Battery Management System (BMS) is a key element of lithium batteries for photovoltaic installations. In this article, we explain what the BMS system consists of, its advantages and why lithium batteries need this management system.
What is a BMS battery management system?
The BMS or battery management system is an intelligent component in charge of the control and advanced management of the storage system. We can say that it is the brain of the battery. And its role is crucial in terms of safety, performance, charge rates and longevity, as we will see below.
What is the main function of the BMS?
The main function of the BMS battery management system is to control the charging and discharging of the battery.
BMS performs other functions such as:
- Battery status estimation;
- Monitoring; and analysis of battery status;
- Safety protection;
- Power control management;
- Battery information management.
So, the BMS can collect, process and store important information during the operation of the batteries in real-time. In turn, it can exchange information with external devices such as controllers. It can also solve key problems related to lithium safety, availability, usability, and lifespan.
But, as we said, its main function is to improve the battery utilization rate, prevent the battery from overcharging and over-discharging, extend battery life, and monitor battery health.
KEY INFO
BMS is a system for managing, controlling, and using battery packs.
How does a battery management system or BMS work?
The battery management system is responsible for monitoring the individual cells of the battery pack. It then calculates how much current can safely flow in (charge) and out (discharge) without damaging the battery.
These current limits prevent the source (usually a battery charger) and the load (such as an inverter) from overcharging the battery. This protects the battery from cell voltages that are too high or too low, helping to increase its lifespan.
The BMS also monitors the remaining charge in the battery. This is very important so that you don’t run out of power. The BMS continuously tracks how much power is going in and out of the battery pack, and monitors the cell voltages. It uses this data to know when the battery is running low and will shut it down if necessary. This is why lithium batteries don’t show signs of dying like a lead-acid battery but simply shut down.
Why do lithium batteries have Battery Management System (BMS)?
The BMS is primarily used in lithium batteries and not in lead-acid batteries. Why? The protection offered by this system has to do with the properties of its own materials, the battery cells, and the possibility of severe overcharging.
These three factors are some of the reasons why lithium batteries must be equipped with a set of specific management systems with which to effectively monitor, protect, perform energy balancing, and manage battery fault alarms. In this way, the working efficiency and lifespan of the lithium battery is improved. It also improves the charge and discharge rates, being much higher than lead-acid batteries.
Material Properties
The plate material that divides the cells in a lead-acid battery is lead dioxide (PbO2). The supplementary board material is pure lead (Pb), similar to a sponge. Thicker materials include partitions and shells. It is made of materials with acid resistance, heat resistance, and shock resistance, as well as providing good insulation and certain mechanical properties. Polycarbonate is made of pure sulfuric acid and distilled water in a certain proportion.
On the other hand, lithium batteries are mainly based on the movement of lithium ions between the positive and negative electrodes. Lithium-ion batteries use an intercalated lithium compound as the electrode material. The most commonly used cathode materials for lithium batteries are lithium cobalt oxide (LiCoO2), lithium manganate (LiMn2O4), lithium nickelate (LiNiO2) and lithium iron phosphate (LiFePO4), which are actually used as the negative electrode of lithium ions. The materials are generally carbon materials, such as graphite, soft carbon (such as coke, etc.), hard carbon, etc.
In terms of materials, the lithium in a lithium battery is more active than the lead in a lead-acid battery. The negative electrode material of a lithium battery is combustible. If the same safety as a lead-acid battery is to be achieved, the lithium battery cell needs a separator or casing. The material is made stronger and thicker, so the lithium battery would be heavier and larger than the lead-acid one. Obviously, manufacturers do not allow this to happen.
Battery Cells
Lithium batteries have more advantages than other types of batteries. However, they are also limited by factors such as cell materials and current manufacturing processes. These can lead to differences in internal resistance, capacity, and voltage between single-cell lithium batteries.
So, in practical applications, individual battery cells are prone to uneven heat dissipation or excessive charging and discharging. Over time, these batteries in poor working condition are likely to be damaged in advance, and the overall battery life is greatly shortened.
Possibility of Severe Overcharge
If the battery is in a state of severe overcharge, there is a danger of explosion. And this, as you can guess, would not only damage the battery pack but may threaten your own personal safety.
What benefits does the use of Battery Management System (BMS) bring to batteries?
Without BMS, battery operators often rely solely on routine maintenance to identify future battery problems and determine when to rehabilitate or replace batteries. So battery monitoring systems complement these efforts by capturing vital operating parameters, such as voltage and current, resistance, ambient temperature, electrolyte levels and more.
This data is automatically recorded and can be used for predictive maintenance and more accurate runtime estimates. But this is not the only advantage of BMS.
Benefits of BMS
Enhanced Safety
Battery monitoring systems offer several safety benefits, including
- Remote monitoring and alarms.
- Reduced maintenance, minimizing user contact with high voltage.
- Early warning for system failure, including hazardous conditions.
- Battery disconnection in the event of failure or unsafe operating conditions.
Easy access to key information
The state of charge (SOC) indicator functions as a sort of “fuel gauge” that shows the amount of usable power—something similar to battery estimates on cell phones and laptops. This helps determine optimal charging and discharging.
Information logging capabilities allow systems to collect trend data and create reports. These tools allow for estimates, long-term tracking, and better battery use. Also, remote access and software alarms can reduce maintenance and transit time and costs. This makes the BMS especially ideal for commercial environments and vacation homes, where maintenance crews or homeowners are not always on-site.
Reduced maintenance and replacement costs
Even “maintenance-free” batteries like lithium batteries require periodic inspection for optimal performance. Besides, stand-alone battery management systems can complement on-site inspections or owner maintenance efforts.
As mentioned, the BMS not only optimizes charge/discharge and other variables; it also helps identify maintenance requirements and predict battery failures. And it can also improve lifespan, reducing the frequency and likelihood of battery replacement.
A feature known as “low voltage shutdown” can reduce maintenance and maximize lifespan, especially in remote applications where routine inspection is more difficult.
Finally, cell voltage monitoring ensures that charging and discharging do not exceed manufacturer recommendations.
Extreme Temperature Protection (Extended Lifespan)
A BMS uses sensors to monitor ambient and battery temperatures, allowing for early warning when battery temperatures are outside optimal ranges. This also contributes to longer life and improved capacity.
Also, this is especially important for lithium batteries, as the temperature reading can influence whether a battery should be charged or discharged (to prevent thermal runaway).
Balancing voltage between cells
The ideal voltage depends on the battery chemistry. But in all cases, using batteries outside this voltage range can reduce cell life.
Besides, to extend life and proper function, each cell has a slightly different voltage window where charging/discharging should occur. Cold cells must be charged at a higher voltage. And weak cells can prevent other cells from being fully charged.
Some BMS systems can ensure equal charging between cells by measuring current and charge rates and performing passive or active cell balancing. Also, the BMS allows for advanced temperature-compensated charging, including float (fixed voltage over time), pulsed high current, and more.
Conclusion
As the saying goes, “Knowledge is power”. And a battery management system allows you to optimize battery reliability, safety, maintenance, performance, and life. So, we can consider that BMS can help save time, headaches and money.
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