ELECTRICAL SYSTEM CONTINUED
10. As the speed of the alternator increases, the voltage at the "BAT" terminal also increases. This impresses a
higher voltage through the field relay contacts and across the voltage regulator shunt winding. The increased
magnetism created by the higher voltage across the winding causes the lower contacts to separate, and field
current then flows through a resistor resulting in reduced field current. This reduced field current causes the
alternator voltage to decrease, which decreases the magnetic pull of the voltage regulator shunt winding. The
spring causes the contacts to reclose, and the cycle then repeats many times per second to limit the alternator
voltage to a pre-set value. As the alternator speed increases even further, the resistor connected across the
contacts is not of sufficiently high value to maintain voltage control on the series contacts. Therefore, the
voltage increases slightly causing the upper or shorting contacts to close. When this happens, the alternator
field winding is shorted and no current passes through the winding. With no current in the field winding, the
alternator voltage decreases, which also decreases the magnetism in the shunt winding and the upper or
shorting contact points open. With these points open, field current flows through the resistor and the field
winding. As the voltage increases, the contacts re-close. This cycle then repeats many times per second to
limit the alternator voltage to a pre-set value at high alternator speeds. The voltage regulator unit thus operates
to limit the value of alternator voltage throughout its speed range. Consequently the electrical accessories are
protected from too high voltage which would damage them.
1. A lead-acid storage battery (Figure 7) of the type used in the electrical system of the loader, does not store
electricity. The hard rubber case stores the chemical ingredients necessary to produce electrical energy. This
energy is produced only when a circuit to which the battery is connected is completed. During periods of
inactivity, when no electrical energy is being supplied, a slow chemical breakdown or discharge is taking place.
If the period of idleness is of sufficient length a condition known as a permanent sulfation will develop. Once
permanently sulfated, a battery cannot be restored to its normal maximum capacity. Routine battery service
greatly extends the useful life of the battery.
2. A storage battery is an electrochemical device for converting chemical energy into electrical energy. The
battery has three major functions:
a. To provide a source of current for cranking the engine.
b. To act as a stabilizer to the voltage in the electrical system.
It can, for a limited period, furnish current when the electrical demands of the vehicle exceed the output of
3. The amount of energy that a fully charged battery can produce depends primarily upon the size and number of
4. The total energy that a good battery can produce when at full charge is indicated by its reserve capacity rating.
A 120 minute reserve capacity battery has greater capacity for storing energy and doing work than a 100
minute reserve capacity battery because the 120 minute battery has larger plates or a greater number of
plates. The reserve capacity rating of a battery is usually stamped or printed on the battery case.