Supercapacitors as Electron "Buckets"

But here is my question: if this 10 farad supercap is charged to only 0.5 volt, does it hold only 5 coulombs?

Yes, the basic formula for capacitors is Q=C*V (where Q is charge in coulombs).

Try googling "capacitor theory" for some pdf's on how capacitors work. Note that supercapacitors work in the same was as standard capacitors (they can just store more).

Don't forget to remember to take that capacitor leakage current into account!

Thanks Jack for the quick reply. I can see why my question probably seems too easy to bother asking you guys, but I had some doubts about whether real capacitors behaved in perfect agreement with theory, or if instead there might be some non-linearity resulting from idiosyncratic details of how real capacitors are built. But from your answer I conclude that they behave according to theory and I can stop worrying

I am aware of the leakage, and know how to quantify it (simply charge a capacitor, disconnect the source, and monitor the capacitor's decline of voltage over time).

Looks like this will be a very short thread since my question was too easy.

It's not that your question was too easy, it's that Jack is too smart.

The fact that your scheme works is the basis for all sorts of timing circuits and measurement circuits. You can pat yourself on the back for having "invented" it without having the answer spoon fed to you.

It's not that your question was too easy, it's that Jack is too smart.

I second that!

And thanks Ken for the kind words, but I have to admit that my "invention" didn't fully coalesce in my brain until after I saw capacitors mentioned as "electron buckets" (I think by bhankii or Shyam). I had already tried using capacitors in this way before that point, but I was unsure until learning more from knowledgeable CR4 members in my Best Method for Accurate Measurement of DC Current? thread (my more recent question concerned the linearity aspect). So I must share the credit -- I wouldn't have gotten as far as I have without CR4

Not sure if you're taking this into account, but supercapacitors aren't the same as normal capacitors in the sense that the capacitance function of the voltage and the effect is substantial "Frequency, thermal and voltage supercapacitor characterization and modeling" Volume 165 Issue 2. This has to do with the very small thicknesses of the dielectric and substantial differences in electron density with the changes in voltage and therefore different dielectric properties and capacitance before breakdown. It would be worth while to perform an experiment at these different voltages with a constant DC input to see the change.

A change from 0.5 to 1V sounds like a 15% decrease in capacitance from what was shown in the article. However, the given capacitance of 10 Farads was probably measured in the 2-2.5V range so overall decrease from 10 Farads sounds like a 30% decrease in capacitance at 0.5V (6.6 Farads). It would be worth while quoting this paper in any research you are doing to account for errors.

Not sure if you're taking this into account, but supercapacitors aren't the same as normal capacitors in the sense that the capacitance function of the voltage and the effect is substantial "Frequency, thermal and voltage supercapacitor characterization and modeling" Volume 165 Issue 2.

Thanks Wild Idea, I need to know about any anomalous capacitance-vs-voltage behavior in my supercaps, so the article you mentioned certainly interests me. The phrase in quotes is the title of the article, correct? If so, what is the name of the journal?

Journal of Power Sources is the journal. Sorry I forgot to put it.

Thanks for the citation -- I look forward to reading the article