There used to be a formula I knew of for RC circuits where you could plug in the starting voltage or current, the ending voltage or current, and the amount of time in between, and project exactly what the voltage or current will be after exactly x amount time has passed. I know it rises/drops to 63% within the first time constant. But where's the formula for the other times? Also would like to have the vise versa: i.e. plug in the voltage or current and find the time.

I doubt that one formula could cover current/voltage and energize/de-energize. It is easy to figure out by differential equations or Laplace transforms by setting initial conditions.

mik3,

Does the above formula cover energizing or de-energizing? What defines a fully energized capacitor? Its dielectric breakdown, maybe?For an RC network with initial voltage on the capacitor Vo its voltage with respect to time is given by:

Vc(t)=V(1-exp(-t/RC)+Vo*exp(-t/RC)

where

V=the steady state voltage across the capacitor when fully charged

Vo=initial voltage (if exists)

Ratch