Normally the rectifier is off, although a time clock does switch it on for two half hour periods a day to keep the batteries charged. Whenever the exchange is taken into use the rectifier is switched on and then remains on for several minutes after the call clears down. The unit is switched on by an earth appearing on the PHR2 lead from some control apparatus.

This arrangement ensures that the rectifier provides charge every time the exchange is taken into use. As the exchange often has a few consecutive days without use, the time clock is set to provide a charge for sufficient time to maintain the battery.

The 50 volt supply is also taken via a second rectifier to isolate the O/P wire from the exchange battery. An output only appears on the O/P wire when the rectifier is on. This output merely lights a lamp via a relay to say that the rectifier is on.

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Page provided by John Bathgate This page was last updated on 9th May 2008