Maxwell Technologies provides WEVTU with this photo of its prototype 42-volt, 20-cell ultracapacitor assembly being developed for vehicle energy storage applications (see WEVTU — Feb 1, '01, p. 6).

Business development manager Richard Smith says the individual cells have a nominal voltage rating of 2.1 volts (and 2.5 volts peak), hence 42-volts to 50-volts nominal/peak for the 20-cell pack, which weighs 38 lbs. (17.3 kg) and is 17 ins. × 12 ins. × 7.5 ins. (43 cm × 30 cm × 19 cm) shown without an outer case, which if needed adds about 2 lbs. (0.95 kg).

The ultracapacitor's operating temperature is from -72°F to 158°F (-40°C to +70°C). Output down to half-nominal voltage is 15 kW for 4 seconds and 7.5 kW for 10 seconds. The buss bars (inter-cell connectors) are made of solid copper for laboratory evaluations but will be made of flexible connector material for vehicle applications.

General Motors Corp. and others are reported to be developing hybrid vehicle uses for the technology, ranging up to 1,000-volt systems in commercial vehicles.

Maxwell has indicated its intention to make dramatic cuts in the cost of its ultracapacitors by 2003, permitting large-volume production of more than 100 million cells in 2008. Maxwell claims its cells will last for the life of the vehicle in passenger car use and six years to 10 years in applications such as city buses.