Three devices must be used for the undersea electric power plant, namely, (1) the dynamo, which generates the electric current; (2) the storage battery, which is charged by the current generated by the dynamo, and (3) the motor, which develops power when a current from the storage battery is made to flow through it. The diagram shown in [Fig. 34] will make the electric connections clear.
About the Dynamo.—The dynamo[21] (see [Fig. 34]) is connected to the crankshaft of the engine and is driven by it. It changes the mechanical motion of the engine into an electric current. This electrical energy must then be stored up so that it can be used later when the craft is submerged and it is wanted.
And Now the Storage Battery.—To store up the electrical energy a storage battery (see [Fig. 35]) is used. When the current is made to flow into this kind of a battery it charges the battery, and if then the battery is connected to a motor it will deliver an electric current, and this runs the motor.
FIG. 35. A SIMPLE STORAGE BATTERY.
The storage battery has been almost as big a bugbear to the submarine builders as the oil engine. It must be as small and as light as possible; it must not absorb the oxygen of the air which the crew breathes, and it must not give off any poisonous gases.
Now, there are two kinds of storage batteries, and these are (1) the lead-plate storage battery, which is the oldest form, and (2) the nickel-steel storage battery, which was invented quite recently by our own Edison. Both kinds are used in submarines.
Last of All, the Motor.—The motor is the last device by means of which the electric energy is made to drive the craft when it is undersea.
Now, a dynamo and a motor are made exactly alike, in fact, a dynamo is a motor and a motor is a dynamo. That is to say, if you turn the armature of a dynamo, it will generate a current of electricity, and if you make a current flow through the coils of a dynamo, the armature will spin round and it is then a motor.