What is the difference between PCB and BMS

 Many lithium batteries, battery packs and battery chargers contain PCB and BMS. For the people who don’t know more about the electronics, they are wondering what is a PCB and a BMS. A lot of electric product DIYers for electric bikes, electric skaters, vehicles, street lamps, etc., hesitate between a PCB and a BMS in order to protect the battery pack of their devices. Now let’s see the definition and difference of them.

What is a PCB ( Protection Circuit Board)?

PCM or PCB ( protection circuit module or board ) is an indispensable part of lithium battery. It play a role in charge and discharge protection of the series and parallel battery packs. And at the same time it can detect the overvoltage, overcurrent, overtemperature, undervoltage and short circuit status of each single cell in the battery pack to extend the battery life, therefore it is the must have to avoid the lithium battery or battery pack from explosion, fire and damage.

The lithium battery protection board also has a equilibrium protection function, which has two modes of energy consumption and energy conversion. Energy dissipation equilibrium refers to consume excess power of the battery pack or the single cell with high voltage through the use of internal resistance. Energy consumption balancing is divided into balancing during charging, fixed-point voltage balancing, and static automatic balancing.

Charging equilibrium: When charging, if the voltage of any single battery is higher than all the average voltages, the protection board starts equilibrium protection.

Voltage fixed-point equilibrium: The lithium battery protection board is set to start equilibrium at a voltage point, which is only performed at the end of the battery charge, and the equalization time is shorter.

Static automatic equilibrium: It is carried out during charging or discharging, even if the battery is in a static store state, when the voltage is inconsistent, the lithium battery protection board will start equilibrium protection until the voltage remains consistent.

The method of energy conversion is to transfer a large-capacity battery to a small-capacity battery in the manner of energy storage, to detect the balance in capacity of the battery. It is divided into capacity constant balance and fixed-point balance.

What is a BMS (Battery Management System)?

A battery management system (BMS) is any electronic system that manages a rechargeable battery (cell or battery pack), such as by monitoring its state, calculating secondary data, reporting that data, protecting the battery, controlling its environment, and / or balancing it. A BMS may monitor the state of the battery as represented by various items, such as:

Voltage: total voltage, or voltages of individual cells

Temperature: average temperature, or temperatures of individual cells

State of charge (SOC) or depth of discharge (DOD): to indicate the charge level of the battery

State of health (SOH), a variously-defined measurement of the overall condition of the battery

Current: current in or out of the battery

Since the lithium battery may damage or even cause an explosion hazard under serious overcharge and overdischarge conditions, the battery management system exists to monitor, protect, and manage the lithium battery in a balanced manner, thereby improving the working efficiency of the lithium battery.

PCB and BMS, what is the difference?

Both the lithium battery protection circuit board and the battery management system play a important role in protecting the lithium battery. The differences between them are:

1. Lithium battery protection circuit board is composed of IC, MOS tube and resistance and capacitance components. It is an important component of lithium battery. The battery management system is more advanced than a PCB. It contains a microcontroller with intelligent software integrated into it. It is equivalent to the brain of a lithium battery, which plays a controlling role.

2. The PCB cannot get a precise status update about the charging level of the battery pack. While the BMS calculates and interprets different types of measurements like the state of battery charge and health, and offers a different level of protection (for example: it can distinguish between a normal and an abnormal event with regard to time).

3. PCB cannot steer a charging unit or a consuming unit (electric motor, etc.). BMS contains a communication bus (I2C, CAN, MODBUS, …), therefore it can steer chargers and/or consuming units (usually a motor) in order to optimize the utilization of the batteries and the behavior of the system.

4. The battery management system operates better than the battery protection board, but its performance at low temperatures is unstable.

Which to choose: a PCB or a BMS?

A PCB or a BMS? Everything depends on the type of application and the level of security which is necessary for it.

PCB or PCM is usually used for small batteries with basic protections, typical for digital batteries, like mobile phone battery, camera battery, mp3 player battery, GPS batteries, heated clothing batteries and so on. Most time, it is for 3.7V or 7.4V battery. Many XTAR batteries use the PCB.

However for bigger lithium battery packs which involves lots of battery cells, a basic BMS should be used. Typical applications which make use a BMS: advanced products like robots, drones, electric bikes, electric vehicles, etc. Many smart battery chargers also use the battery management system, like the XTAR chargers.