Voltage Regulator; Regulator Components; Operation Of Regulator - Piper SENECA II Service Manual

PIPER SENECA II SERVICE MANUAL
11-17.
VOLTAGE REGULATOR.
11-18.
REGULATOR COMPONENTS. Alternator output voltage can within limits of the design capability
of the alternator be controlled by properly varying the average level of current flow in the rotor winding.
The solid state electronic regulator is well suited for this purpose. The alternator, due to its design, has
self-limiting current characteristics and therefore needs no current limiting element in the regulator.
a. Transistor: The transistor (Symbol "Q") is an electronic device which can control the flow of
current in an electric circuit. It has no mechanical or moving parts to wear out.
b. Rectifier Diode: The rectifier diode (Symbol "D") will pass current in only one direction
(forward direction), and in this respect, it may be compared to a check valve.
c. Zener Diode: The zener diode (Symbol
"Z")
in addition to passing current in the forward
direction will also pass current in the reverse direction when a particular value of reverse voltage is applied.
This property makes it useful as a voltage reference device in the regulator.
d. Capacitor: The capacitor (Symbol "C") is a device which will store electrical energy for short
periods of time. This property makes it useful as a filter element to smooth variations of voltage.
e. Resistor: The resistor (Symbol "R") is a device which is used to limit current flow.
11-19.
OPERATIONOFREGULATOR. (RefertoFigure
11-10.)
a. When the alternator is turned on, battery voltage is applied to the "BUS" terminal of the
regulator and via Q4 through the "FIELD" terminal of the regulator to the alternator field terminal F2.
The amount of voltage applied to the field of the alternator is controlled automatically by action of the
regulator in response to alternator output as described below.
b. Current flow through R6 and
Z 1
establishes a reference voltage across Z
1.
c. Resistors R 1 and R2/R3 comprise a voltage divider which is adjustable by means of the variable
portion R3. Voltage at the junction of R 1 and R2 and the reference voltage across Z I are applied to
comparison transistor QI. R3 is adjusted so that these voltages are balanced with the desired alternator
output voltage present on the "BUS" terminal of the regulator.
d. Thereafter, whenever alternator output voltage (as applied to the "BUS" terminal) falls below the
desired regulation value, the comparison transistor Q 1 will supply increased current to driver transistors
Q2/Q3, which in turn will drive power transistor Q4 to a higher value of field current. This will result in
alternator output voltage increasing to a value which will restore balance between the two voltages applied
to QI.
e. Conversely, if alternator output voltage (as applied to the "BUS" terminal) increases due to a
greater engine speed or reduced loading of the electrical system, the comparison transistor QI will act to
reduce current flow to the driver transistors Q2/Q3, and thus reduce the drive to power transistor Q4. This
will result in a reduction of alternator field current and automatically restore balance between the two
voltages applied to comparison transistor Q 1.
f. Capacitors CI and C2 function together with their related transistors in a way to smooth
alternator output ripple and voltage spikes so that the alternator field current is controlled at a steady
value.
g. The solid state regulator controls alternator field current to a steady value as required by the
electrical load conditions and engine speed. It does not continuously switch field current between high and
low values as do mechanical regulators and the switching type of electronic regulators.
h. The design of this unit is such as to provide an alternator output voltage that does not vary with
ambient temperature.
Reissued: 10/11/79
ELECTRICAL SYSTEM
2G9