ACCUMULATOR ELECTRIC TRACTION. THE ELECTRIC AUTOMOBILE
The use of the accumulator or storage battery in electric traction
affords a very good example of how a means of propulsion may fail
in one set of circumstances and contrive to succeed in another. Its
history serves to remind us that the problem of cheap transport is
really a group of problems, each one of which demands a particular
solution.
The accumulator is a device for storing electrical energy in the form
of chemical energy. Its action depends upon the effect of currents of
electricity on lead plates in a bath of sulphuric acid. The passage
of the current through the battery produces chemical changes which
enable the battery to give out current when required. As the battery
may remain 'charged' for several days, and may be discharged slowly
or quickly, it provides a means of 'storing' electrical energy. In
practice, and under favourable conditions, the efficiency of the
storage battery is about 80 per cent. That is to say, there is a loss
of about 20 per cent. in the process of conversion and re-conversion.
[Illustration: Fig. 8. A modern electric automobile.--The electric
battery is placed under the front half of the car, and the motors
drive the back axle through chains. (British Electric Automobile Co.,
Ltd.)]
Great hopes were once entertained of accumulator traction on tramways.
The storage battery offered a means of escape from all the difficulty
and expense of carrying electric mains overhead or underground.
By fitting each car with a storage battery, it could be made an
independent self-contained locomotive, capable of running a certain
number of miles until the battery was approaching exhaustion. By
providing centres where the batteries could be re-charged--or, to save
time, replaced by batteries previously charged--a continuous service
could be maintained on a tramway system.
The advantages of accumulator traction, apart from the saving in
first cost, are the absence of obstruction and danger from overhead
wires, and of the risk of a general stoppage of the service when the
current at the generating station fails from any accidental cause.
When accumulators are used, the conversion of a horse tramway to an
electric tramway becomes a very simple matter. All that is required
is to erect a generating station and provide each car with a storage
battery and electrical equipment. This equipment, it may be mentioned,
is substantially the same as with ordinary electric cars. The current
flows from the accumulator through the controller and the motors back
to the accumulator.
Many trials were made with this system in the early days of electric
traction, but there are no survivals. The failures were due in part to
weaknesses in the batteries and to the difficulty of handling them with
proper care under the rough and ready conditions of tramway service.
The main cause, however, was the inherent drawback of all locomotive
systems--the fact that the tractor has to haul its own dead weight in
addition to the weight of the car and passengers. Lead being one of
the heaviest of metals, this dead weight was a very serious item on
accumulator tramcars. It proved to be a fatal item when the attempt
was made to run large cars on heavy gradients. The rush of current
demanded in starting such cars up-hill was in itself too severe a tax
on the delicate structure of the batteries. In practice, moreover,
the necessity of bringing each car back to the depot for re-charging,
after a limited journey, proved very troublesome. The more extensive
the system and the more frequent the service, the more troublesome this
necessity became. Even the most enthusiastic advocate of the storage
battery was at last forced to admit that it was not applicable to a
system of transport, which demanded comparatively high speeds with
large cars on all gradients and over a range of several miles from the
centre of power.
After the admitted failure of accumulator tramways, the storage
battery was for some time used only on river launches and small
private vehicles. The conditions in both cases--and especially in the
former--are very favourable to its operation. On a river launch the
weight of the battery is not a serious item, as it serves to some
extent in the place of ballast. Launches, moreover, are generally
required for trips of a limited number of miles up and down the river
from the boathouse or charging station of the owner. In contrast with
the tramway, there is no demand for rapid acceleration at starting
or for abnormal power at intervals. The batteries discharge slowly
and fairly evenly, and are not subjected to serious vibration. The
electrical equipment is extremely simple, as the motor is fixed on to
the propeller shaft and operated by a controller on the deck close to
the steering wheel.
However, if economy were the only consideration, it is doubtful whether
the electric launch would have survived against the competition of
steam and petrol launches. It has survived because the simplicity of
the equipment, its silent running, and the absence of heat, smoke and
fumes, make it the ideal thing for river work. The hire of an electric
launch on the Thames costs more than that of a steam launch, but
plenty of people are willing to pay the additional charge to avoid the
drawbacks of steam propulsion on a small vessel.
Similar considerations underlie the extensive use of electric
broughams in cities. Such vehicles are required only for travel within
a restricted area and on streets where the gradients are seldom
severe. Their carrying capacity is generally limited to two or four
passengers, so that the batteries do not require to be unduly heavy. A
maximum speed of 12 miles an hour is quite sufficient for city streets;
and with careful treatment the batteries can be very economically
used and will not deteriorate nearly so rapidly as they would under
tramway conditions. Considerations of economy, on the other hand,
do not weigh very heavily with the class of people who use private
electric broughams. They are prepared to pay for the best available;
and the electric brougham, with its noiselessness, its easy running,
its absence of smell or other nuisance, is regarded as the ideal which
other modes of city transport must do their best to approach.
In London a certain amount of business has been done for some years
in hiring electric broughams for various periods on terms which
include current, maintenance, garage facilities, driver's wages, and
all other charges. The convenience of such an arrangement to the
hirer need not be emphasised, since what is wanted in this case is a
vehicle which is always ready at a telephone call. But the system has
another important advantage, which bears upon the economic prospects
of accumulator traction. By retaining the vehicles under its control
the hiring company not only centralises the arrangements for storing
and re-charging, but it is able to take care that the batteries are
properly treated. Just as the success of the surface-contact system
depends on minutiae of design, so the success of accumulator traction
depends upon minutiae of treatment. Carelessness in driving the
vehicles and in handling the batteries at the garage may transform
a perfectly satisfactory mode of city transport into an extravagant
nuisance. Consequently the success of this class of business depends
upon an organisation which permits of constant supervision over every
vehicle and every driver.
A good deal of ingenuity has been exercised upon the electrical
equipment of broughams; and it is probable that further improvements
will be made. In some cases the front axle is driven by the motor; in
some cases the back axle. The earliest cars used toothed-wheel gearing
in order to reduce the speed of the small fast-running motor. Improved
types on this principle still exist, but there are some interesting
forms in which the motors are placed right at the hub of the wheels and
effect speed reduction and control by electrical means, without any
intermediate gearing.
In addition to these improvements, the storage battery itself has made
a distinct advance in design and construction. It is more efficient,
more durable, and more reliable now than ever it was before. The closer
attention given to its treatment tends in the same direction; and
the result is that storage-battery makers and engineers have a very
accurate knowledge of what the accumulator will do at a certain cost
under certain conditions. The conditions being the variable factors
in the problem, and being in large measure determinable by choice, it
is rather remarkable that the engineers and financiers should have
selected, at the outset, the very conditions which were least suited to
the peculiarities of the accumulator.
The attempt to adapt battery traction to tramway work is a conspicuous
case in point, but it is not perhaps so conspicuous in the public
memory as the efforts to organise electric cab and electric omnibus
services in London and elsewhere. These efforts have been made so often
and failed so regularly that they have made it difficult to obtain
capital for any form of electric battery propulsion.
The electric omnibus has many of the drawbacks of the storage-battery
tramcar, but they are not so serious in the case of an urban service,
adequately met by small cars running at moderate speeds on short routes
with moderate gradients. It is possible that if recent metropolitan
electric omnibus enterprises had been as happy in their finance as in
their engineering, they would have succeeded well enough. But even in
their engineering they had to meet great difficulties. They sought to
protect themselves against excessive costs by entering into maintenance
agreements with the makers of the batteries; and although the terms of
these agreements were satisfactory enough, their validity depended on
careful treatment of the batteries by the drivers of the cars--a matter
which it is rather difficult to guarantee. Moreover, the number of
omnibuses put on the road was so small that the garage costs and other
standing charges were proportionally very heavy. With a larger fleet
and with efficient organisation, much better results might have been
achieved in spite of the inherent difficulties of the situation.
Although the electric cab has the advantage of being a smaller
vehicle and therefore more adapted to economical propulsion by
storage batteries, the conditions of the cab service are not at all
favourable to the system. The essential feature of a cab is that it
should be available anywhere, to go anywhere at a moment's notice. An
accumulator-driven vehicle, on the other hand, is tied by an invisible
cord to the charging station. Even if charging stations were multiplied
enormously, the electric cab would have no real freedom of action,
since several hours are required for the process of re-charging. We
have only to compare the limitations of the electric cab with the
freedom of the petrol cab (which can renew its supply of petrol in a
minute or two at any motor depot) to realise that the roving commission
is not at all suited to the former.
In 1899 a very bold effort was made to establish an electric cab
service in London. To inaugurate the service a procession of the cabs
was formed, but it excited more ridicule than serious interest. The
clumsy appearance of the cabs was against them; and their behaviour
was not satisfactory enough--as to speed and reliability--to overcome
the first unfavourable impressions. They soon disappeared, to add
another failure to the long list of disappointments in connection with
accumulator traction.
The private electric automobile remains, however, because it has been
organised under conditions which suit the peculiarities of the storage
battery. Its survival, in conjunction with the failure of a similar
means of transit for tramway, omnibus, and public cab services, has
pointed to another direction in which the electric automobile should
be a commercial possibility. That is, in connection with the local
distribution of goods from large stores and other centres.
The United States have given a very distinct lead in this matter. In
New York, Chicago, Washington, and other large cities the electric
automobile for private use is highly developed and there is also an
extensive service of electric vehicles ranging in size from a small
parcels van to a large lorry capable of carrying loads up to several
tons. No doubt the local cost of other means of transport has something
to do with this American development, which has, moreover, been
strongly supported by the companies which supply electricity to the
public. But the fundamental reason lies in the special character of the
service demanded.
The vans belonging to a large store all start from a certain point
and return to it after journeys of limited range. Owing to the period
occupied in loading up, and also to the pre-determined hours of most
of the deliveries, there is no difficulty about affording the time
required for re-charging the batteries, or in arranging each journey
so that the vehicle returns before the batteries are exhausted. With a
standardised fleet of vehicles, it is possible to remove the discharged
batteries and replace them with charged ones in a few minutes. The
whole arrangement, in fact, is like a private automobile garage, with
the advantage that the probable demand can be forecast with a somewhat
greater degree of certainty.
Steam and petrol-driven wagons run most economically on long steady
journeys at fairly high speeds, and the electric automobile does not
attempt to compete with them on these lines. But it offers competition
within city limits for door-to-door delivery; and its prospects are
particularly good for light parcel service, where the horse is still
maintaining its position against the petrol vehicle. The advantages
of the electric vehicle in neatness and noiselessness will certainly
secure its success if the cost can be proved to be not appreciably
greater than that of its rivals.
Apart from the necessity of careful organisation, the main essential
of success in electric automobile work is a supply of cheap
electricity. Owners of private electric launches have to pay anything
from 8_d._ to 2_s._ 6_d._ per unit for re-charging their batteries, but
these high prices are due to the intermittent character of the demand
and also (in some cases) to the cost of providing machinery to supply
current at special pressures for particular launches. An electric
automobile garage, situated close to a public generating station and
offering a larger and more regular demand, will of course obtain
current much cheaper. And it is possible that arrangements may be made
for supplying electricity to automobiles at a much lower rate even than
that customary for general power demands. In the metropolitan borough
of Marylebone, for instance, an electric garage may obtain current
during the small hours of the night at 1/2_d._ per unit, which is half
the standard rate for power purposes. This low price is offered because
there is otherwise practically no demand at all for electricity during
these hours. If, therefore, a garage arranges--and the arrangement is
quite feasible--to charge its batteries overnight, the power bill may
be divided by two.
The electric automobile has been used to some extent as a touring car,
but although journeys up to 100 miles have been performed on a single
charge, the time occupied in re-charging, and the difficulty of finding
convenient charging stations, are fatal to any development in this
field.