Special Maintenance Problems - Hobart Pipeliner Instructions Manual

T-964C
PART THREE MAINTENANCE INSTRUCTIONS
(3) Check all wiring connections, switches instruments, and controls for
looseness, wear, and inaccuracy.
SECTION 11 - SPECIAL MAINTENANCE PROBLEMS
36. LOSS OP MAGNETISM
a. INDICATION - .If the generator fails to build up voltage after starting, it
may be due to the exciter having lost its residual magnetism in shipping or moving
the unit.
b. MAINTENANCE PROCEDURE - Raise the exciter brushes and apply an outside source
of D.C. voltage, not in excess of 110 voits, for a few seconds to exciter brushes of
opposite polarity (adjacent brushes). This sets up a magnetic field which leaves
enough residual magnetism to cause the exciter to build up voltage by itself, when
the brushes are again lowered onto the exciter commutator. If, after the outside
voltage has been applied the exciter still fails to generate voltage, reverse the
outside voltage through the exciter brushes.
37. POLARITY REVERSED
a. INDICATION - Reversed polarity is indicated Dy the instruments reading in the
wrong direction, when the polarity switch is in the 'straight' position and the
motor is rotating in the proper direction. With the polarity switch in the
'straight' position the meters should read to the right.
b. MAINTENANCE PROCEDURE - The remedy is to raise all the exciter brushes, con­
nect two terminals of a, storage battery to any two adjacent exciter brush-holders,
and pass the current through the field coils for several seconds. If the desired
results are not secured, reverse the connections and repeat the procedure. A way to
do this, when an outside source of D.C. current is not available, is to operate the
welder with the rheostat in the 'maximum' position, with one exciter brush lifted.
Then raise the diametrically opposite brush, and lower it quickly to the commutator.
If carried out with proper timing the polarity will reverse, DON'T neglect to drop
the brush that was first lifted.
38. BRUSH REPLACEMENT
a. INSPECTION - The brush-holder covers should be removed at least once a month
and the brushes inspected. If the brushes are worn unevenly or are shorter than %
in. they should be replaced.
b. REMOVAL - Remove the cover at the rear of the generator if the generator
brushes are to be removed, or the exciter cover at the front of the generator if the
exciter brushes are to be removed. Disconnect the brush pigtail from the brush-
holder with a screwdriver. Lift the brush-finger and remove the worn brush.
c. INSTALLATION - Lift the brush-finger and insert the new brush. Fasten each
brush pigtail to the brush-holder and be certain that the brush-finger rests cen­
trally upon the brush. Adjust the brush spring, in the locking washer, so that the
exciter brushes bear on the commutator with a pressure of approximately % to ^ lb.,
and the generator brushes bear on the commutator with a pressure of 1% to 2 lb. Lay
a commutator-wide strip of No. oo sandpaper, smooth surface down, on the commutator
and with one hand in place and pressed down on the sand-paper, draw the sand-paper
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