(D) Engine Starting Circuit; (F) Fuse; Load Contactor Circuit Components - Hobart 60PL20 Operation And Maintenance Manual

(d) Engine starting circuit

The pushbutton start switch (13 ) and permissive toggle switch (15) serve to connect power to
the starter solenoid which functions to engage the starter gear with the flywheel ring gear and
apply power to the starter motor to crank the engine. The permissive toggle switch (15) also
stops the engine when the toggle is placed in the STOP (down) position.
(e) Indicating lights
A green indicating light (12) glows to indicate that power is available to the engine protective
system. The light operates only when the engine permissive start switch (15) is in the START
or RUN position. Another green indicating light (9, Fig. 8) glows when the generator output
load contactor is CLOSED and power is available at the generator output cables.

(f) Fuse

A 10-ampere fuse (11) protects the 12-V DC engine control circuit, hourmeter, illuminating
light circuit, and 12-V DC system in the main generator protective system.
G. Load Contactor Circuit Components
Load contactor circuit components are located either attached beneath the control box support panel,
on the trailer assembly, or inside the generator control box. The load contactor and its associated cir-
cuit components provide a means of connecting and disconnecting generator output to and from the
load (aircraft) .
(1) Load contactor
The load contactor (3, Fig. 9) is a sealed unit which contains a magnetic operating coil and four
sets of contacts. The three larger contacts conduct three-phase AC generator output. A smaller
contact set is connected in the protective monitor circuit and supplies 12-V DC power used by
sensing relays to signal the protective monitor when a fault occurs. Three-phase, 400-Hz gener-
ator output power is conducted to the load contactor by 2/0 cables which pass through 3 sets of
current transformers.
(2) Current transformers
These current transformers are located beneath the control box support panel directly below the
control box.
(a) Ammeter current transformers (2, Fig. 10)
Three current transformers lower the output load current to a lesser value of definite ratio
(250-A to 5-A) which will operate the ammeter (4, Fig. 6) movement without damage. The am-
meter dial scale is graduated and numbered so that the ammeter pointer will indicate the true
load current value rather than the meter movement current.
(b) Line-drop current transformers (3, Fig. 10)
The three line-drop current transformers in conjunction with burden resistors, detect the mag-
nitude and power factor of current flowing from generator to load. They feed a signal to the
voltage regulator which interprets the signal and alters the exciter field current as required to
maintain a constant predetermined voltage at the load.
(c) Overload current transformers (4, Fig. 10)
Three overload current transformers, in conjunction with burden resistors monitor the output
load current in each of the three output phases, and supply a reduced value current signal to
the overload module (5, Fig 7)
December 31/91 Revised
OM-2053
1-1
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