Re: Master Clock contact spark quenching

John Haine

Surely now we have cheap reliable silicon diodes the best approach is the now-standard practice of connecting a diode across the coil so that when the contact opens the diode shorts out the inductive kick?  The diode should be reverse biased when the coil is energised.  The only snag with this is that the diode maintains the current when the contact opens for a period which may cause a problem.  That can be made shorter by putting a resistor in series with the diode to dissipate the stored energy more quickly at the expense of a higher voltage.  For example, if the coil carried 1 amp when the contact was closed, and the resistor was 100 ohms, the peak backswing voltage would be 100 volts, quite a lot but probably not enough to cause breakdown in the gap.

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