TESDNG
DIODES
AND
THERMISTER
.
.
REFER
TO
THE
WIRING
SCHEMATICS
TROUBLESHOOTING
GUIDES
AND
COMPONENT
RESISTANCE
CHARTS
IN
THIS
MANUAL
OHMS
THROUGH
THE
DIODE
INFINITE
BLOCKING
====f<}==
INFINITE
TES11NG
DIODES
Six diodes are mounted
on
the exciter rotor; they rectify the
AC voltage produced by
the
three
groups
of
the
auxiliary
windings to
DC
voltages
and
'supply
this
DC
voltage
to
the
rotating field windings.
The diodes can be easily checked
in
place
with
the
use
of
a
colllDl.On
automotive 12-volt high
beam
headlight
bulb,
some
jumper leads
and
the
generator's 12
volt
starting
battery.
A short
or
an
open
in
a diode can easily be
found
with
the
above without having
to
unsolder
and
isolate
each
diode
to
check it with an ohmmeter.
Nata:
Anempting
to
check diodes in place with an ohmmeter
will
give
erroneous
readings
on
the diodes
due
to
the
auxiliary
winding's
connections.
When leads are put across
the
diode,
as
illustrated, voltage
passes through the diode allowing
the
headlight
to
glow
brightly.
12VBA1TERY
Reverse
the
leads
across
the
diode.
The
diode should block
voltage passing through
it,
and
the
headlight should not glow,
or
it
may
glow faintly.
1.
Shogld
the
bulb
not
glow
with leads connected in both
directions,
the
diode
is
open
intemally.
2.
Should
the
bulb
glow
with leads connected in both
directions,
the
diode
is
shorted internally.
In both
1.
and 2. above, the diode should be replaced. Check
the resistance value
of
the rotating field winding and the
integrity
of
the tnermister connected across
the+
and-
connections
of
the rotating field winding.
TESnNG
THE
THERMimR
The
thermistor
is
located
on
the
Exciter Rotor and connects
between
the
+
and
- connection for the rotating field winding
resistance: Infinite.
·
The
Thennister
is
a voltage absorber when amperage
load
changes
take
place with
the
generator
to
help preventl
or
reduce
light
flicker
if
open
circuited,
it
has
no
affect on the
operation
of
the
generator
other
than a flicker in the lights
when
amperage
load
changes
take place not occurring before.
Should
the
thennister
short
it
will negate the
affects
of
the
rotating field winding
on
the
stator windings and no AC output
voltage
Will be prOduced ..
When
exciting
the
generator
in
an
effort
to
locate the cause
of
a
very
low
or
no
AC
output
and the cause is a shorting·
thermister.
There
will
be
no
loading
of
the drive engine. No
growling
from
the
AC
generator. However as the excitation
is
allowed
to
continue
the
short
will
produce
heat
in
the
thennister
and
some
electrical smell/smoke visible in the
area
of
the
rotor
rear
ca.trier bearirig.
The
themiister can be.
removed
and
the
generator operation restored other than for
light
flicker until a replacement
is
installed.
1-.-v-#WESIEHBEKE
I Engines & Generators
91
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