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LFP battery has safer cathode material than NMC battery, and will not degrade at higher temperature. In fact, LFP battery provides the best thermal stability and chemical stability, so it has higher safety than NMC battery. The LFP battery will only enter the thermal runaway state at 195 ℃, and release the least energy during the thermal runaway. The typical NMC battery can enter a thermal runaway state as low as 170 ℃, which will release more energy and may ignite. Although all kinds of lithium-ion batteries are safe, LFP battery is one of the safest lithium-ion battery products.

Temperature and discharge

Generally speaking, UPS has two typical usage models. The first application is when the data center operator plans to use UPS power in a 5 to 10 minute interval, especially during the transition period from power failure to standby generator startup. In this case, UPS provides all available energy at a very high rate. The second application is when the data center operator plans to use UPS to provide 1 to 8 hours of discharge and wants to avoid starting the standby generator.

The internal impedance of LFP battery is very low, and it can discharge at a very high rate without generating too much heat. The internal impedance of the NMC battery is about 10 times higher than that of the LFP battery, and more heat will be generated internally when discharging at the same rate as the LFP battery. For example, 48V, 50A NMC battery (2400Wh) can provide about 50-100A discharge current, while similar size LFP battery can provide about 500-1000A discharge current. Power transmission is a key indicator of UPS power supply. In order to provide a specific current curve, multiple NMC batteries may need to be connected in parallel to achieve the required current, while one LFP battery may provide the required current. Considering the specific space limitation, this means that NMC batteries are more suitable for applications that can withstand lower current transmission during a longer discharge period (i.e. 1h50A), while LFP batteries can also provide higher current transmission discharge time in a shorter period (i.e. 300A within 10min). The expected operation time of UPS is a key factor in battery selection.

Passive or active cooling

In the rack mounted UPS market, UPS has a variety of thermal management options, ranging from passive cooling (no fan) to active cooling (continuously running fans) to dynamic active cooling (variable speed fan drive) to manage battery temperature. The third factor affecting the life of lithium ion battery is the ambient temperature. Lithium ion batteries can operate safely at - 20 ℃ to 60 ℃, but the best temperature range to maximize battery life is 10 ℃ to 30 ℃. High current discharge will generate heat inside the battery, but stable temperature environment can maximize the battery life.

It should be noted that based on the chemical composition and higher impedance of the NMC battery, compared with the LFP battery, they will generate more heat when discharging. Since cooling and heat dissipation is a key issue in the data center, the chemical composition of the LFP battery does give it an advantage in the climate controlled environment.

Advantages of active cooling

In general, increasing product complexity by introducing fans and thermal regulation can be seen as a disadvantage, but there are also some advantages. In applications without climate control, the temperature range of the cabinet can range from very cold and dry to very warm and wet. The battery is large and heavy. In the battery with passive cooling measures, in the event of thermal runaway, the internal temperature of the battery rises faster than the external temperature, resulting in hot spots and limiting the amount of discharge current available. This will also cause premature aging of the battery pack. Active cooling of the battery can better remove battery heat during a discharge or charging event. Compared with the equivalent passive cooling battery, the active cooling technology can also support higher charging battery and discharge current of the battery.

This may also pose the challenge of condensation. In the morning, moist air from the environment may enter the cabinet and contact the battery. Due to the temperature difference, this moist air may condense water to the sensitive electronic equipment inside the battery. Over time, condensation on electronic equipment may change the function of the battery or damage the battery components. Active cooling also has the advantage of keeping the electronics at the same temperature as the air, thus preventing condensation.

In conclusion, there are many rack mounted UPS on the market. Before selecting the UPS manufacturer or model, you should understand the power of these devices to evaluate the power required to maintain operation during power interruption, the required operating time, the environment to be operated, and the role of heat. With these data, you can evaluate the chemical characteristics, passive and active cooling characteristics of lithium ion batteries, and the key characteristics provided by available solutions. Once these functions are included in the selection criteria, UPS manufacturers will ensure that their UPS products provide the required power during power outages.