Scientific American Supplement, No. 430, March 29, 1884

V >> Various >> Scientific American Supplement, No. 430, March 29, 1884

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A complete Faure-Sellon-Volckmar cell, such as is used in the existing
electric launches, is here on the table; this box weighs, when ready
for use, 56 lb.; and it stores energy equal to one horse power for one
hour=1,980,000 foot pounds, or about one horse power per minute for each
pound weight of material. It is not advantageous to withdraw the whole
amount of energy put in; although its charging capacity is as much as
370 ampere hours, we do not use more than 80 per cent., or 300 ampere
hours; hence, if we discharge these accumulators at the rate of 40
amperes, we obtain an almost constant current for 71/2 hours: one cell
gives an E.M.F. of two volts. In order to have a constant power of one
horse for 71/2 hours, at the rate of 40 amperes discharge, we must have
more than nine cells per electrical horsepower; and 47 such cells will
supply five electrical horse power for the time stated, and these 47
cells will weigh 2,633 lb.

We could employ half the number of cells by using them at the rate of
80 amperes, but then they will supply the power for less than half the
time. The fact, however, that the cells will give so high a rate of
discharge for a few hours is, in itself, important, since we are enabled
to apply great power if desirable; the 47 cells above referred to can
be made to give 10 or 12 electrical horse power for over two hours, and
thus propel the boat at a very high speed, provided that the motor is
adapted to utilize such powerful currents.

The above mentioned weight of battery power--viz., 2,632 lb., to
which has to be added the weight of the motor and the various
fittings--represents, in the case of a steam launch, the weight of
coals, steam boiler, engine, and fittings. The electro motor capable of
giving four horse power on the screw shaft need not weigh 400 lb. if
economically designed; this added to the weight of the accumulators, and
allowing a margin for switches and leads, brings the whole apparatus up
to about 28 cwt.

An equally powerful launch engine and boiler, together with a maximum
stowage of fuel, will weigh about the same. There is, however, this
disadvantage about the steam power, that it occupies the most valuable
part of the vessel, taking away some eight or nine feet of the widest
and most convenient part, and in a launch of twenty-four feet length,
requiring such a power as we have been discussing, this is actually
one-third of the total length of the vessel, and one-half of the
passenger accommodation; therefore, I may safely assert that an electric
launch will carry about twice as many people as a steam launch of
similar dimensions.

The diagram on the wall represents sections of an electric launch built
by Messrs. Yarrow and Company, and fitted up by the Electrical Power
Storage Company, for the recent Electrical Exhibition in Vienna. She has
made a great number of successful voyages on the River Danube during the
autumn. Her hull is of steel, 40 feet long and 6 feet beam, and there
are seats to accommodate forty adults comfortably. Her accumulators are
stowed away under the floor, so is the motor, but owing to the lines of
the boat the floor just above the motor is raised a few inches. This
motor is a Siemens D2 machine, capable of working up to seven horse
power with eighty accumulators.

In speaking of the horse power of an electro motor, I always mean the
actual power developed in the shaft, and not the electrical horse power;
this, therefore, should not be compared to the indicated horse power of
a steam engine.

I am indebted to Messrs. Yarrow for the principal dimensions and other
particulars of a high pressure launch engine and boiler, such as would
be suitable for this boat. From these dimensions I prepared a second
diagram representing the steam power, and when placed in position it
will show at a glance how much space this apparatus will occupy. The
total length lost in this way amounts to 12 feet, leaving for testing
capacity only 15 feet, while that of the electric launch is 27 feet
on each side of the boat; thus the accommodation is as fifteen to
twenty-seven, or as twenty-two passengers to forty, in favor of the
electric launch.

Comparing the relative weights of the steam power and the electric power
for this launch, we find that they are nearly equal--each approaches 50
cwt; but in the case of the steam launch we include 10 cwt. of coals,
which can be stowed into the bunkers, and which allow fifteen hours
continuous steaming, whereas the electric energy stored up will only
give us seven and a half hours with perfect safety.

I have here allowed 8 lb. of coal per indicated horse power per hour,
and 10 horse power giving off 7 mechanical horse power on the screw
shaft; this is an example of an average launch engine. There are launch
engines in existence which do not consume one-half that amount of fuel,
but these are so few, so rare, and so expensive, that I have neglected
them in this account.

Not many years ago, a steam launch carrying a seven hours supply of fuel
was considered marvelous.

Our present accumulaton supplies 33,000 foot pounds of work per pound of
lead, but theoretically one pound of lead manifests an energy equal to
360,000 foot pounds in the separation from its oxide; and in the case of
iron, Prof. Osborne Reynolds told us in this place, the energy evolved
by its oxidation is equivalent to 1,900,000 foot pounds per pound of
metal. How nearly these limits may be approached will he the problem
of the chemist; to prophesy is dangerous, while science and its
applications are advancing at this rapid rate.

Theoretically, then, with our weight of fully oxidized lead we should be
able to travel for 82 hours; with the same weight of iron for 430 hours,
or 18 days and nights continually, at the rate of 8 miles per hour, with
one change. Of course, these feats are quite impossible. We might as
well dream of getting 5 horse power out of a steam engine for one pound
of coal per hour.

While the chemist is busy with his researches for substances and
combinations which will yield great power with small quantities of
material, the engineer assiduously endeavors to reconvert the chemical
or electrical energy into mechanical work suitable to the various needs.

To get the maximum amount of work with a minimum amount of weight, and
least dimensions combined with the necessary strength is the province
of the mechanical engineer--it is a grand and interesting study; it
involves many factors; it is not, as in the steam engine and hydraulic
machine, a matter of pressures, tension and compression, centrifugal and
static forces, but it comprises a still larger number of factors, all
bearing a definite relation to each other.

With dynamo machines the aim has been to obtain as nearly as possible
as much electrical energy out of the machine as has been put in by the
prime mover, irrespective of the quantity of material employed in its
construction. Dr. J. Hopkinson has not only improved upon the Edison
dynamo, and obtained 94 per cent. of the power applied in the form of
electrical energy, but he got 50 horse power out of the same quantity of
iron and copper where Edison could only get 20 horsepower--and, though
the efficiency of this generator is perfect, it could not be called an
efficient motor, suitable for locomotion by land or water, because it
is still too heavy. An efficient motor for locomotion purposes must not
only give out in mechanical work as nearly as possible as much as the
electrical energy put in, but it must be of small weight, because it has
to propel itself along with the vehicle, and every pound weight of
the motor represents so many foot pounds of energy used in its own
propulsion; thus, if a motor weighed 660 pounds, and were traveling at
the rate of 50 feet per minute, against gravitation, it would expend
33,000 foot pounds per minute in moving itself, and although this
machine may give 2 horse power, with an efficiency of 90 per cent.
it would, in the case of a boat or a tram-car, be termed a wasteful
machine. Here we have an all-important factor which can be neglected,
to a certain extent, in the dynamo as a generator, although from an
economical point of view excessive weight in the dynamo must also be
carefully avoided.

The proper test for an electro-motor, therefore, is not merely its
efficiency, or the quotient of the mechanical power given out, divided
by the electrical energy put in, but also the number of feet it could
raise its own weight in a given space of time, with a given current, or,
in other words, the number of foot pounds of work each pound weight of
the motor would give out.

The Siemens D2 machine, as used in the launch shown in the diagram on
the wall, is one of the lightest and best motors, it gives 7 horse power
on the shaft, with an expenditure of 9 electrical horsepower, and it
weighs 658 lb.; its efficiency, therefore, 7/5 or nearly 78 per cent.;
but its "coefficient" as an engine of locomotion is 351--that is to say,
each pound weight of the motor will yield 351 foot pounds on the shaft.
We could get even more than 7 horse power out of this machine, by either
running it at an excessive speed, or by using excessive currents; in
both cases, however, we should shorten the life of the apparatus.

An electro-motor consists, generally, of two or more electro-magnets so
arranged that they continually attract each other, and thereby convey
power. As already stated, there are numerous factors, all bearing a
certain relationship to each other, and particular rules which hold
good in one type of machine will not always answer in another, but the
general laws of electricity and magnetism must be observed in all cases.
With a given energy expressed in watts, we can arrange a quantity of
wire and iron to produce a certain quantity of work; the smaller the
quantity of material employed, and the larger the return for the energy
put in, the greater is the total efficiency of the machine.

Powerful electro-magnets, judiciously arranged, must make powerful
motors. The ease with which powerful electro-magnets can be constructed
has led many to believe that the power of an electro-motor can be
increased almost infinitely, without a corresponding increase of energy
spent. The strongest magnet can be produced with an exceedingly
small current, if we only wind sufficient wire upon an iron core. An
electro-magnet excited by a tiny battery of 10 volts, and, say,
one ampere of current, may be able to hold a tremendous weight in
suspension, although the energy consumed amounts to only 10 watts, or
less than 1/75 of a horse power, but the suspended weight produces no
mechanical work. Mechanical work would only be done if we discontinued
the flow of the current, in which case the said weight would drop; if
the distance is sufficiently small, the magnet could, by the application
of the current from the battery, raise the weight again, and if that
operation is repeated many times in a minute, then we could determine
the mechanical work performed. Assuming that the weight raised is 1,000
lb., and that we could make and break the current two hundred times
a minute, then the work done by the falling mass could, under no
circumstances, equal 1/75 of a horse-power, or 440 foot-pounds; that is,
1,000 lb. lifted 2.27 feet high in a minute, or about one-eighth of an
inch for each operation: hence the mere statical pull, or power of the
magnet, does in no way tend to increase the energy furnished by the
battery or generator, for the instant we wish to do work we must have
motion--work being the product of mass and distance.

Large sums of money have virtually been thrown away in the endeavor
to produce energy, and there are intelligent persons who to this day
imagine that, by indefinitely increasing the strength of a magnet, more
power may be got out of it than is put in.

Large field-magnets are advantageous, and the tendency in the
manufacture of dynamo machines has been to increase the mass of iron,
because with long and heavy cores and pole pieces there is a steady
magnetism insured, and therefore a steady current, since large masses
of iron take a long time to magnetize and demagnetize; thus very slight
irregularites in the speed of an armature are not so easily perceived.
In the case of electro-motors these conditions are changed. In the first
place, we assume that the current put through the coils of the magnets
is continuous; and secondly, we can count upon the momentum of the
armature, as well as the momentum of the driven object, to assist us
over slight irregularities. With electric launches we are bound
to employ a battery current, and battery currents are perfectly
continuous--there are no sudden changes; it is consequently a question
as to how small a mass of iron we may employ in our dynamo as a motor
without sacrificing efficiency. The intensity of the magnetic field
must be got by saturating the iron, and the energy being fixed, this
saturation determines the limit of the weight of the iron. Soft wrought
iron, divided into the largest possible number of pieces, will serve
our purpose best. The question of strength of materials plays also an
important part. We cannot reduce the quantity and division to such a
point that the rigidity and equilibrium of the whole structure is in any
way endangered.

The armature, for instance, must not give way to the centrifugal forces
imposed upon it, nor should the field magnets be so flexible as to yield
to the statical pull of the magnetic poles. The compass of this paper
does not permit of a detailed discussion of the essential points to be
observed in the construction of electro-motors; a reference to the main
points, may, however, be useful. The designer has, first of all, to
determine the most effective positions of the purely electrical and
magnetic parts; secondly, compactness and simplicity in details;
thirdly, easy access to such parts as are subject to wear and
adjustment; and, fourthly, the cost of materials and labor. The internal
resistance of the motor should be proportioned to the resistances of the
generator and the conductors leading from the generator to the receiver.

The insulation resistances must be as high as possible; the insulation
can never be too good. The motor should he made to run at that speed
at which it gives the greatest power with a high efficiency, without
heating to a degree which would damage the insulating material.

Before fixing a motor in its final position, it should also be tested
for power with a dynamometer, and for this purpose a Prony brake answers
very well.

An ammeter inserted in the circuit will show at a glance what current is
passing at any particular speed, and voltmeter readings are taken at the
terminals of the machine, when the same is standing still as well as
when the armature is running, because the E.M.F. indicated when the
armature is at rest alone determines the commercial efficiency of the
motor, whereas the E M.F. developed during motion varies with the speed
until it nearly reaches the E.M.F. in the leads; at that point the
theoretical efficiency will be highest.

Calculations are greatly facilitated, and the value of tests can be
ascertained quickly, if the constant of the brake is ascertained; then
it will be simply necessary to multiply the number of revolutions and
the weight at the end of the lever by such a constant, and the product
gives the horse power, because, with a given Prony brake, the only
variable quantities are the weight and the speed. All the observations,
electrical and mechanical, are made simultaneously. The electrical horse
power put into the motor is found by the well known formula C x E / 746;
this simple multiplication and division becomes very tedious and even
laborious if many tests have to be made in quick succession, and to
obviate this trouble, and prevent errors, I have constructed a horse
power diagram, the principle of which is shown in the diagram (Fig. 1).

Graphic representations are of the greatest value in all comparative
tests. Mr. Gisbert Kapp has recently published a useful curve in the
_Electrician_, by means of which one can easily compare the power and
efficiency at a glance (Fig. 2).

The speeds are plotted as abscissae, and the electrical work absorbed
in watts divided by 746 as ordinates; then with a series-wound motor we
obtain the curve, EE. The shape of this curve depends on the type of
the motor. Variation of speed is obtained by loading the brake with
different weights. We begin with an excess of weight which holds the
motor fast, and then a maximum current will flow through it without
producing any external work. When we remove the brake altogether, the
motor will run with a maximum speed, and again produce no external work,
but in this case very little current will pass; this maximum speed is om
on the diagram. Between these two extremes external work will be done,
and there is a speed at which this is a maximum. To find these speeds we
load the brake to different weights, and plot the resulting speeds and
horse powers as abscissae and ordinates producing the curve, BB. Another
curve,

e = B/E

made with an arbitrary scale, gives the commercial efficiency; the speed
for a maximum external horse power is o a, and the speed for the highest
efficiency is represented by o b. In practice it is not necessary to
test a motor to the whole limits of this diagram; it will be sufficient
to commence with a speed at which the efficiency becomes appreciable,
and to leave off with that speed which renders the desired power.

I have now to draw your attention to a new motor of my own invention, of
the weight of 124 lb., which, at 1,550 revolutions, gives 31 amperes and
61.5 volts at terminals. The mechanical horse power is 1.37, and the
coefficient 373.

Ohms.
Armature resistance 0.4 w.
Field-magnet resistance 0.17 w.
Insulation resistance 1,500,000 w.

This motor was only completed on the morning before reading the paper;
it could not, therefore, be tested as to its various capacities.

We have next to consider the principle of applying the motive power to
the propulsion of a launch. The propellers hitherto practically applied
in steam navigation are the paddle-wheel and the screw. The experience
of modern steam navigation points to the exclusive use and advantage of
the screw propeller where great speed of shaft is obtainable, and the
electric engine is pre-eminently a high-speed engine, consequently the
screw appears to be most suitable to the requirements of electric boats.
By simply fixing the propeller to the prolonged motor shaft, we complete
the whole system, which, when correctly made, will do its duty in
perfect order, with an efficiency approaching theory to a high degree.

[Illustration: FIG. 1.--RECKENZAUN'S ELECTRICAL HORSE POWER DIAGRAM.

Draw a square, A B C D--divide B C into 746 parts, and C D into 1,000
parts, or, generally, let a division on C D be 0.746 of a division on B
C, so that we can use the horizontal lines cutting A B as a horse power
scale. A B, in the above diagram, gives 1,000 horse power, if the line
B C represents 746 volts, and C D 1,000 amperes. Let x = any number of
volts, y the amperes, and h the horse power, then

h/x = y/100 :. h = xy/746

A fine wire or thread stretched from o as a center to the required
division on C D will facilitate references.]

Whatever force may be imparted to the water by a propeller, such force
can be resolved into two elements, one of which is parallel, and the
other in a plane at right angles to the keel. The parallel force alone
has the propelling effect; the screw, therefore, should always be so
constructed that its surfaces shall be chiefly employed in driving the
water in a direction parallel to the keel from stem to stern.

[Illustration: Fig. 2--KAPP'S DIAGRAM.]

It is evident that a finely pitched screw, running at a high velocity,
will supply these conditions best. With that beautiful screw lying on
this table, and made by Messrs. Yarrow, 95 per cent. of efficiency
has been obtained when running at a speed of over 800 revolutions per
minute--that is to say, only 5 per cent was lost in slip.

Reviewing the various points of advantage, it appears that electricity
will, in time to come, be largely used for propelling launches, and,
perhaps, something more than launches.

In conclusion, quoting Dr. Lardner's remarks on the subject of steam
navigation of nearly fifty years ago, he said:

"Some, who, being conversant with the actual conditions of steam
engineering as applied to navigation, and aware of various commercial
conditions which must affect the problem, were enabled to estimate
calmly and dispassionately the difficulties and drawbacks, as well as
the disadvantages, of the undertaking, entertained doubts which clouded
the brightness of their hopes, and warned the commercial world against
the indulgence of too sanguine anticipation of the immediate and
unqualified realization of the project. They counseled caution and
reserve against an improvident investment of extensive capital in
schemes which still be only regarded as experimental, and which might
prove its grave. But the voice of remonstrance was drowned amid the
enthusiasm excited by the promise of an immediate practical realization
of a scheme so grand.

"It cannot," he continues, "be seriously imagined that any one who
had been conversant with the past history of steam navigation could
entertain the least doubt of the abstract practicability of a steam
vessel making the voyage between Bristol and New York. A steam vessel,
having as cargo a couple of hundred tons of coals, would, _caeteris
paribus_, be as capable of crossing the Atlantic as a vessel
transporting the same weight of any other cargo."

Dr. Lardner is generally credited with having asserted that a steam
voyage across the Atlantic was "a physical impossibility," but in the
work from which I took the liberty of copying his words he denies the
charge, and says that what he did affirm was, that long sea voyages
could not at that time be maintained with that regularity and certainty
which are indispensable to commercial success, by any revenue which
could be expected from traffic alone.

The practical results are well known to us. History repeats itself, and
the next generation may put on record our week attempts, our doubts and
fears of this day. Whether electricity will ever rival steam, remains
yet to be proved; we may be on the threshold of great things. The
premature enthusiasm has subsided, and we enter upon the road of steady
progress.

Mr. Wm. H. Preece, the chairman, in inviting discussion, said that no
doubt those present would like to know something about the cost of such
a boat as Mr. Reckenzaun described, and he hoped that gentleman would
give them some information on that point.

Admiral Selwyn thought Mr. Reckenzaun was a little below the mark when
he talked about the dream of getting 5 horse power for one pound--he
would not say of coal, but of fuel. For some months he had seen 1/2 lb. of
fuel produce 1 horse power, and he knew it could be done. That fuel was
condensed concentrated fuel in the shape of oil. When this could be
done, electrical energy also could be obtained much cheaper, but if it
were extended to yachts, he thought that would be as far as any one now
present could be expected to see it go. Still he thought there was a
future for it, and that future would be best advanced by considering the
question on which he had touched. First, the employment of a cheaper
mode of getting the power in the steam engine; and, secondly, a cheaper
and higher secondary battery. In a railway train weight was a formidable
affair, but in a floating vessel it was still more important. He did
not think, however, that a light secondary battery was by any means an
impossibility. Mr. Loftus Perkins had actually produced by improvements
in the boiler and steam engine two great things: first, one indicated
horse power for a pound of fuel per hour, and next he had devised a
steam engine of 100 horse power, of a weight of only 84 lb. per horse
power, instead of 304 lb., which was about the average. Those were two
enormous steps in advance, and under a still more improved patent law he
had no doubt things would be brought forward which would show a still
greater progress. Within the last fifteen days, nearly 2,000 patents
had been taken out, as against 5,000 in the whole of the previous year,
which showed how operative a very small and illusory inducement had been
to encourage invention. He had long been known as an advocate of patent
law reform, and, therefore, felt bound to lose no opportunity of calling
attention to its importance. Invention was in the hands of the inventor,
the creator of trade. If, without robbing anybody, one wished to produce
property, it must be done by improving manufactures as a consequence
of inventions. In one instance alone it bad been proved that a single
invention had been the means of introducing twenty millions annually,
upon which income tax was paid.

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