How Does Cell Monitoring Unit Work in BMS?

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Cell Monitoring Unit: A Pivotal Ingredient in Tomorrow’s BMS

Modern rechargeable battery-powered devices require battery management systems to help ensure that the battery is operating within the operating range specified by the manufacturer. Otherwise may lead to cell damage or equipment damage. The battery module consists of a smaller energy battery, in order to achieve the specified energy capacity and power output. The core of the BMS is a cell monitoring unit, which connects the management system to the battery module by providing data on each battery, including voltage, current, and temperature. In today’s article, let’s take a look at why the cell monitoring unit is called the core of BMS and what role it plays.

What is a Cell Monitoring Unit?

A cell monitoring unit (CMU) is a device used to monitor the status of individual cells or battery modules in a battery pack. CMU usually includes multiple voltage sensors, current sensors, and temperature sensors, and converts sensor signals to digital signals through an analog-to-digital converter. Its main task is to collect, record, and transmit key parameters of battery cells or battery packs, such as voltage, temperature, current, capacity, and other data, so as to monitor the performance and health status of batteries in real time.

What is a Cell Monitoring Unit?

CMU: Sensing Part of the BMS

The BMS mainly consists of three parts: a cell monitoring unit, a battery balance adjustment unit, and a charge and discharge control unit. Among them, the cell monitoring unit is the most basic unit, which is the battery sensing part of the BMS. It can accurately measure the battery voltage, take a temperature reading from the battery pack, and balance the battery with a current of up to 300 mA. These measured parameters form the foundation for determining if the battery status is in a normal condition. Once an anomaly is detected, the BMS takes steps to adjust it.

How does CMU Work?

The cell monitoring unit of the working principle through the built-in sensors and electronic circuit monitors the key parameters of a single-cell monomer or battery components, and the data transmission to the BMS, in order to realize the safe and efficient operation of the battery. Here’s how the CMU works in detail:

  1. Sensors: CMU is usually equipped with multiple sensors to measure various parameters of the battery cell. The most common sensors include voltage sensors, temperature sensors, and current sensors. These sensors will continue to collect state data of the battery.
  2. Data collection: The sensor periodically or continuously measures the parameters of the battery monomer, and converts the data to an electrical signal. For example, a voltage sensor measures voltage and converts it to a voltage value.
  3. Data processing: The sensor collects data, and the electronic circuit within the CMU processes and analyzes it. This may include data filtering, correction, and calculation. Data processing to ensure to collection of accurate data.
  4. Communication interface: The CMU usually has a communication interface that allows it to transfer the processed data to the BMS. These communication interfaces CAN adopt different communication protocols, such as CAN, Modbus, RS-485, etc. At present, the communication is using daisy chain or CAN, the more popular is the daisy chain architecture, because the cost is cheap, easy to operate, and there are two-way daisy chains and one-way daisy chains, based on the cost of the choice.
  5. Data transmission: The processed data is transmitted to BMS for further analysis and decision-making. BMS will use this data to monitor the status of the battery cells, identify potential problems, perform equalization controls, and take necessary actions to ensure the safety and performance of the battery system.
  6. Alarm and control: If CMU is a battery monomer that detects anomalies, such as overheating, overcharge, discharge, or other problems, it can be through the communication interface to the BMS alert, and take measures, such as cutting off the battery charging or discharging. This helps to reduce the potential safety risks.
  7. Data logging: CMU can usually record historical data for performance analysis, maintenance planning, and fault diagnosis. These records have the potential to enhance the efficiency of battery system operation and maintenance.

Complete Solutions for BMS by MOKOEnergy

MOKOEnergy is a company specializing in the research and development of BMS, CMU is the core component of BMS. Cheap and unprofessional CMUs can easily affect the performance of the BMS, especially the inability to accurately monitor key parameters. The reason why our BMS is widely recognized in various countries is that every important component, especially the CMU, is at the forefront of development, and our CMU has the following highlights:

Voltage Measurement

  • Extend the capacity to 56 cells by adding more CMUs to the daisy chain, which consists of 4 sets of 14-channel BCCs.
  • Guarantee high accuracy throughout their lifetime, incorporating averaging and advanced filtering techniques.

Temperature Measurement

Advanced filtering and accommodates 4 x 8 analog inputs, which can also be used for temperature sensors, or GPIOs.

Cell Balancing

Integrated temperature-controlled cell balancing allows for a maximum of 300 mA (or 100 mA when using the default configuration).


Two battery-internal communication options: Isolated ETPL or standard CAN/CAN FD.


In conclusion, CMUs are essential technology components in the battery management field, working closely with BMS to ensure the safe and stable operation of battery packs.MOKOEnergy’s CMUs provide excellent solutions for battery management with the advantages of high-precision monitoring, reliability, communication capability, and scalability. If there are any questions, please feel free to consult with us.


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