Electrical Control Systems

The electrical system not only controlled the equipment on the same vehicle, but on other vehicles in the formation.

The technology evolved quickly in the early years when the vehicles were being built leading to several different systems, which we now identify by the coupling codes, these were introduced to show which DMUs could be coupled together.

   

In the early Red Triangle and Yellow Diamond systems relays were not used in the communication between vehicles, and the battery power in the leading vehicle was being directly used to operate equipment on all power cars in a formation, which led to power issues and slow response times at the rear of a longer train.

For the White Circle system relays were introduced, meaning the leading power car only sent a signal to all the power cars in the formation, the relay connected the battery on that power car to operate the item in question. Another change that is believed to have happened at this time was a change from common positive to common negative circuits.

The Yellow Diamond and (79xxx series) White Circle vehicles shared the same cab controls (AEC type), a 'cowhorn' type throttle handle and a gear controller which could rotate 360 degrees. The throttle motor (which controlled the speed of the engine) was of a complicated design.

The Blue Square system introduced a new set of cab controls ('Sharps' type) and a simplified throttle motor, with associated changes in wiring.

The throttle on the Orange Star was based on a variable air pressure rather than electrics, a system common on locomotives, and an extra air pipe was fitted throughout the train to control the engine speed. That reduced the electrical circuits needed, and there were no need for gear circuits as these were hydraulic, so only one jumper was needed rather than two on each bufferbeam (although it was slighly larger).