Danfoss VLT HVAC Drive FC 100 Service Manual page 126

High Power Service Manual for VLT
Adjustable Frequency Drives
2. Ensure that motor check, pre-magnetizing, DC hold, DC brake, or other parameter setups
are disabled that create a holding torque while at zero speed. Current displayed will
exceed 1 to 2 amps if such parameters are not disabled.
3. Run the adjustable frequency drive with a zero speed reference. Note the output current
reading in the display. The display should indicate approximately 1 to 2 amps.
If the current is greater than 1 to 2 amps and a current producing parameter is not active, the
test will need to be made again with the motor leads disconnected.
4. Remove power from the adjustable frequency drive. Monitor the DC bus voltage at power
card connector MK105 (A) and (B) to ensure the bus is fully discharged.
5. Remove the output motor leads from terminals U, V, and W.
6. Apply power to the adjustable frequency drive.
7. Run the adjustable frequency drive with a zero speed reference. Note the output current
reading in the display. The display should indicate less than 1 amp.
If an incorrect reading was obtained from the above tests, further tests of the current feedback
signals are required using the signal test board.
Testing current feedback with the signal test board.
8. Remove power to adjustable frequency drive. Make sure the DC bus is fully discharged.
9. Install the signal test board into power card connector MK104.
10. Using a DVM, measure the resistance between terminals 1 and 4, 2 and 4, and 3 and
4 of the signal test board. Resistance should be the same for all three readings. Table
6-2 shows approximate resistance readings based on adjustable frequency drive power
and voltage rating. Note that values listed are values at the current scaling card. When
measuring with a signal test board, the actual reading may be higher due to meter lead
resistance. Absence of resistance indicates a missing scaling card.
11. Reapply power to the adjustable frequency drive.
12. Using a DVM, connect the negative (-) meter lead to terminal 4 (common) of the
signal test board.
13. Run the adjustable frequency drive with a zero speed reference.
14. Measure the AC voltage at terminals 1, 2, and 3 of the signal test board in sequence.
These terminals correspond with current sensor outputs U, V, and W, respectively. Expect
a reading near zero volts but no greater than 15 mv.
If the control card parameters are set up to provide holding torque while at zero speed, the current
displayed will be greater than expected. To perform this test, disable such parameters.
The current sensor feedback signal at this point in the circuit will read approximately 400 mv at
a 100% adjustable frequency drive load so any reading above 15 mv while the adjustable fre-
quency drive is at zero speed has a negative effect on the way the adjustable frequency drive
interprets the feedback signal.
A reading of greater than 15 mv suggests that the corresponding current sensor be replaced. See
the disassembly instructions in Section 7 or 8.
®
FC Series
MG.90.L1.22 - VLT ® is a registered Danfoss trademark
6 Test Procedures
6
6-35