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Big Battery

The following is taken from a publication titled "Technical Articles from the Exide News" which reprints interesting pieces about batteries in general and Exide batteries in particular. This article appeared during the early 1940s.

"We now give particulars of an Exide battery installed in a Sydney Telephone Exchange. The battery comprises two sets each of 24 cells, having a capacity of 6655 Ampere Hours at the 10 hour discharge rate. Each cell is 3ft. 7ins. long, 1ft. 8ins. wide, 3ft. 8ins. high, contains 45 plates and weighs approximately 1 tons or 72 tons for the 48 cells. The normal charge rate is 915 amperes.

In addition to these cells is a set of 7 Counter-Electro-Motive Force cells, each 4ft. 8ins. long, 1ft. 10ins. wide and 3ft. 6ins. high having 61 plates and weighing approximately 2 tons or 14 tons for the 7 cells.

The Counter-Electro-Motive Force cells are used in conjunction with the main battery to keep a steady voltage on the exchange and are automatically controlled by specially designed switchgear capable of carrying currents to 10,000 amperes."

In this type of early exchange, one battery was used to supply the exchange whilst the other battery was being charged (charge-discharge cycle). The fully charged battery could deliver about 56 volts but the exchange needed a constant 48 volts so 4 Counter-Electro-Motive Force cells were switched in series each "absorbing" 2 volts thus delivering 48 volts to the exchange. As the battery discharged the voltage dropped and the Counter-Electro-Motive Force cells were switched out of circuit until the main battery alone was supplying the exchange at 48 volts. The same Counter-Electro-Motive Force cells were used for both batteries when they were in the discharge cycle.

"This particular telephone exchange has been in operation since 1918 and the batteries have never failed to give the service demanded of them.

When you use the telephone, the electric current that carries your voice over the wire is supplied by an Exide battery.

You, perhaps, think of an Exide battery as the forty pound black box that saves your muscle in cranking your car and gives current for your lights on the road. But to the men in the large telephone exchange, an Exide battery is a huge thing that would fill an ordinary house, for each cell frequently weighs as much as 3 ton, and there are usually 24 cells to a battery. To give an idea of the size of one cell in this Telephone Exchange, we reproduce the attached drawing showing one cell against an average sized male."

The cases of these early batteries were made of dovetailed timber which were lead lined. Glass was used to separate plates and across the top to reduce evaporation and the entry of dust and dirt. Due to the lack of air-conditioning, the open nature of the cells and the continuous charging and discharging, distilled water had to be added at least weekly and sometimes more often.

Today, the largest cells used in telephone exchange batteries in Australia are 3200 Ampere Hour capacity and each cell is approximately the size of a bar fridge. These cells are still "flooded", that is contain acid in liquid form. All new installations are of the "non-spillable" Vented Recombination Lead Acid (VRLA) which come in many sizes up to 1000 Ampere Hour capacity and can be used in any position (except up-side-down).

From: Reprints of Technical Articles from Exide News, 1930 - 1952, with additional comments by the Editor.

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