The Automobile Storage Battery: Its Care And Repair

by Otto A. Witte

Having taken a reading, the bulb is squeezed so as to return the electrolyte to the cell.

Care should be taken not to spill the electrolyte from the hydrometer syringe when testing the gravity. Such moisture on top of the cells tends to cause a short circuit between the terminals and to discharge the battery.

In making tests with the hydrometer, the electrolyte should always be returned to the same cell from which it was drawn.

Failure to do this will finally result in an increased proportion of acid in one cell and a deficiency of acid in others.

The specific gravity of all cells of a battery should rise and fall together, as the cells are usually connected in series so that the same current passes through each cell both on charge and discharge.

If one cell of a battery shows a specific gravity which is decidedly lower than that of the other cells in series with it, and if this difference gradually increases, the cell showing the lower gravity has internal trouble. This probably consists of a short circuit, and the battery should be opened for inspection. If the electrolyte in this cell falls faster than that of the other cells, a leaky jar is indicated. The various cells should have specific gravities within fifteen points of each other, such as 1.260 and 1.275.

If the entire battery shows a specific gravity below 1.200, it is not receiving enough charge to replace the energy used in starting the engine and supplying current to the lights, or else there is trouble in the battery. Use starter and lights sparingly until the specific gravity comes up to 1.280-1.300. If the specific gravity is less than 1.150 remove the battery from the car and charge it on the charging bench, as explained later. The troubles which cause low gravity are given on pages [ 321] and 322.

It is often difficult to determine what charging current should be delivered by the generator. Some generators operate at a constant voltage slightly higher than that of the fully charged battery, and the charging current will change, being higher for a discharged battery than for one that is almost or fully charged. Other generators deliver a constant current which is the same regardless of the battery's condition.

In the constant voltage type of generator, the charging current automatically adjusts itself to the condition of the battery. In the constant current type, the generator current remains constant, and the voltage changes somewhat to keep the current constant. Individual cases often require that another current value be used. In this case, the output of the generator must be changed. With most generators, a current regulating device is used which may be adjusted so as to give a fairly wide range of current, the exact value chosen being the result of a study of driving conditions and of several trials. The charging current should never be made so high that the temperature of the electrolyte in the battery remains above 90° F. A special thermometer is very useful in determining the temperature. See Fig. 37. The thermometer bulb is immersed in the electrolyte above the plates through the filler hole in the tops of the cells.

Batteries used on some of the older cars are divided into two or more sections which are connected in parallel while the engine is running, and in such cases the cables leading to the different sections should all be of exactly the same length, and the contacts in the switch which connect these sections in parallel should all be clean and tight. If cables of unequal length are used, or if some of the switch contacts are loose and dirty, the sections will not receive equal charging currents, because the resistances of the charging circuits will not be equal. The section having the greatest resistance in its circuit will receive the least amount of charge, and will show lower specific gravity readings than for other sections. In a multiple section battery, there is therefore a tendency for the various sections to receive unequal charges, and for one or more sections to run down continually. An ammeter should be attached with the engine running and the battery charging, first to one section and then to each of the others in turn. The ammeter should be inserted and removed from the circuit while the engine remains running and all conditions must be exactly the same; otherwise the comparative results will not give reliable indications. It would be better still to use two ammeters at the same time, one on each section of the battery. In case the amperage of charge should differ by more than 10% between any two sections, the section receiving the low charge rate should be examined for proper height of electrolyte, for the condition of its terminals and its connections at the starting switch, as described. Should a section have suffered considerably from such lack of charge, its voltage will probably have been lowered. With all connections made tight and clean and with the liquid at the proper height in each cell, this section may automatically receive a higher charge until it is brought back to normal. This high charge results from the comparatively low voltage of the section affected.