9.2 General Faults
This table describes situations where the soft starter does not operate as expected but does not trip or give a warning.
Symptom
Probable Cause
Soft starter does not respond to commands.
- 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.
The soft starter does not control the motor
correctly during starting.
- 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.
Motor does not reach full speed.
- 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.
Erratic motor operation.
- 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.
Troubleshooting
MCD 500 Operating Instruction
MG17K402 - VLT
®
is a registered Danfoss trademark
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