Automatic Engine Idle System - Lincoln Electric SAE-300 HE Service Manual

LINCOLN ELECTRIC

AUTOMATIC ENGINE IDLE SYSTEM

The automatic idle system reduces the engine RPM
when there is no electrical demand on the machine.
When an arc is struck, or a load of 100 Watts or greater is
applied to the auxiliary output, the engine speed will
immediately increase to high RPM. When the load is
released, the engine continues to run at high RPM for
about 12 seconds. If a load is re-applied during this time,
the machine will continue to operate at high RPM. If no
load is applied, the engine RPM is reduced to idle speed.
The automatic idle system functions by energizing a
solenoid, which pulls the engine speed control to a preset
low idle RPM position. When this solenoid is deenergized,
the engine speed is controlled by the governor which
maintains the engine RPM at the specified high RPM
setting. The solenoid is supplied with +12VDC power and is
activated when circuitry on the Idler/engine shutdown PC
board completes the solenoid's path to chassis ground.
FIGURE F.3 – AUTOMATIC ENGINE IDLE SYSTEM
SAE-300® HE Service Manual
The automatic idle circuitry on the PC board uses a
magnetic reed switch to sense weld current and a
toroidal current transformer to sense auxiliary current.
When weld current flows the reed switch closes,
connecting the sense lead to chassis ground. When
sufficient AC current flows, the toroidal current
transformer sends a signal to the PC board.
When the idle switch is in the "high" position, the sense
lead connecting the reed switch to the idler/engine
protection PC board is connected to chassis ground. The
SAE-300® will continuously run at high RPM.
If the machine had been operating at low idle and the idle
switch is moved from auto to high, the engine RPM will
increase immediately. If the switch is moved from "high" to
"auto" and if there is no electrical demand from either the
weld or the auxiliary circuits, the RPM will be reduced after
a 12 second delay.
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