Capacitors Blog

Aluminum is used for the electrodes by using a thin oxidization membrane.

Large values of capacitance can be obtained in comparison with the size of the capacitor, because the dielectric used is very thin.

The most important characteristic of electrolytic capacitors is that they have polarity. They have a positive and a negative electrode.[Polarised] This means that it is very important which way round they are connected. If the capacitor is subjected to voltage exceeding its working voltage, or if it is connected with incorrect polarity, it may burst. It is extremely dangerous, because it can quite literally explode. Make absolutely no mistakes.

Generally, in the circuit diagram, the positive side is indicated by a "+" (plus) symbol.

• The capacitor's function is to store electricity, or electrical energy.
• The capacitor also functions as a filter, passing alternating current (AC), and blocking direct current (DC).
• This symbol is used to indicate a capacitor in a circuit diagram.

The capacitor is constructed with two electrode plates facing eachother, but separated by an insulator.

When DC voltage is applied to the capacitor, an electric charge is stored on each electrode. While the capacitor is charging up, current flows. The current will stop flowing when the capacitor has fully charged.

When a circuit tester, such as an analog meter set to measure resistance, is connected to a 10 microfarad (µF) electrolytic capacitor, a current will flow, but only for a moment. You can confirm that the meter's needle moves off of zero, but returns to zero right away.

When you connect the meter's probes to the capacitor in reverse, you will note that current once again flows for a moment. Once again, when the capacitor has fully charged, the current stops flowing. So the capacitor can be used as a filter that blocks DC current. (A "DC cut" filter.)

However, in the case of alternating current, the current will be allowed to pass. Alternating current is similar to repeatedly switching the test meter's probes back and forth on the capacitor. Current flows every time the probes are switched.

Tantalum bead capacitors are polarised and have low voltage ratings like electrolytic capacitors. They are expensive but very small, so they are used where a large capacitance is needed in a small size.

Modern tantalum bead capacitors are printed with their capacitance, voltage and polarity in full. However older ones use a colour-code system which has two stripes (for the two digits) and a spot of colour for the number of zeros to give the value in µF. The standard colour code is used, but for the spot, grey is used to mean × 0.01 and white means × 0.1 so that values of less than 10µF can be shown. A third colour stripe near the leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink 35V). The positive (+) lead is to the right when the spot is facing you: 'when the spot is in sight, the positive is to the right'. 

• For example:   blue, grey, black spot   means 68µF
• For example:   blue, grey, white spot   means 6.8µF
• For example:   blue, grey, grey spot   means 0.68µF

This is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to show the smaller values.

Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):

• µ means 10-6 (millionth), so 1000000µF = 1F
• n means 10-9 (thousand-millionth), so 1000nF = 1µF
• p means 10-12 (million-millionth), so 1000pF = 1nF

Capacitor values can be very difficult to find because there are many types of capacitor with different labelling systems!

There are many types of capacitor but they can be split into two groups, polarised and unpolarised. Each group has its own circuit symbol.

A capacitor is a passive electronic component that storesenergy in theform of an electrostatic field. In its simplest form, a capacitorconsists of twoconducting plates separated by an insulating material called thedielectric. Thecapacitance is directly proportional to the surface areas of the plates, andis inverselyproportional to the separation between the plates. Capacitance alsodepends on thedielectric constant of the substance separating the plates.

The standard unit of capacitance is the farad, abbreviatedF. Thisis a large unit; more common units are the microfarad, abbreviated µF (1 µF =10-6F) and the picofarad, abbreviated pF (1 pF = 10-12 F).

Capacitors can be fabricated onto integrated circuit (IC)chips. They are commonly used in conjunction with transistors in dynamic random access memory (DRAM). The capacitors helpmaintain thecontents of memory. Because of their tiny physical size, thesecomponents have lowcapacitance. They must be recharged thousands of times per second or theDRAM willlose its data.

Large capacitors are used in the power supplies of electronicequipment ofall types, including computers and their peripherals. In these systems,thecapacitors smooth out the rectified utility AC, providing pure, battery-likeDC.

In many ways capacitors are the hidden saving grace of the electronics world. They play an essential role in smoothing switch transitions by storing and releasing a small amount of energy over short time scales. Although inductors can play the same role, I think it is safe to say that without small, accurately valued capacitors the modern electronics industry would be a very different beast. Essentially, capacitors store charge, which means that the amount of charge they can store is related to the area available to put said charges. Over recent years, the development of better control over small scale structuring has lead to large increases in capacitance in relatively small packages. The increases have been such that there have been some thoughts of putting these supercapacitors to work as battery replacements in applications where high currents are required.

Desalination could dramatically help the looming shortage with water. The problem is the membrane.

Right now, desalinting seawater largely revolves around pressurizing water and forcing it through a membrane to purify it. The process takes a lot of energy and hence a lot of cost. Desalinating seawater can cost as much as 50 cents a liter.

A collection of private companies and research institutes in Spain have begun to experiment with capacitive deionization for purifying seawater. In this, two electrodes would be placed in a tank. The ions (i.e., salt particles) would be drawn to one electrode. The ions would absorb the ions, which could then be released in a regeneration cycle. Capacitive purification was considered in the past, but the materials were too expensive. So who knows, it might work now.

Aluminum electrolytic capacitor maker Lelon Electronics has seen extra orders from China appliance makers due to the China government's program to promote sales of home appliances in rural areas. The extra orders have covered Lelon's reduced orders from the US and Europe, the company said.

The price of aluminum electrolytic capacitors has been stable since August 2008, while the price of aluminum foil continues to drop, lowering Lelon's cost pressure. However, order visibility for aluminum electrolytic capacitors is still low, the company noted.

Lelon has entered the wind power market with its large-size capacitors, and plans to apply the product to other applications. The company has already shipped a small volume of large-size capacitors to a motorcycle maker and expects to expand into the automotive segment.