A Quick Guide to Understanding (Electrolytic) Capacitors

[coldfusion]

If you've been reading about the ABIT faulty-capacitor lawsuit, you probably know by know that the capacitors on ABIT motherboards had a nasty habit of oozing electrolytic fluid. For those of you who don't know what electrolytic fluid is and/or how it applys to electronics, here's a quick run-down on how two types of capacitors work.

First, know that the job of a capacitor is to store charge (measured in Coulombs). In the event that the flow of DC power to a device in your computer is interrupted, the capacitor will jump in and administer the correct amount of energy required to make up for what was lost in the drop in DC power.

The most basic type of capacitor is a ceramic capacitor. In it, two charged plates (one positive, one negative) sandwich a layer of dielectric material. This dielectric (could be air, a poor dielectric, or water, an excellent dielectric, or anything in between) conducts, ideally, zero electricity (which would otherwise make the capacitor less efficient), and keeps each plate from touching (which would equalize the positive and negative charges, rendering the capacitor useless).

And now, a crappy text-based diagram:

| - | <------- | + |
| - | <------- | + |
| - | <------- | + |
| - | <------- | + |
| - | <------- | + |
| - | <------- | + |
| - | <------- | + |
| - | <------- | + |
| - | <------- | + |
|__Power__|
Source

Where | - | is a negative plate, | + | is a positive plate, ---- is a dielectric, and < denotes the direction in which the electron travels.

The capacitors which you are most used to seeing in your computer, on your motherboard or videocard, are electrolytic capacitors. In it, a ribbon of metal is wound up, like if you rolled paper around a pencil and took it off--it forms a spiral shape, which is purely to increase surface area, which in turn increases capacitance (how many electrons--and thus, how much charge--a capacitor can hold under a given voltage).

Inside the capacitor is a gooey electrolyte, which acts as the other "plate." When a current is run to the electrolyte and the metal, a chemical reaction occurs, creating a layer of metallic oxide only a few molecules thick on the outside of the metal. This oxide acts as the dielectric. Electrons are thus stored, a charge is created, and that charge can be used to equalize power whenever my power-hungry GeForce 6800 Ultra gets a drop in power from the two 12V Molex connectors crammed into the back of it.

The only downside to electrolytic capacitors is that they leak and, if installed backwards, explode. Major bummer.

Hope that sheds some light on capacitors for you guys!

-coldfusion

P.S. And EE's feel free to correct this if I have any facts wrong, I'll edit it and keep it up to date.

 

[coldfusion]

A quick addendum:

If you wanted to make a capacitor that could hold one (1) Farad (a relatively large amount of capacitance) that used air as a dielectric and had the plates 1mm apart, each plate would have to be something on the order of 11,292,659.4 meters squared, or about 3360.5 meters to a side, if it were a square.

That same capacitor in water would require plates that were only 141,242.9 meters squared... that should give you an idea of how much better water is as a dielectric than air.

 

[UltimaParadox]

Interesting stuff, always good to know how things work...

 

[coldfusion]

Interesting stuff, always good to know how things work...

Don't thank me, thank my high school's Physics department. Ranked number one in the world by the College Board for schools with over 1000 students.