Chemical double-layer capacitor power sources for electrical actuation applications

In this paper, the design, construction, and testing of chemical double layer capacitors made using a composite electrode structure are described. The techniques used to fabricate carbon/metal composite electrodes which eliminate the need for pressure to obtain low values for the equivalent series resistance are discussed along with the methods used to produce multiple-cell stacks capable of operating at 28 volts. Issues concerning the methods of producing uniform electrodes that can be used for bipolar stacking of cells to achieve higher operating voltage levels as well as sealing of the completed device are presented. Sealants that will cure in the presence of the electrolyte (potassium hydroxide) and provide a durable, long-lasting seal have been studied and used in the construction of several capacitor units that we have built. Controller issues related to the use of capacitor power sources for actuator applications are also presented. With the capacitor bank connected to an appropriate DC-DC converter, a constant output voltage can be maintained even though the capacitor voltage decays. Preliminary results using off-the-shelf devices which maintain a constant output voltage level of 28 V for input voltages ranging from 21-32 V are given for tests on a small linear actuator capable of lifting several hundred pounds. These and similar devices are presently limited to fairly low power levels (100-200 W range), but factors concerning the extension to higher power levels are given as well.