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2 Troubleshooting
1.
Command the MCD 500 to start. While the MCD 500 is starting, measure the voltage across each phase. The voltage should fall to less than
2 VAC just before the soft starter reaches Run mode.
•
If the voltage remains near nominal mains voltage, the SCR is not firing correctly. The Main Control PCB, Backplane PCB or connection between
these items may be faulty.
If the voltage starts near nominal mains voltage then falls to less than 2 VAC just before the MCD 500 reaches Run mode, the MCD 500 is operating
2
correctly and the cause of the starting problem is not the soft starter.
2.2.3 Run Performance Test
Models MCD5-0021B - MCD5-0215B incorporate internal bypass contactors. If the internal bypass contactor does not operate, the SCRs will eventually
fail due to thermal stress. This procedure tests the operation of the internal bypass contactors. Use this test if the starter trips with "Bypass Fail" or "Time
Overcurrent".
This test is performed using either an AC voltmeter.
1.
Connect the MCD 500 to mains voltage, control voltage and to a motor.
2.
Measure the voltage across each phase (L1-T1, L2-T2, L3-T3). This should be close to the nominal mains voltage (phase voltage for in-line
connection and line voltage for inside delta connection).
•
If the voltage is zero, the SCR on that phase may have failed.
•
If the voltage is not equivalent to the nominal mains voltage, the bypass contactor may be damaged and should be replaced.
1.
Command the soft starter to start. When the Run LED (green) stops flashing, you should hear the bypass contactor close.
•
If the bypass contactor does not close, the bypass contactor, Main Control PCB, Model PCB or Bypass Driver PCB (models MCD5-0131B -
MCD5-0215B only) may be faulty or there may be a faulty connection between these components.
1.
When the soft starter is running, measure the voltage across each phase. This should be less than 0.5 VAC.
2.
Command the soft starter to stop and listen for the bypass contactor to open. If the MCD 500 is configured for soft stop, this should occur when
the Run LED (green) starts flashing. If the MCD 500 is not configured for soft stop, this should occur when the Run LED turns off.
NB!
The bypass contactors used in the MCD 500 are latching. The MCD 500 control circuits are designed to open the bypass contactors
even in the event of removal or loss of control voltage. However it is still possible that the bypass contactor may be closed when there
is no control supply to the soft starter. The bypass contactors will open when control voltage is next applied.
Control Input Test
This procedure tests the condition of the soft starter control inputs. This test is performed using a wire link.
1.
Disconnect all external wiring from the soft starter's control inputs.
2.
Control voltage must still be connected to the soft starter.
3.
Connect a wire link between each input.
•
If the corresponding LED lights up then the input is operating correctly.
If the LED does not light up, the control input is damaged. Replace the Main Control PCB
2.3 Trip Messages
This table lists soft starter's protection mechanisms and the probable cause of the trip. Some of these can be adjusted using parameter group 2
Protection
and parameter group 16
6
Protection Action
, other settings are built-in system protections and cannot be set or adjusted.
MG.17.L1.02 - VLT
®
is a registered Danfoss trademark
MCD 500 Service Manual
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