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Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
Capacitors A and B are identical in every way with the following exception:
Capacitor A is manufactured in standard fashion by rolling the plates & dielectric into a tight roll (thus compressing the charged up capacitor's electrostatic field into a very compact space). However, Capacitor B plates and dielectric are laid out flat, extending into space, the plates & dialectic are not rolled up (the electrostatic field of the charged up capacitor is not compressed into a compact space, but rather disbursed over the length of the flat plates).
Question: Will Capacitor B exhibit less internal resistance as compared to the tightly rolled Capacitor A?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
The main advantages to rolling capacitors are; ease of manufacture fairly easy to encapsulate physically rugged component physically small component and the terminals can be connected all along the long edge of the plates which gives low esr and low esl.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
The (much unwanted) self-resonant frequency of rolled capacitors is, generally, lower than flat plate types such as silver mica. The self-inductance of capacitors becomes an issue as frequencies rise, with flat plate types generally offering lower self-inductance than rolled types.
Examples: a rolled PTFE or polycarbonate capacitor would be a good choice as a coupling capacitor at audio frequency. A flat plate silver mica capacitor would be a good choice for RF coupling at frequencies up to about 500 MHz.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
There is not such a thing as compressed electric field. Resistance depends on the path between the electrodes and on dielectric losses. Inductance too. A rolled capacitor with the terminals at one end of the roll is a bad idea, but if the metal foil rolls are offset so the terminals can make contact with a whole side of the roll (this is the usual construction) an excellent capacitor results. A flat-plates capacitor with offset metal plates is almost equivalent, but the mean path between the electrodes is certainly longer, resulting in more resistance and more inductance.
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
Let's not forget, if you roll up a flat plate cap, the capacitance increased because now the plates are stacked alternately. In other words a rolled cap can be made with physically smaller plate compare to a flat plate cap while maintaining the same capacitance. Smaller plate = shorter path.
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Question about Capacitor Theory
