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Causes of Plate Deterioration.—Plates may get in poor condition from the following causes: 1st, Impure Electrolyte.— Either a poor quality used at the start, or through the use of impure water or through foreign substances getting into the cells. The remedy in this case, if the plates are physically in fair condition, is to replace the old electrolyte with new, the cells being in a discharged condition, and then thoroughly charge the battery. 2nd, Short Circuits. These are not frequent if the sediment is removed before it touches the plates, as the wash of the electrolyte in most vehicle batteries resulting from the movement of the car would tend to free them. If they do occur, the cell should be completely dismantled, the plates straightened and the cell assembled again, the separators being completely replaced. The cell should then be thoroughly charged. 3rd, High Temperature.At temperatures above 100° F. corrosion is quite rapid, and this limit must not be exceeded. If possible, the temperature should not exceed 90° F. The positives may be sulphated considerably from this cause and the plates grown abnormally and distorted. If they are thoroughly corroded they must be replaced; if not, they should be straightened and thoroughly charged. The conditions should be changed so that the battery will not again be subjected to the high temperature. 4th, Standing Discharged.The positive plates especially may be badly sulphated from this cause. The indication of this condition is a light color of the positive plates, possibly with blotches of a grayish color. The remedy in this case is also complete charge, though care must be taken that too much active material is not thrown off during the charge. Under these conditions the active material is granular and non-cohesive, so care is needed in charging and discharging to restore the plates to efficiency.
Value of Cadmium Readings.—It is possible to make tests to determine the relative capacity of the positive and negative plates of any cell by means of a neutral electrode. Cadmium is well adapted for this purpose, and while such tests are not ordinarily made with small batteries they are very useful in determining the condition of large cells. The cadmium element consists of a stick of that material about the size of a lead pencil and 6 inches
long, which is inserted into a soft rubber tube. Before inserting the cadmium stick, the rubber tube should be perforated with a number of holes about 1/16 of an inch in diameter. The rubber tube should extend at least 1/8 of an inch beyond one end of the cadınium element. A small flexible rubber-covered copper wire should be soldered to one end of the cadmium stick. This wire may be joined to the negative pole of a voltmeter. A regu
lar contact "sticker,” or “stabber,” such as shown at Fig. 21, is connected to the positive pole of the voltmeter.
After the total cell voltage throughout the battery is taken in the regular way, cadmium readings can be taken by inserting the rubber-covered end of the cadmium into the acid of the first cell, being sure that the bare cadmium stick does not touch either of the plate groups. Press the “sticker” leading to the positive pole of the voltmeter against the positive cross bar of the cell and note the reading. The difference between the reading of the positive group and the cadmium and the total cell voltage already taken will represent approximately the negative cadmium reading. For example, if the positive cadmium reading is two volts and the regular cell voltage 1.85, the negative cadmium would be 0.15. A positive is discharged when its cadmium reading at its
regular catalog discharge rate is about 1.95, and the negative when the cadmium reading is approximately 0.25 volt. At these values the cell voltage would be 1.7.
As a cell discharges the positive cadmium reading decreases, while the negative cadmium reading will increase.
The curve shown in Fig. 22 illustrates the discharge of a cell in which the positive plates are low in capacity. Note the rapid drop in cell and positive cadmium voltage after three hours but the slow rise
Fig. 22.—Curves Illustrating the Discharge of a Cell During a Cad
mium Test in Which the Positive Plates are Low in Capacity.
in the negative cadmium voltage. All voltage readings must be taken while the battery is discharging at its catalog discharge rate. The readings should be carefully filed and compared with previous tests. In this way any cell not in condition will be readily found.
Making Electrolyte.—Electrolyte, as used in all lead plate types of batteries, consists of a mixture of pure sulphuric acid and
distilled or other pure waters. Concentrated sulphuric acid is a heavy, oily liquid, having a specific gravity of about 1.835. A battery will not operate if the acid is too strong, and it is therefore diluted with sufficient pure water to bring it to a gravity of 1.270 to 1.300 for a fully charged battery. Stronger electrolyte than this is injurious. To prepare electrolyte from sulphuric acid of 1.835 specific gravity, mix with water in the proportions indicated in Fig. 23 for the desired specific gravity, taking the following precautions:
Use a glass or earthenware vessel, never metallic.
Stir thoroughly with wooden paddle and allow to cool before reading the gravity.
Both the water and the sulphuric acid used in making electrolyte should be chemically pure to a certain standard. This is the same standard of purity as is usually sold in drug stores as “CP” (chemically pure), or by the chemical manufacturers as “battery acid.”
Electrolyte made from sulphuric acid meeting the following specifications will be satisfactory:
Sulphuric acid to be high grade, either the so-called "Brimstone Oil of Vitriol” or “Contact Process Acid” made from sulphur of good quality. Must be water white in color and show no sediment on standing. By analysis, impurities must not exceed the following: Platinum
0.001% Nitrogen in any form
0.01 % Copper
As great care is exercised in the manufacture of storage battery plates and in the furnishing of acid to secure a high degree of purity, obviously attention should be paid to the purity of the water used both in the dilution of concentrated acid, if this is