Kubota WG972-E2 Workshop Manual page 67

WG972-E2, DF972-E2, WSM
3. In Charging
Because BATT terminal voltage just after engine start
is lower than setting value (14 to 15 V), or lower than
zener level of Z1, current is not supplied to base of Q4
and Q4 is off, as shown in figure (B). Q3 is on with base
current which flows thorugh the route of BATT → emitter
/ base of Q3 → R2 → D6 → BATT, and gate current is
supplied to S1 or S2 through the route of GEN → D1 →
emitter / collector of Q3 → R3 → gate / cathode of S2 →
GEN, or GEN → D2 emitter / collector of Q3 → R3 →
gate / cathode of S1 → GEN.
When engine speed is increased so that GEN
genetration voltage becomes higher than BATT terminal
voltage, S1 or S2 is turned on and, as shown in figure
(C), charge current is supplied to BATT through the route
of GEN → D1 → BATT → anode / cathode of S2 → GEN,
or GEN → D2 → BATT → anode / cathode of S1 → GEN.
After S1 or S2 is turned on, collector current of Q1 and
base current of Q3 are supplied by GEN, not BATT.
When key switch is turned to position 1 after engine is
started, BATT is charged, if BATT terminal voltage is
lower than the setting value, or zener level of Z1.
4. Over-Charge Protection
When BATT terminal voltage is higher than the
setting value or zener level of Z1, BATT is not charged
by the function of circuit as shown in figure (D). That is,
Q4 is on with base current which flows through the route
of BATT → emitter / base of Q4 → Z1 → D6 → BATT,
shortcircuiting emitter and base of Q3. Therefore, Q3 is
off with no base current and gate current is not supplied
to S1 and S2. Consequently S1 and S2 are off and BATT
is not charged.
M-27
GASOLINE / LPG ENGINE
W1035755
W1036458
KiSC issued 01, 2006 A