[SOLVED] Capacitor Size vs. Capacitance?

[CapnKosmic]

Hi All,

I'm trying to better understand capacitors and how they work. I know about their plate/dielectric construction. I know that they work much like batteries and store a charge. They have capacitance values measured in Farads, and are rated to withstand certain voltages. What I don't understand is how to calculate the total power a capacitor can store and what is the unit of measurement that expresses their physical size as relates to that total storage 'capacity'.

In the case of a battery, there is the unit of voltage vs. the capacity. A very small alkaline battery, for instance can have a value of 12 volts, like an A23 alarm key fob battery, but only hold a small total volume of power measured in milliamp-hours or mAh.

I've got a metal film capacitor that is about a half inch wide which has a capacitance value of 0.22 mF and is rated for 500 volts. Another one I scavenged from a microwave power supply is about 3 inches wide with the same 0.22 mF capacitance value, but rated for 1600 volts. I also know that the microwave cap has an internal resistor. How do I measure their respective abilities to store power when fully charged?

Cheers,

Cap'n Kosmic

 

[steinar96]

Use the equation for stored energy in a capacitor P = 1/2*C*V^2

 

[KJ6EAD]

Remember to use the applied voltage, not the voltage rating in your calculation.

 

[steinar96]

Remember to use the applied voltage, not the voltage rating in your calculation.

He wants to compare the energy storage when they are fully charged. That would mean he should use the rated voltage since that is the average maximum voltage they can withstand.
Since they have equal capacitance they would store equal power if they have the same applied voltage across them

 

[KJ6EAD]

Thanks, I missed that.:idea: It's a theoretical maximum energy density thing then.

 

[steinar96]

I would assume so. Unless he has not realized yet that since they have equal capacitances, they will store equal power at the same applied voltage even though they are built to withstand different maximum voltages

 

[FvM]

Related to energy storage capability, there are typical numbers for capacitor technlogies. The energy density of polymer film capacitors, as addressed in this discussion, is ranging about an order of magnitude below electrolytic capacitors in the below linked diagram:

https://obrazki.elektroda.pl/48_1234437581.gif