H. L. Strong

The history of the storage battery is older than that of the modern steam turbine, and its application is. broader; but in either ease there seems to be little reliable data or information obtainable which will throw much light on their economic operation or reliability. The reasons for this seem to be that they are compara tively new and the manufacturers are "saying little and sawing wood," hoping, in time, to improve and per-fect their product to the end that they may be more efficient, longer lived and better fulfill the requirements and expectations of those who may invest their money in such apparatus. In many instances, both in large and small installation , storage batteries are proving very satisfactory in operation, and are good investments. One company, at least, in the United States is installing them in many large plants and taking their pay on a profit-sharing plan.

This seems to prove that, where conditions are favorable, a battery will reduce operating expenses. There are other cases where a battery is a great convenience, or where desirable results can be obtained with it which are difficult or impracticable without it. Most of the failures and consequent disappointments in battery installations are due to lack of knowledge of their limitations and requqirements. By this i mean that batter-ies are sometimes installed and operated under adverse conditions, and then storage batteries in general are condemned as being expensive, troublesome and unreliable. The conditions and requirements are so varied that it is not practicable to attempt to cover the ground thoroughly, especially in a short article, but a few lines in this connection may not be amiss.

As a few of the puropese for which storage batteries are used may be mentioned: Telephones, wireless telegraph installations, experimental work, driving automobiles and electric launches, firing submarine mines, lighting cars, yachts and other small vessels, lighting private residences, etc. The principal purpose for which they are used in electric light and power plants, and that for which they are best adapted in this line of work, is for helping the generators on peak loads and acting as a reserve for emergencies. In direct current systems., where the load is continually fluctuating, as in railway work, storage batteries give good results, for they are not only availible for peak load periods and emergencies, but also keep the voltage steadier and the load on, the generators more uniform. When used in this way they are connected to the line in parallel with the generators, usually at some distance from the generating station, and are said to "float on the line." When the line voltage is normal the battery is idle, but should the line voltage drop a little the battery will feed into the line. If the voltage rises above normal, current will flow to the batteiy and charge it. A booster is used to run the voltage up high enough to give the battery a full charge once per week and a normal charge oftener if necessary.

One of the arguments in favor of storage batteries in electric plants is that by their use less generating capacity is required in providing for peak load periods, and, therefore, it is possible to operate the plant with more uniform loads and consequently with better efficiency. Just how this pans out in practice is not easy to determine, and I have never seen any data or figures in this connection. Under laboratory conditions, the efficiency of a storage battery is said to be not over 85 per cent., and from my own observation and what I have been told by those who should know, the efficiency under working conditions probably averages about 75 per cent. However, there are practically no stand-by losses> and a battery is ready to take a load instantly. It is also capable of taking heavy overloads of short duration, although heavy discharges of any considerable duration are neither economical nor desirable. A further advantage is the slight voltage variation on vari-able loads as compared with a generator operating unaided under similar conditions. It is a mistake, except in special cases, to install a battery with the idea of letting it carry heavy loads, especially of long duration. When fully charge a battery will supply its normal rated capacity for about eight hours, but a battery that is worked to the extent of a normal charge and discharge every twenty-four hours will only have a life, at best, of from three to four years. This statement is based on recent information and the most reliable that I have been able to obtain. With proper care and an average daily discharge of 40 to 50 per cent., a good bat* tery will probably last about eight years.

It has been estimated that on an allowance of 10 per cent, per annum for depreciation and repairs, a good battery will last indefinitely. This estimate may strike an average, but I am inclined to think that it is none too liberal. It all depends on how hard, the battery is worked and how well it is cared for. Ordinarily a battery requires no more care than a generator, and may safely be left alone for hours, or, in many places, for days at a time. Most of us know how electric elevators or even motors for other purposes will play the mischief with the lights in a place where both are operated from a small generating plant. A storage battery, properly installed, in such a place will greatly improve the lighting service and cause the generating machinery to operate much more smoothly. As to whether a battery will prove a money-saving investment, in such a place is another question. However, the improvement in the service, and the greater security against total interruption of the service may be worth some extra expense.

In hotels and many other places there are periods during which but little current is used, and if a battery is installed the generating maehineiy need not be run for the light loads. If in addition to this, it is also practicable to reduce the labor expenses, there is little doubt but what a battery will give a good account of itself. As an example of this we have the following instance which is from actual practice:: A small electric plant is operated where there is a demand for current twenty-four hours per day, although the maximum load period is between sunset and 11 P. M. After 11 P. M. the load does not exceed 75 amperes, at 115 volts, and after 8 A. M. very little current is used, even during the short days. There are but two ways to handle this proposition. One is to run a generator continuously, and the other is to install a storage battery, and let one crew operate the plant by running the generators during the heavy load period and putting the light load onto the battery. In this particular case a $5,000 battery installation will save money in competition with any practicable scheme of operating a generator alone, because no attendant is required at the plant when the battery is discharging. If it was necessary to have some one at the plant all the time there would not be much to say in favor of the battery, although 1 believe it would be advisable to install a small battery to supply what little current is used during the daytime.

For private residence lighting, the storage battery is being extensively and satisfactorily employed. Some form of internal combustion motor is generally used to drive the generator for charging the battery. Some people even install a battery in their residence to guard against being left in the dark by failure or interrup-tion of the commercial supply of current. The battery is kept charged and is provided with an automatic switch, which will instantly throw the lights on to the battery, should the commercial supply be interrupted. The action of the switch is reversed when the commercial supply is restored. This is getting it down finer than most people consider necessary or are willing to pay for, but a battery in such service should last indefinitely, with but little expense and care.-'The National Engineer."