The Care of Accumulators

Radio Record, Volume VII, Issue 7, 25 August 1933, Page 25

The Care of Accumulators

Some Practical Hints on the Care and Maintenance of Accumulators.

ERHAPS the most neglected and most abused component of the majority of battery sets is the accumulator. Often it is never disconnected for recharge until signals have fallen off completely, and then the owner wonders why it seems to require recharging more often than it did when it was new. Usually the unfortunate charging station is blamed for not "putting enough into it.’ The accumulator is not at all a complicated device. and if given reasonable care will last for several years. If it is not properly looked after, however, its life will be considerably shortened. Strictly speaking, an accumulator does not accumulate electricity, for when it is fully charged there is exactly as much electricity in it as when it was fully discharged, and that isjust none! All that happens when the charging current is passing is that it changes the chemical constitution of the cell. When the two sets of plates forming the cell are joined together afterwards another chemical action takes place, causing a current to flow. Thus the difference between an accumulator, .or "wet" battery, and a "dry" battery such as we discussed last week, is that thongh the latter requires no preliminary charge in, order. that it may provide current, when it is run down it is no longer useful, whereas the former may be recharged again and again, However, both types cf batteries are similar in that they depend for their action on an electrochemical reaction. a If you examine your accumulator you will find that inside the container is a number of flat plates interleaved with another, the alternate plates being the same colour, one set being brown and the other grey. The clear liquid in which they are fmmersed is a solution of sulphuric acid, which, when the accumulator is fully charged, has a specific gravity of between 1.25 and 1.3. The Chemical Action. When the accumulator is connected to the receiver and the set switched on, an action immediately begins to take place between the plates and the electrolyte. The amount of water in the electrolyte is increased because part of the acid combines with the lead of the plates, leaving water in the electrolyte. The surfaces of. the plates thus change slowly to lead sulphate,

While the liquid becomes more nearly pure water, When the battery is recharged, the sulphate. of the plates combines with part of the hydrogen and oxygen in the electrolyte to form more sulphuric acid. The positive plates then become pexoxide of lead and the negatives are

left as spongy lead. This transformation continues until the sulphate is completely reduced, and the battery is then said to be charged. In this condition the colour of the positive plates will be a deep cliocolate, and of the negative a blue grey. The acid plays an important part in this process ,and as its active material changes, the condition of the acid when the cell is fully charged and when fully discharged is different. It is obvious that if both plates become covered with lead sulphate during discharge, this sulphate must come from somewhere, and actually it is withdrawn from the acid, which becomes weaker, When a cell is fully charged, however, the sulphate on the plates is reduced and the strength of the acid consequently increased, and that is why the acid is stronger in a fully-charged cell than in a discharged one, Testing an Aceumulator. As the amount of charging and the strength of the acid.are inter-connected, it is usual to test the condition of an accumulator by measuring the specific gravity of the acid, usually with a hydrometer. This device, which is illustrated above, ‘is a glass tube having a hollow

bulb with a weight at one end, and @ thin tube with a graduated scale at the other end. It isso weighted that when placed in a liquid, the point on the scale to which it sinks indicates the specific gravity of the liquid in which it is immersed. The hydrometer itself is usually mounted in a syringe, so that some of the electrolyte may be withdrawn from-ench of the cells for testing purposes. After the specific gravity has been read the liquid should: be carefully returned to the same cell from which it was drawn. If the gravity is between 1.250 and . 1.800, the cell is well charged. If it is between 1.200 and 1.250 it is at least half, but not fully charged, while a specific gravity between 1.150 and 1.200 indicates that the cell is nearly discharged. A gravity of 1.150 or below means that the cell is discharged to a point at which no further discharge should be allowed. Tests may be also made with a volt- _ meter, though this method is not nearly so accurate. The voltage of each cell should never be allowed to fall below 1.8 volts. Three Important Precautions. If an accumulator is seriously overdischarged or is left in a discharged or partly discharged condition for some time, the electrolyte will attack the

plates and produce a thick film of lead sulphate, which forms an insoluble and impervious skin over the surface of the plates. This white sulphate can be redissolved. with great trouble and difficulty by experts, but the cell can never be fully restored to its original state.

The top of the accumulator case. should always be kept quite clean and dry, for a covering of acid moisture on the top of the cell not only results in terminal corrosion, but provides a leakage surface between the positive and ‘negative terminals. The level of the electrolyte should never be allowed to fall below the top of the plates. Immediately the level becomes a little low, a small quantity of distilled water should be added to mike up the deficiency, which is caused by evaporation.