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Battery Management Unit-Definition & Choosing

Battery Management Unit-Definition & Choosing

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Today we are going to discuss what a battery management unit is. The reason this system has become so important is that they are used in lithium-ion batteries technology. A battery is an energy storage system where you get multiple numbers of cells connected in series or parallel or even a combination of the two.

The thing to know about these lithium batteries is that they are far more temperamental in terms of the voltage levels that you charge them to or discharge them to. A single cell has a voltage of 3.6V and it can be charged to 4.1V and this is the voltage that should be the voltage that you take them to for their saturation charge and when you discharge them you don’t want to take them below 3V. If you go outside of these minimum and maximum limits two things can happen; outside the maximum charge voltage they can explode or burn out and if none of this happens then their lifecycle will be reduced dramatically. Taking them below the minimum limit of 3V will reduce the lifecycle as well and even can permanently damage the cell which will make it useless.

This makes it very important that when charged these cells are provided with the optimum amount of charge individually that is not outside neither of the charge limits of 4.1V and 3V. A battery management system also acts as a cell balancing system that ensures that each cell in the series is getting the same amount of charge and shows the details of charging digitally.

What is called a battery management unit?

Let’s talk about what is a battery management system, what does it do and why does a lithium battery need this system anyway? Well, all types of lithium batteries need a battery management system for safety reasons and to ensure a long lifespan of the battery pack. This is a new type of technology and it's not often well understood; it's something new that provides many different monitoring and protection functions to ensure that each cell in the battery is in a safe state and takes appropriate action if any cell goes outside of the intended operating parameters.

So, what does a BMS do anyway? The BMS performs important protective functions to maximize the capacity and lifespan of the battery pack. Each cell in the battery pack is monitored so that it doesn’t go too high during charging or too low during a power drop. Also the temperature of each cell is monitored. If the temperature goes high a warning is generated and if it goes high then the pack is disconnected to prevent further charging and discharging.

The state of charge is monitored by sensing how much current goes in and out of the battery and when the battery pack is empty it is disconnected from the load to prevent damage from further discharging. Summarizing the system simply uses the voltage to estimate the state of charge and discharge. These are the functions that make BMS most important for a lithium-ion battery.

How do you choose a good battery management unit?

Battery management units are very essential when it comes to lithium batteries because they control the voltage during charging and discharge of the battery and also controls the temperature of the battery and prevents it from heating up which can destroy the battery permanently.

There are two types of batteries. The first one is low voltage (LV) and the second one is a high voltage (HV). The packs under 30 VAC and 60 VDC are low voltage (LV) battery packs, and those between 30-1000 VAC and 60-1500 VDC are high voltage (HV) battery packs.

No matter LV or HV every battery pack needs a battery management system to function properly and increase the battery life and functionality. Different off-the-shelf BMS is in the market with different topologies. The right selection of these BMS is very much important. These are classified into two types; Classified BMS and Declassified BMS.

A centralized BMS is a single controller with the entire unit housed in a single assembly that monitors, balances, and controls all the cells. It has a series of N cells and temperature sense wires in a series going to the cells of the battery. These wires are used for balancing the temperature and voltage of the cells. The board is supplied with power from the battery and does not require an external power supply. This BMS is suited for low voltage (LV) battery packs.

A decentralized BMS does not have the entire system housed within a single assembly. It has an architecture of various topologies. This BMS is divided into multiple identical modules each going to one of the battery cells in the pack with its bundle of wires. One of the modules is designed as a master which manages the entire pack and communicates with the rest of the pack. This BMS is suited for high voltage (HV) battery packs.

Can you make a battery management unit?

Yes, a battery management unit can be made but knowing its purpose and requirements before its making are very important. BMS can be architected with multiple function blocks and design techniques. Exact knowing about the battery requirements and its life goals will help you in designing it with proper functional blocks and charging schemes to optimize battery life.

A Battery Management System (BMS) is essential for a battery to function properly and to have a long life also. There are different types of BMS for different types of batteries. Choosing the right type of BMS for your battery is very important for it to function as per expectations. It can also be made in house but with proper knowledge regarding the purpose of the BMS and its requirements i.e. for what kind or type of battery it is going to be designed. With this knowledge, anyone can design a BMS but with proper knowledge of electronic equipment and their making and assembly.

 

 

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