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Page 27
I ascertained in Europe that the motive power costs 2 cents per car
mile; that is, the steam power and attendance for charging the
batteries. We have to allow twice as much for the depreciation of a
battery at the present high rate at which we have to pay for the
battery--$12 for each cell. But I believe that as soon as the storage
battery industry is sufficiently extended, the total cost for
propelling these cars will not be more than six cents a mile, or about
one half the cost of the cheapest horse traction.
I have made some very careful observations on the cable tramway in
Philadelphia, which is quite an extensive system. I have never been
able to ascertain the exact amount of waste in pulling the cable
itself; but I have it on the authority of certain technical papers
that there is a waste of about eighty per cent. I do not intend to
depreciate cable or any other tramways, but there is a difficulty
about introducing cable tramways. It is necessary to dig up the
streets and interfere with the roadways. I have been told that the
cable arrangements in Philadelphia cost $100,000 a mile, and that the
cable road in San Francisco cost more than that. One of the directors
of the cable company in Philadelphia told me that if he had seen the
battery system before the introduction of the cable, he would probably
have made up his mind in favor of the former. The wear and tear in the
case of the storage system is also considerable. There is a waste of
energy in the dynamo; secondly, in the accumulator charged by that
dynamo; thirdly, in the motor which is driven by the accumulator; and
fourthly, in the gearing that reduces the speed of the motor to the
speed required by the car axles. It would be difficult to make a motor
run at the rate of eighty revolutions per minute, which is the number
of revolutions of the street car axle when running at the rate of ten
miles an hour. Take all these wastes, and you find in practice that
you do not utilize more than 40 per cent. of the energy given by the
steam engine. But this is quite sufficient to make this system much
cheaper than horse traction.
It is well known that we can discharge the storage battery _ad
libitum_ at the rate of 2 amperes or 200 amperes. I can get out of a
storage battery almost any horse power I like for a short space of
time. I have not the least objection to the direct system. But when
you come to run twenty or thirty or fifty cars on one line, you will
require very large conductors or dangerously high electromotive force.
The overhead system is applicable to its own particular purposes.
Where there are only five or ten, or even twenty, cars running on one
line, and that line runs through a suburb or a part of a city where
there are not many houses, that system is to be preferred. The
objection to the overhead system is not so much the want of beauty,
but the want of practicability. You have to put your posts very high
indeed, so as to let great wagon loads of hay and all sorts of things
pass underneath. Most of the trouble comes in winter, and when it is
snowing hard a great many difficulties arise. As regards the loss,
suppose that the resistance of the overhead lines is one ohm. To draw
one car it will take an average of 20 amperes, and the only loss will
be 20 multiplied by 20, that is, 400 watts through line resistance.
But if there are ten cars on that line, you get 40,000 watts loss of
energy, unless you increase the conductor in proportion to the number
of cars. If you do that, you get an enormous conductor, and have a
sort of elevated railroad instead of a telegraph wire, as most people
imagine an overhead conductor to be.
The current required to run a street car is about thirty amperes, and
an electromotive force of about 180 volts. If cars are run in
connection with an incandescent light station, we can arrange our
apparatus so that we can use an E.M.F. say of 110 volts, and then we
can put in a smaller number of cells with a larger capacity that will
give a corresponding horse power. We can charge such larger cells with
50 or 60 amperes instead of thirty.
In regard to arc lighting machinery, the arc lighting dynamo should
not be used to charge the accumulators. They can be used, but they
require such constant attention as to make them impracticable. We can
only use shunt-wound dynamos conveniently for that purpose.
In regard to using two motors on a car, there are several advantages
in it. I use two motors on all my cars in Europe, and always have done
so from the beginning. One of the advantages is that in case of an
accident to one motor the other will bring the car home; secondly,
with two motors we can vary the speed without changing the E.M.F. of
the battery. If I want very much power, I put two motors in parallel,
getting four times the power that I do with one machine, and an
intermediate power of two motors.
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