card would be suspect if all six signals are incorrect. Replace the corresponding card in accordance
with the disassembly procedures in Section 7 or 8.
6.3.12 IGBT Switching Test
Using the test cable 176F8439 while the adjustable frequency drive is powered and the DC bus is
disabled, a simple test can be made to determine if the IGBTs are actually turning on.
Before proceeding, verify that the DC bus is in fact disabled.
1.
Disconnect the cable from connector MK105 on the power card. With a voltmeter, meas-
ure between white lead of the cable disconnected from MK105 and output terminals U,
V, and W in sequence. Switch between AC and DC scales. Voltage should read nearly
zero.
2.
Measure between the black lead of the same cable and the output terminals U, V, and
W in sequence. Voltage should read nearly zero.
With the DC bus disabled, proceed using a DVM set on a diode scale.
1.
With the adjustable frequency drive in stop mode, connect the positive (+) meter lead
to the black lead of MK105 cable disconnected from the power card.
2.
In sequence, connect the negative (-) meter lead to the adjustable frequency drive out-
put terminals U, V, and W. The meter should indicate a diode drop.
3.
Leave the positive meter lead connected to cable MK105, and run the adjustable fre-
quency drive at 30 Hz.
4.
In sequence, again connect the negative (-) meter lead to the adjustable frequency drive
output terminals U, V, and W. The meter should effectively indicate a short circuit or
around a 0.035 diode drop which indicates lower IGBTs are turned on and shorting the
meter to a negative bus.
NOTE!
Some voltage leakage within the unit may cause the meter to indicate a small neg-
ative voltage drop.
5.
Repeat the test for positive (+) or upper IGBTs.
6.
With the adjustable frequency drive in stop mode, connect the negative (-) meter lead
to the white lead of MK105 cable disconnected from the power card.
7.
In sequence, connect the positive (+) meter lead to the adjustable frequency drive output
terminals U, V, and W. The meter should indicate a diode drop.
8.
Leave the negative meter lead connected to cable MK105, and run the adjustable fre-
quency drive at 30 Hz.
9.
In sequence, again connect the positive (+) meter lead to the adjustable frequency drive
output terminals U, V, and W. The meter should effectively indicate a short circuit or
around a 0.035 diode drop which indicates upper IGBTs are turned on and shorting the
meter to a positive bus.
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
6 Test Procedures
MG.90.L1.22 - VLT
®
is a registered Danfoss trademark
6-33
6
Summary of Contents for VLT HVAC FC 100
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