TM 10-6140-200-14
(see Chapter 4), and (2) that individual cell electrolyte
temperatures, during normal operations, do not exceed
110 degrees F.
1-7. Ampere-Hour Capacity
a. The electrical capability of a storage battery is usually
expressed in ampere-hours. The ampere-hour capacity is
the number of ampere-hours which can be delivered under
specified conditions of temperature, rate of discharge and
final voltage. Basically, ampere-hours are determined by
multiplying the number of amperes which the battery will
deliver by the number of hours during which the current
is flowing. Total cell or battery capacity then is deter-
mined by the size and number of plates which make up
the element. Due to the variety of job requirements
batteries are produced with many different sizes of cells.
b. Battery capacities available for each of the commonly
used battery sizes, at each of the required voltages, and
the utilization of these batteries, by type of equipment,
are detailed by Military Standard MS-15367.
1-8. Voltage
With reference specifically to storage batteries, many
"voltage" conditions have been recognized. The most
important of these are:
Figure 1-8. Discharged cell
a. Open Circuit Voltage. This is the voltage of a cell
or battery at the terminals, when no current is flowing.
The nominal open circuit voltage of an individual fully
charged cell is 2 volts. This is true regardless of cell size.
The voltage of an 18 cell lead-acid battery is stated,
therefore, as 36 volts.
b. Initial Voltage. The initial voltage of a cell or
battery is the closed circuit voltage at the beginning of a
discharge. It is usually taken after current has been
flowing for a sufficient period of time for the rate of
change of the voltage to become practically constant. This
usually occurs within a matter of minutes.
c. Average Voltage. The average voltage of the cell or
battery is the average value of the voltage during the
period of charge or discharge.
d. Final Voltage. The final or cut-off voltage of a cell
or battery is the prescribed voltage at which the discharge
is considered complete. It is usually chosen so that the
useful capacity of the battery is realized without subject-
ing it to harmful overdischarging. Final voltage will vary
with the rate of discharge, cell temperature and the type
of service, but for motive power applications it is
considered to be 1.70 volts per cell.
e. Voltage conditions b, c, and d above are monitored
when conducting test discharges. They are essentially
Figure 1-9. Charging cell
academic as regards normal battery usage in a truck.
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