Danfoss VLT Series Service Manual page 21

STATIC TEST PROCEDURES
TESTING THE SOFT-
CHARGE CIRCUIT
NTC
Resistors
Black Lead Red Lead
–UDC +UDC
Rectifier
Module
The purpose of the soft-charge circuit is to provide an initial high impedance
current path for building up a charge on the Bus Capacitors. The size of the unit
determines whether NTC resistors or PTC/Contactor combination are used.
VLT 3002-3004, 230V
VLT 3002-3008, 380V/460V
Measure the three NTC resistors (R303, R304, R305) located on the ILD Card.
The resistance should read about 10Ω - 20Ω at room temperature.
VLT 3006-3022, 230V
VLT 3011-3052, 380V/460V
1. Inspect the Bus Charge Contactor. Remove the MK6 harness from the Relay
Card (see Appendix for component location) and check that the contacts
measure open and the spring mechanism is functional. The armature
resistance should be approximately 500Ω.
2. Check the resistance of the PTC resistors located on the Relay Card. At
room temperature the resistance value should be about 30Ω.
3. Remove the Balance Resistors from the DC Bus capacitors. Use an
ohmmeter to insure that the resistance values are correct, (18KΩ).
4. If all measurements are correct, re-install all components and proceed with
dynamic tests.
Incorrect readings could indicate a damaged Bus Contactor, Relay Card, or
problems with the DC Bus capacitors. If a balance resistor is damaged, replace
the bus capacitors the resistor mounted across as well as any series connected
Bus Capacitors. See Replacing the Bus Contactor, replacing the Relay Card, and
replacing the Bus Capacitors, page 4-4.
Section Three
VLT 3502-3504, 230V
VLT 3502-3511, 380V/460V
VLT 3508-3532, 230V
VLT 3516-3562, 380V/460V
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