ELECTRIC CARS, BOATS, AND AUTOMOBILES.
=164. Electric Cars=, as well as boats, automobiles, etc., etc., are
moved by the power that comes from electric motors, these receiving
current from the dynamos placed at some "central station." We have
already seen how the motor can do many kinds of work. By properly
gearing it to the car wheels, motion can be given to them which will
move the car.
[Illustration: Fig. 237.]
Fig. 237 shows two dynamos which will be supposed to be at a power
house and which send out a current to propel cars. From the figure
it will be seen that the wires over the cars, called trolley-wires,
are connected to the positive (+) terminals of the dynamos, and that
the negative (-) terminals are connected to the tracks. In case a
wire were allowed to join the trolley-wire and track, we should have
a short circuit, and current would not only rush back to the dynamo
without doing useful work, but it would probably injure the machines.
When some of the current is allowed to pass through a car, motion is
produced in the motors, as has been explained. As the number of cars
increases, more current passes back to the dynamos, which must do more
work to furnish such current.
_Trolley-poles_, fastened to the top of the cars and which end in
grooved wheels, called _trolley-wheels_, are pressed by springs against
the trolley-wires. The current passes down these through switches to
_controllers_ at each end of the car, one set being used at a time.
[Illustration: Fig. 238.]
[Illustration: Fig. 239.]
=165. The Controllers=, as the name suggests, control the speed of the
car by allowing more or less current to pass through the motors. The
motors, resistance coils and controllers are so connected with each
other that the amount of current used can be regulated.
[Illustration: Fig. 240.]
[Illustration: Fig. 241.]
When the motorman turns the handle of the controller to the first
notch, the current passes through all of the resistance wires placed
under the car, then through one motor after the other. The motors being
joined in series by the proper connections at the controller, the
greatest resistance is offered to the current and the car runs at the
slowest speed at this first notch. As more resistance is cut out by
turning the handle to other notches, the car increases its speed; but
as the resistance wires become heated and the heat passes into the air,
there is a loss of energy. It is not economical to run a car at such a
speed that energy is wasted as heat. As soon as the resistance is all
cut out, the current simply passes through the motors joined in series.
This gives a fairly slow speed and one that is economical because all
the current tends to produce motion.
By allowing the current to pass through the motors joined in parallel,
that is, by allowing each to take a part of the current, the resistance
is greatly reduced, and a higher speed attained. This is not instantly
done, however, as too much strain would be put upon the motors. As soon
as the next notch is reached, the motors are joined in parallel and
the resistance also thrown in again. By turning the handle still more,
resistance is gradually cut out, and the highest speed produced when
the current passes only through the motors in parallel.
[Illustration: Fig. 242.]
[Illustration: Fig. 243.]
Fig. 238 represents a controller, by diagram, showing the relative
positions of the controller cylinder, reversing and cut-out cylinders,
arrangements for blowing out the short electric arcs formed, etc. A
ratchet and pawl is provided, which indicates positively the running
notches, at the same time permitting the cylinder to move with ease.
Fig. 239 shows a top view of the controller.
[Illustration: Fig. 244.]
=166. Overhead and Underground Systems.= When wires for furnishing
current are placed over the tracks, as in Fig. 237, we have the
overhead system. In cities the underground system is largely used.
The location of the conducting wires beneath the surface of the
street removes all danger to the public, and protects them from all
interference, leaving the street free from poles and wires.
Fig. 240 shows a cross-section of an underground conduit. The rails,
R R, are supported by cast-iron yokes, A, placed five feet apart, and
thoroughly imbedded in concrete. The conduit has sewer connections
every 100 feet. Conducting bars, C C, are placed on each side of
the conduit, and these are divided into sections of about 500 feet.
Insulators, D D, are placed every 15 feet. They are attached to, and
directly under, the slot-rails, the stem passing through the conductor
bar.
[Illustration: Fig. 245.]
Figs. 240 and 241 show the plow E. The contact plates are carried on
coiled springs to allow a free motion. Two guide-wheels, F F, are
attached to the leg of the plow. The conducting wires are carried up
through the leg of the plow.
=167. Appliances.= A large number of articles are needed in the
construction of electric railroads. A few, only, can be shown that are
used for the overhead system. Fig. 242 shows a pole insulator. Fig. 243
shows a feeder-wire insulator. Fig. 244 shows a line suspension. Fig.
245 shows a form of right-angle cross which allows the trolley-wheels
of crossing lines to pass. Fig. 246 shows a switch. In winter a part of
the current is allowed to pass through electric heaters placed under
the seats of electric cars.
[Illustration: Fig. 246.]
=168. Electric Boats= are run by the current from storage batteries
which are usually placed under the seats. An electric motor large
enough to run a small boat takes up very little room and is generally
placed under the floor. This leaves the entire boat for the use of
passengers. The motor is connected to the shaft that turns the screw.
Fig. 247 shows one design.
=169. Electric Automobiles= represent the highest type of electrical
and mechanical construction. The _running-gear_ is usually made of the
best cold-drawn seamless steel tubing, to get the greatest strength
from a given weight of material. The wheels are made in a variety of
styles, but nearly all have ball bearings and pneumatic tires. In the
lightest styles the wheels have wire spokes.
The _electric motors_, supported by the running-gear, are geared to
the rear wheels. The motors are made as nearly dust-proof as possible.
_Storage batteries_ are put in a convenient place, depending upon the
design of the carriage, and from these the motors receive the current.
These can be charged from the ordinary 110-volt lighting circuits or
from private dynamos. The proper plugs and attachments are usually
furnished by the various makers for connecting the batteries with the
street current, which is shut off when the batteries are full by an
automatic switch.
[Illustration: Fig. 247.]
_Controllers_ are used, as on electric cars, the lever for starting,
stopping, etc., being usually placed on the left-hand side of the seat.
The _steering_ is done by a lever that moves the front wheels. Strong
brakes, and the ability to quickly reverse the motors, allow electric
carriages to be stopped suddenly in case of accidents.
Electric automobiles are largely used in cities, or where the current
can be easily had. The batteries must be re-charged after they have
run the motors for a certain time which depends upon the speed and
road, as well as upon the construction. Where carriages are to be run
almost constantly, as is the case with those used for general passenger
service in cities, duplicate batteries are necessary, so that one or
two sets can be charged while another is in use. Fig. 248 shows one
form of electric vehicle, the storage batteries being placed under and
back of the seat.
[Illustration: Fig. 248.]