CAT-Belts - Inspect/Adjust/Replace

Belts - Inspect/Adjust/Replace
784C and 785C Off-Highway Truck/Tractor

Inspection

To maximize the engine performance, inspect the belt for wear and for cracking. Check the belt tension. Adjust the belt tension in order to minimize belt slippage. Belt slippage will decrease the life of the belt.

To check the belt tension, refer to the Engine Specifications, "Belt Tension Chart". A correctly adjusted belt will deflect 13 to 19 mm (0.50 to 0.75 inch).

Note: The belt tension for the engine fan is spring applied. The fan drive belt cannot be adjusted. If the fan drive belt is loose, see Engine Supplement, Disassembly and Assembly, "Belt Tightener - Remove and Install" for instructions on replacement of the spring. If the fan drive belt is cracked or worn, refer to Engine Supplement, Disassembly and Assembly, "Belt Tightener - Remove and Install" for replacement information.

Adjustment

Alternator


(1) Adjusting nuts

(2) Mounting bolt

1. If necessary, remove the belt guard.

2. Loosen mounting bolt (2) and adjusting nuts (1) .

3. Turn adjusting nuts (1) in order to increase or decrease the belt tension.

4. Tighten adjusting nuts (1). Tighten mounting bolt (2) .

5. If necessary, reinstall the belt guard.

If new belts are installed, check the belt adjustment again after 30 minutes of engine operation at the rated rpm.

Refrigerant Compressor


1. Loosen two bolts (3) .

2. Loosen nut (4) .

3. Use nuts (5) to adjust the belt tension.

4. Tighten nut (4) and nuts (5) .

5. Tighten bolts (3) .

Replacement

For applications that require multiple drive belts, replace the belts in matched sets. Replacing only one belt of a matched set will cause the new belt to carry more load because the older belts are stretched. The additional load on the new belt could cause the new belt to break.

Refer to Engine Supplement, Disassembly and Assembly, "Belt Tightener - Remove and Install" for more information on replacement of the belts.

»»  read more

CAT-Alternator Normal Operation

Systems Operation
30SI Series and 34SI Series Alternator


Normal Operation

The alternator is a brushless, heavy-duty integral charging system. The alternator has a built-in diode rectifier and a voltage regulator. The system produces DC current for electrical systems.

The solid state integrated circuit voltage regulator that is built into the alternator limits the system voltage by switching the ground circuit for the field coil on and off. This is done rapidly in order to control the current that is in the field coil. When the ground circuit for the alternator field is turned ON by the voltage regulator, the field current passes from the diode trio and through the stationary field coil. Nominal regulated voltages of 13.5 to 14.5 volts are available for 12 volt systems. The nominal regulated voltage for the 24 volt system is between 27 and 29 volts.

After the engine is started and rpm rises, the excitation circuit is turned on all the time, and generated voltage rises rapidly. If the "I" terminal is not used, the initial field voltages at start-up are generated by residual magnetism. The residual magnetism can be lost. This results in no output. Loss of the residual magnetism can be caused by extended downtime or a severe shock to the alternator. Refer to Troubleshooting, "T6 Residual Magnetism Restoration". As the speed increases and the output increases, the voltage that is available at the diode trio becomes sufficient to supply field current for normal operation. When the voltage at the "B" terminal exceeds the battery voltage current flows into the battery.

The 34SI model has an "I" terminal. The terminal CAN be used in order to supply excitation current. The current flows from a source that has a keyswitch through an indicator light. The indicator light provides a verification for alternator excitation and the light also provides a indication of faults. The "I" terminal must have an indicator or a resistor in series between the current source and the "I" terminal. This maintains the normal field current around 0.17 amperes. Once the alternator begins charging, the field current is supplied from the diode trio. Current stops flowing through the "I" terminal and the indicator lamp turns OFF.

The voltage regulator cycles the field current ON and OFF many times per second. This maintains the alternator output voltage at a preset level.

For 12 volt systems, an output rating of 105 to 110 amperes is standard. For 24 volt systems, output ratings of 60 to 100 amperes are available. The output ratings of a specific model are located in Specification, "Alternator".

The output of the alternator must be connected to the positive terminal of the battery through the charging circuit for the machine. A ground path is also required. The ground path should run between the alternator ground terminal and the ground terminal for the battery.

While the system voltage is below the setting of the voltage regulator, the regulator turns ON the field current. This allows the alternator to produce the maximum output. When the voltage setting is reached, the regulator turns OFF the field current. When the field current is off, the magnetic field in the rotor collapses and the alternator output voltage begins to fall. The falling voltage causes the regulator to turn on the field current and the current rebuilds the magnetic field. This cycle continues rapidly. The cycle keeps the output and the system voltage very close to the voltage setting. The cycle will continue unless the electrical demands of the system cause the system voltage to fall below the voltage setting. If the system voltage falls below the voltage setting, the regulator will allow full field current to flow so that the alternator's maximum output is realized. Maximum output is dependent on the alternator speed. At low speeds, the maximum output of the alternator is significantly reduced.


(1) Alternator Case Ground

(2) Internal Ground

(3) "I" Terminal

(4) "R" Terminal

(5) Output Terminal

(6) Output Terminal

(7) "R" Terminal

(8) Alternator Case Ground

External connections to the alternator are made to the terminals that are shown in . The standard output terminal is a male type. The connecting bolt is not insulated.

All of the electronic parts of the alternator are dipped in varnish in order to keep out the moisture and the dirt.

»»  read more

Caterpillar-Alternator

Systems Operation
3500B Engines for Caterpillar Built Machines


Alternator


Never operate the alternator without the battery in the circuit. Making or breaking an alternator connection with heavy load on the circuit can cause damage to the regulator.

Illustration

Alternator components (typical example)

(1) Regulator

(2) Roller bearing

(3) Stator winding

(4) Ball bearing

(5) Rectifier bridge

(6) Field winding

(7) Rotor assembly

(8) Fan

The alternator is driven by a belt from an auxiliary drive at the front right corner of the engine. This alternator is a three-phase, self-rectifying charging unit, and regulator (1) is part of the alternator.

This alternator design has no need for slip rings or brushes, and the only part that has movement is rotor assembly (7). All conductors that carry current are stationary. The conductors are field winding (6), stator windings (3), six rectifying diodes, and the regulator circuit components.

Rotor assembly (7) has many magnetic poles. Air space is between the opposite poles.

The poles have residual magnetism that produces a small amount of magnetic lines of force between the poles. As rotor assembly (7) begins to turn between field windings (6) and stator windings (3), a small amount of alternating current (AC) is produced in stator windings (3). This current is from the small, magnetic lines of force that are made by the residual magnetism of the poles. This alternating current (AC) is changed to a direct current (DC). The change occurs when the current passes through the diodes of rectifier bridge (5). Most of this current completes two functions. The functions are charging the battery and supplying the low amperage circuit. The remainder of the current is sent to field windings (6). The DC current flow through field windings (6) (wires around an iron core) now increases the strength of the magnetic lines of force. These stronger lines of force increase the amount of AC current that is produced in stator windings (3). The increased speed of rotor assembly (7) also increases the current and voltage output of the alternator.

Voltage regulator (1) is a solid-state, electronic switch. The regulator feels the voltage in the system. The regulator will start and the regulator will stop many times in one second in order to control the field current to the alternator. The output voltage from the alternator will now supply the needs of the battery and the other components in the electrical system. No adjustment can be made in order to change the rate of charge on these alternator regulators.


General Information

The alternator is an electrical component that is belt driven. The alternator charges the storage battery during engine operation and the alternator supplies electrical power for the machine electrical system. The alternators that are covered by this manual are internally cooled. Air is drawn through baffles. The baffles are located in the rear cover. The air exits from the drive end frame behind the fan.

The alternator converts mechanical energy to electrical energy. This is done by rotating a direct current electromagnetic field on the inside of a three-phase stator. The alternating current and voltage are generated by the stator. The current and the voltage are changed to direct current by a three-phase full wave rectifier. The rectifier uses six silicon rectifier diodes.

The alternator is a brushless unit. The voltage regulator is located inside the alternator. The only movable part in the assembly is the rotor. The rotor is mounted on a ball bearing at the drive end. The rotor is mounted on a roller bearing at the end with the rectifier. The conductors that carry current are stationary. These conductors are in the field winding, the stator windings, the six rectifying diodes, and the regulator circuit components.

The voltage regulator limits the voltage that is produced by the alternator at the output terminal. This is done by controlling the magnetic field that is present in the stationary field coil. The regulator allows current to flow. The current satisfies the electrical loads that are placed on the electrical system and the current charges the batteries.

An internal sense lead is used in order to control voltage. The lead is installed between the "B" terminal and the regulator.

Some of the alternators use a 6.35 mm (0.25 inch) threaded stud as a "B" terminal. This type of terminal is not insulated. When the alternator is connected to the battery, the stud will be energized.

An "R" terminal is located on the end of the alternator next to the "B" terminal. This terminal may be used by one of the following components:

* A Charge Indicator

* A Tachometer

* VIMS, CMS, EMS, etc.

* An Hourmeter

The component is provided voltage pulses at a frequency of 8 pulses for each revolution of the alternator. The current draw across the "R" terminal must not exceed 2 amperes.

The "I" terminal is located on the end of the 34SI alternator. The terminal is the second terminal from the output terminal. This terminal may be used to operate an indicator light. The terminal may also be used in order to ensure when the alternator starts. The "I" terminal is a threaded stud.

The "I" terminal is connected internally to the field circuit. An indicator light that is connected in series with the terminal will glow when there is a difference in potential between the terminal and battery voltage. When the system is charging properly, the light is off.

An isolated ground terminal is located on the end of the 34SI alternator. An isolated ground terminal is also located on the end of the isolated 30SI marine alternator. The terminal is on the opposite side from the "B" terminal. The isolated ground terminal is provided in order to connect a ground lead.

A ground terminal for the case is located on the side of the non-marine 30SI alternator housing. A screw and a lockwasher should be installed in the hole for the case ground. The screw prevents the entry of dirt and water.

»»  read more