Power Electronics

High-Temperature Batteries Target Pressure Monitoring Systems

Tragic accidents due to improperly inflated tires and the subsequent recall of nearly 6.5 million Firestone tires in 2000 prompted Congress to take legislative action to protect American motorists. The result was passage of the Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act in the fall of 2000, which requires installation of tire pressure monitoring systems (TPMS) as one of its five major points.

As a result, the new National Highway Traffic Safety Administration (NHTSA) standard requires automotive manufacturers to begin installing one of two monitoring systems in 10% of their light vehicles beginning in November 2003. Next year, Nov.1, 2004 to Oct. 31, 2005, 35% of the manufacturer’s light vehicles must comply with the new law, and 65% must comply during third year (Nov. 1, 2005 to Oct. 31, 2006).

The two TPMS approaches include a direct measurement system that has a tire pressure sensor for each tire, or indirect measurement systems that determine tire inflation pressure from wheel speeds, or something other than tire pressure. The direct TPMS implements pressure sensors for measuring pressure in each of the four tires, and transmit the pressure data via a wireless RF transmitter to a central receiver, which is linked to a display that informs the driver what tire is underinflated. The indirect system employs wheel speed sensors on vehicle’s antilock brake (ABS) systems to keep track of each tire’s rotation. An underinflated tire has a smaller radius, resulting in higher rotational speed as compared to a properly inflated tire. Consequently, when the sensor detects a faster rotation, the system warns the driver.

Based on new regulations, the number of vehicles with monitoring systems will increase over the next two years as NHTSA learns which of the two systems is more effective. By March 2005, NHTSA will determine which system works best, and by November 2006, every light vehicle sold in the United States will include a tire pressure monitoring system as standard original equipment. The estimated cost per average new vehicle to consumers would amount to only $66.33 to implement direct measurement systems, which would warn a driver when tire pressure is 25% or more below the required pressure for one to four tires. NHTSA estimates that tire-monitoring technology will prevent more than 100,000 injuries and 70 deaths per year in the United States alone. NHTSA reports that 23,000 crashes and 535 fatal crashes annually involve blowouts or flat tires.

To enable TPMS makers comply with the new mandate, Fair Lawn, N.J.-based Maxell Corp. of America has developed two new heat-resistant battery types that have been specifically designed for use in onboard tire pressure monitoring systems. Maxell’s new high-temperature resistant Lithium Manganese Dioxide (Li/MnO2) coin cells power pressure-sensing tags, which mount on the rims of each vehicle’s wheels. The new cells, types CR2450-HR and CR2450HR-EX, include a change in gasket material, a totally new crimping structure, and improved content to operate in the high-temperature environment encountered on rotating auto and light truck wheels. In fact, Maxell employs a proprietary sealing technique to protect the battery's resistance to high- and low-temperature extremes, which are essential to this new set of automotive requirements and applications. The company believes that this may be the first time coin cells have been designed for and exposed to these rigorous extremes.

According to Maxell, the new cells offer a nominal voltage of 3 V, and one lithium battery, with a minimum life span of at least five years. They can also replace two cells of another chemistry. In addition, these coin-type lithium batteries have a very high energy density, making them ideal for use in compact equipment that requires powerful small-sized batteries.

Lithium batteries undergo little change in their internal resistance over time, and deliver stable discharge voltage use after use. Maxell’s advanced sealing technology creates tough lithium batteries that operate safely over extended periods of time.

Maxell offers two versions of the new cell: the CR2450-HR for standard vehicles, and the CR2450HR-EX for high-performance, premium vehicles. The CR2450HR cell operates in the temperature range of –40°C to 120°C, has a standard capacity of 550 mAh, and weighs 6.8 grams. The high-performance CR2450HR-EX cell operates between the temperature extremes of –40°C to 150°C, has a capacity of 525 mAh and weighs 6.7 grams. Both cells measure 24.5 mm in diameter by 5 mm high. Maxell expects the high-temperature Lithium cells to be qualified for full production in 2004, the pricing to TPMS manufacturers for both batteries starts at approximately $1.00 and up, with variations depending on specific terminal configuration.

For more information, visit www.maxell.com.

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