If you visit a hospital hallway or patient room, you will see many portable medical devices mounted on mobile carts or technology workstations, commonly called Workstations-on-Wheels. These IT devices include laptops, monitors, barcode scanners, printers. Other clinical devices include ultrasounds, patient monitors, telepresence, and imaging machines. A common theme for medical devices integrated onto mobile workstations is a portable power source for uninterrupted power.
Mobile powered workstations have been used in hospital settings since 2001, when the first mobile workstations were deployed in a Pennsylvania hospital. But prior to 2012, most medical workstations relied on Sealed Lead Acid (SLA) batteries. Fast forward to 2020, medical 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.
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. Figure B provides an interior view of a medical workstation with in-base power subsystems – the battery and inverter/charger. An in-base power architecture has the following characteristics:
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 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:
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.
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.
If the swappable battery system is used to power a medical workstation, infection control and agency certifications should be considered. Infection control is minimized by using selective PC/ABS materials for the battery and receiver/controller housings. Antimicrobial additives, such as Microban, can be added to the plastic resin to keep plastic parts cleaner by inhibiting the growth of bacteria, mold and mildew. Tight seams can be implemented to minimize microbial growth within those crevices. The industrial design can be optimized so all components are easy to clean. The Ingress Protection (IP) rating should be high enough to ensure the components can be cleaned with antimicrobial cleaning solutions and not penetrate the interior or erode the seals/contacts of the battery.
Most mobile medical workstations have UL and/or CE approvals to ensure safe and non-intrusive operation of their product within a hospital 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 2054. Additionally, the receiver/controller typically has UL 60601 3rd/4th edition, as well as a CE mark for shipment into the EU.
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:
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.
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