WhackJack-18 More Whackjack Info (pdf)

A common killer of airplane electronics is “Load Dump”. This happens when you simply turn OFF a large load. It seems innocent enough but if the alternator field has been cranked up and suddenly there is no need for all the excess power—something’s gotta’ give. This problem takes 10 to 500mS to settle itself but in the meantime the power busses have 60 volts or more on them.The “WhackJack™” is made from three parallel Mosorbs® designed to trip under 1 nanosecond, with a very flat voltage limit and little overshoot. It's potted with tabular-silica epoxy and is UL94-V0.

SnapJacks. More SnapJack Info (pdf)

Mechanical relays and contactors depend upon magnetism generated by an electric current running through a wire coil. When the current stops, the magnetic field collapses. But the relay does not know the difference between a wire coil moving in a magnetic field (as in a generator) or a magnetic field moving in a wire coil (as in a collapsing magnetic field). Thus a large voltage—1000V to 1500V typically—is induced in the coil. This current goes the same direction the original current did—so it slows the contact opening—allowing arcing, chatter, bouncing, contact welding and even re-closure! Yikes! This coil-craziness has to be suppressed for things to function at all. Perihelion Design sells 18V 600W Bi-Directional Zener Transient Voltage Suppressors (for 14.5V systems) that provide the most modern technical solution to relay coil suppression. We sell these as a set of twelve with the typical hardware needed to retrofit a typical small airplane.