If you’re using a lithium battery in your project, it’s important to understand the basics of how the Battery Management System (BMS) works. The BMS protection board for li-ion is responsible for monitoring and protecting the battery cells, and it has a number of settings that you need to be aware of.
In this article, we’ll discuss the most important BMS protection settings and what they mean for your battery.
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What is a Battery Management System (BMS)?
The Battery Management System (BMS) is a critical part of any lithium battery system. The BMS monitors and controls the state of charge, voltage, current, and temperature of the cells in the battery pack.
It also has protection settings which are described below. This allows the battery to be used in a wide range of products, from low-power standby devices to high-powered electric vehicles.
The BMS is typically implemented as a separate circuit board that is connected to the battery cells. It contains a microcontroller, sensors, and MOSFETs (Metal Oxide Field Effect Transistors) or other solid-state switches.
The BMS software runs on the microcontroller and controls the operation of the system. Several steps are needed to produce one BMS protection board.
When choosing a BMS for your product, it’s important to select one that has the features and performance that you need. In some cases, it may be necessary to custom-design a BMS to meet the specific requirements of your application.
There are several different types of BMS available on the market, each with its own set of features and capabilities. Some BMSs are more sophisticated than others, but all BMSs perform the basic functions described below.
The core functions of BMS include:
- Cells voltage sampling
- Cells temperature sampling
- Pack’s total voltage sampling etc
The measurement function monitors the basic state of the battery in real time and is the basis of all functions of BMS. Without these measurements, all core algorithms and application functions of BMS are difficult to execute.
- SOC (battery state)
- SOH (life state)
- SOP (power state)
- Battery equalization etc
Battery equalization has two kinds of technologies: active equalization and passive equalization.
Active equalization is to use of an external power supply to force the voltage and current of each cell to be balanced. So it needs a controller and some external devices, like resistors or capacitors.
Passive equalization means letting the battery self-adjust its own internal resistance so that all cells have approximately the same voltage. Passive equalization doesn’t need extra components, but it takes more time than active equalization.
In addition to these safety features, the BMS can also be used to optimize performance or extend battery life by controlling how much power is drawn from each cell. This article will focus on the BMS protection settings available in most BMS systems.
The battery management system has a number of settings that you need to be aware of.
- Over-discharge protection – This prevents the battery from being discharged below a certain safe level.
- Short circuit protection – This protects the battery against short circuits between cells or between an electrode and the ground.
- Thermal runaway protection – If the temperature of a cell gets too high, this protection will activate and shut down the battery to prevent it from overheating.
- Cell balancing – This ensures that each cell in the battery pack is equally charged and helps to prevent uneven discharge and damage to the cells.
- Current protection – This protects the battery against excessive charge or discharge currents.
- Overcharge protection – This prevents the battery from being overcharged, which can damage or even destroy the cells.
Each of these BMS features is important for protecting the battery and ensuring its long-term performance. In some cases, you may need to adjust these settings to meet the specific requirements of your application.
For example, if you’re using the lithium battery in a high-power product, you may need to increase the BMS current protection setting to prevent damage to the cells.
It’s also important to note that these settings are not static; they can be changed as needed depending on the conditions of use. For example, if you’re using the battery in a cold environment, you may need to reduce the BMS discharge protection setting to ensure that the battery doesn’t shut down prematurely.
The BMS protection features are a significant part of any lithium battery system and should be carefully considered when selecting a battery for your application. By understanding these settings and how they work, you can ensure that your battery will perform safely and reliably in all conditions. Let’s take a closer look at each one.
BMS over-discharge protection (ODP)
BMS over-discharge protection (ODP) or BMS low voltage cutoff (LVC) is a critical safety feature that many battery management systems have. This protection setting kicks in when the lithium battery is discharged below a certain voltage level, typically between two and three volts per cell.
When this occurs, the battery management system will stop discharging the battery any further to prevent it from being damaged.
The over-discharge protection can be customized depending on your needs. For example, you may want to set it higher if you are using the battery for high-powered applications, or lower if you are using it for low-power applications.
This BMS protection setting is important because if a lithium-ion battery is discharged too deeply, it can cause irreversible damage to the cells. This means that even if you charge the battery back up again, it may not be able to hold a charge or it could experience reduced life cycle performance.
In some cases, an over-discharged lithium-ion battery may even catch on fire.
That’s why it’s important to always make sure that your battery management system is set to over-discharge protection. This will help ensure that your battery remains safe and protected from damage.
If the BMS low voltage cutoff threshold is not met, the battery will continue discharging until it reaches 0 volts. At this point, the battery will be damaged and may no longer be usable.
Most BMSes will have an adjustable ODP setting, so you can choose what voltage level you want the protection to kick in at. If you’re using your battery for high-drain applications like e-bikes, you might want to set the BMS over-discharge protection to a higher voltage so that it doesn’t kick in often.
Make sure that your device’s battery management system has ODP enabled so that you can rest assured that your device will be safe no matter how low its battery level gets.
It’s important to note that BMS over-discharge protection is not a 100% guarantee against battery fires – there are other factors that can contribute to them as well. But it’s still an important safety feature to have, and it’s something you should definitely consider when choosing a lithium battery pack.
BMS short circuit protection
A BMS short circuit protection can occur when the battery terminals are accidentally connected, causing a large current to flow. This can cause the battery to overheat and potentially catch on fire. The short circuit protection will disconnect the battery if it detects a short circuit.
Some batteries have multiple levels of short-circuit protection, while others only have one. The most common type of BMS short circuit protection is thermal cutoff, which will activate when the battery temperature reaches a certain point. Other types of protection include fuse cutoff and electronic cutoff.
Most lithium batteries have a short circuit protection setting of around 200-300mA. This is usually plenty to protect the battery from damage, but if you are using high-powered devices that can draw more current, you may want to increase the short circuit protection to 500mA or more.
If you are using a battery with a high discharge rate, make sure to also increase the BMS short circuit protection. A high discharge rate can cause a large current to flow if there is a short circuit, which can damage or even destroy the battery.
BMS short circuit protection is a very important setting to consider when using lithium-ion batteries. Make sure to choose a setting that will protect your battery from damage while still allowing you to use the devices you need.
BMS thermal runaway protection (TRP)
BMS thermal runaway protection is a condition that can occur in lithium-ion batteries when the battery cells get too hot. A thermal runaway event can cause the battery to overheat, leading to a fire or an explosion. To prevent this from happening, most lithium-ion batteries have a BMS thermal runaway protection feature.
The TRP will shut down the battery if it gets too hot, preventing it from going into thermal runaway. Most BMS thermal runaway protection features are set to activate at around 65 degrees Celsius, but you should check your battery’s specific specifications to be sure.
If you are using a lithium-ion battery in a device that has a TRP feature, it is important to make sure that the TRP is enabled. If the BMS thermal runaway protection is not enabled, the battery may overheat and cause a fire or an explosion. To enable the TRP, check your battery’s specifications or consult with the battery manufacturers.
Discover more about the main causes of thermal runaway and techniques for thermal runaway prevention in lithium-ion batteries.
Most lithium-ion batteries also have a thermal cutoff temperature (TCT). The TCT is the temperature at which the battery will shut down to prevent it from overheating.
The thermal cutoff temperature is typically set to around 80 degrees Celsius, but you should check your battery’s specific specifications to be sure. If your battery does not have a TCT, it is important to keep it away from heat sources and use caution when charging it.
It is also important to note that the BMS thermal runaway protection (TRP) and thermal cutoff temperature are not the same things.
The TRP is a safety feature that will shut down the battery if it gets too hot, preventing it from going into thermal runaway. The TCT is the temperature at which the battery will shut down to prevent it from overheating. Both of these features are important for preventing fires and explosions in lithium-ion batteries.
BMS cell balancing protection
When using a lithium-ion battery, it is important to make sure that the cells are balanced. This means that all of the cells in the battery pack have approximately the same voltage. If one or more cells have a higher voltage than the others, it can cause damage to the battery.
BMS cell balancing protection is the process of ensuring that all cells in a battery pack are at or near the same state of charge. This is important to maintain healthy cells and to extend battery lifespan.
Cell balancing protection is usually done by the BMS when it senses that one or more cells have reached a higher state of charge than others. The BMS will then send a charge or discharge current to the affected cells until they reach the same level of charge as the other cells in the pack.
Lithium batteries used in electric vehicles come with built-in cell balancers, which take care of this task without needing input from the BMS. However, most lithium batteries do not have such built-in cell balancing capabilities and will require the BMS to perform this function.
If the BMS is not able to properly balance the cells in a battery pack, it can cause cell damage and even failure. It’s therefore important to ensure that your battery pack’s BMS has adequate BMS cell balancing protection capabilities. Make sure your BMS is enabled and perform this function properly to get the most out of your battery pack.
BMS overcurrent protection (OCP)
The over-current protection function is a key safety feature of the BMS. The OCP will cut off the current if it exceeds the programmed limit, which helps protect the battery and its surrounding components from damage. Most BMSs have an adjustable BMS overcurrent protection threshold, so you can configure it to meet your application’s needs.
When setting the OCP threshold, be sure to consider both the maximum current draw of your load and also the short-circuit current of your battery. The BMS overcurrent protection should be set slightly below these values to allow for some headroom.
If the OCP is set too close to the max discharge current, it could trigger unnecessarily and cause premature shutoff of the battery.
It’s also worth noting that some BMS has a “hysteresis” feature, which prevents false triggering of the BMS overcurrent protection due to small fluctuations in current. This can be particularly helpful in applications where there are large current spikes, such as when starting an electric motor.
The short-circuit current is the amount of current that flows through a battery when it is shorted out. For example, if you have a 12V battery with a 0.05-ohm resistor, its short-circuit current would be 240 amps (12 x 0.05 = 0.60A).
So, when selecting a BMS overcurrent protection threshold for your application, make sure it’s greater than the maximum current draw of your load multiplied by the safety factor (usually around two or three). This will help ensure that the OCP will always cut off before any damage can occur.
In addition to setting an appropriate BMS overcurrent protection threshold, you should also monitor the battery temperature to avoid any false positives caused by the battery heating up. A false positive can occur if the OCP threshold is set too low, and will cause the battery to cut off unnecessarily.
So be sure to take into account both the current draw of your load and the thermal characteristics of your battery when selecting a BMS overcurrent protection threshold.
BMS overcharge protection
BMS overcharge protection is a common battery management system (BMS) protection setting for lithium batteries. If the voltage of a lithium battery exceeds the maximum safe level, overcharge protection will activate and stop current from flowing into or out of the battery. This prevents further damage to the battery and helps ensure safety.
Most BMS overcharge protection settings are adjustable, so you can set the voltage at which protection will activate. It’s important to consult your battery’s datasheet or manufacturer to determine the recommended overcharge voltage for your specific battery.
Overcharging can cause permanent damage to a lithium battery, so it’s important to be aware of your BMS protection settings and to ensure that your battery isn’t being overcharged.
How to choose a high-quality battery with intelligent BMS?
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