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Kawasaki KZ1300-A1 Quick Reference Manual Page 233

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MAINTENENCE--ELECTRICAL
Regulator/Rectifier
The regulator and rectifier are solid-state type
,
and
integrated into
one unit. Since it contains no contacts
or other moving parts, it does not wear out and never
needs to be adjusted
.
It is therefore manufactured as
a sealed unit, and must be replaced as a unit should it
become defective.
The rectifier in the unit rectifies
(changes to direct current, DC) the three-phase alter-
nating current (AC) from the
alternator.
I t contains
six silicon diodes which are connected in a bridge circuit
arrangement for efficient, full-wave rectification. The
regulator in the unit keeps the battery
+
terminal vol tage
level to a maximum of the specified range. The control
circuit in the diagram checks on the voltage level, and
triggers the
thyristors.
Though the actual regulator/rectifier circuit performs
full-wave rectification and regulates each phase of the
three-phase alternator output, a simplified single-phase
circuit of half-wave rectification is explained here to
aid the technician in troubleshooting and in understand-
ing test
procedures.
Fig. K8 shows the basic circuit of
the regulator/rectifier.
The main components of the
regulator/rectifier circuit are a thyristor (Th), or Silicon
Controlled Rectifier (SCR) as it is also called, and a
diode. The diode, thyristor (Th), and zener diode (ZD)
function as follows:
1. Diode
A current of electrons can flow only form the cathode
to the anode of the diode. However, a defective diode
will either conduct in both directions (a short) or not
conduct at all (an open circuit). If any of the diodes is
shorted or open, the voltage from the regulatorlrectifier
will be below normal
,
and the battery may not be charged
adequately
.
Diode Current Flow
No current flows
A
C
+
Battery
2.
Thyristor
Current flows
A
C
The current of electrons will flow from the cathode
to the anode but will not flow in the reverse
direction.
The thyristor differs from a diode in two respects:
(a) even though a voltage of the correct polarity
Thyristor
A (anode)
K (cathode)
G (gate)
(nagative to cathode) may be applied, the thyristor
will not conduct until a signal is received at the gate
input lead; (b) once started, it will not stop conducting
(even
if
the gate lead signal voltage stops) until the
anode to cathode voltage is removed or reversed.
3.
Zener diode
As in a normal diode, current will flow easily from
the cathode to anode, and will not usually flow in the
opposite direction.
Unlike a normal diode, however,
the zener diode will
"break
down", or conduct in the
reverse direction, if enough voltage is applied in the
reverse direction.
When this voltage is lowered or
removed, the diode will stop conducting and return
to its normal state
.
The voltage at which the diode
begins reverse conduction, is called the break down
voltage, and is set at the desired level when the diode
is manufactured.
This property of the zener diode
makes it very useful in voltage regulator
circuits.
Zener Diode
Current flows
Anode
Cathode
~----~~~~+------~
More than break down voltage
In the regulator/rectifier circuit, the diode is connect-
ed in series with the alternator to rectify the alternator
output, and the thyristor is connected in parallel with
the
alternator.
Detailed circuit operation is as follows
:
Basic Regulator/Rectifier Circuit
aD
1.
When battery voltage
is
low (Thyristor
is
off).
®
CD
CD.
2. When battery voltage is high (Thyristor is on to pro-
vide
bypass).
..
CD
®
-
1.
Alternator
4.
Control Unit
2.
Thyristor
5.
Battery
3. Diode
6.
Load
233

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