An ampere-hour or amp-hour (symbol: A⋅h or A h; often simplified as Ah) is a
unit
Unit may refer to:
General measurement
* Unit of measurement, a definite magnitude of a physical quantity, defined and adopted by convention or by law
**International System of Units (SI), modern form of the metric system
**English units, histo ...
of
electric charge
Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...
, having
dimensions of
electric current
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
multiplied by time, equal to the charge transferred by a steady current of one
ampere
The ampere ( , ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to 1 c ...
flowing for one hour (3,600 seconds), thus equal to 3600 A⋅s or
Coulomb
The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI).
It is defined to be equal to the electric charge delivered by a 1 ampere current in 1 second, with the elementary charge ''e'' as a defining c ...
.
The commonly seen milliampere-hour (symbol: mA⋅h, mA h, often simplified as mAh) is one-thousandth of an ampere-hour (3.6 coulombs).
Use
The ampere-hour is frequently used in measurements of
electrochemical
Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically conducting phase (typi ...
systems such as
electroplating
Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric cur ...
and for
battery capacity where the commonly known
nominal voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
is understood.
A ''milliampere second'' (mA⋅s) is a unit of measurement used in
X-ray imaging
Radiography is an imaging technology, imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical ("diagnostic" radiog ...
, diagnostic imaging, and
radiation therapy
Radiation therapy or radiotherapy (RT, RTx, or XRT) is a therapy, treatment using ionizing radiation, generally provided as part of treatment of cancer, cancer therapy to either kill or control the growth of malignancy, malignant cell (biology), ...
. It is equivalent to a ''millicoulomb''. This quantity is proportional to the total X-ray energy produced by a given X-ray tube operated at a particular voltage. The same total dose can be delivered in different time periods depending on the X-ray tube current.
To help express
energy
Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...
, computation over charge values in ampere-hour requires precise data of voltage: in a battery system, for example, accurate calculation of the energy delivered requires integration of the power delivered (product of instantaneous voltage and instantaneous current) over the discharge interval. Generally, the battery voltage varies during discharge; an average value or nominal value may be used to approximate the integration of power.
When comparing the energy capacities of battery-based products that might have different internal cell chemistries or cell configurations, a simple ampere-hour rating is often insufficient.
In other units of electric charge
One ampere-hour is equal to (up to 4 significant figures):
* 3,600
coulomb
The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI).
It is defined to be equal to the electric charge delivered by a 1 ampere current in 1 second, with the elementary charge ''e'' as a defining c ...
s
* 2.247 × 10
22 elementary charge
The elementary charge, usually denoted by , is a fundamental physical constant, defined as the electric charge carried by a single proton (+1 ''e'') or, equivalently, the magnitude of the negative electric charge carried by a single electron, ...
s
* 0.03731
faradays
* 1.079 × 10
13 statcoulomb
The statcoulomb (statC), franklin (Fr), or electrostatic unit of charge (esu) is the unit of measurement for electrical charge used in the centimetre–gram–second electrostatic units variant (CGS-ESU) and Gaussian systems of units. In term ...
s
( CGS-ESU equivalent)
* 360
abcoulomb
The abcoulomb (abC or aC) or electromagnetic unit of charge (emu of charge) is the derived physical unit of electric charge in the cgs-emu system of units. One abcoulomb is equal to ten coulombs.
The name "abcoulomb" was introduced by Kennell ...
s
( CGS-EMU equivalent)
Examples
*An
AA size dry cell
An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its nega ...
has a capacity of about 2,000 to 3,000 milliampere-hours.
*An average smartphone battery usually has between 2,500 and 6,000 milliampere-hours of rechargeable electric capacity.
*Automotive
car starter batteries vary in capacity but a large automobile propelled by an internal combustion gasoline engine would have about a 50-ampere-hour 12 V battery capacity.
*
Battery electric vehicle
A battery electric vehicle (BEV), pure electric vehicle, only-electric vehicle, fully electric vehicle or all-electric vehicle is a type of electric vehicle (EV) that uses electrical energy exclusively from an electric vehicle battery, on-boa ...
capacities are usually given in kWh, but in 2013, the
BMW i3
The BMW i3 is an electric car that was manufactured by German marque BMW from 2013 to 2022. The i3 was BMW's first mass-produced zero-emissions vehicle, zero emissions vehicle and was launched as part of BMW's electric vehicle ''BMW i'' sub-bra ...
60 Ah was named after the capacity of one of its 96 cells, for a total of 96x3.6Vx60Ah=20,736Wh with about 18 kWh usable energy, to match the number of the entry level
Tesla Model S
The Tesla Model S is a battery-electric, four-door full-size car produced by the American automaker Tesla since 2012. The automaker's second vehicle and longest-produced model, the Model S has both received mixed reviews from critics and a ...
60 which had 60 kWh. Later BMW i3 had 94 Ah and 120 Ah batteries, each topping Tesla's S85, S90 and S100 designations.
*Since one ampere-hour can produce 0.336 grams of
aluminium from molten aluminium chloride, producing a kg of aluminium required transfer of at least 2980 ampere-hours.
[T. L. Brown, H. E. Lemay Jr, "Chemistry the Central Science", Prentice-Hall, 1977 page 562] One kilogram of aluminium commonly requires 15.37 kWh, thus electric power represents about 20 to 40% of the cost of producing aluminium.
See also
*
Electrochemical equivalent
*
Kilowatt-hour
A kilowatt-hour ( unit symbol: kW⋅h or kW h; commonly written as kWh) is a non-SI unit of energy equal to 3.6 megajoules (MJ) in SI units, which is the energy delivered by one kilowatt of power for one hour. Kilowatt-hours are a comm ...
(kW⋅h)
References
{{Reflist
Units of electrical charge
Non-SI metric units