I purchased an "assortment" of capacitors from ebay. Being a newb, I figured that would get me started in my project. For the most part, that's probably true but....What's the difference of a 47UF Capacitor in 16V, 25V and 50V?I hate to assume that that's the max voltage it's rated for. I'm only running off a 9V battery. It calls for a 10Uf capacitor, but the assortment came with only 10UF 50V. Would this still work? I know size is a consideration as well.Thanks. Nick
Hope this explains it.
It might to the uninitiated, except that (as you know,) the paper is not an insulator so its thickness is not the directly defining factorThe actual explanation is a trifle more complex than that, isn't it?
The dielectric thickness in an electrolytic capacitor is very tiny - measured in nanometers or micrometersand is a layer of Al2O3 built up on the Al foil by applying a voltage to "form" the capacitor. This layer is whatbreaks down, not the paper separator (actually soaking in electrolyte and conducts very well).A thicker layer of this oxide has to be grown for a higher voltage, and eventually this means thickerfoil to start with. Higher ripple current capacitors need thicker foil too.The energy stored in the capacitor (in the dielectric layer) is 0.5 C V^2, and generally the volume ofa capacitor is roughly proportional to C V^2 for any given type.This means that doubling the working voltage for the same capacitance value means 4 times as largea device, so it usual to pick the minimum working voltage you can get away with for large capacitorsto reduce size/cost.Using a capacitor near to its max working voltage does mean more leakage current however.
Did you not read what we said - the paper is a separator, it is not an insulator it is soaked in electrolyte. The Al2O3 layer formed by electrolytic action (hence the name) is the insulatinglayer and it is very very thin (which is why you can get values of capacitance 1000's of timeslarger than plastic film of the same size).https://en.wikipedia.org/wiki/Aluminum_electrolytic_capacitor
To make a high value, small capacitor, you have to minimize aluminum foil thickness and paper insulator thickness.Now, when the paper insulator is very thin, it won't take much voltage to break it down and short out the capacitor.
We have too many "professors" here.......
I applaud teaching at a correct level - it is the most valuable kind of teaching, and yes - I HAVE had teachers that gave WAY too much information in an introductory lecture.However, when simplifying it is important to either be correct, or to note what parts are modeled for simplicity.Krupski, I like your description of a capacitor made with aluminum foil and paper. In fact, my students actually make such a capacitor to use with a van de graaff generator. That way they can see the mechanism for breakdown with their own eyes.However when you say "Electrolytic capacitors such as the kind you described are made by taking two long, thin sheets of aluminum, separated with paper saturated with an electrolyte and rolled up into a cylinder." confusion can result. This is because the student may recognize from other studies that paper saturated with an electrolyte conducts electricity. (My students also make a battery with saturated paper bridges.) Your simplification would have been more correct if you had just left electrolytes out. Explaining the use of electrolytes in a capacitor requires a greater level of detail.Actually, it's good to have such learned folks here. Through constant peer review, one can be relatively certain that posted information is correct.