microfarad

What is a microfarad?

The microfarad -- symbolized as µF using the Greek symbol mu -- is a unit of capacitance, equivalent to 0.000001 or 10^-6 farad (F). The microfarad is a moderate unit of capacitance. In utility alternating current (AC) and audio frequency circuits, capacitors with values on the order of 1 µF or more are common.

In the field of electronics, capacitance is the ability of a component to collect and store energy as an electrical charge. The components used for such energy storage are called capacitors. Capacitors are often called condensers in aviation, marine and automotive circuitry.

How do capacitors work?

A capacitor's ability to store energy is similar to a battery. However, a capacitor can charge and discharge its stored energy faster than a battery and typically stores far smaller amounts of energy than a battery.

A capacitor is fundamentally two metal plates separated by air or some other dielectric or insulating material. An electrical charge is formed when a voltage is applied between the two plates of a capacitor. The capacitor will retain this charge until the surrounding circuitry calls for the energy.

The size of the metal plates, the distance between the plates and the dielectric material between them determine the capacitance of a capacitor. These factors result in countless different capacitor shapes, sizes and capacities for varied uses and applications.

Capacitors are typically used to block direct current (DC) while allowing AC to flow. Consequently, they're common components wherever electrical signals must be shaped or manipulated, such as power supplies where AC is converted into DC and radio circuits where radio frequency signals must be isolated through tuning.

What is a microfarad used for?

Capacitors designed on the microfarad scale are used in circuits that operate at relatively low frequencies, such as power supplies and circuits that handle signals in the audio frequency range. Circuits that operate at higher frequencies, such as radio frequencies and higher, will use far smaller capacitors with capacities in the picofarad range and smaller.

Circuits that operate at lower frequencies or that must deliver significant amounts of energy for industrial tasks, such as delivering energy to start a motor, handle large voltages. They support thousands of microfarads, sometimes approaching 1 millifarad.

How does a microfarad compare with a farad?

The base measure of the farad was named for 19th-century English physicist Michael Faraday. The scientific notion of electrical charge is based on the concept of a coulomb (C), which is the amount of electricity that 1 ampere (A) of current can carry in 1 second (s). A coulomb is expressed as the following formula:

C = A*s

A farad is generally defined as the ability of a device to store 1 coulomb per volt (V). A farad is expressed using the following two formulas:

F = C/V

or

(A*s)/V

In practice, a farad represents a significant amount of capacitance, and capacitors built to store farads of charge can be too large and unwieldy for use in modern electronic circuits. Electronic circuitry requires a small fraction of a farad, and capacitors are often tiny components designed and built to store minuscule amounts of energy.

This is why microfarads are important. A microfarad is one-millionth of a farad. It would take 1 million capacitors, each storing 1 microfarad, to store the equivalent energy in 1 farad.

What is the difference between a microfarad, nanofarad and picofarad?

The amount of capacitance needed for most modern electronic circuits is extremely small. Where a microfarad provides 0.000001 farad of capacitance, much smaller measures of capacitance are employed for more delicate circuits that operate at far higher frequencies.

These include the following:

• Nanofarad (nF) -- 0.000000001 or one-billionth or 10^-9 farad.
• Picofarad (pF) -- 0.000000000001 or one-trillionth or 10^-12 farad.

Capacitors far smaller than the picofarad scale exist. However, they're rarely practical because they're indistinguishable from naturally occurring or parasitic capacitance present in the printed circuitry used to build modern electronic devices. Such devices would be measured on the scale of femtofarads (10^-15 farad) and are more theoretical than practical. Still, even smaller capacitance can be measured accurately down into the attofarad (10^-18 farad) range.

How do you convert microfarad to another capacitance unit?

The capacitance metric uses a linear scale with straightforward designations based on powers of 10. What follows is a table of various units of capacitance and their farad equivalents.

Larger units of capacitance -- sometimes also called supercapacitors -- are devices providing more than 1 farad. Larger capacitors aren't used in delicate electronic circuitry. Instead, they replace batteries where large amounts of energy must be provided quickly, such as a motor starter. They're also used to drive high-energy industrial devices.

Converting between units of capacitance is a matter of moving the decimal point in the appropriate direction. For example, a nanofarad is a smaller unit of measurement than a microfarad. To convert 1 microfarad to nanofarads involves moving the decimal three places to the right, the equivalent of multiplying by 1,000:

1 µF = 1,000 nF

Conversely, expressing a capacitor in a larger unit of measure involves moving the decimal place to the left. For example, denoting a 1 µF capacitor in millifarads would require moving the decimal three places to the left, or multiplying by 0.001:

1 µF = 0.001 mF

There are numerous charts and conversion calculators available on the internet that can help streamline the conversion process between various capacitance units.

Microfarads and farads are one small part of data center efficiency. Find out more about building an efficient data center.