(2) Install bushings, and grind the valves as
outlined in h above. Drill the horizontal
hole to the same size as the original
bushing after installation.
89. Magnetic Contactors
a. Description.
(1) Magnetic contactors are magnetically
operated switches used for the purpose of
closing and opening the auxiliary or power
circuits; they are operated by low voltage
from the battery circuit.
(2) Each contactor has stationary and
movable contacts, an electro-magnet for
bringing the contacts together, and, in
addition, high voltage contactors have
BLOWOUT COILS to extinguish the arc,
and arc shields and barrier to protect the
metal portions of the switch.
(3) The stationary and moving contacts are
made of hard drawn copper of sufficient
section to give long life. Burning at
opening and closing occurs only at the
Figure 29. Method of grinding inverted valve.
tips of the contacts and does not affect
the current-carrying surfaces; a slight
(b) Contacts wear quickly as the result
wiping action when closing insures a clean
of too small a travel and very little
low-resistance contact area.
A steel
wiping action. This may be caused
compression spring insures positive
by insufficient free movement of the
contact pressure, regardless of wear, and
armature or too strong a finger
also causes quick opening of the contacts.
spring.
(4) The arc shields and barrier are made of
(c) Renew contacts when tips of old
heat resisting materials. The arc shields
contacts are worn thin, when
can be removed readily for inspection of
contacts are burned at the heel or
contacts.
when the contact is badly worn.
b. Maintenance.
Contacts worn until the arc
(1) Do not oil or lubricate any part of this
damages contact bolts will be
contactor.
Keep all parts clean;
difficult
to
remove
without
accumulation of dirt will interfere with the
damaging the switch.
operation.
(3) Renew arc shields before the heat
(2) Copper contacts normally wear to give the
resistant material is burned away
best contact surface without attention;
sufficiently to expose the metal poles; the
however, if rough blistered contact tips
shield may be removed easily by taking
keep the heels of the contacts from
out a single bolt.
closing, smooth tips with a fine file. Do
(4) Keep the flexible copper shunt tight. If it
not file heel of contact.
becomes loose, there is danger of the
(a) Contacts may burn at the heel
shunt burning at the point.
because of improper rolling action
(5) Remove the operating coil by removing
of moving contact on stationary
the armature, disconnecting the terminal
contact. This may be caused by a
leads and removing a screw and nut.
weak or broken finger spring. It
Coils are designed to operate the
should be replaced immediately.
contactor successfully at from 60 percent
to 110 percent of normal voltage and to
without
overheating;
coils
are
impregnated to make them resistant to
moisture and oil.
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