Understanding IIoT Batteries and Power Protection at the Edge

Understanding IIoT Batteries and Power Protection at the Edge
Understanding IIoT Batteries and Power Protection at the Edge

Extending control to the edge has great potential for reducing operational costs and improving efficiency, but it brings a host of new challenges, including assuring power availability to all devices. Uninterruptible power supplies (UPSs), which provide battery backup for operations, are essential for all critical processes and these are now evolving to deliver continuity in the digital age, beginning with their core battery technology.
Conventional UPSs use lead-acid absorbent glass mat (AGM) batteries which are antiquated and have severe shortcomings. AGM Lead batteries are large, heavy, must be vented and mounted upright. Advancements in battery chemistry have allowed for battery cells to decrease in size without compromising in output or efficiency, but these have been slow to replace AGM batteries in the industrial world. This is changing rapidly, however, as UPS manufacturers replace lead-acid AGM technology with Lithium-ion technology.
Lithium-ion technology offers numerous advantages for backing up critical industrial processes. It has superior useable capacity and extended cycle life over lead-acid batteries, which is required for mission critical applications.
AGM batteries typically use only 30 to 50% of their rated capacity and discharging them below this limit greatly reduces their life. Graph 1 shows that the (AGM) lead-acid pack must be limited to 30% depth of discharge (DoD) to get comparable cycle life of a lithium-ion that is used at 75% DoD. Moreover, the AGM battery must be 2.5 times larger in capacity than the lithium-ion to get comparable life.

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Figure 1:  Regardless of depth of discharge, lithium ion batteries can achieve 100% capacity repeatedly over 2000 cycles, whereas the number of charge cycles attainable from AGM batteries is significantly diminished with each decrease in depth of discharge.

Li-ion batteries also have the following advantages over AGM batteries:

  • Flexible Deployment. Li-ion units are sealed and can be mounted in any orientation.
  • Fast charging.  Li-ion units charge 10 times faster than conventional AGM Lead batteries.
  • Extended Life.  Li-ion units charge 10 times faster than conventional AGM Lead batteries; they also have a 12 amp-hour capacity, and a 10-year life @ 40ºC.
  • Lower de-rate Li-ion batteries can deliver 75% of their original capacity after 2000 charge cycles. AGM batteries are not suited for a continuous trickle-charge environment that is common in remote industrial installations. AGM batteries are dependent on a full depth of discharge to obtain the maximum amount of charge cycles. 

Improved capacity retention. Li-ion batteries operate across a wider temperature range with longer life. They maintain 100% their load capacity between -10ºC to +50ºC versus 30% for AGM batteries. (Figure 2) Lead-acid batteries operate best at 25°C (77°F) and lose half of their life with every 8°C (15°F) rise in temperature. Even valve regulated lead-acid (VRLA) batteries, which are designed to maximize AGM efficiency, would last only 10 years at 25°C, and only 5 years if operated at 33°C (95°F) and only one year at 42°C (107°F). In hot regions such as the U.S. Southwest, where summers can reach triple-digit temperatures, AGM-based UPSs typically need replacement every year.

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Figure 2: Lead-acid batteries operate best at 25°C (77°F) and lose half of their life with every 8°C (15°F) rise in temperature. Lithium ion batteries maintain the majority of their capacity regardless of temperature.

 

Lithium needs protection as well

Despite the performance advantages of lithium over lead-acid, the UPSs need protection as well.  Batteries consist of multiple cells, depending on how much power is needed. Rather than stack cells and monitor, control, and contain that stack, advanced Li-ion battery safety requires every cell to be engineered as an independent system. This starts with galvanic isolation of charging circuits and dedicated circuit boards, sensors, electronics and passives to monitor, control and limit charging current, charging voltage, and discharge current.  In this way, the battery pack becomes less vulnerable to the status of a single cell and the charge and discharge of each cell is independently optimized for safety and performance.  The cells should be encapsulated and protected by multiple layers as shown in figure 3, including compliance with NEMA 4x, FIPS 140 and ingress protection (IP) standards from an all-metal housing discussed above.

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Figure 3: Like the automation systems they power, UPSs deserve multi-layer protection

Completing the package

With li-ion technology at their core, UPSs are evolving in many other ways to optimize reliability at the edge. This includes improvements in intelligence, integration, ruggedness, and cyber security. 
Embedding secure microcontrollers with high memory capacity enables collection and analysis of operational data, which can be used to identify and prevent critical errors, optimize performance, integrate with other technologies, and enforce authentication and encryption to protect the end device from cyber security threats.
Advanced rugged designs improve reliability in remote and hazardous environments.  UPSs are also evolving to protect power supplies from ambient contamination and stress by removing all moving parts and venting and replacing them with advanced thermo and electromechanical designs for component placement, thermal bonding, and contiguous thermal conduction which metal construction enables. 

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Figure 4:  This Bedrock UPS augments its li-ion battery technology with a 32-bit secure ARM microprocessor, built-in cyber security and is encased in an all-metal, environmentally resistant anti-tamper enclosure.

Metal enclosures enable anti-tamper cyber integrity as well and extend life significantly, 50 years is possible.  The casings are hermetically sealed compliant with NEMA 6 and EMP standards. Standard power supply protection should be IEC Class A rated for vibration, relative humidity, extreme weather and temperature conditions, external shock conditions, water immersion, and water and dust ingress protection.
Armed with advanced li-ion technology, state of the art computational capability, and encased in all-metal environmentally resisttant enclosures, UPSs stand ready to meet the challenges of the digital age.

About The Author


Bedrock-IIoT-Batteries-Shawn-Hatton.pngShawn Hatton has 15 years of experience in electrical, instrumentation, and control system design. He is a senior field automation specialist at Bedrock Automation.
 

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