Kubota D1803-CR-E4 Workshop Manual page 173

MECHANISM
8. Electrical system
When Main Switch Is Turned to "ON" Position
As the battery voltage is added to the terminal IG, M.IC
circuit detects it and makes current pour to the Tr1.
It results to pour the initial exciting current to the rotor
coil (2).
(In this case, M.IC circuit makes current pour on and off
the Tr1 in pulse and limits the battery discharging
current to small value (Approx. 0.17 A) when the main
switch (3) is turned on.)
As the alternator (7) is not rotated, it doesn't generate.
Therefore the voltage of terminal PI is zero volt.
M.IC circuit detects it and makes current pour to the
Tr2.
It results light on the charge lamp (4).
(1) Stator coil
(2) Rotor coil
(3) Main switch
(4) Charge lamp
(5) Battery
(6) Load
When Engine Starts
When the engine starts and the alternator (7) rotates,
M.IC circuit makes current pour continuously to the Tr1
instead of the uncontinuous (in pulse) current.
Therefore a sufficient exciting current flows and a
generated voltage rises rapidly.
As a result, the current to the Tr2 is shut and lights off
the charge lamp (4).
When terminal B voltage rises over the battery voltage,
a charged current flows to the battery (5).
When the terminal B voltage further rises over the
regulated voltage (14.2 to 14.8 V: 25 ℃, 77 ℉ ), M.IC
circuit shuts the current to the Tr1.
Therefore the current to the rotor coil (2) is shut,
resulting to decrease the terminal B voltage.
When the terminal B voltage lowers below the
regulated voltage, the Tr1 turns on again and makes
current pour to the rotor coil(2).
D1803-CR-E4,D1803-CR-TE4,D1803-CR-TIE4,V2403-CR-E4,V2403-CR-TE4,V2403-CR-TE4BG,V2403-CR-TIE4
(7) Alternator
(8) IC regulator
M.I Monolithic IC
C
Tr1 Transistor
Tr2 Transistor
4. ENGINE
4-73
KiSC issued 12, 2018 A