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What Are SPIKES?

SPIKES are high frequency oscillatory variations from a steady state level generated when reactive loads are switched.

In a properly operating electrical systems, spikes can be expected to reach +/- 250 volts for durations up to 70 us decaying slowly to a steady state voltage.

In vehicles, windscreen wiper motors, lamp flashers and ignition sparks are typical sources of spikes. In the marine environment, bilge pumps, relays and solenoids produce spikes capable of damaging semiconductors.

For example, the small (and sometimes not so small) blue spark that occurs when the contacts of a switch are opened are a good example of this. Current flowing through the switch is interrupted but the inductance of the load AND wiring tries to keep the current flowing by charging stray capacitance. This can also happen when the switch contacts bounce open after its initial closing.

When the switch is opened (or bounces open momentarily) the current that the inductance wants to keep flowing will oscillate between the stray capacitance and the inductance. When the voltage due to this oscillation rises at the contacts, breakdown of the contact gap is possible since the switch opens slowly compared to the oscillation frequency and the distance may be small enough to permit 'arcing'. The arc will discontinue at the zero current point of the the oscillation, but as the oscillatory voltage builds up again and the contacts move further apart, each arc will occurs at a higher voltage until the contacts are far enough apart to interrupt the current.

The arcing is usually visible as a small blue arc even in 12 volt systems. It reaches levels that will damage integrated circuits and other components. This damage tends to be 'cumulative' by nature and does not cause immediate failures. Successive exposure eventually leads to component degradation and complete failure.

 

 

 

         
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