Crane digital engine controls (DEC9000, DEC9500
and mini-DEC series) and ignition systems (HI-6, HI-6S,
and HI-6DI2) have inputs used to select rev limit and/or
retard stages. In some applications, these inputs are
directly connected to external circuitry that may include
solenoids (or solenoid operated valves) controlled by a
switch or relay. Common examples include line lock and
transmission brake solenoid valves connected to a stage
limit input and nitrous oxide injection solenoid valves connected
to a retard input.
When the switch or relay opens and current flow to the
solenoid is interrupted, very large electrical transients
(500 volts or more) may occur. These transients can lead
to glitches in the electronics. Arcing also occurs in the
switch contacts. Arcing greatly decreases switch life and
may result in erratic operation. These conditions may
cause inconsistent launch and 60 foot times.
Other large inductive loads, such as a throttle stop
solenoid, may cause severe electrical glitches, even if
these devices are not directly connected to any engine
control or ignition system.
Inexpensive surge absorbers, also referred to as
MOVs (metal oxide varistors), installed directly across all
solenoids eliminate problems with switching transients.
Some solenoids have current draws in excess of 10
amps. Switching of these devices may cause excessive
jumps in the 12 volt supply. A filter capacitor is recommended.
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