On Jan 31, 6:53 pm, john smith wrote:
In article .com,

wrote:
Any contactor has a coil, the starter has several coils, and
the alternator has a field coil. All coils create a sharp voltage
spike when the current is cut off. Switching the master off, the
alternator off, or releasing the start switch all create that spike
(I've measured the master contactor's spike at 600 volts) and those
expensive radios aren't all built to put up with it, especially
considering that the spike creates an electron flow in the wrong
direction through the bus. That's why many aircraft have an avionics
master switch (that has no coil involved). The rest should have the
radios shut off before shutdown.

Coils (inductors) are current storage devices.
Capacitors are voltage storage devices.

As if current and voltage were independent of each other?
The coil will produce a surge of current, which has a specific
pressure that we call voltage. You can't have current flow without
voltage; any flow (amperage) requires pressure (voltage) to drive it.
Just like water in a hose.
The magneto produces a pressure upward of 20,000 volts. It
does this using a pair of coils and a switch (points). Your
automobile's ignition system probably produces 40,000 volts, again
using paired coils. Both of those systems have a primary coil that
produces the current surge (which has a voltage spike) when its
current flow is interrupted, and the collapsing magnetic field
produces the huge spike in the secondary coil for use at the spark
plug.
The argument re current vs. voltage is a little like
Bernoulli's vs. Newton's theories of lift. They're both right, but
they address different aspects of the phenomenon.

Dan