Whos right? - capacitor to capacitor discharge.

In summary, the conversation discusses the efficiency loss in charging one capacitor and discharging it into another. The person believes that this process does not result in a 50% efficiency loss, but rather the only losses are due to the capacitors' ESR and voltage difference. They provide a mathematical illustration using two capacitors of the same size, showing that the energy stored in each capacitor is reduced to 1/4 of the original after being connected in parallel. The conversation also references the famous Two Capacitor Problem and discusses the concepts of conservation of charge and energy. A resource is shared for further reading on the two-capacitor problem and addressing the 'lost' energy.
  • #1
spaceball3000
41
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I read on another forum, some person says (read below) when you charge one cap, then discharge into another, there is 50% efficiency loss?

I think this is wrong, as the only losses I can think of, are due to the caps ESR when there is a voltage difference between the caps. Can someone help show his\her Math is wrong..


Also you lose 1/2 the energy in this process.

I can illustrate with a little math

Given capacitors C1 and C2 of the same size (C). One charged to V and one uncharged then the energy stored is

1/2 C * V *V

If you hook these two capacitors in parallel then they will settle (after a current pulse) to a voltage in each of 1/2 V. The energy in each will then be

1/2 C * 1/2 V * 1/2 V

or 1/4 of the original energy in each capacitor for 1/2 of the original energy.
 
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  • #2
This is the famous Two Capacitor Problem. You have two identical capacitors separated by an open switch. One is charged to V. Then the switch is closed. After the voltage has equalized what is the resultant voltage on both capacitors?

The answer depends on conservation of charge or conservation of energy.

Charge (coulombs), Q = C*V
Energy (joules), E = C*V^2/2

Obviously they can't both apply.
 
  • #3
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Related to Whos right? - capacitor to capacitor discharge.

1. What is capacitor to capacitor discharge?

Capacitor to capacitor discharge is a process in which the stored energy in one capacitor is transferred to another capacitor, resulting in a rapid discharge of electrical energy.

2. How does capacitor to capacitor discharge work?

When two capacitors are connected in parallel, the charge stored in one capacitor will flow to the other capacitor until both capacitors have the same voltage. This results in a rapid discharge of energy.

3. What are the applications of capacitor to capacitor discharge?

Capacitor to capacitor discharge is commonly used in power electronics, such as in voltage converters and motor drives, as well as in high energy physics experiments and equipment testing.

4. How is capacitor to capacitor discharge different from resistor to capacitor discharge?

In capacitor to capacitor discharge, the energy is transferred directly from one capacitor to another, while in resistor to capacitor discharge, a resistor is used to gradually discharge the energy from the capacitor.

5. What are the safety considerations for capacitor to capacitor discharge?

Capacitor to capacitor discharge can produce high voltages and currents, so it is important to use proper safety precautions, such as wearing protective gear and ensuring the capacitors are fully discharged before handling them.

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