Appliance Design - March 2008 - (Page 33)

POWER packs can be quite high when compared to the previous generations of nickel-cadmium-based battery packs. Users of these new generations of packs want to experience increases in performance as well as extended run times and shorter charging times. One method to provide the improved user experience is to implement cell-balancing within the battery pack. Cell-balancing is a method to maintain all cells within a pack at the same state of charge. The more cells that are connected in series, the greater the benefit that cell-balancing will provide to maximize the performance and usable life of the battery pack. Most cells from a manufacturer, especially within the same lot, are fairly well matched in terms of ability to accept, retain, and deliver charge. However, small variations between cells, as well as the differences in temperatures of cells during charge and discharge can lead to unbalanced conditions. These unbalanced conditions can dramatically reduce the usability of a battery pack. In any battery pack, the charging process must be stopped once the cell voltages have reached the charge termination voltage specified by the manufacturer. Similarly, the discharge process must also be stopped once the cell voltages have reached the discharge termination voltage specified by the manufacturer. The termination of charge or discharge based on a single cell voltage reaching the termination point leads to an unbalanced pack. Some cells may have a tendency to charge and discharge faster than the other cells due to their physical location within the pack and/or perhaps small differences between the cells during the manufacturing process. In a balanced pack, charge is transferred from series cells at higher states of charge to series cells at lower states of charge. (Parallel cells self balance.) This process can occur during charge, as well as discharge of the pack, although it is typically implemented during the charge cycle only for simplicity. Fig. 3 shows the impact of not balancing series cells within a battery pack over multiple charge and discharge cycles. When originally assembled into the battery pack, the cells were all well matched and at the same state of charge, but over multiple charge and discharge cycles, they gradually become unbalanced. This results in a significant loss of capacity and significantly reduced usability of the pack. Arguments against cell-balancing in the past were typically based on the longer charge times that were required for balancing or and other advantages these new devices offer. designs that were too complex to realize at By using the techniques discussed, it is possible a reasonable cost. That is no longer true. By to design high-power Li-ion packs that meet all using internal-balance FETs with the ability to the safety requirements and still provide a rich handle up to 200 mA of balance current, the user experience at a reasonable cost. Using an ISL9208 can perform cell-balancing quickly integrated AFE provides a very robust design at a low cost, and it is simple for designers to with a minimum of external components and a implement. relatively low total-solution cost. < AD01074Rosen:_ 12/12/06 eager for PM Page 1 Users of Li-ion battery packs are 12:15 the lighter weight, performance improvements, For more information, enter. . . . . . . . . . . . . . . . . . . . . 302 EC does it Rosenberg’s electronically commutated (EC) fans dramatically outperform other AC and DC designs. Compact and low-noise, they offer exceptional variable speed capability, greater efficiency, higher speeds and wider operating range. With no carbon brushes to wear out, you also get longer service life. They’re ideal for pressure control, master-slave designs and RS485 networks. Call today to see what Rosenberg EC fans can do for you. Call: (704) 893-0883 Fax: (704) 882-0755 e-mail sales@rosenbergusa.com www.rosenbergusa.com Representatives wanted See us at AHR Booth #3162 For more Information Enter 109 www.applianceDESIGN.com applianceDESIGN March 2008 33 http://www.rosenbergusa.com http://www.rosenbergusa.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - March 2008

Appliance Design - March 2008 Contents Editorial Shipments/Forecasts News Watch A New Appliance is Set to Break into Homes Soon - the Micro CHP Unit, which Generate both Heat and Power. Thermally Enhanced Varistors Help Protect Low-Power Systems Against Damage Caused by Over-Current, Over-Temperature and Over-Voltage Faults. Hybrid Controller Reduces Standby Power Consumption and Improves Active-Mode Efficiency. Battery-Management ICs Solve Design Challenges for Cordless Appliances Using High-Voltage, Lithium-Ion Battery Technology. A Semiconductor Solution Protects the Relay in a Temperature Controller for a Cooking Appliance. New Polyurethane Foam Insulation System Optimizes both Insulation Performance and Productivity. Innovations in Decorative, Pre-Finished Metals Expand Range of Design Options for Appliance Designers. Design Marts Association Report: AHAM Advertiser's Index

Appliance Design - March 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.