Capacitor Prefered Values

Smallest value electrolytic at a quick glance in the RS book is 0.1µF (100nF) at 63Vw. Can't imagine quite why one would use this... not much smaller than a 100nF poly. The larger ones (about 2,200µF) are used as smoothing capacitors in power supplies aren't they? I believe Michael Faraday invented a Huge 1 Farad Capacitor.
Largest 470,000uF (0.47F). In a big can with bolts for terminals. A snip at Ł125... each!!!
Electrolytics are polarised because of the way they are made. It's to do with the way the anode & cathode films are produced on the aluminium apparently.
You can get non-polarised electrolytics, but they are less common & more expensive.
Tantilium beads go from 0.1µF to 100µF. Polarised. Don't like reverse bias at all. Go short circuit. Make hideous smell when they short out high power circuits.
Ceramic capacitors. Depends what dielectric you're talking about. Values go from about 2.2pF to 10µF though 100nF is the usual max for through hole discs. 10µF tend to be surface mount. They are used to despike fast clocking IC's across their power pins. A mini-battery.
Not forgetting Mica caps which used to be used in high Q tuned circuits. Expensive these days.
Plastic caps go from 1nF to 3.3µF or so.
Then there's Supercaps, available up to 10F for memory backup. Weird. Tend to leak sulphuric acid which is a bit of a disadvantage...
If Faraday invented a 1F capacitor with the technology of the 1840s...

Posted by Dean_huster on Monday, 10 July, 2006 - 12:53 pm:
United Chemi-Con manufactures "ultra capacitors" up to 2700F in a single cell. These aren't the "toy" capacitors used by the idiots with the 1000W audio systems in their pocket rockets. These are industrial-grade. At those values, voltage ratings are typically around 2.5V, so the caps have to be "banked" in series/parallel to get higher voltage ratings for a given capacitance value. You can check them out at http://www.chemi-con.com.
Ceramic caps tend to have wild temperature coefficients, making them impossible for any circuits requiring a stable capacitance, such as timers, oscillators and filters. The only exception to this are NP0 (that's en-pea-zero, not en-pea-oh) ceramics, available in the small pF values and usually marked with a black swatch of paint on the top edge or the designation "NP0".
You'll notice that nearly all caps do not have the selection of values per decade that resistors do. While you have 24 values of 5% resistors per decade, you may have only six 5% caps per decade. This is because caps are typically used with resistors in circuits where cap value is critical. They work together to determine circuit operation, so it's more economical to select from a very few expensive caps and then vary the value of the cheap resistor to trim up the circuit parameters.