Rosslare Battery Pack Commercial grade Wi-Fi telephone handset

Wi-Fi has expanded the ability to use VOIP in a mobile manner, providing the ability to easily access data services on smartphones and tablets. To deliver on their promise, these devices must perform reliably with long battery life and rugged commercial grade performance.
Rosslare was commissioned to provide unique battery and charger products for a specialty Wi-Fi portable communications provider.

Unique Challenges

The challenges evolved in this project were many and in different aspects. On the business side, the client expected to achieve low project non-recurring engineering (NRE) and product cost to produce a substantial ROI. Worldwide safety agency approvals were additionally required for the product's successful launch within a reasonable time-to-market.

On the technical side, the handset's engineering team needed to meet the product's requirements for two battery versions for low and high capacity, along with fuel-gauge technology, battery cycle counter, error logging, and a high-security battery authentication function. Furthermore, the 3.7V Li-Ion battery package requirements included a custom molded plastic cover case, fit for a commercial grade Wi-Fi telephone handset.

Project scope integrated both mechanical and electrical battery design. The client provided only the basic industrial design files for completing the battery and charger engineering. Additional, Rosslare was to manage the electrical contact design on the battery and handset and the mechanical latching of the battery into the handset. The battery must pass severe drop tests and never disconnect in any manner from the handset or sustain damage.

To meet the product's rigid size requirements for a compact handheld device, Rosslare needed to develop a low profile battery pack. To enable "smart" battery features, Rosslare further needed to develop proprietary communications, unique fuel gauge parameters, and an authentication protocol between the battery and handset.

Rosslare Solution - Li-Ion Smart Battery with…

Rosslare was chosen based on its strong engineering expertise, commercial and technical support, together with a highly integrated, wholly-owned, large scale manufacturing facility in Shenzhen China. This along with Rosslare's history in serving market leaders in the Communications Industry such as Qualcomm, Polycom and others has made Rosslare the partner of choice for this project.

After reviewing all options, Rosslare selected a top tier cell manufacturer with a proven record for safe construction and high capacity cell assembly processes to supply the Li-on cell for the Lithium-ion battery.

The company's Chicago-based product development team worked directly with the client’s mechanical designers to develop a reliable latching mechanism that passes the clients reliability and abuse requirements. A low cost contact system was designed to meet the reliability needs and space limitations.

Rosslare concluded that a custom gas gauge system was required to physically fit into the limited space of the battery pack. Using a single microcontroller, Rosslare developed the hardware and firmware to provide a highly accurate system that also allowed cycle counter, history logging and encrypted battery authentication.

Reliable, Durable and Secure Rechargeable Battery Power

Rosslare’s engineering team worked concurrently and closely with the client’s firmware team to ensure the handset and battery communications were reliable, consistent and were completed within the project’s timeline.

All necessary testing and assistance for safety agency approval was provided on time.

Rosslare met each and every timeline and cost parameter set forth by the two teams at the outset, helping its client ultimately bring its product to market at a low NRE cost.

Case Study 2

Application Overview

  • Develop a Li-Ion battery solution for a professional model, handheld AV controller where the mechanical design for the device was completed prior to finding a battery solution. This client did not want to change the existing mechanical design or compromise battery performance. This required creative changes to conventional battery design.

  • Two Li-Polymer cells in series
  • Metal battery case with screw down mounting tabs
  • Gas gauge
  • Battery cycle counter
  • Battery error log
  • Safety Agency approval: UL, CE, PSE

Unique Challenges and Rosslare Solution
  • Rosslare met with one of our approved suppliers (extensive auditing by Rosslare is required to gain approval status as a cell supplier to Rosslare) for Lithium Polymer cells (Li-Po). Li-Po cell technology is similar in performance to Li-ion, but a unique feature to Li-Po is that a cell can be custom made to meet unique capacity and dimension requirements. This usually allows for higher capacity in Li-PO for lower profile cells. We developed a custom cell size to conform to the application requirements.
  • Li-Po cells do not use a firm metal case, but instead use a plastic film material as the external case. This plastic film is thinner, much more flexible than, and not as rugged as, the metal cans used on Li-Ion cells.
  • To keep the overall dimension size to a minimum, and provide mechanical protection of the Li-Polymer cells, Rosslare designed and tooled an ultra-thin metal exterior battery case. This case design created the lowest profile and best protection for the cells. Additionally, this unique design allowed the battery pack to be electrically shielded and grounded.
  • A standard gas gauge IC could provide basic functions, but the host device had a non-standard communications protocol. Rosslare developed firmware, running on a low cost microcontroller tha which acts as a communications buffer/translator between the commercially gas gauge IC and the host device. Additional functions, such as error and history logging were also implemented in the microcontroller firmware.

Case Study 3

Application Overview
A cylindrical single cell Li-Ion battery in a molded plastic case, with unique contacts, to power a high power flashlight which uses a xenon filled incandescent bulb.

Single cylindrical Li-Ion cell
Thin walled custom molded plastic case in a cylindrical form factor.
Electronic circuit to protect against overcharge, over discharge, over current and short circuit
Unique electrical contact arrangement

Unique Challenges
The cylindrical battery case diameter must be less than 2mm larger than the cell diameter.

A unique low profile contact system was needed to carry significant current and prevent the possibility of short circuit in a low profile configuration.

The flashlight's high current light bulb has a high inrush current tha looks like a short circuit to standard protection circuits. This causes them to trip open, leaving the user to think the battery is dead. Simply setting the over current circuit trip threshold very high to accommodate the peak inrush current of the bulb would render the protection circuit unsafe in the event of an actual overload.

Rosslare Solution
Using 3D CAD software, Rosslare modeled the battery mechanical design that precisely fit the necessary components into the limited space allowed by the application. Rosslare’s experience and expertise in thin wall plastic tooling and injection molding allowed the parts to be successfully realized.

To overcome the nonlinear characteristics of the lightbulb load, Rosslare fully characterized a large sample quantity of bulbs in a variety of conditions, to define the worst case Time vs. Current profile of a bulb turning on. We then designed a protection circuit that would allow the peak inrush current of a bulb turning on, but also trip when an actual overload occurred at the battery terminals.


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