" The wiring as shown in Figures 41
and 42 is probably not the same as will be found on a rheostat which
may be bought, but when installing a rheostat, the wiring should be
examined to make sure that the "live" wire is connected to the
rheostat resistance and does not connect directly to the charging
circuit. If necessary, change the wiring to agree with Figures 41 and
42.

Figures 43 and 44 show the wiring of the charging circuits. In Figure
43 each battery has a double pole, double throw knife switch. This is
probably the better layout, since any battery may be connected in the
circuit by throwing down the knife switch, and any battery may be cut
out by throwing the switch up. With this wiring layout, any number of
batteries from one to ten may be cut-in by means of the switches.
Thus, to charge five batteries, switches 1 to 5 are thrown down, and
switches 5 to 10 are thrown up, thereby short-circuiting them.

[Fig. 43 Wiring for a charging circuit, using a DPDT switch for
each battery; and Fig. 44 Wiring for a charging circuit, using
jumpers to connect batteries in series]

Figure 44 shows a ten-battery charging circuit on which the batteries
are connected in series by means of jumpers fitted with lead coated
test clips, as shown. This layout is not as convenient as that shown
in Figure 43, but is less expensive.

Using Motor-Generator Sets

[Fig. 45 Ten battery motor-generator charging set]

Where no direct current supply is available, a motor-generator or a
rectifier must be installed. The motor-generator is more expensive
than a rectifier, but is preferred by some service stations because it
is extremely flexible as to voltage and current, is easily operated,
is free from complications, and has no delicate parts to cause trouble.

Motor-Generator sets are made by a number of manufacturers.
Accompanying these sets are complete instructions for installation and
operation, and we will not attempt to duplicate such instructions in
this book. Rules to assist in selecting the equipment will, however,
be given.

Except in very large service stations, a 40 volt generator is
preferable. It requires approximately 2.5 volts per cell to overcome
the voltage of a battery in order to charge it, and hence the 40 volt
generator has a voltage sufficient to charge 15 cells in series on one
charging line. Five 6 volt batteries may therefore be charged at one
time on each line. With a charging rate of 10 amperes