
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!

Capacitor Discharging Rate

  1. Sep 8, 2015 #1
    Hi , Can we replace battery with capacitor?? I know that energy stored in a battery is far greater than in the capacitors ,but still can we some how convert a charged capacitor into a temporary battery?? So the Question is how to control the discharge rate of capacitor? Is this have something to do with RC Time constant?
  2. jcsd
  3. Sep 8, 2015 #2
    Changing the resictance would be an obvious way to go.
  4. Sep 8, 2015 #3
    Is there some IC or something like that for slowing the discharging rate exponentially?
  5. Sep 8, 2015 #4
    See "ultracapacitors" for some applications where the batteries are replaced by capacitors.

    From what I seen, the voltage decreases a lot more sharply during discharge than in a battery.
  6. Sep 9, 2015 #5


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Batteries approximate to a constant voltage source, a capacitor doesn't. For a capacitor..

    I = CdV/dt
    dV/dt = I/C

    So the voltage "curve" depends on the load current. If you discharge at a constant current the voltage falls in a straight line. If it's a constant resistance load you get the classic exponential curve.

    If the load must get a constant voltage (not all need that) then some sort of voltage regulator, perhaps a switching type, can be used to provide it.

    You don't always need a voltage regulator. The motor in an electric car for example doesn't necessarily need a constant voltage but it does need some form of speed control. It may well be possible to build one control unit that accepts the variable voltage from a capacitor and outputs whatever the motor requires.