Battery management systems offer powerful tools to “see inside” battery banks and improve lifespan, reliability, safety and performance.
A battery management system uses a specialized computer and sensors to make batteries “smart” – and provide real-time information about their performance, along with data collection.
The three core functions of BMS are battery monitoring, state of charge (SOC) estimation, and cell balancing.
Accurate measurement of temperature is also important for battery pack operation, including temperature measurement of individual batteries and temperature monitoring of battery pack cooling fluid measurement. This requires a reasonable setting of the position and number of the temperature sensor, and a good fit with the BMS control module.
The monitoring of the heat dissipation liquid temperature of the battery pack focuses on the fluid temperature at the inlet and outlet, and the selection of the monitoring accuracy is similar to that of the single battery.
4, single cell SOC calculation
Single-cell SOC calculation is the key and difficult point in BMS. SOC is the most important parameter in BMS, because everything else is based on SOC. Basic, so its accuracy and robustness (also known as error correction capability) is extremely important. If there is no precise SOC, more protection functions
It is also impossible to make the BMS work properly because the battery is often protected and the battery life cannot be extended. SOC estimation The higher the accuracy, the higher the cruising range of the electric vehicle for the same capacity battery. High precision SOC estimation can make the battery
5, Balance technology
Passive equalization generally uses the method of resistor heat release to release the “excessive power” of the high-capacity battery to achieve the purpose of equalization. The circuit is simple and reliable, the cost is low, but the battery efficiency is also low.
Active balancing, the excess power is transferred to the high-capacity battery during charging, and the excess power is transferred to the low-capacity battery during discharging, which can improve the use efficiency, but the cost is higher, the circuit is complicated, and the reliability is low. In the future, as cell consistency increases, the need for passive equalization may decrease.
How does it work?
In short, a BMS analyses real-time measurements from the chemical battery, then adjusts charging/discharging parameters and communicates this information to end-users. These sensors can monitor battery voltage, state of charge (SOC), state of health (SOH), temperature and other critical measurements. They can even display charging time on an easy-to-read “fuel gauge.”
When and where is BMS used?
Battery management systems offer numerous benefits for many battery chemistries (as explained below).
For these reasons, a BMS is used frequently in off-grid applications and battery backup applications, including generators and power utilities, telecom, hospitals, data centers and more.
But for lithium-ion batteries, a BMS doesn’t just offer benefits; it’s an absolute safety requirement to reduce the likelihood of fires and explosions. That’s because li-ion has the highest power density, and overcharging lower-capacity cells can cause thermal runaway and combustion.
Thus, in li-ion batteries, BMS ensures battery cells operate within their ideal operations window (including temperature, current, voltage, maximum charge and discharge current limits, etc.). A BMS can also help ensure cells are balanced properly.
Key Benefits of BMS for all battery chemistries
Without BMS, battery operators often depend solely on routine maintenance to identify upcoming battery problems and determine when to rehab or replace batteries.
Battery monitoring systems supplement these efforts by capturing vital operating parameters, cell/unit voltage and current; resistance; cell/unit/ambient temperature; electrolyte levels; and more.
This data is automatically recorded and can be used for predictive maintenance and more accurate runtime estimates.
Battery monitoring systems offer several safety benefits, including:
* Remote monitoring and alarms
* Reducing maintenance – which minimizes users’ contact with high voltage
* Early warning for system failure, including dangerous conditions
* Battery disconnection in case 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 displays the usable amount of energy – similar to battery estimates in cellphones and laptops. This helps determine optimal charging and discharging.
And data logging capabilities allow systems to collect trending data and create reports. These tools allow for estimations, long-term tracking and improved battery use. And remote access and software alarms can reduce maintenance and transit time and costs. This makes BMS ideal for commercial settings and vacation homes, where maintenance crews or owners may not always be onsite.
Reduced maintenance and replacement costs
Even “maintenance-free” batteries require periodic inspection for optimal performance. And standalone battery management systems can supplement on-site inspections or owners’ maintenance efforts.
BMS not only optimizes charging/discharging and other variables; it also helps identify maintenance requirements and predict battery failure.
And BMS can improve lifespan, reducing the frequency and likelihood of battery replacement.
A feature known as Low-Voltage Shutoff can reduce maintenance and maximize lifespan, especially in remote applications where routine inspection is more difficult.
Finally, cell voltage monitoring ensures that charge and discharge won’t exceed manufacturer’s recommendations.
Protection against extreme temperatures (extended lifespan)
For every 15°F to 20°F below 80°F, batteries lose ~10% capacity – while PV production decreases and electrical demand increases. Conversely, every prolonged 15°F above 77°F halves battery lifespan.
A BMS uses sensors to monitor ambient and battery temperature, allowing for early warning when battery temperatures are outside optimal ranges. This can prolong lifespan and improve capacity.
These features are especially important in lithium-ion batteries, where temperature readings can influence whether a battery should be charged or discharged (to avoid thermal runaway).
Cell balancing for equal voltage
Ideal voltage depends on battery chemistry. But in all cases, using batteries outside this voltage range can slash cell life.
In addition, each cell has slightly different voltage window where charging/discharging should occur, for long life and proper operation. Cold cells must be charged to a higher voltage. And weak cells can prevent other cells from charging completely.
Some BMS systems can ensure equally charging among cells by measuring current and charge rate–and performing either passive or active cell balancing.
In addition, BMS allows for advanced, temperature-compensating (“smart”) charging, including float (fixed voltage over time), pulsed high current and more.
Knowledge is power. A battery management system can optimize battery reliability, safety, maintenance, performance and lifespan. So it may be worth considering whether a battery management system could help save time, headaches and money.
For more information, including key requirements and battery compatibility guidelines, contact your systems installer or battery manufacturer/supplier.
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