Which is the most suitable for a UPS system?
There are several types of batteries used for UPS devices, and deciding which one is best for your particular requirements takes some consideration. Two options are lithium ion and lithium iron phosphate batteries which do share some similarities, but differ on a number of key features.
What is a lithium-ion battery?
This rechargeable battery has been used to power everything from laptops and cellphones through to electric vehicles – and uninterruptible power supply (UPS) devices! It lowers the real estate footprint of batteries by almost half, and has battery life which is three times longer than lead acid batteries.
What is a lithium iron phosphate (LiFePO4) battery?
Lithium iron phosphate is another new battery type that is gaining traction because of its cost-effective materials, stability and enhanced life span. While not the cheapest batteries available, the many advantages associated with lithium iron phosphate have seen them become a prime choice in UPS devices.
What are the differences between lithium-ion and lithium iron phosphate batteries?
While lithium iron phosphate batteries are effectively a type of lithium-ion battery, there are several differences between the two UPS battery types.
– Energy levels
Lithium iron phosphate batteries have a lower voltage – 3.2V – compared with other lithium battery types, although this is still comparable to other lithium chemistries in terms of power availability. It also has a lower energy density – 90/12Wh/kg – when compared with lithium-ion sitting at 150/200 Wh/kg which makes lithium ion the preferred chance for powerful electronics.
Lithium iron phosphate batteries have a 1 000 to 10 000 cycle which is a lifespan of up to 15 years in UPS applications. This is not only significantly more than traditional lead acid batteries, but also outpaces the 500 to 1 000 cycles of a lithium-ion battery. In addition, the lithium iron phosphate is much more lightweight, providing significant reductions in system weight.
In terms of operational safety, lithium iron phosphate is the preferred option for UPS operation. The reason for this is that lithium iron phosphate has incredible thermal and chemical stability so that, even when temperatures start increasing, the battery remains cool. And, because of the oxygen being bonded tightly to the molecule, there is no danger of the battery erupting into flames, as can happen with lithium-ion batteries. It has a wide temperature range of between -20°C and +60°C for operation, charging between -10°C to +60°C, with storage between -40°C to +60°C. Lithium iron phosphate is also incombustible when it’s mishandled or during short circuit issues. Unfortunately, the lithium-ion chemistry doesn’t offer the same level of safety and stability as it has a high energy density. It heats up faster when charging making it sensitive when temperatures rise.
Any lithium-ion battery made with lithium cobalt dioxide chemistry is hazardous, causing allergic reactions in eyes and skin if exposed, and severe medical conditions if consumed. This makes the disposal of a lithium-ion battery costly when meeting required guidelines. Lithium iron phosphate, however, is non-toxic and can be easily disposed of once the battery has expired.
Also referred to as ‘usable energy’, the depth of discharge on a lithium-ion battery is around 80 to 100%, making it a great energy storage device. While this outdoes the former VRLA batteries which had an average DoD of 50%, they’re not quite as good as the lithium iron phosphate batteries which outmatch lithium-ion in DoD every time. The speed of discharge is critical for UPS applications as they need to keep facilities operational during the switchover to backup power – otherwise the system will crash. In addition, the discharge rate won’t degrade the lithium iron phosphate battery as capacity decreases. If you choose to go with a lithium-ion battery, you will require additional battery strings to deliver adequate power to the UPS for this critical changeover period.
Which battery is best for a UPS device?
Clearly, when compared against the other lithium battery chemistries, the lithium iron phosphate comes out ahead in all categories for use with a UPS device. It’s safer to use, performs better, has a longer life cycle and is easily disposed of – making it cost-effective in the long run and environmentally-friendly. In addition, the lithium iron phosphate batteries will often come with a battery management system that protects the cells by preventing them from exceeding limits of the cell voltage and discharge.
To find out more about the various UPS battery types, contact the industry experts in backup power supply systems, JUP Solutions. They will advise on the most suitable UPS topology and battery backup system for your requirements.
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