Manual 36541
Solenoid Troubleshooting Guide
Woodward
3
Three Methods for Turning Off the Pull Coil
After energizing and pulling in the plunger, the pull coil in a dual coil solenoid must
be turned off as soon as possible to prevent overheating. The three basic methods
for switching off the pull coil are discussed below.
EXTERNAL SWITCHING
The externally switched (3-wire)
solenoid is used in applications
where an operator/driver
manually turns a key switch
that temporarily energizes the
pull coil to pull in the plunger.
The most popular application is
for start-stop control of engines
in trucks and mobile equipment
where moisture, dirt, dust, and
high vibration are present. The
sealed 3-wire solenoid is well
suited for these harsh
conditions.
EXTERNAL SWITCHING WITH TIMER MODULE
With the addition of a Woodward
pull coil timer module, the
externally switched (3-wire)
solenoid can be used not only in
operator/driver controlled
vehicles, but also in unattended
equipment, throttle, and choke
controls. The timer ensures that
the pull coil is turned off within
approximately 1-1/2 seconds
after energizing, which prevents
overheating of the coil in
situations such as abusive
overcranking of an engine.
INTERNAL SWITCHING
The internally switched solenoid
utilizes a mechanical double
contact switch, mounted on the
rear of the solenoid, to turn off
the pull coil. Best suited for
applications such as standby
generator sets or other
applications where vibration,
dirt, moisture, and excessive
cycling are not present.
