Piper Comanche PA-24 Service Manual page 675

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PIPER COMANCHE SERVICE MANUAL
windinl is reduced, the spital Sprinl teGsion pulls the armature up, the c('I'Itact
poiDts
close and
directly c""aec' the pn_or field to
arourul.
Outpu' increa .. s and the above cycle is repeated.
The cycle continues to take place while the current recul.tcr is in operation SO to 200 times a
second, prevea.tiD& the pnerator from exceed.iDl its rated maximum. When the electrical load is
reduced (electrical devices turned
off
or battery comes up to charp). then the volta .. increase.
so thOt the voltoge re",lo,or beaia. to operate and tapera the generator output down. This
p~
vents the cunent reaulator frem oper.tina. Either the yolt • • regulator or tbe ·current re~lator
operates at anyone time-the two do not operate at the same time.
9-25. R ••
i,toIIc ••. tne current and
vo1tese replator circuits
use •
common resistor which is
inserted in the held circUIt .. ben either the current or volta. reaulator operates. A sKond fe·
s!Stor· is caanectlld between the .. cuI0tor field tettainal and the cutOlltreloy frome. ",h'Ch ploce.
it in paraUel .. ith the generator field coils. The sudden reduction
III
field cunent occurring .. hen
the current
a
volta.e regulator contact points open. is aecompuied by a surge or U1duced. volt ..
age in the Held coils as the streneth of the mapetic field cbanges. These swges are partIally
d.issipated by the two resistors. thus preventing excessive areiDe at the contact pOInts.
*(The second resistor is not presem on all reculators. Marry Aircraft regulators have this resistor
omitted. )
9-26. Temperatur. COfIIpenlation. Voltaa;e regulators are compensated for temperature by means
of a blmetal thermostauc biaae on the armature. This causes tne reculator to regulate at a hIgher
voltap whea cold which partly comp.:nsates ror the ract that a hilher voltage is required to
charle a cold battery. Many current regulators also have a bimetal thermostauc hm.ge on the a:-
mature. This permits a somewhat hiper pnerator output when the unit is cold. but causes the
output to drop off as temperature U1creases.
9-27. R.,ulotar Polarity. Some reculators Ire designed ror use with neaauve grounded. sysre!:ls.
while other reculators are desicned for use with positive erounded systems. Using the wrong
polarity regulator on an installation will cause the regulator contact points to pit badly and give
short life. As
a
safecuard acainst installauon of the wronc polarity regulator. all :,egulators
of
this type have the medel ,,"umber and the polarity dearly stamped .on the end orthe regulara' base.
9-28. Retulator Main .. nDnc •.
9-29. General Inltructionl .
•. Mechanical checks and adjustments
(air
gaps. point opening) must
be
made with battery
disconr.ected and regulator preferably off the aucraft.
CAUTIOH
The c:Jtout relay contae!: pOints must never be closed by hand with
the battery coonected to the regulator. This would cause a high
cur.ent to flow through the units which would senously damage
them.
b. Electncal checks anci. adjustments may be made either,," or ort the alrcrat! The regulator
mUSt always be operated With the type generator for which it
:s
deSigned.
3
A23
ELECTRICA.L SYSTE:.I
ISSUED: 8118172