Piper Comanche PA-24 Service Manual page 706

PIPER COMANCHE SERVICE MANUAL
9-61111. Ret.lato. (Pro.tolite).
~61n.
Ret.letar
C ...
pon •• tl. Alterlator output volta .. can. ",ithio the Umits 01 the desi",
capability of
the
altemator.
be
controlled by proporly vatylng the avar.,_ level of current flo",
in the rotor ",indiog .nd the PrestoUte full electronic loUd state .. .wator is _II luited lor this
purpose. The Preotolite altemator. due to its design. bas .elf-limiti", current characteristics
and needs no current-limiting
unit ill
the Nlulator.
I.
Transistor: The transistor
is
an electronic switch wruch can turn
OD
and
twn
otf the flow
of
cumtnt
in an electric circuit. It bu no mechanical or movinl parts to wear out.
b. Rectifier Diode:
The
rectifier diode "'ill pasl current in one direction only (fo",·ard
direction); and in this respect. it may be compared to a ooe-... y check valw.
c. Zener Diode: The Zener dinde.
in
addition to passi", cuneltt in the fo""ard direction.
will pass CUlmt1t in tbe reverse direction only when a particular value of voltaae is applied in
the reverse directioa. It is this Zener action whicb makes
it
adaptable for lise as a voltage
senaina device in the reaulator.
d. Resistor: The ralStar
is
a device whicb is aed. to
limit
current
flow.
9-610.
O~.ration
Of Ret.lotar. (Refer to Figure 9-27p.)
a.
When the alternator switch is twned on. battery voltage is
ap~lied to the "I" terminal of
the regulator.
b. The "I'n (negative-poeitive-necatiw) po1"er transistor. T3. is twned on by CUtTent flow
from the ignillon terminal through R6 and the collector emitter junction 01 T2 'hrouCh 02 throulh
the base emitter junction of T3 to I'ound.
c. Whenever the power transistor. T3. is on tT2 is also
CD
and T1 is off). current "ill flow
from the ignitl0n tenlUnal throulh the field "inding. throuCb the collector • eautter of T3 to
ground.
d. With the
ignition
switch on, current will flow {rom the'
II" terminal regulator ground through
a voltage diViding network consistin.g of R1. R2 and Pi. This network determines the system
operating voltage relative to the Zener diode.
Zl.
reverse conduct
ina
voltage.
e. When
the
system voltate connected to "I" termiaal reaches a value at which the Zener
diode connected to
the
divider network conducts. cwrent
will flow
from
the
"I" termInal through
R1 through Z1 and tbrough tbe base emitter junction 01 T1 to ground. This causes the collector
emitter junctlon of
Tl
to conduct which diverts the bale cunent of T2
flOWing
from "1" terminal
throulh R4 to ground. turning off T2 which turns off T3. de .... nerCizing the rotor winding; then.
when the alternator output vo1tace falls to a value which permits Zt to cease
coruiuction, Tl will
turn off .,luch turns on T2 and T3 ..... nerctZi", the rotor winding.
f. This sequence
is
performed. so rapIdly that the rotor currel'lt average appears as a value
usually less than
fuji
rotor cwrent depending on rotor RP'II and system load connected.
,. Each time the power transistor. T3. is turned off. current flow in the rotor Winding
15
reduced.. This causes the rotor maanetic field to collapse which would lenerate hIgh voltage at
the power transIstor. T3. if a path were not provu:1ed so that the held current can decay at a
slower rate. The field suppression diode. 01. provtdes this path. thu.s protectll'll the system and
relWator lrom possible dalllOge.
h.
Tempera~ure
compensation is nat which !Deans the regulator will hold the alternator out·
put voltage constant with temperature increase or decrease after irutial warm-up.
i.
The Prestolite solid state regulator uses three npn silicon transistors.
ELECTRICAL SYS-:-EM
ISSUED: 8/18172
3 C6
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