7.

Batteries

A battery is a voltage source that uses chemical action to produce a

voltage. In many cases the term battery is applied to a single cell, such

as the flashlight battery. In the case of a flashlight that uses a battery

of 1.5 volts, the battery is a single cell. The flashlight that is operated

by 6 volts uses 4 cells in a single case, and this is a battery composed of

more than one cell.

There are three ways to combine cells to form a

battery.

a. *Capacity and Rating of Batteries.*

The capacity of a battery is

measured in ampere-hours. The ampere-hour capacity is equal to the product

of the current in amperes and the time in hours during which the battery

will supply this current.

The ampere-hour capacity varies inversely with

the discharge current. For example, a 400 ampere-hour battery will deliver

400 amperes for 1 hour or 100 amperes for 4 hours.

Storage batteries are rated according to the rate of discharge and ampere-

hour capacity.

Most batteries are rated according to a 20-hour rate of

discharge.

That is, if a fully charged battery is completely discharged

during a 20-hour period, it is discharged at the 20-hour rate. Thus, if a

battery can deliver 20 amperes continuously for 20 hours, the battery has a

rating of 20 amperes x 20 hours or 400 ampere-hours. Therefore, the 20-hour

rating is equal to the average current that a battery is capable of

supplying without interruption for an interval of 20 hours.

Aircraft batteries are rated according to a one-hour

rate of discharge.

All standard batteries deliver 100 percent of their available capacity if

discharged in 20 hours or more, but they will deliver less than their

available capacity if discharged at a faster rate.

The faster they

discharge, the less ampere-hour capacity they have.

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