Lithium Batteries for Industrial Portable Workstations

Mobile Industrial Workstations

If you visit a distribution center or warehouse, you will see many portable IT devices mounted on mobile carts or technology workstations, commonly called Workstations-on-Wheels. These IT devices include laptops, monitors, barcode scanners, printers. A common theme for IT devices integrated onto mobile workstations is a portable power source for uninterrupted power.

But prior to 2012, most industrial workstations relied on Sealed Lead Acid (SLA) batteries. Fast forward to 2020, industrial workstations continue to mobilize many devices, and the underlying power architecture has converged around two competing power configurations – in-base power and swappable battery systems.

In-Base Power Architectures

Most mobile workstations offer 120 or 240 VAC power to the user devices installed on workstations.  An in-base power architecture typically consists of two major subsystems – a 12 Volt, 40 (+/- 10) Ahr, 480 Whr, U1 format Li-ion battery and a 100 – 150 Watt inverter/charger.  The inverter/charger performs several functions, including AC/DC power conversion, battery charging, DC/AC power inversion, an Internet of Things (IOT) processor, a communications (SMBus, CANBus) transceiver, and electronics to drive a Remote User Interface (RUI) or Fuel Gauge to inform the user about system performance.  An in-base power architecture has the following characteristics:

• Reliability – This architecture has a permanent hard-wired cabling system.
• Nonintrusive Operation –This architecture is nonintrusive, and all the equipment is hidden in the workstation base.
• Larger Capacity – Given the physical capacity in most workstation bases, this architecture can accommodate large batteries to support multiple shifts.
• Stationary Charging – Once the battery is depleted, this architecture dictates that the workstation be plugged into an AC outlet to recharge the battery, which could take up to three hours.  Therefore, the workstation is tethered and stationary while charging.

• User Notification – The fuel gauge function can be integrated into the user Interface on the touchscreen display within the work surface. 
• User Training and Charging Behavior Issues – No battery system is foolproof. However, an in-base power architecture is very easy to train and understand.  Simply plug the workstations in when not in use.
• Lower Total Cost of Ownership – The in-base power architecture (battery and inverter) has a lower initial capital cost than a distributed swappable solution (batteries, docking station, inverter, charging stations, AC/DC power supply). Additionally, when comparing the cost-per-WHr of both solutions, the cost-per-WHr of the in-base power architecture is substantially less than a distributed swappable battery solution.

Swappable Battery Systems

In the last few years, mobile workstation manufacturers have embraced swappable battery systems as a method of powering their workstations. These swappable batteries are the main power source when the workstations are mobile. Quite simply, when a nurse or warehouse employee wishes to use his/her workstation for rounds, they drop a swappable battery into the receiver on the workstation, and the workstation (and the affiliated IT devices) have access to AC and/or DC power throughout the shift. A swappable battery system typically consists of a 12 Volt, 20 Ahr, 240 Whr Li-ion battery and a 100-150 Watt inverter/charger. Most workstations are designed to accommodate one or two batteries.

There are more components to a swappable battery system than an in-base battery architecture. From a block diagram perspective, the system has at least three distinct subsystems; the battery, the battery charger, and the battery receiver/controller mounted on the workstation. The battery receiver/controller can perform several functions, including AC/DC power conversion, battery charging, DC/AC power inversion, Internet of Things (IoT) processor, WiFi transceiver, a small reserve battery, and electronics to drive a Remote User Interface (RUI) or Fuel Gauge. A fully integrated controller/receiver will have all these functions.

Hot-swapping a battery refers to the removal of a depleted battery and insertion of a charged battery without shutting down the workstation’s electronics and IT devices. This useful feature enables a mobile workstation to supply uninterrupted power, rather than docking a workstation for a battery recharge or shutting down the workstation’s electronics when the batteries are swapped. Hot-swapping can be achieved with two swappable batteries installed into a common receiver/controller, or developing a single-bay swappable battery system with a small reserve battery embedded in the receiver/controller. Most modern workstations support hot-swapping, as the alternative is an interruption of power delivery to the workstation, which is disruptive to the user’s devices.

Characteristics of a swappable battery system are:

• 24/7 Operation – Workstations can be used 24/7, so the workstation does not experience any downtime to recharge depleted batteries. 
• Eliminates Need for AC Outlets on the Floor – An older hospital or warehouse may not have enough distributed AC power outlets on each floor or near the work area to accommodate concurrent charging of workstations, so swappable batteries are charged in a centralized location and then distributed out to the floor.
• Upgrades and Retrofits – Non-powered workstations can be upgraded to powered workstations in the field. 
• More Components – There are three distributed components – battery, battery charger, and receiver/controller – which may make the operator’s workflow more complex.

Swappable battery systems are available from workstation manufacturers, as well as third-party vendors with universal solutions that operate with all workstation brands. In the last five years, almost all workstation manufacturers have introduced swappable battery options to complement or replace their in-base power architecture.

Integration with the Workstation

Other considerations for the design of a swappable battery system include human factors and ergonomics, such as the weight of the battery, the height of the mounting position of the battery on the workstation, the impact the battery has on the center of gravity of the workstation and where/how to display the state of charge.

Most mobile industrial workstations have UL and/or CE approvals to ensure safe and non-intrusive operation of their product within an industrial setting. For the components of a hot swappable battery system, this typically dictates that the battery has the following regulatory approvals – UN 38.3, IEC 62133 and UL 1642. Additionally, the receiver/controller typically has UL62368, as well as a CE mark for shipment into the EU.

Cell Chemistry Options for Workstation Power

All in-base and swappable batteries use lithium-ion rechargeable cells within their battery to store power. The two predominant cell chemistries are Lithium Iron Phosphate (LFP) and Lithium Nickel Manganese Cobalt Oxide (NMC). For these smaller format batteries, the typical cell formats are 18650 (18 mm diameter X 65 mm height), 21700 (21 mm X 70 mm), or 26650 (26 mm X 65 mm) metal-cased cylindrical cells. These individual cells are connected in series and parallel to provide the desired voltage, capacity, and current parameters of the battery.

When in-base power and swappable batteries were introduced, OEM’s offered either a LFP or NMC version of their products. Over time, the medical workstation market gravitated towards the LFP chemistry for several reasons:

• Longer Cycle Life – LFP Batteries provide superior cycle life over the life of a mobile workstation.  LFP batteries deliver at least 2000-3000 full charge/discharge cycles before reaching 80% of original capacity.  Typical NMC batteries deliver 500 – 1000 full charge/discharge cycles before reaching 80% of original capacity.  Assuming that the typical nurse’s shift is 8 – 12 hours daily, a single cart could be used continuously across a 24-hour period. This means that the typical battery is fully cycled each day. Industrial workstations experience a similar pattern of usage.
• Intrinsically Safer – LFP Batteries have an intrinsically safer cathode material than NMC batteries, and do not decompose at higher temperatures.  This means LFP batteries provide the best thermal and chemical stability, which results in superior safety over NMC batteries.  A LFP battery enters a thermal runaway condition at 250 – 270 Celsius and releases minimal energy during thermal runaway, compared to a NMC battery.  All Li-ion batteries are safe, but LFP is the safest Li-ion battery chemistry available.  Given the amount of active battery material in a U1 battery offered with in-base batteries (i.e. 500 Whrs), the medical industry opted for the safest Li-ion option.

Currently, despite the fact that LFP chemistry has a higher cost per Whr than NMC, almost all batteries powering workstations utilize LFP chemistry. LFP Batteries demonstrate superior total cost of ownership over Sealed Lead Acid (SLA) and NMC batteries. The upfront cost is higher, but over the lifetime of the workstation, the total cost is lower.