Re: Master Clock contact spark quenching

Simon Taylor

The GPO used a 200 ohm resistor in series with a 1 micro farad capacitor across the contacts on later type 36 clocks with simple make contacts. The earlier types with make before break contacts had a 2000 ohm resistor. and worked with the earlier relay 90A which had 2 x 500 ohm coils in parallel.

All of the contacts are made of 10% iridium and 90% platinum. The hipp toggle contacts pass between 400-500mA for the pendulum drive coil. Although running a GPO slave cct direct it is quite possible, I would still recommend using either traditional relay (coil 2000-5000 ohms) or a solid state device or arduino system.
Simon GPO Clocks

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