Brake Igbt Test; Current Sensors Test - Danfoss VLT HVAC Drive FC 100 Service Manual

6 Test Procedures
Incorrect Reading
An incorrect reading indicates some of the IGBTs are not turning on. Replace the IGBT module
according to the disassembly instructions in Section 7 or 8.

6.3.13 Brake IGBT Test

Use the signal test board to test the operation of the dynamic brake IGBT and gate drive circuitry.
The following procedure can be used to force the brake circuit to activate for testing.
6 1.
2.
3.
4.
5.
Incorrect Reading
If the signal on terminal 13 is not correct, first check that the adjustable frequency drive is correctly
programmed for dynamic braking (parameter 2-10). If the programming is correct, replace the
control card in accordance with procedures in Section 7 or 8.
If the signal on terminal 13 is correct but the signal on terminal 14 is not, the brake IGBT gate
signal must be checked to determine whether the fault lies in the IGBT or the gate drive card. See
Gate Drive Signal Tests.

6.3.14 Current Sensors Test

The current sensors are Hall effect devices that send a signal proportional to the actual output
current waveform to the power card. The current scaling card, attached to the power card, scales
the signals from the current sensors to the proper level for monitoring and processing motor
control data. A defective current sensor can cause erroneous ground faults and overcurrent trips.
In such instances, the fault will usually only occur at higher loads. If the incorrect current scaling
card is installed, the current signals will be improperly scaled. This could cause erroneous over-
current trips. If the current scaling card is not installed, the adjustable frequency drive will trip.
A couple of simple checks can be made to determine the status of the sensors.
1.
6-34
NOTE!
Some voltage leakage within the unit may cause the meter to indicate a small neg-
ative voltage drop.
Connect the signal test board to connector MK104 on the control card.
Set the voltage test switch labeled Over V to the ON position.
Turn the potentiometer on the test board until the brake circuit activates. This causes
the brake IGBT to turn on and off at approximately 1.2 KHz. Duty cycle (pulse width)
increases as the potentiometer is increased.
Using an oscilloscope or DVM, measure at terminal 13. Terminal 13 represents the gate
signal to the brake IGBT. This should be 4.04 VDC when brake is OFF and drop to zero
when brake is ON.
Use an oscilloscope or DVM at terminal 14. Terminal 14 is a logic level (5V) signal rep-
resenting voltage across brake IGBT. This should measure 5.1 VDC when brake is OFF
and drop to zero when brake is ON.
Apply power to the adjustable frequency drive.
MG.90.L1.22 - VLT
High Power Service Manual for VLT
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FC Series
Adjustable Frequency Drives