Swappable Power Subsystems

Swappable Battery Systems

Mobile medical workstation manufacturers have embraced swappable battery technology as a method of powering their workstations for many years. These swappable batteries are the main power source when the workstations are used in mobile mode. Quite simply, when a nurse wishes uses his/her workstation for clinical rounds, he/she drops a swappable battery into the receiver on the workstation and the workstation (and the affiliated IT devices – PC, display, barcode reader, printer, etc.) have access to AC and/or DC power throughout the shift. 

Reasons for a swappable battery work flow are; 1) workstations are used 24/7 (so the workstation does not have enough downtime to recharge a depleted in-base battery), 2) an older hospital may not have enough distributed AC power outlets on each floor to accommodate concurrent charging of all workstations with in-base batteries (so the swappable batteries are charged in a centralized charger and then distributed), 3) the elimination of an unsightly power cord from the rear of the mobile workstation and 4) non-powered workstations can be upgraded to powered workstations in the field. 

In recent years, the swappable battery work flow has been adopted by; distribution centers for mobile technology workstations (scanning/labels), motorbike rental companies for additional on-the-fly power and electric car manufacturers for renting access to charged batteries (rather than selling the battery with the vehicle).

Components of a Swappable Battery System

There are more components to a swappable battery system than an in-base battery system. From a block diagram perspective, the system has at least three distinct components; the battery, the battery charger and the battery receiver/controller mounted on the workstation. The battery receiver/controller could include AC/DC power conversion, battery charging electronics, DC/AC power conversion, 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 integrated, while a less integrated version may have some of this functionality in external accessories (such as battery charging electronics, DC/AC power conversion, or WiFi transceiver).

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 in the receiver/controller, or developing a single swappable battery system with a small reserve battery embedded in the receiver/controller. The alternative to hot-swapping is that power delivery is interrupted to the workstation and the user devices, which is disruptive to the nurse’s workflow.

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. 

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 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. 

Benefits of a Swappable Battery System

Swappable battery systems, whether installed on a medical or industrial workstation, enable the continuous operation of that workstation and eliminate any potential downtime for battery charging. Swappable battery systems have enabled innovative companies to offer “batteries-as-a-service” where the swappable battery becomes the delivery vessel for incremental purchases of power by the consumer.