Lithium-ion drives military apps power needs

Lithium-ion drives military apps power needs

The army needed drastic improvements for its mission-critical portable power needs and Li-ion technology fit the bill.

BY JIM HESS
Saft Batteries
Cockeysville, MD
http:/www.saftbatteries.com

A system is only as good as the sum of its parts. This is especially true when it comes to electronics. Batteries are an integral part of electronic systems, whether they are in a car, a cell phone or a defense weapon. They are responsible for powering the critical functions of the system. If the battery in your car is dead, you can’t drive anywhere; if the battery in your cell phone is dead, you can’t make a call; and if the battery in a defense weapon fails, it could be a matter of life or death.

Technicians with the U.S. Army understand this concept more than anyone because they are constantly dealing with mission critical systems and power specifications. When it came to powering the Tube-Launched, Optically Tracked, Wire-Guided (TOW) Improved Target Acquisition System (ITAS), the Army’s Technology Reinvestment Program specialists realized the legacy silver-zinc (Ag-Zn) batteries were not meeting their needs.

Operating from a tripod platform or the hybrid electric High-Mobility Multipurpose Wheeled Vehicle (HMMVW), the ITAS is an advanced fire control system that guides the TOW weapon systems to their targets. It is comprised of day/night sight with laser rangefinder target acquisition and fire control subsystem. The battery is one part of this integrated system, responsible for providing power for silent watch and long-range surveillance in all battlefield conditions.

Fig. 1. The tube-launched, optically tracked, wire-guided (TOW) system for a hybrid electric high-mobility multipurpose wheeled vehicle (HMMWV). (Courtesy of the Department of Defense)

There were many drawbacks to the previously installed silver-zinc batteries that impacted the overall functioning of the ITAS system. First, the silver-zinc battery required the electrolyte, potassium hydroxide (KOH), to be added shortly before use. This was a challenge because soldiers or service people had to pour the chemical into the cells while they were in the field. The KOH is hazardous in the battlefield and once this process was complete, the battery needed three days to fully activate. Clearly this is not the best use of the soldiers’ time and could cause a number of problems in the field.

Not only did the battery have to be recharged frequently, it could take up to 16 hours to completely recharge. In addition, the battery only lasted six to nine months, resulting in the Army having to replace each pack approximately 1.33 times per year. This translated into millions of dollars spent in life cycle costs.

With this amount of money at stake, plus the time spent maintaining the batteries, the Army knew it needed to find a better solution. They needed a battery that would provide fast re-charge, longer run times, and longer overall life. They also needed a solution that would require little maintenan(ce, reduce operating costs, and most importantly, be safe. The Army realized it was time to replace the legacy silver-zinc battery technology with a lithium-ion (Li-ion) battery for the TOW ITAS.

The main advantages of Li-ion battery technology are that it is very light weight, providing more power relative to weight than any other battery chemistry, and it has a long life cycle, making it an ideal solution for the ITAS. The Army’s engineers identified the ideal solution with fast re-charging capabilities (80% in three hours), long run-time (16 hours of operation), and long life cycle (80% capacity after 1,200 full cycles).

In contrast to the legacy silver-zinc batteries, the Li-ion batteries re-charge in as little as four hours, have no activation time and can last up to five years. In addition, Li-ion batteries can go through approximately 500 charge/discharge cycles compared to silver-zinc’s 50 cycles. These advantages have added up to a pack replacement rate of 0.33 times per year, saving the Army millions of dollars in life cycle costs.

The Army selected Saft’s 28 V Li-ion battery packs and started working with prototypes in August of 2000. After tests showed strong performance, the battery packs were selected for use with the TOW ITAS and have been fielded in Iraq and Afghanistan since 2004.

Fig. 2. Improved Target Acquisition System (ITAS) with a Li-ion battery pack.

The 28-V Li-ion batteries are cylindrical cells and provide high performance over a wide range of temperatures, which is essential for the rugged conditions of the battlefield. The battery is supplied as a complete pack, to plug-and-go, and provides a nominal 80-Ah capacity at 21C. The cells are housed in a robust, pressure compensated box with carry handles, burst prevention mechanism and keyed connectors, and in recognition of the wide range of conditions in which the ITAS might be deployed. Additionally, the box can be operated even when wearing arctic gloves for cold environments, like the mountains in Afghanistan.

Aside from the convenience, dependability and versatility of the battery, of paramount importance to the war fighter is safety. The battery box selected for the ITAS incorporates sophisticated on-board electronics to ensure enhanced battery performance and current protection as well as providing thermal and safety management systems. Its built-in safety features include overcharge/over discharge protection and pressure compensated housing.

The battery packs are supported by a special software package developed for use with the ITAS battery pack that enables it to interface with a PC to provide a direct readout of the battery condition. This enables the operator to run a suite of health checks on key criteria such as individual cell voltages, enabling accurate prediction of battery life, so the pack can be swapped and recharged before it reaches a critical level. This provides the user with added confidence and peace of mind for ITAS operators.

There are more than 1,000 of these battery packs currently deployed in the field. The shift from silver-zinc to Li-ion has provided a lower life cycle cost and longer life span benefits as well as increased readiness and reliability for the ITAS. Using Li-ion batteries has reduced high maintenance costs and downtime that was experienced with the legacy power source. By upgrading the battery, the Army has significantly reduced its costs and enhanced the performance of the ITAS, and ultimately the TOW missile.

For more on lithium-ion batteries, visit http://electronicproducts-com-develop.go-vip.net/power.asp.