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electric motor is the simplest and most dependable source of power known, as it has but one moving part, and that is a rotating one. It is started reversed, stopped, and its speed varied by a simple wheel or lever. The battery may be easily stowed away under the floor boards, and if an Edison alkaline battery is employed, as in the launch shown at Fig. 83, the boat may be used in salt water just as well as fresh.
The alkaline battery gives absolute reliability to the electric launch by eliminating battery troubles. It is practically as rugged as the motor itself, and never disappoints the owner by going dead at critical periods. As there are no obnoxious, irritating or corrosive fumes given off by this type during charge, the charging may be done directly in the boathouse, without discomfort or the discoloration of metal trimmings on the launch or other vessels near it. During the period of idleness, which practically all pleasure craft of this kind experience, the Edison battery does not deteriorate. If charged before being laid up there will be ample power to run the launch many miles as soon as it is put into commission again. Those who have experienced the difficulties of "taking down,” packing and reassembling other types of batteries will appreciate this advantage.
Reliability is of paramount importance in every detail of wire: less telegraph apparatus. No doubtful or suspiciously weak device can be tolerated in a system upon which the lives of passengers and crew are likely to depend at any moment. And the auxiliary apparatus, the part that has to be ready at an instant's notice, but
may be left to take care of itself for weeks and months in the absence of emergencies, must be always ready beyond the possibility of a doubt. This reliability for auxiliary service is found only in the storage battery. During periods of idleness there should be no internal deterioration or wasting away of active material. Left charged, the alkaline battery may be recharged at any time without injury, no matter how much or how little of the previous charge has been used. In the severest storms or in case of collision there is no danger of broken jars or spilled electrolyte because of the strength of the steel construction. The lighting battery of small boats may, of course, be used to operate the wireless equipment, and often the auxiliary wireless telegraph battery of larger vessels is used for a reserve lighting system, including "police” lights around the decks and cabins and emergency lamps, in the running-lights. Lead-plate storage batteries have been used successfully for wireless work, but more care is needed as regards charging and discharging. Where the lighting battery is used for a wireless auxiliary, the use of the lights keeps the battery in proper condition, and the lead-plate type will give excellent service. Under conditions where the battery is apt to be neglected as regards regular charging and discharging, the alkaline type is the best.
Railway Switch and Signal Service.—An absolutely dependable source of power is needed for operating the block signals on our railways, and any failure of a semaphore or signal lamp to answer the control switch in the signal tower may result disastrously. The stored energy in a secondary battery is always available for this work, and either lead plate or alkaline batteries are suitable. The illustration at Fig. 84 shows the compact installation possible when batteries of the alkaline type are used. Lead batteries may be placed under a hood and the gases allowed to escape to the outside through a suitable vent if they are installed in the same room as apparatus that may be affected by fumes evolved during the charging process.
For railway signaling the alkaline battery has great advantages by reason of its electrolyte. There being no corrosive fumes or vapors produced, the batteries may be placed anywhere in the signal tower. There is no danger of injuring the most delicate apparatus, and many installations of such batteries are in the same room as and in close proximity to relays, generators, air-compressing machinery, etc.
The Stand-by Battery. The storage battery is used in many central stations as an emergency source of current to cope with unusual current requirements or to supply electricity for a brief time in event of damage to the dynamos or their prime mover. Among some of the conditions that would call for discharge of a stand-by battery would be interruption of current supply, due, for instance, to low steam or belt breakage in a steam plant or collection of ice in the forebay of a hydraulic generating plant. A breakdown of the generating machinery, putting some of the dynamos out of commission, thus reducing the plant capacity, would necessitate the use of the emergency current. An accidental opening of a transmission line or unexpected increase of load, such as is caused by everyone turning on the electric lights because of a sudden darkening in the daytime prior to a rainstorm, will also draw on the reserve source.
In the early applications of storage batteries to central station service one of the main objects sought was to improve the daily load factor in a steam plant by discharging the battery during the evening peak or period of heavy demand and recharging it during the hours of lighter load. This will result in a marked improvement in plant efficiency because power costs less if produced at a uniform rate. Where the peak is of short duration, the cost of a battery will be less than the added steam equipment it displaces, and as it conduces to greater economy of current production, this is a clear gain. When a charged storage battery is
Battery 4100 Distribution load at550 Volts
Nov.17th. Nov.18th. Nov.19th. Nov.20th. Nov.21st. Nov.22nd. Nov.23rd Nov. 24th.
Fig. 85.—How Stand-by Battery Helps on Peak Load Work. available as an auxiliary source of energy, it is always ready for emergency use, and this advantage is one of great value and can hardly be considered fairly on a purely pecuniary basis. The chart at Fig. 85 shows the operation of a battery in daily peak-load work. That at Fig. 86 shows how the output of a stand-by battery helped to handle an unexpected lighting load on a central station due to a particularly heavy thunderstorm.
These curves are merely graphic records of the amount of current used under certain conditions and in a given time, and are easily understood.
A stand-by battery uses rugged plate construction and is always composed of very large-size cells. Type H Exide plates, which are widely used in the larger installations, are 31 inches high by 15 5/16 inches wide. The grids are castings of leadantimony alloy and are provided with very heavy connecting lugs. When it is considered that a plate of this size may be called upon to discharge 600 amperes or more for several minutes, it will be realized that great care must be taken in proportioning the plates. The plates are hung from the cell tops by the plate lugs, which rest on vertical pieces of heavy glass arranged on either side of the tank, suitably notched to receive the plate lugs. The glass plates rest upon the reinforced lead lining at the bottom of the cell. A space of 34 inch is left between the outside negative plate and side of the tank at one end to permit the taking of hydrometer readings. An instance of the large size of the cells is the sediment space allowed, which is 12 inches in a type H cell.
A tank suitable for an Exide element having a capacity of 3,000 amperes for one hour measures about 225/8 inches long by 2112 inches wide. For a capacity of 6,000 amperes at the hour rate the length is increased to three feet, and for 9,000 amperes the length is nearly five feet. The height of such a cell from the floor to the busbar is about 512 feet, or high enough so the average man can barely look into the cell. The tanks are built of specially selected yellow pine, put together with glued, dovetailed and doweled joints. No nails or metallic fastenings of any kind are used. The lumber used is of sufficient strength to be entirely self-supporting. These tanks are treated with two coats of acidresisting paint inside and out.