| NOTICE |
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Improper grounding can cause uncontrolled or unreliable circuit paths and electrical noise resulting in damage to the engine bearings, and other engine components. |
Proper grounding of the unit and the engine electrical systems is necessary for proper performance and reliability.
All return paths to the negative battery must carry any likely fault currents.
The starter should be connected directly to the negative battery post. The alternator must be connected to the negative battery, bus bar, or negative side of the starting motor.
Negative Battery Connection for Multiple Engines
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| Illustration 1 | g01635383 |
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Isolated components | |
If multiple bus bars are used to connect components to the negative battery, a common reference should be provided. All bus bars must be wired together for proper engine synchronization for multiple engine installations.
Welding on a Vessel that is Equipped with an Electronic Controlled Engine
Refer to the appropriate Troubleshooting Guide for more information about welding on a vessel that is equipped with an electronic controlled engine. Also refer to the appropriate Operation and Maintenance Manual for more information about welding.
Switched Positive Battery and Unswitched Positive Battery
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| Illustration 2 | g01264533 |
Note: All battery connections to the ECM must be utilized in order to prolong the service life of the ECM.
The electronic control system can operate on either a 12 V electrical system or a 24 V electrical system. The switched positive battery and the unswitched positive battery connections to the ECM are made at the P61 Customer connector.
The ECM receives electrical power through the input for the switched positive battery. Protection for this circuit must be rated at 15 Amp (12 V or 24 V system).
The input for the unswitched positive battery is used to power the ECM memory that contains maintenance information and certain logged diagnostics. Protection for the unswitched positive battery circuit is specified as 20 Amp.
Powering the electronic control system through dedicated circuits with circuit breakers reduces the possibility of performance problems of the electronic control system. This also minimizes the chance of an engine shutdown due to a short in the electrical system. Additional loads should not be connected between the ECM and the circuit protection for the ECM.
Note: Do not use in-line fuses for circuit protection. Caterpillar recommends the use of circuit breakers for circuit protection. Circuit breakers should be located with other devices for circuit protection in a centrally located, dedicated panel. If circuit breakers that automatically reset are used, consideration of the environment of the location of the breaker is critical and the effect on the trip point is critical. The trip point of some circuit breakers can be reduced below the rated trip point if the circuit breaker is exposed to high temperatures. This reduction can cause intermittent shutdowns that result with needless replacement of electronic components.
Suppression of Transient Voltage
The installation of transient suppression at the source of the transient is recommended. Refer to Illustration 4. Caterpillar follows a stringent electrical environment standard that is similar to SAE recommended practices.
The use of inductive devices such as relays and solenoids can result in the generation of transient voltage in electrical circuits. Transient voltage that is not suppressed can exceed SAE specifications and lead to the degradation of the performance of the electronic control system.
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| Illustration 3 | g01264857 |
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Use of a diode in a relay as a transient voltage suppressor | |
The OEM should specify relays and solenoids with built-in voltage transient suppression. Refer to Illustration 3 for ways to minimize transient voltage from relays and solenoids without built-in voltage transient suppression. Techniques include the installation of a diode or resistor of the proper size in parallel with the solenoid or the relay coil. Other techniques may also be used.
Inductive devices such as relays or solenoids should be located as far as possible from the components of the electronic control system.
Wiring harnesses that are installed by the OEM should be routed as far as possible from the wiring harness of the electronic control system in order to avoid problems that are associated with electrical noise.
Examples of devices that require suppression of transient voltages include any device that switches inductive loads on and off. The following list provides examples of such devices:
- Solenoids (trim tab solenoids, etc)
- DC electric motors
- Relays that use the same power and ground as the sensor
The following list provides other examples of situations that may cause transient voltages:
- Improperly grounded electronic components
- Improperly grounded cable shields
- Improperly grounded antennas
- Signal wires that are installed too closely to power wires
All of the components that are connected to the ECM must have return wires (ground) that are connected to the engine's − Battery. The return wires (ground) should be connected as close to the battery as possible. Caterpillar recommends the use of a separate return wire for each component. Each return wire (ground) should be attached to the engine's − Battery bus bar.
Caterpillar recommends the use of a 218-4935 Arc Suppressor on all inductive devices such as relays and solenoids. The 218-4935 Arc Suppressor is not polarized. This arc suppressor can be wired into the circuit without any concern for the direction of current flow.
| Required Parts | ||
|---|---|---|
| Part Number | Description | Quantity |
| 218-4935 | Arc Suppressor | 1 |
| 155-2270 | Connecting Plug Kit (2-PIN) | 1 |
| 186-3736 | Connector Socket | 2 |
| 130-5300(1) | Clip | 1 |
| 130-5301(1) | Clip | 1 |
| (1) | Optional mounting clips |
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| Illustration 4 | g01093137 |
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Typical wiring for 218-4935 Arc Suppressor | |
The electrical system has two separate circuits:
- Starting circuit
- Low amperage circuit
Some of the electrical system components are used in more than one circuit. The following components are used in each of the three circuits:
- Battery
- Circuit breaker
- Ammeter
- Battery cables
The charging circuit is in operation when the engine is running. A voltage regulator in the circuit controls the electrical output in order to keep the battery at full charge.
| NOTICE |
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The disconnect switch, if equipped, must be in the ON position in order to let the electrical system function. There will be damage to some of the charging circuit components if the engine is running with the disconnect switch in the OFF position. |
If the engine has a disconnect switch, the starting circuit can operate only after the disconnect switch is put in the ON position.
The starting circuit is in operation only when the start switch is activated.
Both the low amperage circuit and the charging circuit are connected to the same side of the ammeter. The starting circuit is connected to the opposite side of the ammeter.
A solenoid is a magnetic switch that does two basic operations:
- The solenoid closes the high current starting motor circuit with a low current start switch circuit.
- The solenoid engages the electric starting motor pinion with the ring gear.
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| Illustration 5 | g00285112 |
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Solenoid | |
The solenoid has windings (one set or two sets) around a hollow cylinder. The plunger can move forward and backward. When the start switch is closed and electricity is sent through the windings, a magnetic field is created. The magnetic field pulls the plunger forward in the cylinder. Pulling the plunger forward moves the shift lever in order to engage the pinion drive gear with the ring gear. The front end of the plunger then makes contact across the battery and the motor terminals of the solenoid. After the contact is made, the starting motor begins to turn the flywheel of the engine.
When the start switch is opened, current no longer flows through the windings. The spring now pushes the plunger back to the original position. At the same time, the spring moves the pinion gear away from the flywheel.
When two sets of solenoid windings are used, the windings are called the hold-in winding and the pull-in winding. Both sets of windings have the same number of turns around the cylinder, but the pull-in winding uses a wire with a larger diameter. The wire with a larger diameter produces a greater magnetic field. When the start switch is closed, part of the current flows from the battery through the hold-in windings. The rest of the current flows through the pull-in windings to the motor terminal. The current then flows through the motor to ground. The solenoid is fully activated when the connection across the battery and the motor terminal is complete. When the solenoid is fully activated, the current is shut off through the pull-in windings. Only the smaller hold-in windings are in operation. The hold-in windings operate for the duration of time that is required in order to start the engine. The solenoid will now draw less current from the battery, and the heat generated by the solenoid will be kept at an acceptable level.
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| Illustration 6 | g01363366 |
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Electric starting motor components (1) Brush assembly (2) Field windings (3) Solenoid (4) Clutch (5) Pinion (6) Armature | |
The starting motor is used to turn the engine flywheel at a rate that will allow the engine to start running.
Note: Some starting motors have ground straps that connect the starting motor to the frame. But, many of these starting motors are not grounded to the engine. These starting motors have electrical insulation systems. For this reason, the ground strap that connects the starting motor to the frame may not be an acceptable engine ground. Starting motors that were installed as original equipment are grounded to the engine. These starting motors have a ground wire from the starting motor to the negative terminal of the battery. When a starting motor must be changed, consult an authorized dealer for the proper grounding practices for that starting motor.
The starting motor has a solenoid. When the ignition switch is turned to the START position, the starting motor solenoid will be activated electrically. The solenoid plunger will now move a mechanical linkage. The mechanical linkage will push the pinion in order to engage with the flywheel ring gear. The pinion will engage with the ring gear before the electric contacts in the solenoid close the circuit between the battery and the starting motor. When the circuit between the battery and the starting motor is complete, the pinion will turn the engine flywheel. A clutch gives protection for the starting motor so that the engine cannot turn the starting motor too fast.
When the ignition switch is released from the START position, the starting motor solenoid is deactivated. The starting motor solenoid is deactivated when current no longer flows through the windings. The spring now pushes the plunger back to the original position of the plunger. At the same time, the spring moves the pinion gear away from the flywheel ring gear.