Capacitors as a Spark Suppressor

This project is a Relay buzzer circuit which is used to show the effects of a Capacitor as a transient suppressor. Note that in project Spark Gap Transmitter in Radio section, spikes of energy are obtained which are so narrow in width and high in amplitude that two things are accomplished.

The first is the generation of RF energy that can be heard through a nearby radio. The second is the undesirable erosion and eventual destruction of the Relay contact points.

Obviously no one wants to destroy an expensive Relay, and spark transmitters cannot be used any more, so why not eliminate this destructive spike? This can be done in most cases by adding the proper size (value) Capacitor across the Relay contacts.

This is no new idea. It has been used in automobiles for almost 50 years. The "condenser" (as it is called) which is across the ignition points performs this very function. Your dad can tell you that without this Capacitor, the car engine will probably not run.

The best and most scientific way of checking this action is by using an oscilloscope connected across the Relay contacts, but even without this expensive instrument we can still get a rough idea of what is happening.

Connect the circuit and close the Key a few times to listen to the sound. Now disconnect the lead from terminal the capacitor and close the Key a few times. The sounds you hear should be distinctly different.

The original sound (with the Capacitor) should be low in pitch and mellow. Without the Capacitor it is raspy and higher in pitch. The difference in tone is a direct result of the change in waveform of the current in the circuit. The raspy high-pitched sound is a result of a narrow high spike of current. The mellow low pitched sound is a result of the lack of such a spike.