have the total number of cells too high. For
instance, if the 10 battery Tungar is used, ten 6-volt batteries (30
cells), or any combination which gives 30 cells or less may be used.
For instance, five 12-volt batteries (30 cells), or six 6-volt
batteries (18 cells) and two 12-volt batteries (12 cells), or any
other combination totaling 30 cells may be used. The same holds true
for motor-generators.

The charging rate is generally determined by the size of the charging
outfit. The ten battery Tungar should never have its output raised
above 6 amperes. A charging rate of 6 amperes is suitable for all but
the very smallest batteries. In any case, whether you are certain just
what charging rate to use, or not, there are two things which will
guide you, temperature and gassing.

1. Temperature. Have a battery thermometer (Figure 37) on hand, and
measure the temperature of the electrolyte of each cell on the line.
If you note that some particular cell is running hotter than the
others, keep the thermometer in that cell and watch the temperature.
Do not let the temperature rise above 110 degrees Fahrenheit, except
for a very short time. Should the highest of the temperature of the
cells rise above 110 degrees, reduce the charging rate.

2. Gassing. Near the end of a charge and when the specific gravity has
stopped rising, or is rising very slowly, bubbles of gas will rise
from the electrolyte, this being due to the charging current
decomposing the water of the electrolyte into hydrogen and oxygen. If
this gassing is too violent, a considerable amount of active material
will be blown from the plates. Therefore, when this gassing begins,
the charging rate should be reduced, unless the entire charging has
been done at a low rate, say about five amperes.

If gassing begins in any cell soon after the charge is started, or
before the specific gravity has reached its highest point, reduce the
charging rate to eliminate the gassing.

If one battery or one cell shows a high temperature and the others do
not, or begins gassing long before the others do, remove that battery
from the charging line for further investigation and replace it with
another so as not to slow up the charge of the other batteries which
are acting normally.

As long as excessive temperatures and too-early gassing are avoided,
practically any charging rate may be used, especially at the start.
With a constant potential charging set, as shown in Figure 48, t