Originally Published MPMN July/August 2007

ENGINEERING SOLUTIONS

Charging Forward

A redesigned battery system enhances a ventilator’s portability and reliability

Shana Leonard

When stressing the simplicity and naturalness of a task, people sometimes spout the comparison: “It’s as easy as breathing.” But for some individuals, breathing comfortably isa luxury and perhaps even a rarity.

Patients with such disabilities as paralysis, muscular dystrophy, and amyotrophic lateral sclerosis may have to rely on ventilators for an adequate oxygen supply. In the interest of increasing mobility—and thus potentially the quality of life—of patients burdened with these critical devices, Viasys Healthcare Inc. (Conshohocken, PA; www.viasyshealthcare.com) decided to redesign the battery pack for its LTV series of ventilators.

After the engineering director for the company read an article by Robin Tichy, technical marketing manager for Micro Power Electronics Inc. (Beaverton, OR; www.micro-power.com), Viasys approached the provider of portable power products with the project. Specializing in manufacturing and technology integration of battery packs and chargers, Micro Power was prepared for the challenge.

“We do all custom work at Micro Power,” Tichy says. “In this case, we had to work very closely with [Viasys] to understand what their end-users’ needs are and then we proposed a number of different solutions and features that we thought would help Viasys differentiate in their market.”

When designing the new system, Micro Power focused on ensuring reliability. The entire system consists of two lithium-ion battery packs and a charging system. Patients can operate off of battery power indefinitely, owing to the hot-swappable nature of the system. This feature enables the ventilator to draw power from just one battery when the second is being changed. Furthermore, the incorporation of two batteries supplies a higher degree of reliability since there is a backup if one battery fails, Tichy says.

“We also made it so the battery pack can be charged opportunistically whenever there’s a power outlet available,” Tichy adds. “It can be compatible with any type of power that might conceivably be available.” Compatible power sources include ac wall outlets, dc, car cigarette adapters, and even the batteries employed in electric wheelchairs.

Designed with an internal backup battery, the ventilator also features the Micro Power battery pack, which allows for mobility of the device. To achieve portability, the ventilator required high-capacity batteries and cells. Each battery has a capacity of 95 Wh, which increases the overall run time over the previous battery pack used in the system by almost 50%, according to Micro Power. In addition to improving portability, the redesigned battery pack contributes to a lighter and more-compact product than previous iterations of the ventilator; the power system is even compatible with versions of the machine already on the market.

Enhanced portability was the main goal of the redesign; however, the inclusion of safety features also proved to be paramount. Mechanical and electrical tests are applied to every pack and safety features include a positive temperature coefficient, thermal protection circuit, overvoltage protection circuit, and mechanical isolation of the PCA from the cells.

“In medical [applications], the patient’s safety is always of the utmost concern, so we designed this with every safety feature possible,” Tichy says. “We want to make sure absolutely that if for some reason there is a defect or the battery pack is misused in some way it doesn’t present a safety issue.”

In addition to safety, simplicity of the product is important to users. Micro Power addressed ease of use of the system by incorporating the latest in gas-gauging technology. “Previously, users had to do a learn cycle once a month and completely discharge and charge the battery so the fuel gauge could be calibrated,” Tichy says. “And in this case, that’s not necessary. They have 99% accuracy without the learn cycle, so the patient can be confident that whatever the fuel gauge says is indicative of how much run time they have left.”

Copyright ©2007 Medical Product Manufacturing News