6.4.4 DC Bus Voltage Test
DC bus voltage test part I
1.
Using a voltmeter, read the DC bus voltage. See
chapter 6.2.1 Access to DC Bus
for DC bus location.
The measured voltage should be at least 1.35 x the AC
input voltage.
An incorrect reading could indicate a problem in the
inrush circuit, or with the rectifier. See
.
DC bus voltage test part II
1.
Power down the adjustable frequency drive.
2.
Wait for the DC bus to discharge.
3.
Remove the control card mounting plate. See
chapter 7.3.2 Control Card and Control Card
Mounting Plate
or
chapter 7.4.2 Control Card and
4.
Use an ohmmeter set to measure ohms.
5.
Measure from (+) DC bus to power card MK902,
pin 1.
6.
Measure from (-) DC bus to power card MK902,
pin 2.
A short circuit (0 ohms) is the correct reading.
An incorrect reading indicates a bad connection between
the DC bus and the power card. Replace the wire harness.
DC bus voltage test part III
-
Measure across fuse F901 on the top of the
power card.
An open fuse indicates a failure of the power supplies on
the power card. Replace the power card.
6.4.5 Switch Mode Power Supply (SMPS)
Test
The SMPS derives its power from the DC bus. The first
indication that the DC bus is charged is the DC bus charge
indicator light on the power card being lit. This LED,
however, can be lit at a voltage still too low to enable the
power supplies.
First test for the presence of the DC bus.
1.
Install the signal test board (with extension).
2.
Install the split bus power supply. Power the
power card using split bus mode.
chapter 8.1.1 Split Bus Power Supply
.
3.
Connect the negative (-) meter lead to terminal 4
(common) of the signal board. With a positive (+)
meter lead, check the following terminals on the
signal board.
Terminal
Supply
Voltage Range
11
(+)18 V
16.5–19.5 V DC
12
(-)18 V
(-)16.5–-19.5 V DC
23
(+) 24 V
23–25 V DC
24
(+) 5 V
4.75–5.25 V DC
Table 6.4 Measured Voltages at Select Terminals
In addition, the signal test board contains three LED
indicators that indicate the presence of voltage as follows:
Red LED (
±
)18 V DC supplies present
Yellow LED (+)24 V DC supply present
Green LED (+)5 V DC supply present
The lack of any one of these power supplies indicates that
the low voltage supplies on the power card are defective.
Replace the power card in accordance with the
disassembly procedures in
.
6.4.6 Input Imbalance of Supply Voltage
Test
All three phases should have an equal current draw. Some
imbalance is possible, however, due to variations in the
phase to phase input voltage.
A current measurement of each phase reveals the
balanced condition of the line. To obtain an accurate
reading, it is necessary for the adjustable frequency drive
to run at more than 40% of its rated load.
1.
Perform the input voltage test before checking
the current in accordance with
. Voltage imbalances automatically
result in a corresponding current imbalance.
2.
Apply power to the adjustable frequency drive
and place it in Run mode.
3.
Using a clamp-on amp meter (analog preferred),
read the current on each of three input lines at
L1(R), L2(S), and L3(T). Typically, the current does
not vary from phase to phase by more than 5%.
If a greater current variation exists, it indicates a
possible problem with the line power supply to
the adjustable frequency drive or a problem
within the adjustable frequency drive itself.
Test Procedures
Service Manual
80
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
MG94A222
6
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Summary of Contents for VLT FC 103
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