing current over time to get the total sum of energy entering or leaving the battery pack. This produces a capacity value that is typically measured in ampere-hour.
DTC: (Diagnostic Trouble Code) intelligent error code that gets set when a fault is encountered. DTCs can be read and cleared by various different tools. The most common way to access DTCs is through OBD2.
ECU: (Electronic Control Unit) another name for an intelligent control computer that performs a specific task. Typically this term is used in automotive applications but it can show up elsewhere as well. For instance, a battery management system would be considered an ECU because it is a separate computer system that performs a specific task.
Internal Resistance: actual electrical resistance of the battery itself. This value determines how much the voltage drops when the battery is under load (current flowing in or out of the battery). It’s measured in ohm (Ω) and 1 Ω means that 1 volt is lost for each amps flowing. The resistance of a battery is usually measured in milliohm (1 mΩ = 0.001 Ω). A higher internal resistance means more energy is wasted and turned into heat. The voltage drop times the current flowing gives the wasted power. The lower the internal resistance is, the more efficient the battery is. The internal resistance of a battery is often higher in cold temperatures and lower in warm temperatures. There are two different types of internal resistance when it comes to batteries:
• AC internal resistance: voltage drop that occurs in a battery over a very short period of time (less than a second). This value is important for applications where energy may be put in and taken out of the battery in very quick bursts.
• DC internal resistance: voltage drop that occurs in a battery over an extended period of time (typically 10 to 30 seconds). This value can be much higher than the AC resistance and it’s important for applications with sustained high current draw.
Thermistor: resistor that can be used to determine the surrounding temperature. The measured resistance of a Thermistor varies with the temperature. Thermistors are essential to determine the temperature of a battery pack and secure it.
EV: (Electric Vehicle) vehicle that drives entirely using electric energy stored in a high capacity battery pack. Electric vehicles typically have a battery charger, a battery management system and a motor controller.
PHEV: (Plugin Hybrid Electric Vehicle) hybrid vehicle (HEV with both an electric motor and a combustion engine) but the buffer battery is oversized. The main point is that it’s possible to charge the battery from a socket so that a PHEV can be used as an EV for small trips.