A new study has examined the feasibility of using nickel-zinc batteries (NiZn) batteries accompanied by supercapacitors on power mobility devices.
The research — Design and Feasibility of a Nickel–Zinc Battery-to-Supercapacitor Hybrid Power System with Active Voltage-Gap Control for Powered Mobility Devices — was published by Basel, Switzerland-based Multidisciplinary Digital Publishing Institute (MDPI) on June 12. The authors are Jonathan Duvall (Human Engineering Research Laboratories [HERL], Department of Veterans Affairs, Department of Physical Medicine and Rehabilitation, University of Pittsburgh); Benjamin Gebrosky (HERL, Department of Veterans Affairs, University of Pittsburgh); Garrett Grindle (HERL, Department of Veterans Affairs, University of Pittsburgh), Stephen Layton (HERL, Department of Veterans Affairs, University of Pittsburgh); Arianna Ciregna (HERL, Department of Veterans Affairs, University of Pittsburgh; Department of Systems Engineering, Stevens Institute of Technology); and Rory A. Cooper (HERL, Department of Veterans Affairs, Department of Physical Medicine and Rehabilitation, University of Pittsburgh; Department of Bioengineering, University of Pittsburgh).
Researchers noted that power mobility devices “have used lead–acid batteries for decades with some recent designs using lithium-ion batteries.” But both battery types also “have concerns related to safety and environmental impact.”
Compared to lead-acid and lithium-ion batteries, “Nickel–zinc batteries can charge much faster and are safer and more environmentally friendly,” the authors said. “However, nickel–zinc batteries must be discharged at high rates to prevent degradation of the batteries. This project developed a prototype power system using nickel–zinc batteries and supercapacitors to power a scooter.”
Creating a hybrid power source
Supercapacitors are defined by ScienceDirect.com as electronic devices “that store and deliver electric charge through electrostatic action. They exhibit high power density and rapid charge/discharge rates, bridging the gap between traditional capacitors and batteries in energy storage applications.”
The combination of NiZn batteries and supercapacitors designed by the researchers “uses the nickel–zinc batteries to periodically and quickly charge the supercapacitors, which then provide the power [to] the scooter. Testing confirmed that the power system maintained appropriate voltage and current during use and that the scooter was able to perform with the same range, speed and power as a current commercially available scooter.”
The system was tested on a Golden Technologies Eagle scooter, in what the authors said “is, to our knowledge, the first application of this approach for PMDs [power mobility devices] and the first integration of NiZn batteries into a PMD power system. The scooter was able to operate with the same or greater speed, power and range as it could” using its original batteries.
The NiZn batteries were “similar in size” to the lead-acid and lithium-ion batteries currently used to power scooters, but “the supercapacitors used in this development were also physically large (418 × 66 × 179 mm),” the authors noted. “If these were used commercially on PMDs, there would need to be additional space to house the supercapacitors.”
The researchers added it would be possible to position the capacitors in different configurations “to fit where space is available on the PMDs,” and that “smaller, equivalent-capacity modules could become available” as the capacitor industry continues to progress.
For the study, the supercapacitors and electronics were in a junction box “strapped to the footrest of the scooter,” and the authors acknowledged that a production version of the system “would need to be placed under the seat with the batteries or somewhere else out of the way of the user. Testing factors such as weight distribution, center of gravity, vibration resistance, and ingress protection would need to be completed.”
The NiZn battery-supercapacitor combination did perform successfully, the authors said, noting the system “maintained appropriate voltages and currents, and the PMD was able to function with similar range, speed and power as is currently available with [lead-acid] batteries.” The researchers’ system also “could be safer, more environmentally friendly, and allow for faster charge times than existing [lead-acid] and [lithium-ion] batteries.”
Researchers noted that many PMD riders are currently restricted in their travels due to battery range, and that “they need to plan some days around the distance that their PMD can go and at times have had to change plans based on the charge status of their batteries.”
