Battery Management System

Generally, battery management system (BMS) monitor and manage the health of batteries. Often considered the brain of the battery, the BMS keeps track of the voltages and currents in and around the battery along with other key operating parameters. It is basically a battery charger and a tester in a single package.

Battery Management System: A Brief Introduction.

The Need for a Battery Management System

As our electronic devices became smaller and more mobile, they required more powerful and longer lasting batteries. Some devices such as electric vehicles (EV) need batteries that could handle harsh environments without failing, leaking, or otherwise cause hazardous situations.

While our electronics require rechargeable batteries, the original NiMH and NiCad cells were not great. While they did last for a while, they did not have the power to drive complex circuitry, leading to severe performance issues.

Things changes when manufacturers moved to Lithium-ion (Li-ion) technology. Li-ion cells afferent the power and lifespan we need to run our devices the way we want to run them. They could handle high current with low resistances and still remain thermally stable for decades. However, they come with their own set of problems.

Lithium in inherently unstable. Because of this, lithium batteries tend to discharge quickly and overheat, especially when short-circuited. This overheating can lead to leaks, ruptures, and even explosions. While using the ion form makes the metal safer, Li-ion batteries can still start fires with no precautions in place. That is where a BMS comes into the picture. A BMS protects its lithium-cell battery and user. It does this by shutting off the battery when it detects an unsafe operating environment. It also regulates the power output to ensure consistent performance as the battery ages.

The Main Components of a BMS

A BMS maintains a consistent battery output by regulating the voltages coming out of the cells. It does this through a series of functional blocks. Each block can be as simple as an analog front end to a complex circuit with lots of subcomponents.

These blocks include:

  • Cutoff field-effect transmitters (FETs) - FETs connect and disconnect the battery from the circuit load and the battery charger based on cell voltages, current measurements, and real-time detection circuitry.
  • Fuel-gauge sensors - The fuel-gauge block tracks the charge going in and out of the battery.
  • Cell-voltage testers - Tests each cell in the battery to ensure it stays within optimal voltage values
  • Cell-voltage balance - Maintains proper load balance between individual battery cells.
  • Real-time clock
  • Temperature sensors - The thermistors track circuit temperatures to prevent the battery from overheating and to know when to charge or discharge it.
  • State machine - The main computer at the heart of the BMS. Manages the other blocks and calculates and manages the battery’s state information.
  • Real-time clock and memory – the battery’s “black box’ that time-stamps and records the current state of the BMS.
  • Battery authentication – This optional block prevents third-party additions.
  • Daisy-chain connectors – an Optional block that lets you link several BMS and batteries together.

Functions of a Battery Management System

Each block is responsible for maintaining one of the many functions of the BMS. These functions exist so that the BMS can withstand the harsh and unpredictable environment of an EV's engine. They also let the BMS produce highly accurate readouts of the environment itself.

To reach these goals, a BMS has two key functions:

  • Calculate the battery SOC and SOH to predict its overall range and life expectancy.
  • Ensure the safety of the vehicle and passengers by preventing the battery damaging conditions

A BMS exists to protect the battery from an overheating engine while protecting the engine from an overcharged battery.

How to Test a Bad Battery Management System?

Like any other piece of technology, a BMS can break down. However, you can only truly test a BMS under real-world conditions.

Ideally, you would test the BMS with an actual battery. This will let you check the BMS against every possible situation, but it can be dangerous. A bad BMS can leave you and the battery unprotected. Connecting the BMS to an actual battery may also be impractical.

Your other option is to use a battery emulator. While emulators limit your testing conditions, you will have a safer setup. Your strategy will ultimately come down to personal preference and your budget. If you need help evaluating your options, contact us as soon as possible. Our representatives will work with you to find the battery and BMS testing solution that will fit your needs and budget.

For complete understanding of basics of batteries, check out our related articles.

You might also want to look at article of 7Ah battery charger using microcontroller.

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Tim Miller

I’m Tim Miller, an automotive mechanic and blogger from Denver, Colorado. I’m the founder of autozik.com, an automotive blog about OBD2 scan tools. My Fanpage is facebook.com/autozikcom. I’ve had over 10 years’ experience in car repair and using OBD scanners. Some of my posts about car diagnostic tools can be found on my own website autozik.com.

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