Brookes Four Cylinder Gasoline Engine Direct Connected to Dynamo.
After the zinc container is filled with the electrolyte and pulverized carbon, the top of the container is closed hermetically by means of sealing wax. Granulated carbon is used for it presents a large surface to the electrolyte, reduces the internal resistance of the cell, and therefore increases the current output of the battery.
As soon as the battery starts generating current, polarization begins, with the liberation of hydrogen gas. If the cell is discharged at a high rate, the manganese dioxide will be unable to absorb all of the gas, and consequently pressure will be erected within the cell. The greater the rate of discharge, the greater will be the amount of hydrogen set free, and the higher the pressure.
If a short circuit exists for any length of time, the pressure of the excess hydrogen will speedily ruin it, as the cell will puff up, or even burst under the pressure. If the rate of discharge be kept so low that all of the gas will be absorbed by the manganese, as soon as generated, the cell will furnish a steady current until the elements of the cell or the electrolyte are exhausted.
The steady current limit, or non-polarizing limit is about one-half ampere and if long life of the cell is expected, the current drain should be less than this amount. A good spark coil will develop a satisfactory spark on a quarter to one-half ampere, so that the demand of a good coil is well within the safe limits of battery capacity. The voltage of the average dry cell when in good condition is 1.5 volts on open circuit. When the cell is old or exhausted, the voltage falls rapidly when any demand for current is made on the cell, and the voltage also varies with the rate of current flow, the voltage decreasing with an increase of current.
As there is not much difference in voltage between a new and old cell when on open circuit, it will be seen that the ammeter giving the current output will give a more accurate determination of the condition of the battery. The voltage is independent of the size of cell.
The battery showing the greatest amperage is not necessarily the best for general use, as cells having an unusually high current capacity are generally short lived. The strong electrolyte used in high ampere batteries causes them to burn out or deteriorate rapidly when not in use.
Under ordinary conditions, a correctly proportioned No. 6 ignition cell should show a current of from fifteen to twenty amperes on short circuit when the cell is new, although higher results may be obtained safely with some makes of cells.
While the voltage is the same for all sizes of batteries, and depends on the material used in the construction, the amperes increase with the size of the cell, and the area of the electrodes.
If a cell does not show more than ten amperes on short circuit, it should be thrown out and another substituted for it, as the cell is liable to go out of commission at any minute when reaching this point of exhaustion.