The rectifier supplies up to 7 amps of charge current but the output tracks the discharge current quite closely. Nevertheless the rectifier is not switched on permanently. It is connected via a time clock which switches the rectifier on and off several times a day. This course was adopted to prevent the batteries being overcharged. The previous battery set had been subject to a continuous charge current and were always warm to the touch and it was felt that this constant charge contributed to the demise of the battery set.

The power supply normally places around 54 volts onto the exchange busbars. The voltage will drop to 48 should the mains be switched off for a working day.

The three way switch and fuse box is mounted outside the locked exchange room so that the 50 volt battery can be disconnected easily should there be a fire or similar. There is also an isolating switch mounted outside the exchange which similarly removes all 240 volt mains supplies to the exchange room.

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Page provided by John Bathgate This page was last updated on 17th March 2009