Inductance Converter
Convert Henry (H), millihenry (mH), microhenry (µH), nanohenry (nH), abhenry, stathenry.
Result
0
Base Unit
Relative Value
*Diagram shows values relative to the selected base unit (Henry).
Unit Information
What is a Henry (H)?
The Henry (symbol: H) is the SI derived unit of electrical inductance. One Henry is defined as the inductance of a circuit in which an electromotive force of one volt is produced when the electric current in the circuit is changing at a rate of one ampere per second (1 H = 1 V·s/A). The unit is named after Joseph Henry, an American scientist who discovered electromagnetic induction independently of Michael Faraday.
What are Kilohenry, Millihenry, Microhenry, etc.?
These are standard SI multiples and submultiples of the Henry. A Kilohenry (kH) is 1000 H. A Millihenry (mH) is 10⁻³ H. A Microhenry (µH) is 10⁻⁶ H. A Nanohenry (nH) is 10⁻⁹ H. A Picohenry (pH) is 10⁻¹² H. These are used to conveniently express the wide range of inductance values found in electronic components, from large power chokes to tiny traces on a circuit board.
What is an Abhenry (abH)?
The abhenry is the CGS-EMU (electromagnetic) unit of inductance. It is a very small unit, equal to 1 nanohenry (10⁻⁹ H). It's primarily of historical interest.
What is a Stathenry (statH)?
The stathenry is the CGS-ESU (electrostatic) unit of inductance. It is an extremely large unit, equivalent to about 8.99 × 10¹¹ Henries. Like the abhenry, it is rarely used in modern practice and is mainly of historical or theoretical interest.
Formulas
V = L (di/dt)
The fundamental inductor formula: Voltage (V) across an inductor is equal to its Inductance (L) multiplied by the rate of change of current (di/dt).
E = ½LI²
The energy (E) in Joules stored in an inductor's magnetic field is one-half its Inductance (L) multiplied by the square of the current (I).
X_L = 2πfL
Inductive Reactance (X_L) in ohms is the opposition to alternating current, where 'f' is frequency and 'L' is inductance.
1 H = 1000 mH = 1,000,000 µH
Shows the relationship between Henrys, millihenrys, and microhenrys.
1 µH = 1000 nH = 1,000,000 pH
Shows the relationship between microhenrys, nanohenrys, and picohenrys.
Key Reference Points
- Small chip inductors for RF applications: Often in the nanohenry (nH) to microhenry (µH) range.
- Inductors in power supply filters: Typically in the microhenry (µH) to millihenry (mH) range.
- Large chokes for audio or industrial power: Can be several Henries (H).
- The inductance of a straight piece of wire is usually very small, often in nH per unit length.
- An AM radio ferrite rod antenna might have an inductance of a few hundred microhenries (µH).
- A guitar pickup uses a coil with a high inductance (several Henries) to convert string vibrations into an electrical signal.
- The primary coil of a typical car ignition coil has an inductance of a few millihenries (mH).
- An inductor in a passive audio crossover might be 1-10 mH.
- Inductors used in resonant circuits for radio transmitters can range from nH to µH.
- The leakage inductance of a transformer, an undesirable property, is often measured in µH or mH.
Did You Know?
Inductors store energy in a magnetic field created by the current flowing through them. The amount of energy stored is proportional to the inductance and the square of the current (E = ½LI²). This energy storage capability is utilized in various applications, including switch-mode power supplies, resonant circuits, and ignition systems.
Lenz's Law states that the direction of the induced electromotive force (voltage) in an inductor is such that it opposes the change in current that produced it. This is why inductors resist changes in current.
The inductance of a coil can be greatly increased by winding it around a core made of ferromagnetic material like iron or ferrite. Air-core inductors have lower inductance but are used in high-frequency applications where core losses would be problematic.
Mutual inductance is the principle that allows transformers to work. A changing current in one coil induces a voltage in a second, nearby coil, allowing voltage to be stepped up or down without any physical connection.
Inductive charging, used in wireless phone chargers and electric toothbrushes, relies on the principle of mutual inductance. A coil in the charging base creates a changing magnetic field, which induces a current in a coil inside the device to charge its battery.
In high-fidelity speakers, inductors are used in crossover networks. They act as low-pass filters, directing low-frequency sounds (bass) to the large woofer speaker, while capacitors direct high-frequency sounds to the tweeter.
The Quality Factor, or Q factor, of an inductor is a measure of its efficiency. It's the ratio of its inductive reactance to its resistance. A higher Q factor means the inductor is closer to an 'ideal' inductor with less energy loss.
A car's ignition coil is a type of transformer that uses inductance to convert the low 12-volt supply from the battery into the very high voltage (thousands of volts) needed to create a spark at the spark plug and ignite the fuel.
At high frequencies, alternating current tends to flow only on the outer surface or 'skin' of a conductor. This 'skin effect' increases the effective resistance and can change the inductance of a wire.
When two wires carrying AC current are close together, the magnetic field from each wire induces eddy currents in the other, causing the current to redistribute and increasing resistance. This is the proximity effect, a key consideration in transformer winding.
Circuits containing resistors (R), inductors (L), and capacitors (C) are fundamental in electronics. They can act as oscillators, filters, and resonant circuits, forming the basis for radio tuners and many other technologies.
Maglev trains use powerful electromagnets to levitate and propel the train. The principles of inductance are central to the design of the magnetic coils and control systems that make this possible.
Much like the Farad for capacitance, the Henry is a very large unit of inductance. Most inductors used in common electronic circuits have values in the millihenry (mH) or microhenry (µH) range.
Joseph Henry discovered the principle of self-induction in 1832, but Michael Faraday published his results on mutual induction first. In honor of his work, the SI unit of inductance was named the 'Henry'.
Metal detectors work by using an inductor coil to generate a changing magnetic field. When a metal object enters the field, it induces eddy currents in the metal, which in turn create their own magnetic field that is detected by a second coil in the device.
Inductive reactance (Xₗ) is the opposition an inductor presents to alternating current, and it's proportional to the frequency of the current (Xₗ = 2πfL). This means an inductor blocks high-frequency AC more than low-frequency AC, while allowing DC to pass freely (in an ideal inductor).
A saturable reactor is a type of inductor where the inductance can be changed by varying a DC control current in a separate winding. This was an early method for controlling large AC currents, used in applications like theater lighting dimmers before the advent of modern power electronics.
A gyrator is an electronic circuit that can simulate an inductor using capacitors and active components like op-amps. This is useful in integrated circuits where creating a physical inductor can be difficult and expensive.