HMS Alliance -The Motor Room

The Motor Room with its giant switchboards is immediately abaft the Engine Room. Alliance was one of the last type to have open switchboards with hand operated knife switches and speed/voltage control hand wheels. The speed and direction of the main motors — ahead or astern —were controlled from here as well as battery charging and the supply of auxiliary circuits. The main engines were unable to go astern so all manoeuvring in harbour had to be done on the main motors with the engine clutches disconnected.

CThe Motor Room

The supply from the main batteries coming to the switchboards was, of course, Direct Current and it was led from here to a ring main running around the submarine with junction boxes and distribution boxes in the various compartments to supply the numerous electrical units on board. AC power was needed for certain equipment and this was supplied by motor alternators.

The main battery was split into two sections, each consisting of 112 lead-acid  ½  ton cells. No1 section, beneath the accommodation space, supplied the starboard switchboard and main motor; and No.2 section, beneath the heads and wash place area, supplied the port switchboard and main motor- The bus bars of the port and starboard switchboards were normally linked so that the two battery sections were effectively connected in parallel. By removing the links, either side could be isolated in the event of damage. The nominal battery voltage was therefore 224V, but it varied from about 190V to 270V according to the state of charge. Maximum motor speed was achieved by “grouping up” the main motor armatures in parallel for speeds between 5 and 10 knots; at 25 knots the armatures were “grouped down” in series; and for maximum economy at very slow speed all four motor armatures were connected in series.

A Submarine Battery