Shape of Electrolytic Capacitors

The differences between ceramic capacitor and electrolytic capacitor are:

• The electrolytic capacitor has large capacity, polarity, and large equivalent series inductance; the ceramic capacitor has small capacity, no polarity, and the equivalent series inductance is small.
• The low-frequency characteristics of electrolytic capacitors are good, and they are mostly used in low-frequency circuits. The high-frequency characteristics of ceramic capacitors are good, and they are mostly used in high-frequency circuits.
• Electrolytic capacitors can filter out low-frequency ripple, so they can be used as low-pass filtering. Ceramic capacitors can filter high-frequency ripple, so they can be used as high-pass filtering.
• Electrolytic capacitors cannot be used in pure AC power circuits; ceramic capacitors can be used in pure AC circuits.
• Ceramic capacitors are used as loop capacitors and pad capacitors in high-stability oscillator circuits for filtering, decoupling, and signal coupling.

https://www.xuanxcapacitors.com/the-difference-between-ceramic-capacitors-and-electrolytic-capacitor.html

"Murata's polymer capacitor has the feature of low ESR, low impedance, and large scale. Furthermore, there is no DC bias characteristic of capacitance, and since temperature characteristics are also stable, it excels in the Ripple absorption, smoothness, and the transient response performance.

Therefore, it is suitable for smoothing of input-output current of various power supply circuits, and the backup use over the load change of the CPU circumference. This contributes to reduction of the number of parts, or reduction of substrate area."

"There are two kinds of polymer aluminum capacitors: the "surface mount" type (also known as H-Chip), which uses a multilayer aluminum foil structure, and the "Can" type (also known as V-Chip), which consists of a rolled aluminum structure.

Murata's H-Chip type (ECAS Series) is designed with a resin molded case structure, which utilizes multilayer aluminum foil for anode and solid conductive polymer for negative cathode."

By wrapping the two foils and two electrolytic insulators into a spiral wrap one also effectively increases the area of the conductive plates for a charge build on both sides of the foils inside the spiral.

This is what I am referring to;is there a shape with more surface area of the plates vs

the typical stacked or circular concentric winding?

Specific use is for energy storage,not filtering,per se.

For instance a wavy shape for the components instead of flat.

Perhaps even a fractal shape?

There are three areas in power design where capacitors can positively impact the efficiency of the system, each have a slightly different requirement from the capacitor:

1. DC-LINK requires high voltages, high temperatures, high frequencies, and high ripple current
2. Snubbers can require high dV/dTs, high ripple currents, high voltages, and high temperatures as well as low inductance.
3. Resonant converters need high ripple currents, a wide operating voltage range, and capacitance stability over temperature, DC and AC voltage.

Combining these requirements demands a capacitor with very low loss, high ripple current handling capabilities, the ability to withstand high voltages and accept higher operating temperatures while exhibiting stable capacitance and high mechanical stability. Let’s look at which capacitor packages can deliver this.

https://ec.kemet.com/blog/what-ceramic-technologies-are-best-for-high-power-density-applications-part-1/

Just interesting...

https://www.nap.edu/read/10595/chapter/8

I'll have to think about this some more to produce a full blown derivation but I'd expect irregular plate surfaces would mean a lower breakdown voltage for the whole assembly and thus less possible energy storage for the same plate areas. Remember that similar charges repel each other so any sharper edge on the plate surface (fold or conductive debris) will be where charges will gather until breakdown is achieved in a localized area.

Not necessarily sharp edges;I am thinking similar to a corrugated sheet rolled up.

I said "sharper" not "sharp". There is an important difference.

Yes,sharper is sharper than sharp.

I was not thinking of any type of sharp fold,but a rather smooth wavy shape,with equal spacing between layers of the turns.

It is hard to beat the reliability or economy of just having two plates. Anything other than two plates rolled up would involve countless connections. With two plates there are only two connections. Connections can't fail if they don't exist.

No: the area per unit volume is almost exactly the same whatever shape you make them. Square or rectangular cross sections would be more efficient in terms of total volume used, but only by a factor of (4/pi). Plus manufacturing costs would rise considerably.

Imagine making a capacitor with aluminium foil and cling film: you could put down a square of cling film followed by a square of aluminium....film, al, film, al...&c., all al sheets need to have their own electrical connection; or, you could put down the end of a roll of film, followed by the end of a roll of al, roll of film, roll of al, then just roll all four sheets into one big roll, only two electrical connections needed.

Of course the processes are completely different between an al/foil and an electrical capacitor but in pricipal the comparison holds.

I don't seem able to get my idea across:

Imagine a sheet of corrugated aluminum foil and cling film,say for instance in a sine wave pattern, with corrugations running across the sheet.

Imagine the sheet is longer than it is wide.

Roll the sheets with the corrugations as you would if they were flat.

Only 2 connections.

The surface area of the aluminum and plastic(or your choice of material) would be greater than if they were flat,would it not?

Of course,this is not exactly the idea,but close.

This is just a sheet of al or electrolyte after it has been corrugated.

The middle line is the same length as it was before the corrugation. Do you think the top or bottom are longer than they were?

How amazing that no one has ever thought of this before.

They were invented in the days of vacuum tubes. Long sheets of aluminum foil were rolled up and stuffed in a can. They stood up on the chassis like the tubes did, and took up little real estate on the chassis. It made sense then and still does.

Same principle as I suggested,but using corrugated foil instead, to give more surface area.

But the corrugations won't match up when you wind it, so you won't get nearly as much material in the tube.

They will match up if you vary the spacing of the corrugations appropriately.

I am sure this calculation easily performed by a computer program.

I am pretty sure this is a wild goose chase.

Many people much smarter than me are constantly searching for better ways to increase contact area and capacity/vs board space.

I will just pursue other ventures.

Thanks for all the feedback from everyone.!

Exit(0)

After thoughtful consideration of all of the valuable feedback from everyone,I can see that my idea is a non-starter,and I have a better understanding of the factors involved.

Thanks again to everyone that contributed to my further understanding of the process.

Well I believe the surface of the foil is already etched to provide more surface area, same principal, smaller scale....

I think the efficiency of manufacturing the cylinder also has a play in it.

I vaguely remember research and small scale lab tests were being conducted into increasing the surface area using tightly packed rows of carbon nanotubes on flat sheets sandwhiched together (or some such thing) to greatly increase the capacity.

This was about 10 years ago or so and I don't have a link. After a quick internet search it may have been this (or something similar)

https://newatlas.com/nawa-nanotube-ultracapacitor-production/59684/