Onan MJA Series Service Manual page 123

121 CONTROL SYSTEM
6.2.1. 1 Starting Solenoid. - The starting solenoid controls the heavy
currents required by the exciter starting motor. If it appears defective,
test it for welded contacts across the main terminals or an open circuit
in the energizing coil.
If
the solenoid sticks energized (contacts welded together) check for the
following conditions - ­
-- Excessive tightening of the main connection terminals (Fig 6. B) on
the solenoid. This tilts the contact surfaces inside the solenoid,
'-"-'.. CU.H!'.
burning and welding. All current models have epoxy-filled
solenoid switches to eliminate cocking of contact
surf~ces
(Fig 6.B),
as are all current replacement parts. The epoxy-filled solenoids
are identified by two part numbers stamped on the bottom; the early
style solenoids h::>ve only. One number stamped on the
-- Improper use. If the start switch is released when an engine slows
at the peak of the first compression stroke, the large current pass-
through the solenoid may burn Or weld the contacts.
6.2.1.2 Stop Relay (#307B253) - This relay controls voltage to the
tion coil. Wheri energized
it
closes the ignition coil circuit. During
starting, the stop relay pulls in at the same time as the start solenoid.
The generator's dc output maintains it energized throughout operation.
To stop, the stop button grounds the relay, which de-energizes, open­
ing the ignition coil circuit.
NOTE: This is a S volt relay and must be used in series with the 30
ohm voltage dropping resistor.
To test this relay, check the coil resistance (it should be about 30 obms),
inspect the contacts, and check contact operation when voltage is applied
to the coiL
If
the contacts are dirty, they can be cleaned with hard
paper or gauze mOistened with carbon tetrachloride.
6.2.1. 3 Start-Disconnect Relay (#30SA28) - The start-disconnect relay
is energized by the generator dc output, so
it
pulls in when the output
builds up to 10 or
11
volts and remains energized throughout plant oper-'
ation. When the relay pulls in, it opens the circuit to the start solenoid
coil, opening that solenoid to break the starting circuit. To test this
relay, inspect the contacts, check the coil resistance (it should be 20 to
24 ohms) and check contact operation when the plant starts.
6.2. 2BATTERY CHARGING CIRCUIT - The generator dc windings sup ­
ply current for the battery charging circuit. The current flows through
the reverse current relay, charge ammeter and the adjustable charge
rate resistor, located outside the control box.
The battery charge rate can be adjusted between 2 and 5 amps by mov­
ing the slider on the charge resistor.
6.2.2.1 Reverse Current Relay (#307B180) - This relay allows current
flow only from the generator to the battery and opens wben current