With the body restoration of this car nearing completion, it was moved to the workshops on the 7th of September 2013 to start on the electromechanical fit out of the car. The electrical section have been working for some time on the PC5 auto-acceleration controller and other equipment required. Two sets of equipment are being refurbished so that that PR1 1573 will also eventual take it’s place in the restoration hall and get fitted out.
The following is the ‘PC5’ controller that will be fitted to 1729. This unit is effectively new, having been used in a rig for training new tramway fitters on the equipment.
The PC5 is often referred to as an ‘automatic acceleration unit’, as this controller does not directly follow the ‘commands’ from the master controller in front of the driver, but instead ‘notches up’ by itself. A driver of a PC5 equipped tram basically has 3 speeds on their controller – ‘shunt’ (First series, all resistances in circuit) for slow speed shunting, then ‘series’ and ‘parallel’.
A current sense relay monitors the motor current, and as the tram speeds up the current falls. When it falls to a preset value, the current relay opens an air valve that cause an air-motor (The black thing in the middle front next to the gear) to kick the shaft around one ‘notch’. This continues through each resistance notch till all resistances are cut out. If the driver has selected ‘parallel’, the system just switches through transition and keeps cutting out resistances automatically till full parallel is reached.
This air operated cam shaft is why PC5 equipped trams need to get a certain amount of air pressure up before they can be moved, as air pressure causes the shaft to move. The P class tram has an extra air tank to store more air than other similar sized Sydney trams to ensure plenty is available to the controller.
This ‘remote controller’ is also a key part of the ‘multiple unit’ control system. One ‘master controller’ can drive two (or more in a railway application!) of these ‘automatic accelerators’, thus the rear car in a coupled set is getting instructions from the lead car’s ‘master’ controller.
Various issues have seen work on this car halt. Illness of a volunteer who was working on the body as seen body work mostly cease and an issue in New Zealand has delayed the fabrication of the new trucks required. As a result the car was removed from the workshop and Ballarat 37 returned.