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15/05/2024

The crane hook goes up slowly. The cargo crane is not working. Troubleshooting

Greetings! The hook of the cargo crane goes up very slowly. There is no accompanying information or prompts from the automation.

Crane control panel

In this article, let's figure out what this problem is and how to fix it. First of all, you need to understand that we are only interested in the section of the circuit that is responsible for the “hoist up” hook command (not the jib). 

Accordingly, we look at the instructions for troubleshooting the problem associated with the definition of “hoisting”.

Hoisting circuit
Hoisting circuit

The instructions indicate checking the circuit: Joystick - PLC - relay - Proportional drive - Proportional valve. In simple words, the operator, using a joystick, transmits a command to the proportional valves (hook up and down) through the PLC module and proportional driver.

The main visual indicator that the joystick is working are the LEDs on the driver "Output A" and "Output B". They light up when commands are executed on the hook up and down. Also, the 58K circuit preparation relay and PLC module work without any problems.

Circut of operation of the crane (hook up and down)
Circut of operation of the crane (hook up and down)
Joystick and driver operation diagram
Joystick and driver operation diagram

The first thing to check in this case is the 24V DC that comes to the solenoid valve coils. Voltage comes to both coils. The next task is to check the readings of the currents that go from the driver to the coils of the proportional valves.

Proportional driver
Proportional driver

To do this, you need to connect a multimeter in milliammeter mode to the open circuit of T0235 and T0239.

Tester connection diagram
Tester connection diagram
Two multimeters for two coils
Two multimeters for two coils

We connected two multimeters to the open circuit of the hook up and down. We measure the current when the crane is operating. It can be seen that with maximum position of the joystick, the current reaches 300 mA on both (hook up and down) lines. This suggests that the problem is not with the driver, it is working good. Otherwise, if there was a problem with it, then you can do a calibration using potentiometers or replace the driver.

Crane drivers for various operations
Crane drivers for various operations

When replacing, be sure to install the jumpers on the rear panel as they were on the original driver.

Jumpers on the rear panel
Jumpers on the rear panel

It is also necessary to check the currents, although from the factory they should be set to a maximum value of 300mA.

In our case, referring to the instructions, we move on to a proportional valve with two solenoids.

Proportional valve with two coils
Proportional valve with two coils

It is necessary to check the coils, the resistance of which should be 41 ohms. This action should be performed at the very beginning of checking the circuit. After testing the coils, we made sure that the resistance values also corresponded to the instructions.

Checking the coils
Checking the coils

All that remains is to disassemble, clean and check the proportional valve. 

Disassembling and cleaning the proportional valve also did not give a positive result. The problem was discovered directly in the operation of the pump itself (it did not produce enough pressure), after which it was disassembled and defects were discovered.

Crane hydraulic pumps with proportional valves
Crane hydraulic pumps with proportional valves

Some worn parts were found in the hydraulic pump for hoisting operation. As a result, the pump had to be replaced.

The problem turned out to be in the hydraulic pump, but to get to this point we had to check many other components of the system and spend a lot of time. Despite this, the article shows all the automation points that may fail when this problem occurs.

Crane model: DMC DDKC-3026-00 (Dongnam Marine Crane)

Also read other articles about DMC cargo cranes:

  1. Problems with cargo cranes. Some problems with cargo cranes that occur on the ship
  2. The cargo crane does not slew. Troubleshooting
  3. PLC failure. The cargo crane does not start. Troubleshooting
  4. Motor Fault on the crane. Troubleshooting
  5. The crane jib is luffing down under its own weight. Troubleshooting

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