case of a "third"
brush. High mica, loose brush spring, or a commutator which has been
turned down off-center may cause the trouble. This trouble most
frequently occurs on cars using third brush motor-generators having a
3 to 1 or more speed ratio between them and the engine. These
motor-generators operate at such high speeds that high mica and a
commutator which is even slightly off center have a much greater
effect than the same conditions would cause in separate generators
which operate at much lower speeds. The remedy for this trouble is to
keep the mica under-cut, and to be very careful to center the armature
in the lathe when taking a cut from the armature. In turning down the
commutators of high speed motor-generators, special fittings should be
made by means of which the armature may be mounted in its own
ball-bearings while the commutator is turned down.

ADJUSTING GENERATOR OUTPUTS

The repairman should be very slow in adjusting generator outputs. Most
cases of insufficient or excessive charging current are due to the
troubles enumerated in the foregoing paragraphs, and not due to
incorrect adjustment of the regulating device. Before changing the
adjustment of any generator, therefore, be sure that everything is in
good condition. The third brush generator, for instance, will have an
excessive output if the brushes are dirty, loose, or not well seated
on the commutator. The use of a third brush which is too wide, for
instance, will change the output considerably. A high resistance third
brush will decrease the output, while a low resistance brush will
increase the output. On the other hand, an increase in the resistance
of the charging circuit will cause an increase in the output of a
third brush generator, which is just the opposite to what is
ordinarily expected. Such an increase in resistance may be due to
loose or dirty connections, dirty cutout contact points, corroded
battery terminals and so on. Remember also that the third brush
generator sends a higher current into a fully charged battery than it
sends into a discharged battery. It is, therefore, essential that a
fully charged battery be on the car when the output of a third brush
generator is adjusted.

There are two things which determine whether any change should be made
in the charging rate on the car, viz: Driving, Conditions and the
Season of the Year.

Driving Conditions. A car which makes short runs, with numerous stops,
requires th