Lincoln Electric Classic 300 MP Service Manual page 56

LINCOLN ELECTRIC
IMPORTANT: The following procedures should only be attempted if all the other systems have been
thoroughly checked and are functioning normally.
6. A tachometer will be required for this phase of the test.
PROCEDURE
Initial rocker placement:
7. The rocker should be initially positioned so the center of brushes visually lines up with the center of
the main poles. Lining up the four brush holder studs with the four exciter bracket mounting bolts is
acceptable for initial placement. The rocker should be tight against the shoulder of the hub and the
clamping screw should be tightened only enough to assure the rocker cannot move.
IMPORTANT: DO NOT OVER TIGHTEN. Over tightening the rocker clamp screw can destroy the
rocker.
8. Check that the brush holders are properly installed and positioned correctly. See the Welding
Generator Brush and Commutator Inspection and Service Procedure.
9. Start the engine, place the idle switch in the high idle position and seat the brushes using a
commutator stone. See the Welding Generator Brush and Commutator Inspection and Service
Procedure.
10. Use a load bank to apply a 100% duty cycle load (250 amps @ 30 volts). Look at the brushes while
the load is applied. If excessive sparking is observed, adjust the rocker position to minimize
sparking. Generally, moving the rocker slightly in the direction of the armature rotation will reduce
sparking.
11. Continue running the machine under load for at least 30 minutes to bring the machine up to normal
operating temperature and to fully seat the brushes.
Check for max output:
12. Remove the load, set the output control and rheostat to maximum, re-apply the load and adjust the
load bank to apply a 300 amp load to the machine.
WARNING: Do not move the selector switch while the machine is under load.
13. Measure the output voltage, it should read at least 32 VDC.
14. Measure the engine RPM, it should measure between 1650 and 1750 RPM.
15. If the weld output voltage is lower than specified above, the rocker position will need to be
adjusted. Generally, moving the rocker opposite the armature rotation direction will increase
output voltage. When making this adjustment, the rocker should only be moved in very small
increments. The adjustment may need to be repeated several times to achieve the desired result.
16. Remove the load and check the voltage at the output studs (OCV). The voltage should measure
approximately 90 VDC.
17. After the rocker has been adjusted and the machine is operating normally, the rocker locking screw
should be tightened to 70 – 75 inch-lbs.
18. If new parts had been installed, the new rocker and/or exciter bracket location should be marked
with a 1/8" drill mark.
19. Perform the Case Cover Replacement Procedure.
Classic® 300 MP Service Manual
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