Talk:Capacitor

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e·h·w·Stock post message.svg To-do:
  • Expand the History section: what about more modern developments (Surface mount components etc)? Needs a lot of references!
  • Add references to theory section and copyedit
  • Draw a diagram of the equivalent circuit and add to the appropriate section
  • Improve references in nonideal behaviour section
  • Copyedit and improve references in Capacitor types section
  • Restructure and tidy the applications section: there are too many small sections!
  • Add references to the safety section

Parallel vs. series network: voltage and current output when discharging[edit]

Which setup produces higher voltage and which produces higher current, or both? Series or parallel? That is information that should be stated more clearly in the article. ZFT (talk) 01:10, 6 August 2016 (UTC)

Capacitors in series, for all intents and purposes, increase the total thickness of the dielectric, so they can be used at higher voltages. (It's a little more complicated than that, but...) Just like two 1.5 volt, AA batteries in series become 3 volts, two 450 volt capacitors in series will be able to handle 900 volts. The drawback is that it cuts the capacitance in half and increases both inductance and resistance.
In parallel you get more capacitance (thus more amps), but at no more than the designed voltage.Zaereth (talk) 01:33, 6 August 2016 (UTC)
On a side note, I notice this article doesn't mention the use of capacitors to actually increase system voltage (a phenomenon usually relegated to power supplies), such as voltage multipliers. I'll look up some sources and maybe add enough to provide a link to the article. Zaereth (talk) 22:03, 11 August 2016 (UTC)

Capacitors do store charge "temporarily"[edit]

Until recently the lead sentence read:

A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store electrical energy temporarily in an electric field.

Recently an editor removed the word "temporarily" from this sentence. He gave his reason as: Capacitors can store charge for a long time. They are not batteries but they do not bleed off their charge quickly. It can be dangerous to think energy is stored temporarily.

I think the word should be put back. This is an example of how Wikipedia technical leads become unintelligible. Without the word "temporarily", nontechnical readers are going to get the idea a capacitor is like a rechargeable battery, serving as a long-term power source for electrical devices. Only a few capacitors (supercapacitors) have that function. In most applications, capacitors store energy for a tiny fraction of a second, during part of a cycle of alternating current, and return the energy immediately. The article already has a section on Hazards and safety. The idea that the word "temporarily" in the sentence will make people reckless with capacitors is ridiculous. --ChetvornoTALK 02:07, 29 August 2016 (UTC)

Agree that the intended use is temporary energy storage and that having the word temporarily would not encourage unsafe behavior. On the other hand modern polypropylene capacitors can have self-discharge time constants on the order of decades. I guess I’m neutral. Constant314 (talk) 02:41, 29 August 2016 (UTC)
I think either way the sentence is a bit too vague. Batteries store their energy chemically, whereas capacitors store it in a field surrounding a dielectric. It may be helpful to elaborate on the differences in the first or second sentence. Perhaps something like: "A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store electrical energy temporarily in an electric field. Unlike batteries which store energy chemically, capacitors can hold a charge for long periods of time or can release all of their energy very quickly." ...or something like that. I think that would help the reader to understand immediately what a capacitor is and what it is not. Zaereth (talk) 07:14, 29 August 2016 (UTC)
@Constant314: I think the point is intended use. Most applications require (extremely) temporary storage and (extremely) fast charge & discharge, unlike a battery. Try reading the existing sentence as if you knew nothing about electronics (as many readers of this intro will not). It describes a rechargeable battery, not a capacitor.--ChetvornoTALK 07:53, 29 August 2016 (UTC)
@Zaereth: I think the 2nd sentence is a little misleading. It makes it sound like capacitors can either hold a charge for long periods or release energy quickly, not both.--ChetvornoTALK 07:53, 29 August 2016 (UTC)
Yeah, that's just a bit of late-night conjecture, which I hadn't fully thought through. it was more intended to give ideas of how we could word it better, so as to avoid the confusion mentioned by both you and the IP. I'd be happy to hear your thoughts on how to improve it. Lacking that, I think the word "temporarily" should be restored. Zaereth (talk) 08:51, 29 August 2016 (UTC)
I support putting the word temporarily back into the sentence. Here are my thoughts. The sentence is a correct statement if temporarily is not in it. But the overwhelming majority of the intended uses are for temporary storage (I don’t know of any counter examples), so the statement is also correct if temporarily remains in the sentence. Also, temporary has no upper time limit. The local elementary school has had temporary classrooms for over a decade. So having the word temporarily does not preclude having the capacitor store energy for decades. In this light, even batteries could be said to store energy temporarily. There is, of course, a big difference between a capacitor and a battery. But, in the introduction, we need to say what a capacitor is. It is not required to distinguish how a capacitor is different from every other energy storage device. Constant314 (talk) 13:09, 29 August 2016 (UTC)
Good point. I guess any form of energy is stored, whether in a field (potential) or in an object (kinetic). The only brief moment where it's useful is when it encounters resistance and changes form (work). The big difference between a capacitor and other electrical-energy storage-devices is the use of two oppositely-charged conductors separated by a dielectric. I went ahead and restored the adverb, but placed it closer to the verb for better grammatical construction. (No change in meaning, only better flow.) I assume the IP has not watchlisted the article, but hope they'll join in the discussion if they feel strongly that it should be changed back. Zaereth (talk) 10:06, 30 August 2016 (UTC)
Looks fine. --ChetvornoTALK 23:00, 30 August 2016 (UTC)

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Thanks to the author(s) from the Tatar Wikipedia participants[edit]

Thank you, the author(s) of this article. We translated your article into the Tatar language.--A.Khamidullin (talk) 12:34, 26 March 2017 (UTC)

Displacement used incorrectly[edit]

Displacement is being used incorrectly in the third paragraph of the lede. Displacement current only occurs inside the capacitor. There is no displacement current in the source circuit or the battery. There is conduction current in the source circuit that is equal to the displacement current in the capacitor, so it is not egregiously incorrect. But, the notion of displacement current is not displacement through the external circuit. It is the displacement of bound charges in the dielectric from their equilibrium position. In the case of a high permittivity dielectric, it is easy to visualize the electron orbitals slightly distorted such that the electrons spend more time on one side of their molecules compared to the orbital with no applied field. In the case of a vacuum, it is harder to visualize. In Maxwell’s time, the vacuum was thought to be a polarizable media just like any other dielectric. But no matter how hard it is to visualize, the displacement current occurs between the plates of the capacitor and not in the battery. Constant314 (talk) 20:25, 11 April 2017 (UTC)

Agree, this paragraph is confused. I think "displacement current" should not be mentioned in the introduction, as this advanced term is bound to confuse general readers, making them think an actual current of charges passes between the capacitor plates. --ChetvornoTALK 20:59, 11 April 2017 (UTC)