Development of Nickel-Zinc power system for powered wheelchairs

The power systems for powered mobility devices (power wheelchairs and scooters) have largely remained unchanged for decades. They all revolved around Lead-Acid batteries, but some more recently have started to use Lithium-Ion batteries for their lighter weight and higher energy density. However, there are still limitations

to both of these current battery technologies related to charge rate, range, fire and explosion safety, and environmental concerns. Studies have shown that power wheelchair users travel can travel over 10 kms/day and that the distance travelled is impacted by the accessibility of the environment and the type of activities in which the user is

participating. However, current battery technology largely restricts the power mobility device users to the distance that the device can travel on a single charge, no matter how accessible the environment is. This is because the current batteries used require 5-8 hours to recharge. Because of this, most power mobility device

users will charge their device overnight and then use the device the next day on that single charge. While this appears to be sufficient for most users on most typical days, there are some underlying factors. Firstly, power mobility device users have become familiar with the range that their device can go and have planned their days

around that range. Secondly, there are many times when power mobility device users may want to go farther than they do on a typical day, such as vacations and other leisure activities (e.g., sporting events, tours, concerts, etc.). Powered mobility device users have reported that they need to plan daily activities around the

distance that their chairs can go and at times have had to change plans based on the charge status of their batteries. Powered mobility device users have also expressed a strong desire for more research on the development of new and alternative power sources for powered mobility devices. This is primarily due to the

limited range and long charge times. Nickel-Zinc batteries may provide many advantages over the current Lead-Acid batteries including: higher energy and power density, higher cycle life, higher charge rate, more recyclable, safer, and less susceptibility to extreme temperatures. Many of these characteristics are superior to Lithium-Ion batteries as well. The

limitation with the Nickel-Zinc batteries that are most similar to the Lead-Acid and Lithium-Ion batteries is that they need to be discharged at a rate of more than 40 amps or their life-cycle is significantly reduced. This makes them not suitable for a direct application in powered mobility devices as typical powered mobility

devices use 0-20 amps during use. Supercapacitors, on the other hand, can be repeatedly charged and discharged at any rate for millions of cycles, but have low energy density (meaning they can’t hold much energy in a small package). The goal of this project is to develop a new power system for powered mobility devices using a combination of

Nickel-Zinc batteries and supercapacitors. The supercapacitors will be used to power the wheelchair motors and actuators and the Nickel-Zinc batteries will be used to frequently recharge the supercapacitors (at a rate of over 40 amps). This takes advantage of the higher energy of the Nickel-Zinc batteries while bypassing the

limitation of the need for high discharge rates. The development activities will include developing the battery management system, which will trigger and control the transfer of energy from the Nickel-zinc batteries to the supercapacitors. The new system will also be bench and laboratory tested for safety and performance viability.

The range that the new system will be able to travel will also be compared to the ranges of currently available Lead-Acid and Lithium-Ion batteries using the ISO-7176 Section 4 range calculation, a flat test track, and a community test track.