Motors and Motor-Driving/Chapter 13

by Alfred Charles William Harmsworth

CHAPTER XIII

ELECTRIC CARS

By the Editor of 'The Automotor'

An electromobile is a vehicle propelled by one or more electric motors driven by current supplied by accumulators carried on the car itself.

In dealing with the subject it is not proposed to go into detail as regards matters of car-construction, arrangements of gearing, or the other features which every electromobile necessarily possesses in common with other self-propelled vehicles; the intention is to deal mainly with the special features which characterise it, the assumption being made that readers are now familiar with the general mechanical principles involved in all classes of self-propelled vehicles.

An electric vehicle may be regarded as consisting of a body, a running gear, with one or two motors mounted on it and arranged to operate the driving wheels of the vehicle through speed reduction gearing, of a battery of accumulators carried on the car itself, of connections between this battery and the motors, and of a controller, the functions of which will be explained.

It will perhaps be best to deal with the subject in accordance with this general division, and first of all to consider the principles and characteristics of electric motors and accumulators, after that the connection between the two—under which heading the construction of the controller will be discussed, and the general principles will be considered. Then it is proposed to give a cursory description of different types of running gear, illustrated by a couple of actually running electric vehicles; finally to treat of the ailments and misfortunes to which electromobiles are subject, and the general prospects and position of electromobilism at the present day.

An electric motor is a machine which produces rotary movement owing to the magnetic action caused by an electric current.

Everyone is doubtless familiar with the ordinary magnet, a piece of steel either straight or, more often, shaped like a horseshoe, possessing the property of attracting certain metals which are termed magnetic, or more accurately para-magnetic. Nickel and iron are amongst those which are attracted, but iron is much more powerfully attracted than nickel.

Next to the faculty of attracting iron, the most characteristic property of the ordinary magnet is what is generally known as polarity. Its two opposite ends possess different properties. This is not apparent when a magnet is applied to soft iron, which is unmagnetised, but is obvious when one magnet is applied to another. The ends and poles of the magnets are usually distinguished by being called north and south poles, and designated by the letters N and S. By the north pole of a magnet is generally meant the end which, if the magnet be very freely pivoted or floated on water, will point towards the north. The south pole is the other end. Sticklers for accuracy call these different ends the northward-pointing pole and the southward-pointing pole. We will content ourselves with designating them simply by the letters N and S. If a bar magnet be broken in two, each broken portion also displays polarity. If two magnets be confronted with the N pole of one opposite the S pole of the other, they will attract one another. If the two N poles or the two S poles be brought together, repulsion will result.

The main property of electricity, or, to be more correct, of an electric current, which is of most importance in connection with the production of movement by its means, is its power to produce magnetism.

We do not know precisely what electricity is, and by implication we do not know precisely what an electric current is, but we have all requisite knowledge about it for practical purposes. An electric current is a something which occurs in a conductor, i.e. a piece of metal when it connects two points between which there is electric pressure. The current may be only momentary, as in the case of Franklin's kite with a wire attached which was sent up into a thundercloud, or when a so-called Leyden jar is discharged; or it may last a little longer, as when we discharge a dry cell. Finally it may last some hours, as in the discharge of an accumulator; but while it lasts its characteristics—the effects it produces—are the same. It heats the metal through which it flows, and it produces magnetism in the neighbourhood. The difference of electric pressure between two points is termed potential difference, and it is measured in 'volts.'

Every conductor opposes a certain amount of resistance to the passage of the electric current. This resistance is measured in what are called 'ohms,' the ohm being a unit of electrical resistance. It is the electrical resistance of a rod of copper of a certain length and thickness when at a certain temperature. The electric pressure or difference of potential which will send a certain amount of current, called an 'ampere,' through a conductor the resistance of which is an ohm, is one volt. It is half the pressure approximately existing between the terminals of an ordinary accumulator, and is about enough to heat half an inch of thin platinum wire red-hot. Volts, amperes, and ohms are all mutually dependent units of measurement—thus, if along any wire, the resistance of which we know to be an ohm, there is flowing one ampere of current, we know that the electric pressure or voltage between the ends of that wire is one volt. If there be a difference of pressure at the ends of the conductor of one volt, and we find that there is half an ampere of current flowing, we know that the resistance is two ohms. If we have a pressure of two volts maintained between two points, and we connect those two points by a wire, and find that two amperes of current flow through it, we know the resistance of the wire is one ohm. The analogy with the phenomena presented by liquids, such as water moving in pipes, is very close. Voltage corresponds to the pressure or head of water, ohmic resistance to the skin friction between the pipe and the running water, and amperage to the amount of water passing, say, in gallons per minute. Voltage, amperage, and ohmic resistance are measured in practice by special instruments called voltmeters, ammeters and ohmmeters.

The novice is sometimes troubled by having to familiarise himself with the notion that an electric current can flow through, or in, such a solid thing as a copper wire. Some people would perhaps find it easier to understand electric phenomena if conducting wires were made hollow. Persons who take this point of view may, however, console themselves with the reflection that a wire is not as solid as it looks, and also that some of the electric current runs along the outside. An electric current produces a magnetic condition, generally called a magnetic field, in the neighbourhood of a conductor—say a wire—along which it is passing. If a wire be twisted up into a helix, as at w in fig. 1, and if an electric current be led into it through the flexible conductors or brushes b and b¹, it would act in a feeble way like a magnet. If the current be stronger, it will act like a stronger magnet, and it will have one pole near where the current comes in and another pole where the current goes out. If a rod or core of soft iron c be slipped inside the coil of wire w, and insulated or electrically separated from it, so as to prevent the electric current from passing through it instead of through the wire, the core c will become a powerful magnet. As long as the electric current is passing it forms an electro-magnet. When the current ceases to flow, the iron will lose its magnetism—that is, provided it is soft. If a core of hard steel be used, it will take some time to become magnetized, but when it is magnetized it will be a permanent magnet. It is in this manner that soft iron and steel differ magnetically. If N, in fig. 1, be the north pole of a magnet (whether the pole of a permanent magnet or of an electromagnet does not matter) and if the current passes along the wire w so as to produce a south pole near the top of c slightly below N, and if the coil and core be capable of upward movement only, there will be a tendency for w and c to rise.

If a casting of soft iron or mild steel, shaped like m in fig. 2, have an insulated wire w wound round it in the manner shown, and a current passed round it in the direction of the

Fig. 1

Fig. 2

arrow, an electro-magnet will be produced with powerful poles, capable of strong attraction as at N and S. It will be understood that the windings are of course merely diagrammatic, many more turns of wire being used in actual practice.

If a soft iron ring, c, fig. 3, have a wire w continuously wound round it, and the current is supplied to this wire through the flexible brushes b, b¹, from leads l and l¹ coming from a battery of accumulators, the ring will become magnetic, and will resemble two half ring magnets put together, there will be a double pole of one kind where the current enters, and another double pole of the opposite kind where the current goes out. If the brushes be arranged to slip from one coil of the wire w to another, then if the whole wire-wound ring c be turned round, the magnetic poles will remain constant in space, although the ring turns round. If such a ring be mounted between the poles of such an electromagnet m, as shown in fig. 2, there will be a permanent pull on one of its pairs of poles in one direction and a permanent pull

Fig. 3

on the other pair of poles in the opposite direction. Now the position of these poles in space is permanent, and depends upon the position, as already explained, of the brushes b and b¹ . The result is that perpetual rotary pull or torque is produced in the ring and it turns round. The amount of torque produced is dependent upon the amount of magnetism present, that is upon the strength of the poles N and S, and the strength of the poles produced in the ring c; and this depends on the strength of the current flowing, and the number of turns of insulated wire. It will be understood that if the magnet m, fig. 2, were a permanent magnet instead of an electro-magnet, movement would still occur, and an electromagnet can be made much more powerful than a permanent magnet. The power of such a motor may consequently thus be increased.

The ring shown in fig. 3 represents a Gramme ring, which was one of the earliest and simplest forms of armature, i.e. revolving portion, employed in electric motors. In practice the current is not brought to it as shown in fig 3, but a device called a commutator, shown at k, fig. 2, is employed. The ring is mounted on a spider or on a centre which revolves in suitable bearings. The commutator k consists of a ring of conducting segments r r, separated by insulating pieces o o. Each one of the conducting segments r r is joined up by a wire or rod to equidistant portions of the armature winding w, so that the current supplied to the commutator by the brushes b, b¹ enters the winding w, in the same manner as shown in fig. 3.

Fig. 2 shows a simple form of electric motor, of what is called the 'separately excited' type—that is to say, the electro-magnet is rendered magnetic or excited by an electric current proceeding from some separate source of electricity, such as a battery separate from that which supplies the electric current to the rotating part or armature. Fig. 3 represents, as already stated above, the Gramme ring. This is a form of armature which is but little used in electric motors, some form of drum armature being now almost universally adopted. The drum armature is a development of the Siemens shuttle armature, and will be best understood from the inspection of a section of that arrangement, fig. 4. In this section x is the spindle of the armature, c being the iron core, shown in the rounded h section, and w the coil of wire covered with insulating material i. The whole arrangement is very much longer than it is thick, and really does resemble a shuttle. The two poles are formed by the sides of h. Instead of arranging all the wire in a single winding, we may distribute it over the surface of a soft iron cylinder, connecting it up to the sections of the commutator. This forms a drum armature, and is used in the great majority of electric motors employed on electromobiles. Such drum armatures of course differ in proportions, but the general arrangement is the same.

Fig.4

Figs. 2, 5, and 6 illustrate the three main types of the two-pole electric motors. Fig. 2 shows, as already explained, a two-pole separately excited motor. This may be looked upon as a motor in which the magnet is rendered magnetic by a current from a separate battery (a few accumulator cells usually sufficing for this purpose). To all intents and purposes it may be regarded as if the separately excited magnet were a permanent hard steel magnet of the same shape.

The two other types of motor are the shunt-wound motor, fig. 5, and the series-wound motor, fig. 6. In the shunt-wound motor the current, which is led by two conductors from opposite ends of the battery of accumulators to the brushes which supply the current to the commutator, and so to the

Fig. 5

armature, branches off from those brushes and goes round the coils wound on the field magnet. In the series motor the current traverses the field winding either before or after passing through the armature. There is a fourth variety of motor, known as the compound, in which the field magnet has both series and shunt windings. This type of motor is used in the Krièger cars.

The characteristics of series and shunt motors are different. The shunt motor tends to run at constant speed, no matter what the load may be, provided the voltage or pressure of the current supplied to it be the same; and it will consequently try its best to force a car provided with it through mud or uphill at the same pace as it would drive on the flat. The series motor, on the other hand, more or less apportions its speed to the load, and will go slower uphill and faster on the flat. The series motor has this additional advantage compared with the shunt motor, that it produces a greater starting torque or turn-

Fig. 6

ing moment—that is to say, series motors are better calculated than shunt motors for starting a car from a state of rest or getting it out of difficulties. Generally speaking, we may say that, for automobile purposes, series motors and separately excited motors, which present some of the characteristics of a series motor, are to be preferred for the propulsion of vehicles.

The majority of motors actually employed in electromobiles have four poles, and the brushes which lead the current to the commutator are usually of carbon, held in special brush-holders suitably pivoted. This is well illustrated in the case of the Krièger or Postel-Vinay motor, fig. 7, designed by M. Cuènod, which is in general use on the Krièger vehicles, and has in consequence become generally known as the Krièger motor. This motor has four poles with four flat coils, c, c. Each of the coils on each of the poles is of a twofold composition, being partially a thick wire winding designed for use as a series winding, and partially a thin wire winding designed for use as a shunt winding; the Krièger vehicle, as we shall subsequently show, using the motors sometimes as series motors, and sometimes as shunt motors, according to the conditions

Fig. 7.—Motors of 'Powerful'

of running. The motors, which are pivoted, and swung on springs, are provided with only two brushes, b. It might be supposed that, having four poles, four brushes should have been provided, and some of the original four-pole motors were so constructed. It was shown, however, by Mr. Mordey that by connecting the opposite wires on an armature in parallel with one another two brushes only might be employed instead of four. Electrically this is of course the same thing as using four brushes and cross-connecting them.

Other types of motor have also been employed successfully for the propulsion of electromobiles. Noticeable amongst these is the Joel, in which the armature constructed on the drum principle is arranged outside an eight-pole field, round which it revolves.

The modern electric motor is the most efficient machine in existence. Motors can be constructed which convert upwards of ninety per cent, of the electric energy supplied to them into mechanical energy. The efficiency declines as the size of the motor. diminishes, but motors of an eighty per cent, efficiency are practicable for automobile purposes.

The electric motor is also exceedingly compact. As regards the amount of space it occupies, it compares favourably with any other form giving the same amount of power. As regards weight it is slightly heavier than the petrol motor.

Its leading feature, however, is its magnificent flexibility. It will start from a position of rest and run up gradually to the required speed without jolt or jar, and as varying speeds can be obtained by grouping parts in the motors and the batteries, no change-speed gears are required in an electric car, a single speed reducing transmission gear being all that is needed.

Above all, the electric motor is practically noiseless, and it emits neither visible vapour nor effluvium.

Assuming a vehicle with running gear complete and motors mounted and geared to the driving-wheels, the motors have to be fed with energy in order that the car may be propelled— that is to say, we must in addition to the motors have a source of electric current present. A car with body, running gear, and motors geared in position, is a potentiality only. It requires an electric current to vivify it and enable it to move.

Attempts have been made to propel electric vehicles with primary batteries. They have neither been successful technically nor commercially. At the present day the secondary battery or accumulator is the only adequate source of electric current for the propulsion of motor vehicles which is self-con tained and trustworthy. It is just conceivable that a car might be propelled by the recently introduced Cupron battery, but the attempt could hardly have commercial success.

An accumulator may be looked upon as a reversible primary battery.

It has already been assumed that everybody is familiar with the common or horseshoe magnet. It will also be assumed that everybody is acquainted with the ordinary galvanic battery, but it may not be amiss to recapitulate its leading features.

If a plate of pure zinc and a plate of pure carbon be immersed in dilute sulphuric acid and connected outside the vessel in which they are placed by a metal wire, an electric current will flow along the wire from the point at which it is connected with the carbon to the point at which it touches the zinc. The current, however, will not flow for long. Soon after the wire connection between the two plates has been made, it will be observed that the surface of the carbon plate becomes covered with a layer of bubbles of gas, which increase in quantity till the whole plate is covered and the bubbles disengage and rise to the surface. The bubbles are hydrogen gas (due to the decomposition of the acidulated water by the zinc), and their formation on the carbon plate stops the further production of the electric current, and is known as polarisation. In the ordinary Bunsen battery, the carbon plate is set up inside a porous vessel containing nitric acid—a powerful oxidising material—the zinc remaining immersed in dilute sulphuric acid. The nitric acid oxidises or burns up the disengaged hydrogen, and by so doing produces additional electric energy; and therefore the voltage of a Bunsen cell is higher than that of a plain zinc carbon combination. If we could keep all the contents of the porous pot from escaping outside it, we could restore a Bunsen battery to its original condition by passing an electric current in the opposite way to that originally produced. This would reproduce the nitric acid which had reacted with the hydrogen and redeposit on the zinc plate the zinc that had been dissolved by the sulphuric acid, in the same way as a metallic deposit is produced by electroplating. In this manner the battery would be restored to its original condition. This cannot be done in practice because the nitric acid escapes from the porous pot and attacks the zinc directly.

One element of a secondary battery, or accumulator, consists of a so-called positive plate and a so-called negative plate immersed in dilute sulphuric acid. The positive plate consists of a leaden framework or grid filled up with electrically produced peroxide of lead. The negative plate consists of a corresponding leaden framework filled up with porous or spongy lead, also produced electrically. The positive plate corresponds to the carbon plus the nitric acid, the negative plate corresponds to the zinc in the primary battery. When the positive plate is connected by a conductor—say through a motor to the negative plate—an electric current passes from the one to the other, and the battery discharges. Instead, however, of the negative plate dissolving as in the case of a primary battery, the spongy lead becomes converted into sulphate without dissolving. The hydrogen gas which would appear at the surface of the positive plate is oxidised by the lead peroxide and reduces it. The electric pressure registered by a voltmeter arranged in the external circuit and connected to the positive and negative plates is a little over two volts when the accumulator is freshly charged. When the accumulator has given a certain amount of current for a certain length of time, a large proportion of the spongy lead on the negative plate becomes covered with sulphate of lead, and a large proportion of the lead peroxide on the positive plate becomes reduced. The electric pressure which the cell furnishes becomes diminished, and the accumulator is said to be discharged. The accumulator should under no circumstances be discharged after a voltmeter connected from plate to plate shows that the voltage has sunk to 1·75 volt per cell.

When a primary battery is discharged it cannot be used again except by renewing the materials, but an accumulator when it is discharged, by having furnished current for a certain prolonged period, can be charged—that is to say, restored to its original condition—by forcing the current through it the wrong way, that is in the opposite direction to that in which the current flows when the accumulator is being discharged. It is this feature of the accumulator which renders it a practical appliance. When it has given out an electric current for a certain time, it is merely necessary to connect it to the terminals of a suitable source of current at the required pressure to recharge it. It is generally advisable to charge an accumulator at about the same rate that is to say, at about the same number of amperes that it normally discharges at, but this is not absolutely essential, as the charging rate may exceed that very considerably, and with a good type of cell it is practically only limited by the heating produced. The pressure or voltage required to charge a battery is somewhat higher than that which it gives out, and is generally about 2·5 to 2·6 volts per cell.

There are two types of accumulator batteries, those in which both positive and negative plates are 'pasted,' and those in which the positive plates are originally composed entirely of metallic lead, cast so as to expose a large surface to the action of the dilute sulphuric acid, a coating of peroxide of lead being formed upon it by the action of the electric current. In both types at the present day the negative plate is 'pasted.' Electromobiles have also been built by the Electric Motive Power Co. and successfully propelled with Plante positives and negatives, in which zinc in a pure form is deposited on a special conducting support unacted upon by dilute sulphuric acid. This gives the advantages of the Plante; positive durability and great length of life without increased weight. Batteries of this type have been two years in constant use. In general it may be assumed, however, that the type of automobile battery chiefly employed has both negatives and positives formed by 'pasting.' The process of manufacture of an accumulator cell will be best comprehended by reference to a special example. Fig. 8 shows the type of plate employed in the construction of the batteries built by the Accumulator Industries, Ltd. for the vehicles of the British Electromobile Co., Ltd., of which the 'Powerful' is a good example.

The first step in the process of manufacture of the plate depicted in fig. 8 consists of mounting a sheet of thin pure lead, perforated in the manner shown, in a heated mould, in which a raised edge undercut at the sides is cast on to it, together with the lug or connecting piece projecting from the top of the plate. The grid thus constructed is smeared level with a paste mainly composed of ground litharge moistened with dilute Fig. 8 sulphuric acid. The paste contains other things also. After smearing, the plate is dried in a warm room until the paste is thoroughly dry and hard, and the plate is then mounted with several others in a forming vessel of dilute sulphuric acid, in which it is connected to the negative pole of a battery of accumulators or a dynamo. The action of the current finally reduces the litharge to the condition of porous metallic lead, and the plate is then a negative, suitable for being assembled with other plates to form a battery cell. The positive consists of somewhat thicker plates, similarly formed as negatives in the manner described, and then connected to the positive of a forming battery or dynamo till all the porous lead is changed into lead peroxide, when the plate has become a positive. Each of the plates, whether positive or negative, is covered over as shown in fig. 8 by a grille of ebonite, which assists in maintaining the actual material in position, and also serves to keep the plates apart. A number of positive and negative plates, generally an even number of positives and an odd number of negatives, are assembled together in a cell as shown in fig. 9, additional vertical rods of ebonite being there shown in position to give wider separation Fig. 9 between the plates. It will be observed that in fig. 9 the plates repose upon two longitudinal prominences at the bottom of the cell, which are technically known as bridges. These serve to keep the plates off the bottom of the vessel, so that if any of the material falls out between them, it shall not bridge across between the plates, causing a conducting connection to be formed, and the plates thereby discharged when not in use and injured. Each of the connecting lugs of each of the positive plates visible on the near top side of fig. 9 is autogenously soldered to a cross-connecting bar of lead, which is brought up vertically to form the positive terminal. The negative plates are similarly connected to another cross bar, this being brought up through the cover on the far side and forming the negative terminal. The process of soldering is carried out either by a hydrogen flame or by an electric welder. When the formed plates are mounted in position as shown in fig. 9, the cover is provided with a central hole for pouring in the acid and allowing the escape of any gases generated when the cell is charged, is put on.

The containing vessel of automobile cells is almost invariably of ebonite, which has proved itself to be a light acid-resisting material, and the most suitable for the purpose. The general arrangement of the plates and cells is very similar in all automobile batteries. The plates themselves, however, differ in the shape and construction of the grid, which sometimes resembles an open network, as in the Rosenthal and Oppermann batteries, and also in the composition of the paste and the methods of formation adopted.

As it will be recollected that each such cell, as shown in fig. 9, gives only a voltage of approximately 2·0, and as it is found that, owing to various reasons, the most satisfactory design of motors for electromobile purposes involves their being supplied with current at between fifty and one hundred volts— preferably nearer one hundred volts than fifty—a number of accumulator cells have to be arranged in series—that is to say, the positive terminal of one connected to the negative terminal of the next fifty cells thus connected giving approximately one hundred volts. Of course, according to the power of the motors they will take more or less current, which is measured, as already explained, in amperes, and the size of the cells supplied to a car is consequently so arranged that the normal rate of discharge of the battery that is, the amount of current measured in amperes it can give without inconvenience to itself shall be the same as the amount of amperes required by the motor or motors to develop their normal power.

It must be remembered that an accumulator or battery of accumulators can be so utilised that twice or three times the amount of current that it was designed to give may be taken out of it. This will not do much harm if it happens only rarely, and for short periods, but if it happens for long and often, it will shorten the accumulator's life. To get good results an accumulator should be treated with every possible care and consideration. An electric motor will also stand considerable overloading, but it is not so patient as the accumulator, for under most circumstances of at any rate prolonged overload, the motor will burn up before the accumulator is seriously injured of course assuming that the accumulator has been properly designed for the work that it has to do.

For use in a car, accumulators are usually—or at any rate preferably—mounted, about half a dozen together, in what are termed nesting-boxes that is, wooden cases a little shallower than the cells themselves. Such a bunch of accumulators forms a unit which can be separately handled for removal or insertion in the vehicle. The connections between the cells composing it should be flexible and should be easily removable when required. Some constructors mount the whole of the cells in one nesting-box or tray, so that they can be inserted by mechanical means into a vehicle when charged, and instead of the vehicle being kept waiting for the process of charging, the discharged battery box can be withdrawn and a fresh one inserted.

Let us consider the running gear of a car such as is shown in fig. 12. The two motors are mounted on the rear axle and adapted to drive by means of spur gearing, consisting of a pinion and a rack both enclosed, each of the rear wheels of the vehicle independently. We will suppose that we have a battery of accumulators mounted on the framework above described, consisting, say, of forty cells, arranged in two groups of twenty cells each, one at the front part of the frame, and one at the rear. We have to consider the problem of connecting the batteries with the motors. This would be a simple business if the car were designed to run on the flat at an always uniform speed, and if the surface on which it would be its fate to run could always be satisfactory, such as an asphalted street, for example. It would then suffice to connect the two terminals of one of the batteries to the two brushes of one of the motors and the two terminals of the other battery to the two brushes of the other motor, by means of cables covered with insulating material, switches for making and interrupting the connection being arranged in between. Such a car, however, would only have one speed, and it would take an enormous current at starting, which would be very liable to burn up the motors and injure the accumulators. In order to give different speeds and to enable the amount of current taken by the motors at starting to be reduced, arrangements must be made for connecting either the motors or the parts of the motors, or the two halves of the battery, or both in different groupings. It must be pointed out that more current can be put into an electric motor at starting than when running, owing to the fact that when running it produces a kind of back electric pressure.

If, then, we used on each of the motors at starting the full electric pressure our battery is capable of supplying, a great deal too much current would be forced through the motors and they would probably be burnt up. We may reduce the effective pressure applied to the motors by putting the two halves of the battery in parallel, when we should be working with a pressure of forty volts instead of eighty. We may also work further in the same direction by putting the motors in series, thereby doubling the effective resistance opposed to the current. To enable this to be done we want, however, to take several connections from the motors and several connections from the battery, and connect them by cables to a number of different points between which the required electrical connections can be established by means of an appliance termed a controller. This usually involves some such arrangement as is depicted in fig. 10, which shows the controller used in the Joel car. It consists of a non-conducting cylinder along which strips of metal are arranged, the cables uniting the different terminals of the battery and the motors being brought up to the flat springs which are shown pressing against the cylinder. Turning the cylinder round by means of the lever connected with it on the right produces electrical junction of such a kind as to group the motors and batteries in various ways according to the requirements for starting, for producing different speeds, forward and reversing in accordance with the principles above described.

A multiplicity of arrangements may be adopted and have been adopted in electric cars, involving corresponding differences of structure in the running gear and the controlling arrangements. To begin with, a car may have one motor, which may

Fig. 10

be arranged to drive the rear wheels by chains from the ends of the motor-shaft, the driving wheels in this case running on a fixed rear axle. Or the driving wheels may be mounted on a live rear axle, the motor driving on to the compensating gear, either by a chain, by spur gearing, or by means of worm gearing, which gives a nice silent drive, and is used in the Oppermann cars. In any case the use of a single motor involves, in addition to the motor, a differential gear. What is to be avoided is a live rear axle with the motor so mounted that any large proportion of its weight comes on this live axle. This tends to cause distortion, with ultimate increased friction in the bearings and loss of efficiency. A very good system of mounting a single motor is illustrated by the recent De Dion vehicles, in which a single motor drives on to a separately supported compensating gear through an arbor-shaft, the compensating gear being connected to the driving wheels by jointed rods. This enables motor and compensating gear to be mounted on the upper side of the springs, both being thereby comparatively protected from vibration.

The advantages of a single motor are that it can be built with a somewhat higher efficiency than can be obtained with two separate motors, each of half the power. It is questionable whether there are any other advantages.

Cars employing two motors may have them mounted either to drive the front wheels, in which case the motors are necessarily mounted so as to turn with the wheels, or the motors may be mounted one to drive each of the rear wheels either by spur gearing (fig. 12) or by chains.

The Krièger cars are conspicuous examples of the former class, and are in fact the only electromobiles in this country in which this method of driving has been utilised. The disadvantages are that there is a tendency for the wheels to slip when the car is going uphill on greasy roads.

The latter class with two motors comprises an immense number of most conspicuous and successful vehicles, amongst which are those of the City and Suburban Electric Vehicle Co., Ltd. The advantages of two motors are numerous. In the first place, they practically ensure the car being supplied with sufficient motive power, as the limit in si/e of an efficient motor makes it practically certain that a car provided with two will be able to get along. In the second place, if anything happens to one of the motors at a distance from home, it is almost always possible at a sacrifice of speed to get home with one. Thirdly, a greater variety of speeds can be obtained; and fourthly, no mechanical compensating gears are necessary, two series or separately excited motors acting as differentials to one another.

As regards the class of motor employed, the majority of electromobiles are propelled by series motors, a smaller number by compound motors, some very successfully by separately excited motors, and very few by shunt motors. The great majority of motors in actual use have four poles.

The principle of separate excitation has some advantages. It enables great torque or rotary pull to be obtained, without as much loss in the windings of the field magnets as is involved in the case of the series motor. In the separate excitation method of arranging, two or four cells are usually connected separately to the windings of the field magnets, the main battery supplying current to the armature. With the armatures in series an excellent differential gear is produced, while with the armatures in parallel, which only occurs at high speed, a steadying effect tending to keep the car straight results. This arrangement is employed in the cars of the Accumulator Industries, Ltd. The separately excited field motor, in addition to possessing, as already stated, certain of the advantages of the series motor, enables a very agreeable variation of speed to be obtained economically between the regular speeds by inserting resistance into the field magnet circuits. This acts like the accelerators on a petrol car.

According as one motor or two are employed, the groupings which the controller is arranged and designed to effect will of necessity vary also. Where a single motor is employed, unless it be compounded and used in some such way as in the Krièger system, differences of speed must be arranged for by grouping the battery cells in different arrangements. Thus a position of the controller will be arranged for which puts all the cells in series on to the motor. Running on the flat this will give the highest speed. The next lower speed will naturally be obtained by putting the cells in two bunches in parallel with one another; that is to say, the positive terminals of each half battery will be connected together to one brush of the motor, and the negative terminals connected together to the other. This will provide half the pressure of the whole battery, and as the speed of the motor at the same load is dependent on the pressure at which the current is supplied to it, the car will travel more slowly. Lower speeds are produced by similar groupings giving lower pressure. Where two motors are employed a smaller number of groupings of the cells may be adopted, or double the number of speeds obtained with the same number of cell groupings, as with each cell grouping the motors may be arranged either in series or parallel with one another. In this case the maximum speed will of course be with the cells in series and the motors in parallel, the lowest speed with the motors in series and the cells grouped so as to give the lowest pressure. Generally one of the lower speeds that is, with the cells arranged to give the lowest pressure will be used for starting; as the motor, owing to its taking a large current before its speed increases, should not be supplied with current at a high pressure. As the batteries also, when arranged in parallel groups, are able to yield a heavier current, the arrangement is mutually satisfactory to both batteries and motors. For reversing, the controller is brought into such a position as to send the current the reverse way through the motor.

An electric car does not require change-speed gear because it contains practically a gear in itself. It accommodates itself to the load and does its best at any given load, or by varying the electric pressure it may be caused to increase or diminish its power within limits. Thus a series or separately excited motor can develop proportionately more torque in overcoming an increased load than it was developing before the load was enlarged. This effect may be increased by arranging the field magnets with a large amount of iron in their cores, and working under ordinary circumstances with a small magnetic density. On heavy loads, as when going uphill, the increased magnetic intensity produced by the increased current passing through the windings of the field magnets increases the torque, and at the same time tends to check the actual speed of the motor, thereby giving what may be looked upon as an electric gearing effect.

Another point of interest is that a motor when being driven becomes a dynamo, and is capable of charging accumulators. Thus a suitable motor, when the car is running downhill, will give back current to the cells—will in fact 'recuperate' them. A good deal of misunderstanding has arisen in connection with this question of recuperation. It is

Fig. 11

not merely that some of the energy which would otherwise be lost in friction produced by putting on the brakes is, as it were, caught and put back into the cells, but that the conditions of running are more favourable to the battery, when occasional short charges are put into it in this way, than when it is subjected to continuous discharge. The car is also rendered more controllable. It is advisable for every electric car to be provided with a voltmeter and ammeter in view of the driver's seat, so that he may know the condition of his cells and the amount of current he is taking out of them.

Fig. 11 shows a side elevation of a typical modern electric car—the 'Powerful' of the British Electromobile Co., Ltd. This car made the record long distance run in this country and an extended tour. It is of the Krièger type, and has a motor mounted on each of the front wheels, which they drive

Fig. 12

by spur gearing. It has two batteries of Leitner accumulators, one under the bonnet and one under the rear seat. The controller for arranging the connection between these latter and the motors, and grouping the parts of the motors as required, surrounds the vertical steering pillar.

Fig. 12 shows the running gear of one of the City and Suburban Electric Carriage Company's electric vehicles. Two series motors mounted on the fixed rear axle drive by pinions on to gear rings secured to the spokes of the wheels. This Company has adopted a system of trading by which for an annual payment of 186l. a purchaser of any vehicle can have it kept practically new for an indefinite period.

In accordance with the practice that has been observe d in treating of other types of automobile vehicles, it is proposed to give a short description of the ills and misfortunes to which electromobiles are subject, together with some very cursory directions for detecting them and effecting their cure. To begin with, however, it may be observed that an electromobile is much less liable to disarrangement of its functions than almost any other type of automobile. When the car is finished and provided with properly designed and geared electromotors, and furnished with an adequate battery and properly constructed controller and connections, it very rarely happens that anything gets out of order, and practically mishaps can only occur when a heavy electric vehicle is being forced up a steep, hill either through heavy mud or at irrational speed. There is no doubt whatever that the trustworthiness of an electromobile is one of its most attractive characteristics, and that it comes nearer to being a 'fool proof' vehicle than any other type of automobile.

If anything goes wrong with an electromobile it is well-nigh bound to be something happening either to:

The electric motors

The battery

The controller, or

The connections.

Of course, in addition to these things, gears may get out of order, tyres may puncture or come off, axles may break; but such misfortunes are common to all cars, and it is not proposed to treat of them here. As regards the gearing breaking or stripping, that is comparatively inexcusable in an electromobile, as the kind of effort which an electric motor exercises is a steady and continuous one, and the gearing is subjected to none of the jerks and jars which occur when an explosion engine is the motive power, and when change-speed gear is varied by an inexperienced hand.

The motors may fail from various causes. The most common of these is burning up, due in general to forcing too much current through them either to get up a steep and muddy hill, or less generally in an attempt to run the vehicle up to or beyond the due limit of speed. When the motor proposes to bum up there is no doubt at all about the fact. It begins usually some minutes previously to diffuse an agreeable perfume, not very dissimilar to the smell of incense, the result of the vaporisation of the shellac which is used in the insulation of the windings. It is quite possible for a motor to diffuse this perfume without actually burning up, this merely being an evidence that the motor is getting extremely hot; but the wise man when he perceives it will usually, if possible, put his controller into position to give less current to his motors. Burning up may take place either in the field magnets or the armature, not very often in both at once. It nearly always means rewinding the part affected an expensive performance. The burning up of an armature, however, is always much worse than the burning up of a field, as nearly everybody can wind a field, but an armature winder is a skilled mechanic, who commands high wages and often puts on airs. Sometimes, without actually burning up, the heating will cause failure of insulation between the windings of a motor, and then the motor, though continuing to run, will take considerably more current for the same power developed. It is better to rewind or get rid of a motor in this condition.

A motor may under circumstances refuse its work altogether, that is to say object to starting, though in a well-constructed car this is a very unusual occurrence. It may be due practically to two causes: to the brushes not making contact on the commutator, which can easily be seen by pressing on the brushes with the hand, or to imperfect contact between some of the segments of the commutator and the windings, where they are soldered into it. The best way to ascertain whether this latter defect occurs is to get a dry cell and a galvanometer or voltmeter, and test the motor through from section to section of the commutator. If a point is found in which no current passes through the motor from a segment of the commutator, the conductor running to that segment ought to be properly sweated, i.e. soldered, in.

It is, perhaps, as well to explain the manner in which this kind of testing should be conducted, and the principle on which it is based; as a great number of possible faults in an electric vehicle may be detected by its means.

For an electric current to pass from the positive terminal of a battery or dry cell to the negative there must be a metallic or conducting circuit from one to the other. If the galvanometer or voltmeter be included in this circuit, then if the metallic connection be all right, on making contact to the dry cell or other battery used, the needle of the galvanometer will move. Thus, let a flexible wire be attached to one terminal of the cell, the other end of it being preferably soldered to a point mounted in a wooden handle, and let this point be pressed upon one section of the commutator. The other terminal of the cell should be connected to one terminal of the galvanometer, and the other terminal of the galvanometer to a similar metal point by a flexible wire to that first described, also preferably mounted in a handle. If this be then pressed upon the section of the commutator which should correspond with the first, then, if all be right, the current will pass from the positive of the cell through the coils of the motor, through the galvanometer, back to the negatives of the cell, and the galvanometer needle will move. This shows that there is metallic connection from one point to the other. If this connection be imperfect the needle will not move.

Failure occurring in the batteries is practically never a sudden affair. It generally makes itself apparent by gradual diminution of capacity that is to say, the batteries refuse to give their proper amount of current for the required time, and this state of things gradually gets worse and worse. It is nearly always due to the batteries being forced to give more current for prolonged periods than they should, and generally results from the dropping out of paste from the positive plates, or to an interference with the continuity of the paste and the conductor. In badly mounted batteries that is to say, those in which the plates are set up either without a bridge or without a sufficient bridge failure may be due to short circuiting, owing to some of the active material falling out on to the bottom of the cell, and bridging the plates across. In general, however, the failure of a well-constructed battery, within the period for which it ought to run, is due to overwork.

It is well at intervals to employ a cell-testing voltmeter to test all the different cells, as it may sometimes happen that one or two cells get into bad condition. If their voltage is low towards the end of a run the main battery will be charging them round the wrong way, and they will in consequence be injured. If the same cells persistently show low voltage, they ought to be removed and examined. Hence easily detachable connections are advisable.

The injury nearly always occurs to the positive plates. Consequently a battery that has been maltreated may practically be rendered as good as new by renewing the positive plates. As the connections, battery boxes, and negative plates are not influenced, renewal of the positive plates can generally be effected at a reasonable price.

All battery connections should be seen to every day, and if any sign of oxide or verdigris appears should be promptly removed and cleaned. They should also be kept thoroughly tight. Perhaps the proprietor of an electric vehicle would do better, if he suspects his batteries of being in an unsatisfactory condition, to get them inspected by the builder of the cells, as it requires some special experience to know whether a battery really requires renewal, whether the positive plates only should be renewed, or in fact how it should be treated.

Failure of connection between the controller, cylinder, and the contact springs may also give rise to stoppage. That is very easily tested by putting the controller in the position in which the car refuses to move, and testing the contact springs by pressing them against the cylinder. If the car then goes on they require tightening.

If the batteries and motors are all right in any particular position, and the car refuses to move even when the controller is tested in the above-described manner, there may be failure in the connections. Whether this is so or not can to a certain extent be judged by noticing whether the controller sparks when moved from one position to another. If it does so the current is passing and the connections are presumably all right; otherwise the connections are probably faulty. They can be conveniently tested with a dry cell and galvanometer in the same way as the motor is described above as being examined. Heating at any point is usually the effect of a loose contact.

If the conducting cables are badly arranged, so as to rub on any metallic portion of the car, the insulation may be worn through and short circuiting ultimately result. It is therefore of the greatest importance to see that no such contact of the cables with any portion of the car ever occurs.

Similarly, accumulator connections should preferably only be made to the nesting-boxes and the connections with the cables made from contacts on these.

Electric vehicles can be charged in two ways, either by connecting the car directly to a suitable source of current, or by employing two or more batteries, one of which is always kept charged at the charging station, the arrangement being that when the battery on the car is run down it is taken out and a freshly charged battery inserted. This latter arrangement is usually only practised in stations or 'garages' where a number of cars are kept. Charging on the car is a much more common proceeding. For this purpose the car should be provided with a plug and short length of cable, which should be carried with it. It is also advisable to have variable resistance. In charging the battery the cells are of course all arranged in series. Forty-four cells are often selected as the number employed, as such a battery can be conveniently charged at any ordinary direct current electric light station, which are usually designed to supply current at 110 volts or more. It is as well that every car should be provided with a switch which can be used for interrupting all connection between the cells and the motors of the vehicle while charging, as otherwise somebody moving the controller may cause the car to start off suddenly at full speed and take a header into a wall or a piece of moving machinery. A lock for the controller is nearly as good.

It must be borne in mind in charging a battery of accumulators that the voltage required is in excess of that which the cells give when discharging. Thus a forty-four cell battery will give about eighty-eight to ninety volts for car propulsion, but it will require something over one hundred volts to charge it. The variable resistance mentioned above should be inserted in the circuit so as to enable the amount of current charged into the cells to be controlled. When it is desired to economise the time occupied in charging, more current may be run in during the earlier stages, the amount being gradually diminished towards the end of the charge. The approach of the completion of the charge is marked by the 'gasing' of the cells—that is, the dilute acid fizzes more or less like soda water. The strength of the acid also increases as the cells are charged, and the increase may be used to show when charging is complete. A small glass vessel called a hydrometer, which can be inserted into the acid, and indicates its specific gravity, is used for this purpose.

Of course batteries can be charged from any electric lighting circuit that gives the necessary pressure or a higher one, as the forty-four-cell battery could be charged from a two-hundred-volt circuit, but a great deal of resistance would have to be used in series with the battery, which consumes energy, and hence makes the process an expensive one. The cost would be very nearly double that of charging from a hundred-volt circuit.

In conclusion a few words may be devoted to the characteristic features, position and prospects, of the electric vehicle.

The Electric Car on which the Marquis de Chasseloup-Laubat, on March 4, 1899, covered a kilometre, from rest, in 483/5 seconds, and with flying start in 384/5 seconds

Since the first long-distance run to Brighton on a single charge was made by the Electrical Undertakings car, in June 1898, there is no doubt that the position of electromobilism in this country has steadily improved. The electric vehicle, however, does not enjoy anything like the same amount of popularity in this country, even at present, that it does in America and France. This was until recently no doubt partially due to the comparative dearth of charging stations. With the inauguration of a wise and sensible policy such as that initiated by the City and Suburban Electric Carriage Co., Ltd., and referred to above, and with the increase in the number of charging stations, and their more general availability, the prospects of the electric vehicle are bound to improve.

With cars built as they now can be and are, to run a hundred miles on a single charge, the electromobilist can practically go

City and Suburban Co.'s Electric Brougham

anywhere. All he need do is to exercise a certain amount of foresight, and arrange that the end of his day's run lands him in the neighbourhood of a charging station.

The car has many very great advantages. As already pointed out it is comparatively 'fool-proof.' It is practically noiseless, or can be made so. It has great flexibility and changes from one speed to another without jolt, jerk, or jar. The driver is not compelled to keep his eye on a water-gauge or the contents of a fuel tank, or to manipulate change-speed gears, sparking levers or the like. All he need trouble about is his steering gear and the position of his controller, with a very occasional glance at his voltmeter and ammeter. Above all the electromobile has no odour of its own, nor does it incur any danger of being run in by intelligent police constables for showing vapour and at the same time travelling above four miles an hour.