Fiat 411 R Service Manual page 48

The damper resistance coil (10) protects the voltage and current regulator contacts from the sparking
deg-iying from the electromagnetic energy of the field coils during the opening cycles by grounding part
of the energy»
When the generator slows down to a' point where its voltage is lower than the battery voltage, a reverse
current is produced from battery to generator. This reverse current will go through the series windings
of the current regulator and cut~out in the opposite direction. No consequences will derive to the
current regulator, as the current is not strong enough to pull the armature, but it will cleznagnetize some-
what' the cut-out relay which has the contacts closed, so that as soon as the reverse current will reach
a certain value the armature will be released causing the contacts to open and consequently discharging
from battery to generator will be prevented.
Finally note the functional importance of the bi-metallic blades which together with the steelgones make
up the fastening hinges of the armatures (1, Figs. £49 and 1503. ~
The passage of current across the shunted windings oi the control box units causes a temperature rise,
which produces an increment of the ohmic resistance, and consequently the quantity ol current going
through them is reduced. As for the armature-s, the current reduction results in less magnetic pull,
there-lore a voltage higher than the set values would be needed in Summertime to open the voltage regulator
contacts and close the out~out contacts.
To compensate the reduction of the magnetic pull on the armatures, the bimetallic blade which makes
up the hinges is so disposed as to gradually reduce the tension in the spring as the temperature rises.
in the case of the voltage regulator the action of the bi—metalllc blade is more than sufficient to maintain
the set voltage against the variations of ambient temperature (thermal overcompensation), therefore the
setting is slightly lower in the summer and slightly higher in the winter. This setting value ot the voltage
which varies slightly according to the temperature favours long lite of the batteries the voltage of which,
when current passes through, decreases as the electrolyte temperature increases, and on its part elec-
trolyte also is sensitive to the surrounding temperature.
Therefore, should the voltage setting of the voltage regulator not follow the requirements of the battery
temperature conditions, the following trouble would develop:
-- when room temperature is high, the voltage would exceed the set limits and the battery would be
compelled to absorb a very strong current resulting in excessive electrolysis and consequently wear
of plates, insulators, etc.;
— when room temperature is low, the voltage would be scarce and could not ensure a correct recharg~
ing rate.
Also in the current regulator, the bi-metallic blade (1, Fig. 152) which is part oi the spring hinge of the
armature is so disposed as to gradually reduce the tension as temperature rises.
But, as explained'el:iove regarding the other two units (voltage regulator and cut~out}, as the shunt winding
temperature rises the current put across it decreases and consequently also decreases the magnetic pull
on the armature. When the unit is cold this results in a higher regulated current and when it is hot a
lower current because of the hi-metallic blade.
The bi-metallic spring of the current regulator works as thermal compensation of the current going
through it and determines the following advantages:
-~ at the start or aster an interval of about 2 hours from the last period of operation, the control box is
at room temperature (that is, not thermally stabilized) and theretors, as explained beto re, the regulated
current is higher than the maximum continuous permissible one tor the generator, and should the
$Y$l9l"='l "squire it, the generator DC.l'l5_l24,l7,'3E can be overloaded. '
when the control box and generator temperatures rise, the l:>i~metalli<: blade reduces (in about 20
to SD minutes) the regulated current to a value which the generator can tolerate. therefore the tem-
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