Soft Charge Rectifier Test: D-Frame Size - Danfoss VLT HVAC Drive FC 100 Service Manual

High Power Service Manual for VLT
Adjustable Frequency Drives
Main rectifier circuit test part IV
1. Reverse meter leads by connecting the negative (–) meter lead to the negative (-) DC
bus connector MK105 (B) on the power card.
2. Connect the positive (+) meter lead to L1, L2 and L3 in sequence. Each reading should
show infinity.
Each reading should show infinity. The meter will start at a low value and slowly climb toward
infinity due to capacitance within the adjustable frequency drive being charged by the meter.
Incorrect reading
With the Part IV test connection, the diodes in the SCR/diode modules are reversed biased as well
as the lower diodes in the soft charge rectifier. If a short circuit exists, it would be possible that
either the diodes in the SCR/diode modules or the lower diodes in the soft charge rectifier are
shorted. To isolate between SCRs or the soft charge rectifier, perform the Soft Charge Rectifier
Test, 6.2.2.

6.2.2 Soft Charge Rectifier Test: D-frame Size

Testing the soft charge rectifier requires access to the soft charge card connectors. It requires
removing the control card and power card mounting plate. Refer to removal instructions for soft
charge card in Section 7.
Do not remove the soft charge card completely or unplug any connectors not called out. Doing so
will break the continuity path of these measurements and may result in a false interpretation of
a failure. Although an open reading is possible, it is unlikely since that indicates that both the
diodes in the SCR/diode modules and the lower diodes in the soft charge rectifier are open. Should
that occur, replace both diodes.
1. Extract the soft charge card far enough to access the connectors.
2. Disconnect the DC cable at the connector MK3.
Since the rectifier test requires the soft charge resistor to be in the circuit, verify the resistor is
good before proceeding.
3. Measure the resistance between pins A and B of connector MK4 on the soft charge
card. It should read 27 ohms (±10%) for 380–500V adjustable frequency drives and 68
ohms (±10%) for 525–690V. A reading outside this range indicates a defective soft
charge resistor. Replace the resistor in accordance with disassembly procedures in Sec-
tion 7. Continue tests.
Should the resistor be defective and a replacement not readily available, the remainder of the
tests can be carried out by disconnecting the cable at connector MK4 on the soft charge card and
placing a temporary jumper across pins A and B. This provides a path for continuity for the re-
maining tests. Ensure any temporary jumpers are removed at the conclusion of the tests.
For the following tests, set the meter to diode check or Rx100 scale.
4. Connect the negative (-) meter lead to the positive (+) MK3 (A) (DC output to DC
bus), and connect the positive (+) meter lead to MK1 terminals R, S, and T in sequence.
Each reading should show a diode drop.
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FC Series
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6 Test Procedures
6
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