I'm design my first circuit and plan on use a RC timer effectively as a battery (12v system). My question is since I plan on useing the bled off power to drive the device (relay coil) am I correct in needing to size the cap in terms of Joules so I get the proper wattage for the required time? Basic number I've come up with is 12v, .100A (going to test this to get better number) on coil, and 4.5secs. Forgot the formula but remember comming up with about 17μF. Since a Joule is a Watt second. I came up with needing 1.2W*4.5sec, 5.4 J. Right?