Can a large electrolytic capacitor be substituted for a NiCd?
The quick answer is: probably not. The charger very likely assumes that the NiCds will limit voltage. The circuits found in many common appliances just use a voltage source significantly higher than the terminal voltage of the battery pack through a current limiting resistor. If you replace the NiCd with a capacitor and the voltage will end up much higher than expected with unknown consequences. For more sophisticated chargers, the results might be even more unpredictable. Furthermore, even a SuperCap cannot begin to compare to a small NiCd for capacity. A 5.5 V 1 F (that’s Farad) capacitor holds about 15 W-s of energy which is roughly equivalent to a 5 V battery of 3 A-s capacity – less than 1 mA-h. A very tiny NiCd pack is 100 mA-h or two orders of magnitude larger. Determining the Actual Capacity of a NiCd Battery Pack When a battery pack is not performing up to expectations or is not marked in terms of capacity, here are some comments on experimentally determining the A-h rating. W
