General Faults - Danfoss MCD500 Service Manual

Troubleshooting

2.3 General Faults

This table describes situations where the soft starter does not operate as expected but does not trip or give a warning.
Symptom
Soft starter does not respond to commands.
The soft starter does not control the motor
correctly during starting.
Motor does not reach full speed.
Erratic motor operation.
Soft stop ends too quickly.
MCD 500 Service Manual
Probable Cause
- If the soft starter does not respond to the RESET button on the LCP:
The soft starter may be in Auto On mode and will only accept commands from the remote
control inputs. In Auto On mode, the Auto On LED on the LCP is illuminated. Press the Hand
On or Off button to enable control via the LCP (this will also send a start or stop command to
the MCD 500).
- If the soft starter does not respond to commands from the control inputs:
The soft starter may be in Hand On mode and will only accept commands from the LCP.
When the soft starter is in Hand On control mode, the Off or Hand On LED on the LCP is
active. To change to Auto On mode, press the Auto On button once.
The control wiring may be incorrect. Check that the remote start, stop and reset inputs are
configured correctly (see Control Wiring for details).
The signals to the remote inputs may be incorrect. Test the signalling by activating each
input signal in turn. The appropriate remote control input LED should activate on the LCP.
The soft starter will only execute a start command from the remote inputs if the remote stop
input is inactive and the remote reset input is activated (the Reset LED on the starter will be
on).
- If the soft starter does not respond to a start command from either the local or remote
controls:
The soft starter may be waiting for the restart delay to elapse. The length of the restart delay
is controlled by Par. 2-11 Restart Delay.
The motor may be too hot to permit a start. If Par. 2-12 Motor Temperature Check is set to
Check, the soft starter will only permit a start when it calculates that the motor has sufficient
thermal capacity to complete the start successfully. Wait for the motor to cool before
attempting another start.
The emergency stop function may be active. If Par. 3-3 is set to Emergency Stop and there is
an open circuit on the corresponding input, the MCD 500 will not start. If the emergency
stop situation has been resolved, close the circuit on the input.
- Start performance may be unstable when using a low Motor Full Load Current setting
Par. 1-1). This can affect use on a small test motor with full load current between 5 A and
50 A.
- Power factor correction (PFC) capacitors must be installed on the supply side of the soft
starter. To control a dedicated PFC capacitor contactor, connect the contactor to run
relay terminals.
- If the start current is too low, the motor will not produce enough torque to accelerate to
full speed. The soft starter may trip on excess start time.
NOTE
Make sure the motor starting parameters are appropriate for the application and
that you are using the intended motor starting profile. If Par. 3-3 is set to Motor Set
Select, check that the corresponding input is in the expected state.
- The load may be jammed. Check the load for severe overloading or a locked rotor
situation.
- The SCRs in the MCD 500 require at least 5 A of current to latch. If you are testing the soft
starter on a motor with full load current less than 5 A, the SCRs may not latch correctly.
- The soft stop settings may not be appropriate for the motor and load. Review the
settings of Pars. 1-10, 1-11, 7-10 and 7-11.
- If the motor is very lightly loaded, soft stop will have limited effect.
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MG.17.L4.02 - VLT is a registered Danfoss trademark
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