CHAPTER XVIIELECTRIC VEHICLES
The construction of electrically-equipped cars is one which requires pages of explanations and illustrations to do it justice. The scope of the present work was originally intended to cover only gasoline-driven cars, so that this chapter, which in a measure only sets forth the manner in which such automobiles are built, will more particularly point out the mechanism which pertains to the operation, and the care needed to maintain them.
It is a long and difficult study to understand the electrical details necessary to build, repair, or maintain electric cars, but it is part of the general mechanic’s duty to understand where the troubles lie, when themechanismfails to respond, and most of the electrical devices are now so made that the ordinary mechanic is able to make repairs, even though he may not have a technical knowledge ofelectricity.
Within the past five years this type of automobile has been improved to such an extent that it is steadily gaining ground, and their use growingto such a degree that it may soon become a great rival of the gasoline car, especially for pleasure purposes.
There never has been any question as to the value of electric motors for traction service. Wherever a current of electricity can be distributed and transmitted to a motor, it is the most satisfactory method of moving vehicles, as has been shown in street railways.
Requirements.—But on individual cars, incapable of getting current from a system of wiring, the matter presents an entirely different aspect, and brings forth new problems, hence storage batteries must be resorted to, and this involves the consideration of many elements that may be ignored with the usual traction system.
Inventors have vied with each other to produce a type of battery that would possess at least three particular features of excellence, which may be stated as follows:
First. Exceeding lightness, proportioned to the energy exerted, and compactness of structure.
Second. A form of grid which will hold the matter, or active material, within it, and prevent it from disintegrating or falling out of the recesses into which it is pressed.
Third. To add to the life of the battery, or to the individual grids, or plates, which means thediscovery of new material, available to receive and accumulate the electric charge.
Gasoline-electric Trucks.—Of late someprogresshas been made in constructing a type of electrics in which a gasoline engine is used, that is connected up with an electric generator. The latter is used to charge a storage battery also mounted on the truck, and the storage battery supplies the motor.
The gasoline engine being connected with the electric generator is constantly in condition to charge the storage battery and may be set in motion, whenever the charge in the storage battery falls below a certain electro motive force. At other times the motor is at rest.
In this type the electric motor is connected with the axle of the vehicle, so that it is always ready for service whether the gasoline motor is running or not.
In the ordinary gasoline automobile it is essential that the motor must be maintained in service at all times, so that any derangement in that part of the system, which includes the mechanism intermediate the motor and axle, or the electrical devices, or the carbureter, means a dead car.
It is urged that by combining the two systems a much wider range of usefulness will be obtained, and practice shows such to be the case. It has,however, some defects, one of which is the great weight necessary to maintain the entire train of mechanism thus described.
The other disadvantage is the great first cost, although it is maintained that the decreased cost of maintaining the cars, while in use, is sufficient to warrant an increased cost in the selling price of the machines.
It is undeniably true that such mechanism means additional care, and is liable to add to the complications necessary to operate the system, and it is obvious that these considerations will prevent the use of this type in all small vehicles, whereas it may be most serviceable and available in heavy trucks for transporting merchandise.
The Current Used.—Storage batteries are charged with and use adirect current. The difference between a direct and an alternating current is, that in the first the current flowscontinuouslyover a wire in one direction, whereas in the latter it changes its direction, going, for an instant, from the north pole to the south pole, and the next instant from the south pole to the north pole, and for this reason it is said toalternate.
Mechanically-produced electricity.—The alternating method is the natural form of flow in a current derived from mechanism, as, for instance, by means of a rotating armature.
The electricity, in this case, is produced by a metallic body moving through a magnetic field, and as it passes through it takes up a certain electric impulse in one direction when the body approaches the field, and instantly reverses and flows in the opposite direction as the body recedes from the magnet, or field.
To convert this alternating phase into what is called a direct current, certain dynamos are provided with a commutator, and the function of this commutator, which has two oppositely-disposed fingers contacting therewith, is to so divert the alternating impulses that they will go over the wire in one direction only.
Current from Batteries.—Currents derived from batteries do not have the alternating flow. Instead, the movement is in one direction only, and it is in connection with this method of producing electricity that the termspositiveandnegativeare found convenient in describing the current, and the action of the mechanism operated by it.
Primary Battery.—The primary battery is one whichgeneratesan electric current. It comprises one or more pairs of plates, of which zinc and copper are examples, although other couples are found to be equally serviceable.
Two metals, or materials, such as carbon andzinc, are selected, which are termed electrical opposites, or which are positive-negative to each other, and when such couples are immersed in an electrolyte a current will be set up between the two plates, if a wire is attached to each plate, and the outer ends of these wires brought together, acontinuouscurrent will flow through the wire.
The electrolyte is a solution of water, with a small amount of sulphuric acid. Numerous acid solutions are made, and salt, or saline solutions are also frequently employed.
Secondary, or Storage Batteries.—These are also calledAccumulators, because they are so constructed that they will accumulate a certain charge. The termSecondaryis used to indicate the idea that they receive their charge from an outside source, in distinction from a Primary, which generates its own current.
After the secondary is once charged it then begins to work on its own account, the same as a primary battery.
Reversal of Currents.—When a storage battery is being charged from an outside source of electricity, the current flows within the battery in one direction; but the moment the outside source is discontinued, and the battery itself is connected up with mechanism, it becomes a source of energy, butthe current output is in the opposite direction.
The foregoing suggestions and features of explanation are thought to be desirable, in view of the following statements which pertain to the operation of machines of this type.
Charging.—One of the most important things in the care and handling of machines of this character, is the charging of the batteries. The utmost caution must be exercised to prevent derangement of the batteries.
Thus, to connect the positive pole of the charging generator with the negative pole of the storage battery would reverse the current and quickly destroy the plates.
Time Required, and Current.—It requires time to charge a battery, usually from twenty to thirty hours. The usual charging rate is about fifty amperes for a cell with a capacity of forty ampere hours, and the voltage should be somewhat higher than the normal voltage output designed for the battery when it is in action.
Troubles in Use.—The most frequent trouble in the use of batteries comes from short circuiting. This arises from two causes. The grids of the batteries are made of lead, cast in the form of flat plates, having small interstices, or openings, which are filled with various preparations, principally peroxide of lead.
Other types use iron and nickel, and many are composed of lead and zinc, but in any case the object of the grid is to receive and hold the active material, and present as large a surface of the minum as possible to the action of the electrolyte.
When in use the lead particles begin to disintegrate, more or less, and fall out of the cavities of the grid, dropping to the bottom of the cell. In time the material thus deposited will form a path between the two adjoining plates, producing what is called a short-circuit, and if the accumulation is not removed, the plates will be seriously injured.
Overcharging.—Sometimes the plates are overcharged, and the result is they will buckle, so that they touch each other, and a short circuit results. These hints are usually sufficient to indicate where the trouble will be found if the current measuring instruments indicate an excessive flow of current. In such cases the first direction to which the examiner turns is the battery.
The Circuiting.—It has been found necessary, in providing for the operations of an electric vehicle, that the motor should have a means whereby the speed and power of its output can be regulated.
This may seem a very simple matter, at first glance, because, without stopping to examine theproblem, and all the elements involved, it would be easy to settle it by simply giving the motor more or less current. To do so would turn the motor faster or slower.
In the gasoline car provision is made whereby, through the change speed gears, the engine gets the benefit of the leverage, by reducing the speed of the axle, relative to the engine shaft, at first speed, and this enables the motor to pull the car up steep grades, or over difficult roads, which it would not be able to do if the relative rotations were the same as at high speed.
Economy in Use of Current.—The same thing is necessary in the operation of the electric motor. The current must be so arranged that at certain periods it will be more effective than at others, and this effectiveness is generally wanted at times when the axles turn very slow, just the same as with the gasoline car.
This economizes, and prevents the waste of current. It is accomplished by connecting up the cells in such a manner that they may give a large voltage and small amperage, or a low voltage and great amperage, and in doing so will not detract from the efficiency of the battery.
Series and Parallel.—The device resorted to, whereby this may be accomplished, is in the manner that the cells are connected up with each other.In a general way, it may be said that thevoltagehas reference to the force, or pressure of the current, whereasamperageis the quantity which flows over the wire.
Each cell has a voltage of, approximately, one and a half volts, and it matters not how large the cell may be, the voltage is no more. The amperage, however, depends on the surface area of the plates comprising the active agents in the cell, so that each cell has, say one and a half volts, and ten, or twenty, or more amperes.
If a number of such cells are connected up in one way the output may be represented in high amperage, or in high voltage. If we have a certain number of cells, which, when combined, give ten volts and hundred amperes, the result would be 10 × 100, equal to 1000 Watts.
But they may also be so connected together that they will have an output of 100 amperes and 10 volts, the total of which is also 1000 Watts. Such a current would be put through the motor under ordinary running conditions, as a high driving power is not necessary.
But suppose it is desired to have a high or strong driving power; then the force of all the volts is required, so that one hundred volts are used, and only ten amperes.
The Connections.—This is brought about byconnecting up the cells inseries, or, inmultipleor inparallel. The series connection is where the cells are placed in a row, for instance, and are connected together so that the carbon plate of one cell is joined by a wire with the zinc plate of the other cell; or the positive plate of one is connected with the negative plate of the other, and so on.
In that case all the current generated in all the cells join and flow along in one stream, from one end of the battery to the other. But now, all the positive plates may be connected together with one wire, and all the negative plates may be connected together with another wire, so that these two wires will thus be parallel with each other, and the lead wires which go to the motor are attached to these two parallel wires, and would represent the parallel type of connection.
But it is the most common practice to divide the cell into two sets, each of which is called aunit. Each unit, having a certain number of cells, can also have them connected up in series, or in parallel, and the different parallel units may be connected up together, so as to form a connection which is inmultipleor inseries multiple.
Suppose there are eight units, each of ten volts, the motor would receive eighty volts. But now, if the cells are in parallel, or in multiple, as thecase may be, then the pressure at the motor is equal to that of a single unit, but the current flow is eight times that of the foregoing example.
The object, therefore, is to change the battery pressure on the one hand, and to produce the most effective action on the other hand, at the motor, and to do so make both battery and motor more efficient.
The Controller.—The device which performs this operation, at the will of the operator, is called theController, which changes the wiring connection from series to multiple, or the reverse.
The Controller is, in all probability, the most complicated piece of mechanism in the entire electric car. It must make an entire series of changes for each of the different speeds, of which there are frequently six.
The fields of the motor are also connected in series, or both series and multiple, so as to give a still greater efficiency. By this means the terminal points of the Controller may be turned, (1), so they will connect the batteries in multiple and the field windings in series; or, (2), the batteries in multiple and the fields in series multiple; or, (3), the batteries in series and the fields in series; or, (4), the batteries in series and the fields in multiple.
The figures in parentheses indicate the first,second, third and fourth speeds, respectively, and in such an arrangement two battery units are used, and also two motors.
The same rule as to efficiency applies with one motor, and two or more battery units. The battery unit may be of any desired number of cells, as stated.
The General Equipment.—Cars for pleasure purposes are of different types, such as runabouts, roadsters, victorias, coupés, broughams, and the like, provided with batteries which will permit runs of at least 100 miles on each charge.
Speeds.—The Controller will permit of speeds ranging from five to thirty miles an hour. The number of cells vary with different makes, from twenty to forty, and the number of plates in each cell average about fifteen.
It will thus be seen that the operating limit is wide enough to permit considerable latitude; but recharging stations are now found everywhere, particularly in the cities, and in the large towns.
Accessories.—A fully-equipped electric, designed for the greatest luxury and comfort, has two head lamps, two side, and a tail lamp, and one in the interior, a lighting switch to control all the lights, a ventilator, voltammeter, shaft odometer, for showing speed and distance traveled,complete outfit of tools, novelty toilet set and case, cut glass flower vase, eight day clock and mirrors suitably arranged within the body.
Seating Arrangement.—The broughams and coupés are especially arranged for comfortably seating the occupants.
In some the drive is at the rear seats, and the steering mechanism may be by means of a wheel, as in gasoline cars, or through a lever.
MostBodiesare now made with aluminum panels, and sashless quarter windows, with drop doors, front and rear windows, and rain vision front windows.
The Transmission.—This varies in the different types, and in the makes. Chains, bevel, or worms gears, are employed, and in some cars two of these types are used, some of these devices being the products of the highest engineering skill.
The rear axles of the smaller vehicles are generally of the semi-floating type, usually made ofvanadiumsteel, while the housing is drawn from sheet steel.
For heavier vehicles of the brougham style, the rear axles are full-floating and furnished with extra large annular ball-bearings in the hubs.