Curve, Charging.
In secondary battery manipulation, a curve indicating the increase of
voltage as the charging is prolonged. The rise in voltage with the
duration of the charging current is not uniform. In one case, shown in
the cut, there was a brief rapid rise of about 0.1 volt; then a long
slow rise for 0.15 volt; then a more rapid rise for nearly 0.40 volt,
and then the curve became a horizontal line indicating a cessation of
increase of voltage. The charging rate should be constant.
The horizontal line is laid off in hours, the vertical in volts, so that
the time is represented by abscissas and the voltage by ordinates of the
curve.
Fig. 121. CHARGING CURVE OF A SECONDARY BATTERY.
Curve, Discharging.
A characteristic curve of a storage battery, indicating the fall in
voltage with hours of discharge. The volts may be laid off on the axis
of ordinates, and the hours of discharging on the axis of abscissas. To
give it meaning the rate of discharge must be constant.
Curve, Electro-motive Force.
A characteristic curve of a dynamo. It expresses the relation between
its entire electromotive force, as calculated by Ohm's Law, and the
current intensities corresponding thereto. To obtain the data the dynamo
is driven with different resistances in the external circuit and the
current is measured for each resistance. This gives the amperes. The
total resistance of the circuit, including that of the dynamo, is known.
By Ohm's Law the electro-motive force in volts is obtained for each case
by multiplying the total resistance of the circuit in ohms by the
amperes of current forced through such resistance. Taking the voltages
thus calculated for ordinates and the corresponding amperages for
abscissas the curve is plotted. An example is shown in the cut.