Appliance Design - March 2008 - (Page 32)

POWER designer a great deal of flexibility to deal with the charge and discharge profiles of various types of equipment, while using the same battery pack protection electronics. Over-voltage and under-voltage conditions of individual cells within the battery pack are also important to monitor. If any cell voltage exceeds the manufacturer’s specified upper limit, charging must be disabled to prevent a potentially hazardous condition to exist. Fig. 3. Illustration shows the impact of not balancing series cells within a battery pack over multiple charge and discharge cycles. Problem: Find a small footprint thermal control with big range. Solution: Small. Reliable. Proven. The creepaction PEPI Model A brings a unique versatility to everything from hairsetters to heating pads. Preset calibrations can range from 5 - 200°C so many companies use it on different applications. When it comes to combining cost, size and range, the Model A has done it all. Only Pepi® thermostats and thermal protectors offer so many options in fit, configuration, cost and customization. For a close look send for our new 2006 Disc-Type and Conductive-Type Catalogs today. www.pepiusa.com Portage Electric Products, Inc. N. Canton, OH U.S.A. salesinfo@pepiusa.com • 1-888-GO4-PEPI Similarly, if any cell voltage drops lower than the discharge cutoff limit specified by the manufacturer, discharging will need to be disabled. In some cases where the cell voltage becomes very low, alternate charging techniques may need to be employed, or the pack may need to be totally disabled for safety reasons. Individual cell voltages are read by the microcontroller and are therefore digitally filtered to eliminate noise and improve system accuracy. As mentioned earlier, some packs may also have the ability to monitor and control current during the charge cycle as well as the discharge cycle. In a pack that can monitor current during both cycles, the charge cycle is suspended in the case of charge over current or short circuit events. Using a separate set of charge limits, similar indications are provided from the AFE to the microcontroller, and the charge MOSFETs are then disabled by the AFE using either automatic protection or by reporting an error condition to the microcontroller and having it command the AFE to disable the MOSFETs after executing the proper error-handling firmware. Pack and cell temperatures must be monitored for safety reasons. Most cell manufacturers have both upper and lower temperature limits on cells during the charge and discharge cycles. In densely populated battery packs there can be a significant differential temperature across the cells from the inner region to the outer region of the pack as it is cycled through charge and discharge phases. Pack designers must take this into consideration and place thermistors in locations that adequately represent the cell temperatures. While safety is the single most important issue in battery pack design, well-designed products also take appropriate steps to help ensure a good user experience. New generations of Li-ion packs typically have high cell counts, as well as the added cost of protection and monitoring electronics within the pack and system. Costs for additional/replacement www.applianceDESIGN.com For more Information Enter 108 32 applianceDESIGN AD02084Port.indd 1 March 2008 1/17/08 9:34:33 AM http://www.pepiusa.com http://www.pepiusa.com http://www.appliancedesign.com

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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

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