Onan NHC Series Operator's/Service Manual And Parts Catalog page 35

6. Testing Field Coils for Grounds. Place one lead
on the connector and the other on a clean spot on
the frame after unsoldering shunt field coil wire. If
the ohmmeter reading is low, the fields* are
grounded, 'either at the connector or in the
windings (Figure 44).
9. Inspection for Brush Spring Tension. Measure
brush spring tension with a tension meter as
shown in Figure 47. Push the brush and take a
reading just as the brush projects a little from the
brushholder. On a new brush the spring tension
should be 29 to 38 ounces.
F I G U R E 44. F I E L D C O I L G R O U N D T E S T -
7. Testing Field Coils for Open Circuit. Place one
lead on the connector and the other on a clean
spot on the brushholder. If the ohmmeter reading
is high, the field coil is open. Check the other
three brushholders in the same manner (Figure
45).
F I G U R E 45. F I E L D C O I L O P E N C I R C U I T T E S T
8. Inspection of Brushes. Replace brushes when
they are worn less than .3" as shown in Figure46.
See that all brushes move freely in their holders.
rL_m_n
W E A R L I M I T — j -
.3"
. 5 5 '
F I G U R E 47. B R U S H S P R I N G T E N S I O N T E S T
INSPECTION AFTER OVERHAUL
1. For no load test, the starting motor is wired as
" shown in Figure 48 and revolved. The meter
readings for this test should be:
Voltage 11.5 volt
Speed. 3700 rpm minimum .
Current Draw 60 amp maximum
T h e c o n d u c t o r f o r this test s h o u l d be large e n o u g h to c a r r y 60
a m p s a n d as s h o r t as p o s s i b l e . If a n y t h i n g is w r o n g . i n t h e
a b o v e test, i n s p e c t the f o l l o w i n g i t e m s :
A n n e a l e d b r u s h s p r i n g s
I m p r o p e r l y seated b r u s h e s
I n s u f f i c i e n t a r m a t u r e e n d p l a y
S h o r t e d , o p e n or g r o u n d e d a r m a t u r e
G r o u n d e d o r o p e n f i e l d c o i l
P o o r e l e c t r i c a l c o n n e c t i o n
D i r t y c o m m u t a t o r
S W I T C H
A M M E T E R
— < A ) —
B A T T E R Y
VOLT /-S.
METER ( y )
R P M
I N D I C A T O R
F I G U R E 46. B R U S H W E A R L I M I T
F I G U R E 48. S T A R T I N G M O T O R W I R I N G
33