Capacitor voltage rating - why do so many voltage ratings exist?

[matrixofdynamism]

Capacitors have a voltage rating. This is supposed to be the maximum voltage that can be applied across them that can be sustained by its dielectric. Applying higher voltage than this could cause permanent damage to the capacitor. For Class II ceramic capacitors for which the capacitance changes as a function of the DC and AC applied voltage, the voltage rating also helps to determine how much of the total capacitance will be left when DC/AC voltage is applied across the capacitor since the closer we go to the voltage rating the more % of capacitance we keep loosing.

The basic question is, why not make all capacitors upto a very high voltage rating e.g 100V or 1000V? This just means that the part is robust and suitable for use in a wide variety of applications? I am puzzled to see so many different values for the voltage rating. I thought that just choosign a small number of values to design against, it will become simpler to buy capacitors.

[BrokenYugo]

Because voltage rating drives the size of the part, and people care about how large and heavy many modern electronic devices are, so there is great demand for parts as small as possible. Larger parts also use more materials and cost more money.

EDIT: This of course does not stop you from designing things with oversized parts to simplify your catalog, but what's cheap and available is cheap and available because it goes into mass produced stuff.

[Eraldo]

The higher the voltage the lower the capacitance for the same footprint. There are capacitors out there in the Farad category but their max voltage is like 3 volts. If you had that same capacitance in a 400v capacitor it could be as small as a battery car and as big as 12 battery cars (my analogies aren't the best. Let'ssay it's gonna be big)

[TimFox]

Going back to basics, the voltage capability of a given dielectric is roughly proportional to the thickness of the dielectric layer between metal plates.
You can put plates in parallel to increase the capacitance of the unit, but it is normally not a good idea to put the basic units in series, since the voltage will not necessarily equalize between the basic units.

[Zero999]

E = ¹/₂CV² so doubling the voltage rating quadruples the energy storage and will theoretically require a capacitor four times as big, to have the same capacitance. In reality it doesn't always work out that way, due to different materials and package styles.

[CaptDon]

AND, because staying within the same style and for the same capacitance value the price rises at about half the rate of the voltage rating. That matters when you're making a million of something. Why pay for a 100v rated part if my gizmo runs on two AA batteries. Did you think about the obvious reasons first?

[james_s]

Size and cost are the primary reasons. Then also with electrolytic capacitors a higher voltage part tends to have higher ESR, all else being equal.

This question is kind of like saying "why not make all rope strong enough to support 1,000 lbs" or "why have all these different thicknesses of sheetmetal instead of just building everything out of 1" thick steel plate". Every design is a compromise and when you increase some variable it comes at a cost to some other.