Talk:Electrolytic capacitor

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Are tantalum electrolytic?[edit]

I might be wrong, but i believe tantalum caps are polarized, but not electrolytic. The original sulphuric acid filled tantalums would have been, however i understand from my 10 second search that the normal, current ones might not qualify. —Preceding unsigned comment added by (talk) 08:48, 2 December 2010 (UTC)

Polarity in circuit[edit]

So in what direction should i put a electrolytic capacitor in my electric circuit? minus on plus? or minus on ground? thanks, --Abdull 16:15, 6 Dec 2004 (UTC)

The negative terminal goes to the more negative terminal.  :-) So if your power supply is +V and Ground, the negative terminal of the cap goes to ground. If your power supply were Ground and -V, then the negative terminal of the cap would go to -V. - Omegatron 02:52, Mar 21, 2005 (UTC) - Please use this as citation for 'bursting' capacitors. -- (talk) 07:56, 22 August 2010 (UTC)


I don't think much of the extended discussion of safety precautions for handling electrolyte leaks. I think that's of questionable relevance and value. I'm also dubious about some of the factual information in that passage - I already removed one howler (about tantalum capacitors being military-only) which looks like the information may be about 20 years out of date, and I suspect other nearby statements may be incorrect also. I think at some point in the future I'll probably delete that stuff, or move it to some other page. Not sure where yet, which is why I haven't done so already. 21:05, 2 Jun 2005 (UTC)

I think we should keep that kind of information, but if it is out of date it should be updated. - Omegatron 23:00, Jun 2, 2005 (UTC)

Breakdown voltage and capacitance[edit]

I don't think that high break down voltage implies high capacitance as this entry suggests. -RG Atlanta

Where does it say that? - Omegatron 02:17, Jun 12, 2005 (UTC)
"the thinness of this layer, along with its ability to withstand an electric field strength of the order of 109 volts per metre, is what produces the high capacitance." - it's only the thinness that makes high capacitance, not the ability to withstand high field strength -RG Atlanta


This Page seriously needs an explanation of correctly connecting axial polarized capacitors. I have to look that up every time I work with Caps. I don't feel qualified to write it up or I would add it myself!! —Preceding unsigned comment added by (talk) 17:00, 1 July 2010 (UTC)

I remember reading somewhere that electrolytic capacitors only acquire a polarity after they have been used. The testing after manufacturing supposedly gave the polarity for most capacitors. Is this true? There are "non-polar" capacitors with cases and capacitances that are similar to normal electrolytic capacitors for sale here: --Pyrochem 03:47, 21 September 2006 (UTC)

You may find this enlightening: Quote: Non-polar electrolytics are two conventional electrolytic capacitors in series with the cathodes connected together. In actual construction, they are composed of two pre-anodized aluminum foils wound together. --QEDquid 16:24, 22 September 2006 (UTC)

I'm pretty sure the polarity for the -)|- symbol is wrong. I think the flat side should be positive. 01:05, 14 January 2007 (UTC)

Degradation due to age[edit]

I think this page should include a note that, compared with other types of capacitors, electrolytic capacitors break down with age. There's sort of a statement to this effect, that a positive voltage must be maintained or the electrolytic will break down. But old electrolytics are the overwhelming cause of hum in old AV equipment, so a statement along these lines might be helpful to someone.

Rock it out. max

  • Yes, this is very true. The Polarity section of the article makes reference to the increased life of the capacitor when forward biased. I added additional information to the variants section, under the Aluminum, about electrolyte drying out / failing in the absence of a sufficient rejuvenating voltage. With regards to older AV equipment my experiences have been more to do with poor quality in the capacitor construction and excessive temperatures in use and storage. Treat old capacitors with respect, replace them with modern counterparts where ever possible. ADevNull 05:36, 11 April 2007 (UTC)

Inventer of electrolytic capacitor[edit]

"..electrolytic capacitor was invented in 1921 by Julius Edgar Lilienfeld ..." can this be true? There are numerous earlyer patents from Charles Pollak:

  • Charles Pollak: Improvements in or connected with Electrical Condensers. In Patent number: GB189601069 (1896)
  • Charles Pollak: Improvements in Electrolytical Condensers and Electric Current-directing Devices. In Patent number: GB189800933(1898)
  • Charles Pollak: Improvements in or connected with Electrolytical Condensers and Electric Current Directing Devices. In Patent number: GB189818956 (1898)

-- 09:46, 12 February 2007 (UTC)

    • Charles Pollak, German Patent 92564, 14. Jan. 1986, Flüssigkeits-Kondensator mit Aluminium-Elektroden

--Elcap (talk) 17:31, 27 December 2007 (UTC)

Tantalum capacitor edit[edit]

I just edited this out of the page (it was an extra copy at the end of the list of types), maybe someone can check and edit:

Tantalum: compact, low-voltage devices up to about 100 2000µF, these have a lower energy density and are more accurate than aluminum electrolytics. Compared to aluminum electrolytics, tantalum capacitors have very stable capacitance and little DC leakage, and very low impedance at low frequencies. However, unlike aluminum electrolytics, they are intolerant of voltage spikes and are destroyed (often exploding violently) if connected backwards or exposed to spikes above their voltage rating. Tantalum capacitors are also polarized because of their dissimilar electrodes. The cathode anode electrode is formed of sintered tantalum grains, with the dielectric electrochemically formed as a thin layer of oxide. The thin layer of oxide and high surface area of the porous sintered material gives this type a very high capacitance per unit volume. The anode cathode electrode is formed of a chemically deposited semi-conductive layer of manganese dioxide, which is then connected to an external wire lead. A development of this type replaces the manganese dioxide with a conductive plastic polymer (polypyrrole) that reduces internal resistance and eliminates a self-ignition failure[1

Yes, 2200uF tantalums and even larger ones exist (check digikey). But the general use of tantalums dont't go beyond several hundred uF. 07:52, 4 June 2007 (UTC)

Possible erroneous statement at the end of this article?[edit]

"However, unlike batteries, capacitor voltage is directly proportional to the total energy remaining" - the voltage is proportional to the square root of the remaing energy, isn't it? —Preceding unsigned comment added by (talk) 23:55, 8 September 2007 (UTC)

Energy = 0.5 x capacitance-in-Farads x voltage-squared - 13:10, 14 September 2007 (UTC)

I think it's using a more general sense, indicating that raising one will raise the other. Might be directly proportional, but not linearly proportional, if I get the idea right. KronesR (talk) 23:41, 7 March 2012 (UTC)

Polarity marking[edit]

"The correct polarity is indicated on the packaging by a stripe with minus signs and possibly arrowheads, denoting the adjacent terminal that should be more negative than the other."

This article is generally pretty well done, but this statement about polarity marking is greatly over-simplified, with no acknowledgement of a century of history and different capacitor packages. It is too bad the article does not have a picture of a typical unpainted metal can electrolytic capacitor from decades ago. I think polarity was usually marked with a dot of red paint. Did this mark positive? And current small drop caps are also polarity marked with a dot of color. But does this mark positive or negative?- 13:10, 14 September 2007 (UTC)

--- I agree. See above about dire need for instructions on correct reading of polarity and why its important when using polar caps. —Preceding unsigned comment added by (talk) 17:10, 1 July 2010 (UTC)

the cylindrical aluminium casing fell off[edit]

does this interfere with the functoning of the capacitor or the capacitor should be replaced? —Preceding unsigned comment added by (talk) 14:06, 14 October 2007 (UTC)

Electrochemical double-layer capacitors (EDLCs), also known as supercapacitors or ultracapacitors[edit]

Electrochemical double-layer capacitors (EDLCs), also known as supercapacitors or ultracapacitors are NOT electrolytic capacitors. They have to be cancelled here. Please compare with the german article. --Elcap (talk) 08:54, 20 December 2007 (UTC)

NP caps error[edit]

"Essentially, a 10 microfarad AC capacitor behaves like two 20 microfarad DC capacitors in inverse series."

If one cap shorts during each half cycle, then to obtain a result of 10uF one would need to connect 2x 10uF back to back, not 20uF. —Preceding unsigned comment added by (talk) 14:10, 6 October 2008 (UTC)

No, I think the article is correct as they are connected such that both are partially charged during the whole AC cycle. Han-Kwang (t) 14:13, 6 October 2008 (UTC)

What exactly does that mean? Why dont you descrbe what you mean step by step. —Preceding unsigned comment added by (talk) 14:16, 6 October 2008 (UTC)

I'd rather ask: what do you mean when you say that one cap "shorts during each half-cycle". By the way, you can add ~~~~ to sign your posts. Han-Kwang (t) 06:11, 7 October 2008 (UTC)

OK then... when wrong polarity is applied, the insulating layer begins to conduct. Hence for each half cycle we have one working capacitor in series with a low impedance. Hence 2x 10uF 'lytics in series gives 10uF, not 5.

I can indeed sign my posts with tildas, but I don't think it would be very useful given that I'm not logged in. —Preceding unsigned comment added by (talk) 16:12, 7 October 2008 (UTC)

Service life[edit]

IRL there are a vast number of capacitors in successful service at over 15 yrs old. 15 year life expectancy is not a real world figure. Caps can die with age, but in reality the great majority don't. Some are even still in service from the 1930s. —Preceding unsigned comment added by (talkcontribs)

Apparently this number is an example. The given reference explains that capacitors are rated for a specific service life. If you can find a reference (data sheets, manufacturer catalog) with a service life, you can replace the number by a typical range of service lifes. Han-Kwang (t) 06:24, 7 October 2008 (UTC)

I think that would be missing the point. The point is that despite these oft quoted short ratings, a sizeable percentage of lytics from half a century ago and longer are still working fine. Otherwise readers are liable to imagine that after 15 or 20 years most lytics are dead - and this is far from the case.

Capacitance Change with misuse[edit]

I have heard and read that Electros will change their capacitance if used on a much lower voltage circuit them they were designed for. I.E; a 100 mF 400V unit will lose capacity on a 16 Volt circuit due to less electrolytic action. To restore such a cap, or, any old one that you have a doubt about; simply connect it to a current-limited (a few mA) voltage source of about 70% of its rated voltage overnight. It will work in a "pinch" or if it is a vintage or very expensive cap you don't wish to,or can't, simply replace (ARRL Handbook)Tintinteslacoil (talk) 13:43, 24 November 2008 (UTC)


The section discussing tantalum capacitors seems to contradict itself:

Is it really true that tantalums simultaneously "have a lower energy density ... than aluminum electrolytics" and yet have "higher capacitance per unit volume" ? Is that "higher capacitance per unit volume" than aluminum electrolytic, or is that compared to the other kinds of capacitors in cell phones?

Rather than vaguely saying one is "higher" than another thing, would it be OK to print a typical value for each one? -- (talk) 22:02, 16 October 2008 (UTC)


this sounds like a cross between a battery and capacitor its sounds weird that a capacitor would use a electrolyte where would you distinguish the difference between a battery and capacitor because this is made the same way as a battery?urName (talk) 08:05, 8 February 2011 (UTC)


Two things about it, more wording/formatting issues.

"These capacitors are stable in use between -55°C to practically 125°C in theory." "practically" and "in theory" don't go too well in the same sentence. Does it mean "close to 125 in theory" or that it could actually go as high?

The whole topic about OS-CON should go right after the Tantalum one. Seems there is a break, some text, then it goes to OS-CON. That "extra" part seems to belong to the Tantalum section. Should it be joined? — Preceding unsigned comment added by KronesR (talkcontribs) 22:07, 4 January 2012 (UTC)

Polarity: no reduction of oxyde layer[edit]

Most electrolytic capacitors are polarized and require one of the electrodes to be positive relative to the other; they may catastrophically fail if voltage is reversed. This is because a reverse-bias voltage above 1 to 1.5 V[4][5][6] will destroy the center layer of dielectric material via electrochemical reduction (see redox reactions). Following the loss of the dielectric material, the capacitor will short circuit, and with sufficient short circuit current, the electrolyte will rapidly heat up and either leak or cause the capacitor to burst, often in a spectacularly dramatic fashion.

This seems to be the general opinion, but I haven't seen a WP:RS confirming it. Both anode and cathode are made of aluminium. I know they say that the electrolyte is really the cathode, but that's when one only considers what happens at the anode oxide layer. In fact, apart from the larger surface and the thickness of the oxide layer, both anode and cathode are identical. The oxide non-oxide region forms a diode, with the thickness of the oxide layer determining the breakdown voltage. If correct voltage is applied, the diode at the anode junction will be reverse biased so no current will flow; at the cathode junction the diode is forward biased and conducts current. Applying an overvoltage, the anode junction will breakdown and current will flow through the capacitor.
If voltage is reversed anode and cathode switch places, so now the cathode junction is reverse biased. The main difference is the thin oxide layer that can only withstand a small voltage before breaking down.
In both cases, when the applied voltage is too high, current will flow. This has three effects: growth of the oxide film, gasses forming, and ohmic heating. Depending on the magnitude of the current, you get a capacitor with lower capacity, a swollen capacitor due to gas build-up, or a cap that blows because you're boiling the electrolyte.
See ref 6, or an application guide from a manufacturer. Main point is: there's no reduction of the oxide layer, at least not enough to have any effect. Ssscienccce (talk) 16:19, 2 September 2012 (UTC)
The “redox reactions” in the sentence: “…a reverse-bias voltage above 1 to 1.5 V will destroy the center (?) layer of dielectric material via electrochemical reduction (see redox reactions)” are wrong. Aluminum oxide goes in solution in acid or basic liquids. Reverse voltage can accelerate this whereby the oxide layer will be weakened. The layer gets thinner. If the voltage is high enough and the power behind is high enough (low ohmic) than after a while a breakdown occur (short circuit). It is a demolition of oxide layer thickness in an acid or basic solvent which lead to this behavior. --Elcap (talk) 09:47, 18 November 2013 (UTC)