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advantage in building the battery types intended for automobile engine-starting work.
Storage-Battery Locomotives.—The conditions under which storage batteries used in mine locomotives or those intended for industrial work operate call for very careful selection and installation. The battery should always be mounted in the locomotive se the flat of the plate comes against the direction of motion. When the plates are thus assembled in the jars there is no opportunity for displacement, as would be the case with the plates arranged so the edges were facing the direction of movement. A cushioning effect is obtained by the electrolyte against the plate, which is very valuable, as the many shocks incidental to the none too gentle coupling and uncoupling of the locomotive to the loaded cars and shocks due to sudden starts are thus minimized. Rubber cell jars should be considerably heavier for this service than are ordinarily used in automobile work. The trays in which the cells are carried should be provided with substantial partitions so the jars at the ends of the trays will not be subjected to the inertia of the remaining cells. Inasmuch as metal enters so largely into the construction of locomotives, the battery trays should be thoroughly insulated from the frame and should be securely blocked in place so there will be no possibility of shifting. The battery should be mounted apart from the propelling machinery or motor, and so mounted on the frame to permit drainage of the battery compartment. The illustrations at Fig. 76 show typical locomotives for mine and industrial use, and in one the sides of the battery compartment are dropped to show how the battery is mounted and how accessible the trays are.
In case it is desired to make a rough approximation of the size of battery needed, the Electric Storage Battery Company gives a method that is very simple, and while the figures are approximate, they enable the engineer to determine the type and size of battery best adapted for the individual requirements. If boosting charges can be given then batteries of lesser capacity can be used than if the machine must operate for more extended periods on one charge. The number of cells used will, of course, vary with the type of locomotive and its weight. A three-ton locomotive can be operated on 48 MVII-type cells, and by increasing the capacity of the cells by making them larger the same number can be used for a twenty-five-ton locomotive for freight-yard use and shifting loaded freight cars over tracks in city streets during the night hours when the traffic is light. Of course, the charging current available must be taken into consideration. A 48-cell battery can be charged directly from a 110-volt direct current. In some cases, where a power circuit of 220 volts direct current is used, more cells may be provided and charged directly from the power line. An example of this kind is an eight-ton mine locomotive equipped with 100 MV19-type “Iron Clad” Exide cells.
How to Figure Mine Locomotive Battery Capacity.—The figure of 30 pounds per ton, which is taken as the tractive effort required to overcome friction, is considered sufficient to include an allowance for curves which may be encountered as well as some allowance for tracks that are not up to good railroad standard. The efficiency of 663 per cent. assumed between the battery and locomotive wheels includes an allowance for rheostatic and braking losses as well as for motor and gear losses. Different values may be assigned these constants, as the judgment of the engineer making the approximate calculations may dictate, without changing the method of figuring. The typical round trip should be divided into as many parts as have different characteristics, such as different weight of train and different grades to be encountered. The requirements of each of these sections in each direction of haul should be treated separately in the following manner:
(a) Determine the tractive effort required for level running by multiplying the weight of the train in tons, including locomotive by 30 pounds per ton to get the tractive effort to overcome friction on the level.
(b) Find the tractive effort for grade, if any is encountered, by multiplying the grade expressed in per cent. by 20 and multiplying this by the weight of the train in tons, taking this figure as positive for up grade and negative for down grade.
(c) Add the tractive effort level running and the tractive effort for grade to get the total tractive effort. If the sum is negative, it means the train is coasting and no power is required.
(d) Multiply the total tractive effort by 3 to get watt-hours battery per train mile. (1 watt-hour equals 2.655 foot-pounds, which is very nearly 12 a mile per pound; tractive effort X 2 = watt-hours per train mile at the locomotive wheels. Assuming 663 per cent. efficiency between the battery and the wheels, we have
tractive effort X 2
.66 = tractive effort X 3 watt-hours
train mile.) (e) Multiply the watt-hours per train mile by the number of miles of total operation on this section of the track in this direction to get the watt-hours required for this portion of the operation. Repeat the above for all sections of the track and in both directions.
(f) Add the watt-hours required for all portions of the operation, and the sum of these gives the total watt-hours of battery capacity required.
(g) Divide the total watt-hours by the voltage of the battery (the number of cells multiplied by 2) to get the ampere-hours of battery capacity.
(h) Divide the ampere-lours of battery capacity by 31.5 to get the number of positive plates per cell. The figure 31.5, which is the 41/2-hour capacity of a positive plate in ampere-hours, can only be used when there are at least 5 cycles of operation approximately evenly distributed over 41/2 hours or longer.
(i) Multiply the number of positive plates by 2 and add 1 to get the number of plates per cell.
The example which follows considers only one case, and, of course, applies only to the conditions stated. Each individual application must be considered with full realization of the conditions obtaining, but the procedure to be followed is substantially the same as outlined in any case. In any event, it is always well to consult the engineering department of the battery maker before using batteries for any purpose, as this results in securing advice that will assure a successful installation.
Example.—Assume 600 feet level track and 800 feet of 1.2 per cent. grade, a 3-ton locomotive, a 15-ton trailing load in the
direction against the grade and 6 tons trailing load in the direction with the grade, 20 round trips per 8-hour day, 48-cell battery.
This round trip can be considered in three parts:
Third, all level running can be grouped, using the full distance and the average load 1,200 feet level, 13.5-ton train.