Understanding the Electrical System of the Hitachi EX120-2 Excavator

[MikePhua]

The Hitachi EX120-2 is a well-regarded model in the field of hydraulic excavators, known for its reliability, precision, and efficiency. To maintain optimal performance, it’s crucial to have a clear understanding of its electrical system. The electrical schematic of the Hitachi EX120-2 provides invaluable insight into the various electrical components, circuits, and systems that ensure the smooth operation of the machine. Proper comprehension of these components helps with troubleshooting, maintenance, and repair.
Key Components of the Hitachi EX120-2 Electrical System

1. Battery and Charging System:
   The Hitachi EX120-2 operates on a 24-volt electrical system, powered by two 12-volt batteries connected in series. These batteries provide power to the starter motor and other electrical components. The charging system, including the alternator, ensures that the batteries remain charged during operation.
   • Alternator: The alternator generates electricity to charge the batteries while the engine is running. It also powers electrical systems such as lights and the control panel.
     
   • Battery Isolator Switch: This switch is used to isolate the battery from the electrical system, preventing accidental discharge when the machine is not in use.
     
2. Fuse Box and Circuit Protection:
   The electrical circuits of the EX120-2 are protected by fuses located in a central fuse box. These fuses prevent electrical components from being damaged in the event of an overload or short circuit. The fuse box is typically located near the operator’s station for easy access.
   • Fuses: Each fuse corresponds to a specific circuit, such as the control panel, lights, or hydraulic system. If a fuse blows, it needs to be replaced with one of the same rating to prevent damage.
     
   • Circuit Breakers: These are used in certain circuits to protect against prolonged electrical faults that could lead to equipment damage.
     
3. Main Control Panel and Electrical Wiring:
   The control panel is the hub for monitoring and operating the electrical systems of the excavator. It displays critical information such as battery voltage, engine temperature, and fluid levels. The wiring connects the various electrical components to the control panel, ensuring the appropriate signals are sent and received.
   • Wiring Harness: The wiring harness connects all electrical components to the control panel and the main battery. Proper routing and protection of these wires are essential to prevent shorts and ensure reliability.
     
   • Connectors and Relays: Connectors and relays are used to direct electrical current to various components based on user inputs. They play a crucial role in switching between different circuits within the system.
     
4. Starter Motor and Solenoid:
   The starter motor is responsible for starting the engine of the EX120-2. When the ignition key is turned to the start position, the solenoid activates the starter motor, which turns the engine over. The solenoid itself is part of the electrical system and uses electrical current from the battery to engage the starter.
   • Solenoid Function: The solenoid acts as a switch that directs the battery’s electrical current to the starter motor when the ignition is activated. If the solenoid malfunctions, the engine may fail to start.
     
5. Sensors and Electronic Control Unit (ECU):
   The EX120-2 utilizes various sensors that monitor critical machine functions such as temperature, pressure, and hydraulic flow. These sensors send signals to the ECU, which processes the data and adjusts the machine’s operation accordingly.
   • Sensors: Temperature sensors, pressure sensors, and level sensors are used to monitor vital engine and hydraulic system performance.
     
   • ECU: The ECU processes information from sensors and makes adjustments to the engine or hydraulic system to optimize performance. It also plays a role in controlling fuel injection and ignition timing.
     
6. Hydraulic Control System:
   The hydraulic control system relies on electrical signals to control valves and actuators that manage the flow of hydraulic fluid to various components, such as the boom, arm, and bucket. The electrical system communicates with the hydraulic system to ensure precise control and smooth operation.
   • Hydraulic Valve Solenoids: Solenoids control the flow of hydraulic fluid through valves, and electrical signals from the ECU or control panel dictate their operation.
     
   • Pressure Sensors: These sensors ensure that the hydraulic system maintains the proper pressure to avoid system failure.
     
7. Lighting and Warning System:
   The electrical system of the EX120-2 also powers the lighting and warning systems, which are vital for safety during operation. The warning system provides alerts for low oil pressure, high engine temperature, and other potential issues, while the lights provide visibility in low-light conditions.
   • Lights: The excavator is equipped with work lights, front and rear lights, and other illumination systems to ensure visibility.
     
   • Warning Alarms: Alarms notify the operator of any system malfunctions or dangerous operating conditions, helping to prevent further damage or safety risks.
     

Understanding the Electrical Schematic for Troubleshooting
The electrical schematic is a crucial tool for understanding the EX120-2's wiring and circuits. It outlines how electrical components are connected, which fuses protect specific circuits, and how power flows throughout the system. Here’s how to use the schematic for troubleshooting:

1. Identifying Faults:
   When troubleshooting an electrical issue, the schematic helps identify the components involved in the malfunction. For example, if the lights are not working, the schematic can guide you through the fuse box, connectors, and switches that control the lighting system.
   
2. Locating Components:
   The schematic shows the exact location of electrical components, such as the starter motor, sensors, and control panel, allowing technicians to pinpoint the source of the problem quickly.
   
3. Diagnosing Wiring Issues:
   A broken wire or loose connector can cause issues such as intermittent operation or complete failure of electrical systems. The schematic allows you to trace the wiring path and identify where a fault may have occurred.
   
4. Checking Fuses and Relays:
   The schematic also details the fuse ratings and relay locations for each electrical circuit. If a fuse blows or a relay fails, the schematic will help you identify the specific fuse or relay to check or replace.
   
5. Verifying System Grounds:
   Many electrical problems arise from poor grounding of components. The schematic shows the ground connections for various components, enabling technicians to ensure they are properly connected and functioning.
   

Best Practices for Maintaining the Electrical System

1. Regular Inspections: Periodically inspect the battery, wiring, and connections to prevent corrosion, wear, or loose connections.
   
2. Keep the Fuse Box Clean: Ensure the fuse box is clean and free from debris or corrosion that might affect the fuses or wiring.
   
3. Use Proper Tools: When working on the electrical system, always use the correct tools to avoid damaging sensitive components, such as connectors or wiring harnesses.
   
4. Replace Worn Components: If any electrical component shows signs of wear or malfunction, such as corroded terminals or damaged wiring, replace it immediately to avoid further system failures.
   

Conclusion
The electrical system in the Hitachi EX120-2 is intricate and plays a critical role in the performance and functionality of the machine. By understanding the key components, how they interact, and how to troubleshoot using the electrical schematic, operators and technicians can ensure that the machine remains operational and efficient. Regular maintenance, proper inspections, and a solid understanding of the electrical system can help extend the lifespan of the excavator and reduce costly downtime.