A battery that has, for example, a capacity of 100 Ah, theoretically can give a current of 10 amps for 10 hours, or 1 amp for 100 hours.
At a practical level there are certain performance losses conditioned by the battery discharge rate, the faster a battery discharges, the more energy is lost due to internal resistance. Therefore, the load capacity is usually given with reference to a standard discharge time (10 or 20 hours), and for a specific final voltage.
The Faraday constant is used in electrochemical calculations. The Faraday constant is the charge in one mole of electrons, approximately equal to 26.8 amps per hour.
How many Coulombs is an ampere-hour equivalent?
One hour of amps equals 3,600 coulombs (amp-seconds) of electrical charge transferred to a constant current of 1 amp for 1 hour, that is. In 1 second at 1 amp, current will flow 1 load pending.
The unit of electric charge in the International System is coulomb C. Coulomb is a derived unit that is defined in terms of the ampere: 1 coulomb is the amount of total electric charge that passes through a cross section of a conductor through which a electric current of one ampere for one second.
What is the amp-hour used for?
The Ampere-hour is used in batteries, in solar batteries or in electric batteries in general to indicate the capacity. In automobile batteries it is maintained that the 12 V battery must be capable of supplying a discharge electric current of 1 / 20º of the nominal capacity indicated in A · h for 20 hours at a temperature of 25 ° C at a voltage higher than the cutoff which is 10.5V.
The amp-hour is also frequently used in measurements of electrochemical systems, such as electroplating.
The milliampere-second (mA · s) is a unit of measurement used in X-ray imaging, diagnostic imaging, and radiation therapy. This amount 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 administered in different periods of time depending on the current of the X-ray tube.
Often battery manufacturers indicate in their specifications only the charge stored in mAh (mAh), others indicate only the energy stored in Wh · h (Wh). Both characteristics can be called the term "capacitance" (not to be confused with electrical capacitance as a measure of a conductor's ability to accumulate charge, measured in farads ).
In general, it is not easy to calculate the stored energy from the stored charge: the integration of the instantaneous power generated by the battery is required for the entire duration of its discharge. If greater precision is not needed, instead of integration, you can use the average values of voltage and current consumption, for this, use the formula that follows the fact that 1W = 1V · 1A :
1 W · h = 1V · 1A · h.
That is, the stored energy (in watt-hours) is approximately equal to the product of the stored charge (in ampere-hours) and the average voltage (in volts):
E = q · U ,
and in joules it will be 3600 times bigger
E = q · U · 3600
Examples where the amp-hour unit is used
- An AA size battery has a capacity of approximately 2 to 3 amp-hours.
- The average smartphone battery generally has between 2,500 and 4,000 milliamps-hour of electrical capacity.
- Car batteries vary in capacity, but a large car powered by an internal combustion engine would have a battery capacity of about 50 amps per hour.
- Since one hour of amps can produce 0.336 grams of aluminum from molten aluminum chloride, producing one ton of aluminum requires a transfer of at least 2.98 million hours of amps.