Chevrolet 10 Series 1970 Service Manual page 412

ENGINE-ELECTRICAL 6Y-20
A typical w irin g diagram is illu strated in Figu re 2D.
The basic operating p rin cip les are explained as follow s.
When the switch is closed, current from the E n e rg ize r
flo w s through the r e s is to r to the gen erator No. 1 t e r m i­
nal, through re s is to r R l, diode D l, and the b a s e -e m itter
o f tran sistor TR1 to ground, and then back to the battery.
Th is turns on tra n sistor TR 1, and current flow s through
the gen erator fie ld coil and TR1 back to the E n e rg ize r.
With the gen erator operating, a.c. voltages a re gen er­
ated in the stator windings, and the stator supplies d.c.
fie ld current through the diode trio , the field , TR1, and
then through the grounded diodes in the r e c t ifie r bridge
back to the stator. A ls o , the six diodes in the r e c tifie r
b rid ge change the stator a.c. voltages to a d.c. voltage
which appears between ground and the generator " B A T "
term in al. A s gen erator speed in creases, current is p r o ­
vided fo r charging the E n e rg ize r and operating e le c tric a l
acce s s o rie s .
The No, 2 term inal on the generator is always con­
nected to the E n e rg iz e r, but the discharge current is
lim ited to a n egligib le value by the high resistan ces
o f R2 and R3. A s the gen erator speed and voltage in­
crea se, the voltage between R2 and R3 in crea ses to the
point where zen er diode D2 conducts. T ra n s is to r TR2
then turns on and TR1 turns off. W ith TR1 off, the field
current and system voltage decrease, and D2 then blocks
current flow , causing TR1
current and system voltage in crease, and this cycle then
repeats many tim es p er
voltage to a p re -s e t value.
Capacitor C l smooths out the voltage a cro ss R3, r e ­
s is to r R4 prevents e x c e s sive
high tem peratures, and diode D3 prevents high induced-
voltages in the fie ld windings when TR1 turns off.
M ost charging system troubles show up as an under­
charged o r overch arged battery. Since the battery its e lf
may be defective, it should be checked fir s t to determ ine
its condition. A lso , in
b attery, check fo r battery drain caused by grounds or
by a c c e s s o rie s being le ft on.
A basic w irin g diagram
presented in Figure 3D. The follow ing precautions must
be observed when working on the charging c ircu it. F a il­
ure to ob serve these precautions w ill result in seriou s
damage to the e le c tric a l equipment.
• Do not p o la riz e the gen erator.
• Do not short a c ro s s or ground any of the term inals
in the charging circ u it except as s p e c ific a lly in­
structed in these procedures.
• N e v e r operate the gen erator with the output te rm i­
nal open circu ited.
• Make sure the gen erator and E n e rg ize r are of the
same ground p o la rity.
• When connecting a ch a rger or a booster E n e rg iz e r
OPERATING PRINCIPLES
to turn back on. The field
second to lim it the gen erator
current through TR1 at
CHARGING CIRCUIT CHECKS
the case o f an undercharged
showing lead connections is
Fig. 2 d —In te g ra l C harging System C ir c u itr y
to the veh icle E n e rg ize r, connect negative to nega­
tive and positive to positive.
STATIC CHECKS
B efo re making any e le c tric a l checks, visu a lly inspect
a ll connections, including slip-on connectors, to make
sure they are clean and tight.
cracked, frayed or broken insulation. Be sure gen erator
mounting bolts a re tight and unit is p ro p erly grounded.
Check fo r loose fan belt.
UNDERCHARGED ENERGIZER
C O N D IT IO N CHECK
This condition, as evidenced by slow cranking and low
s p ecific g ra vity readings, can be caused by one o r m ore
o f the follow in g conditions even though the am m eter may
be operating norm ally.
Inspect a ll w irin g fo r
CHEVROLET TRUCK SERVICE MANUAL