General Principles

The operation of the storage batteries is taken up first, because the equipment will not function successfully unless the batteries are properly handled.

In systems using the 1-FD type battery charging panel (Fig. 8), one set of storage batteries, called the H batteries, is used to supply magnetizing current to the receivers attached to the horns, and two other sets, F1 and F2, supply filament current for the amplifiers, exciting lamps, and indicating lights. The Fl and F2 sets are used alternately, one set being on charge while the other is supplying current. It is very important to always follow this practice, which is necessary in order to maintain the charge and ensure that adequate power will be available for every show.

In systems using the 4-0 type battery charging panel (Fig. 9), there are two sets of batteries, #1 and #2, supplying current for the horns, amplifier filaments, exciting lamps, and indicating lights. These two sets are used alternately, one set being on charge while the other is supplying current. It is very important to always follow this practice, which is necessary in order to maintain the charge and ensure that adequate power will be available for every show.

How long to run each set of batteries before putting it on charge will depend on the extent to which the equipment is used; furthermore, in the case of the 1-FD battery panel, the charging period may be different for the F sets as compared with the H set. This makes it impossible to lay down any general rule as to how long each set should run. It is therefore essential to use the hydrometer supplied with the batteries, to find out when each set needs charging, as explained below.

The charger is set by our engineer to give the proper charging rate, and this setting must not be changed except on his instructions. The charging switch of the AC charger may be kept on all the time, as the charger circuit is opened and closed by the switches on the battery panel.

The meters mounted on the panel are primarily for use by our engineer in adjusting the charging rate, and ordinarily the projectionist does not need to read them.

Hydrometer

As a storage battery becomes discharged and loses its energy, there is a corresponding fall in the specific gravity of the acid - that is, the weight of the acid in comparison with the weight of an equal volume of pure distilled water. Knowing this figure for any battery, it is possible to tell at once whether or not it needs recharging. The hydrometer is an instrument for ascertaining the specific gravity of the acid in a batteryusually called for short the "battery gravity".