How can the discharge rate of a capacitor be controlled?

  • Context: Undergrad 
  • Thread starter Thread starter Hamza Abbasi
  • Start date Start date
  • Tags Tags
    Capacitor Rate
Click For Summary

Discussion Overview

The discussion revolves around the control of the discharge rate of capacitors and the feasibility of using capacitors as temporary power sources in place of batteries. Participants explore theoretical and practical aspects of capacitor discharge, including the influence of resistance and potential applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether a charged capacitor can be converted into a temporary battery and seeks methods to control its discharge rate, suggesting a connection to the RC time constant.
  • Another participant proposes changing resistance as an obvious method to control discharge rate.
  • A subsequent post reiterates the idea of changing resistance and inquires about integrated circuits (ICs) that could slow the discharge rate exponentially.
  • One participant mentions "ultracapacitors" as examples where capacitors can replace batteries, noting that the voltage drop during discharge is sharper compared to batteries.
  • Another participant provides a technical explanation of capacitor behavior, stating that the voltage curve during discharge depends on the load current, with different behaviors for constant current versus constant resistance loads. They also mention the potential use of voltage regulators for applications requiring constant voltage.
  • The same participant notes that not all applications require constant voltage, using electric car motors as an example where variable voltage from a capacitor could suffice with appropriate speed control.

Areas of Agreement / Disagreement

Participants express various viewpoints on the control of capacitor discharge rates, with no consensus reached on the best methods or the feasibility of using capacitors as temporary batteries.

Contextual Notes

Participants discuss the dependence of discharge characteristics on load conditions and the potential need for additional components like voltage regulators, but do not resolve the implications of these factors.

Hamza Abbasi
Messages
47
Reaction score
4
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?
 
Physics news on Phys.org
Changing the resictance would be an obvious way to go.
 
LittleMrsMonkey said:
Changing the resictance would be an obvious way to go.
Is there some IC or something like that for slowing the discharging rate exponentially?
 
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.
 
  • Like
Likes   Reactions: davenn
Batteries approximate to a constant voltage source, a capacitor doesn't. For a capacitor..

Q=CV
I = CdV/dt
so
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.
 
  • Like
Likes   Reactions: Hamza Abbasi and davenn

Similar threads

Undergrad Why is current defined as the rate of change of charge?
  • · Replies 6 ·
Replies
6
Views
3K
Graduate Charging and Discharging of a capacitor in an LC circuit
  • · Replies 50 ·
2
Replies
50
Views
15K
Undergrad Parallel Capacitor safety at 10 micron plate spacing
  • · Replies 32 ·
2
Replies
32
Views
2K
Undergrad Grounding a circuit through a capacitor/parallel RC circuit
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad How does smoothing an AC voltage with a capacitor work?
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Prove to me how capacitors in parallel can have the same V across plates
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Parallel plate capacitor, charge imbalance VS charge redistribution
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad How Does the Time Constant Relate to Charging and Discharging in Capacitors?
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad Can current flow in an open circuit?
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad Energy of a Capacitor: Basics & Explanation
  • · Replies 22 ·
Replies
22
Views
3K