An Evaluation of NiCd Battery and Direct Ethanol Fuel Cell DC Systems Output Characteristics

The paper presents an analysis of direct ethanol fuel cell (DEFC-mesh, and DEFC-foam), and Nickel-Cadmium battery (NiCd) systems interfaced to DC-DC converters. The output voltage characteristics of the three systems are compared. Experimental results show that NiCd batteries present variable, nonlinear impedances as a function of frequency. Similar to NiCd batteries, DEFCs exhibit impedance variations, with lesser degree of predictability. It is shown, through experimental results, that the output voltage of NiCd powered systems is proportional to the duty cycle, for a given switching frequency. By contrast, DEFC systems do not exhibit predictable output as a function of duty cycle alone. Consequently, output voltage control through pulse width modulation (PWM) techniques applicable to NiCd systems cannot be employed for DEFC systems of similar power output.