Elna capacitors

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i took some photos of these Elna caps. I found it interesting, the difference in cap sizes between Elna's audio grade series capacitors. The ROA Cerafine series seem to be the largest size in diameter at least, maybe length too..
As you can see the biggest difference was between a 25v 220uf R20 series and a 25v 220uf ROA series cap. The R20 series are miniature series so it makes sense but i wonder what the significance in material used to make these.


The SilmicII RFS series 35v 47uf was the same size as a 50v 22uf ROA series. SilmicII are the highest grade audio cap Elna makes which is interesting since it is a smaller cap. So obviously material not size determines the quality of capacitor.


Another huge difference in size was the ROA 50v 22uf and a Starget ROD 50v 22uf. Im not sure which of the two are the higher grade. I do know that they stopped production of the ROD series.



anyways just found it interesting. if anyone has knowledge on production and material used in making caps please share. Or if size effects the quality or electrical behavior. Not talking about saving room or real estate.
It all comes down to the dielectric material that is used in the capacitors.

The most significant difference between dielectrics is found in their relative permittivity. The higher the relative permittivity of the material, the higher the capacitance for a given surface area and thickness.

If you've even taken apart an electrolytic cap, it is actually two long strips of metal foil with two strips of dielectric-soaked material all rolled together. To obtain a greater surface area (more capacitance) you have to use a longer and wider strip, therefore the size of the capacitor increases.

The physical size of a capacitor has nothing to do with it's quality. Different dielectrics exhibit different properties, there's actually quite a bit more to capacitors than just capacitance and voltage rating, it gets quite complex actually.

Bottom line is, size of capacitors doesn't mean much.
In electolytic capacitors the function of the paper between anode and cathode foils is to mechanically isolate the anode and cathode and to contain the electrolyte. Electrolytic capacitor uses pure aluminum as the anode and cathode. The dielectric material is the thin oxidized material (aluminum oxide, aluimina, Al2O3; thickness of nanometers !!!!) on the anode foil and of course not the paper (please note the difference between foil capacitors;here the Polypropylene/polyester acts as dielectric).

This can be understood once if you understand the manufacturing process of foils. Anodic foils are etched in acidic solution first to increase the surface area and then anodized. It the foil is etched severely the capacitance for a given area can be increased. Generally anode foils are ( + terminall) anodized at a voltage, about 30~40 % more than the rating of the capacitor to grow thin Al2O3 film on the surface. Similarly cathode foils are also anodized to a few volts (3~5V), but not etched.

High voltage rating capacitor, normally should have high dielectric thickness to withstand high electric field (E=V/t; =Applied voltage/thickness of dielectric film), and therefore is anodized to greater time (to increase the thickness) and I think the anodic foils are etched only lightly in this case to avoid any failure in the dielectric. This is the reason for the increase in size for higher voltage rating capacitors.:)

I think that good grade capacitors are only lightly etched:confused:. The quality of a electrolytic capacitor of course depends on the purity of the foils and the stability and compatibility of the electolyte.
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