Ampere hour


An ampere hour or amp hour is a unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3,600 coulombs. The commonly seen milliampere hour is one-thousandth of an ampere hour.

Use

The ampere hour is frequently used in measurements of electrochemical systems such as electroplating and for battery capacity where the commonly known nominal voltage is dropped.
A milliampere second is a unit of measure used in X-ray imaging, diagnostic imaging, and radiation therapy. 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, 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 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.

Other measures of electric charge

The Faraday constant is the charge on one mole of electrons, approximately equal to 26.8 ampere hours. It is also used in electrochemical calculations.

Examples