44 of 132
M-SV-001-EN Rev.E
Compressor Components
3.5 Silicon-Controlled
Rectifier
3.5.1 Function
3.5.2 Connections
3.5.3 Verification
The AC input voltage is connected to the SCRs
by the Mains Input bus bars. The SCRs are used
to convert the AC voltage into DC voltage. SCRs
maintain the high voltage DC bus necessary
to provide power to the Inverter to run the
compressor motor.
Using both the AC input voltage and the DC
voltage output from the SCRs, the Soft Start
Board generates the gate signal and outputs
pulses of 0-12VDC to the SCRs to control the in-
rush current when power is initially applied to the
compressor. This is used at compressor start-up
while the DC capacitors are charging up.
The DC bus voltage output from the SCRs is
about 1.35 times that of the AC input voltage
(460-900VDC).
See Figure 35 (SCR Connections) to locate the
connections to the SCRs:
1. AC input voltage to SCR
2. SCR Gate cables to Soft Start
3. SCR to DC bus
Figure 35 - SCR Connections
(TT300 - left/TG230 - right)
3.5.3.1 Diodes
Verification
NOTE
A faulty SCR module can cause the DC bus and Mains Input current to be imbalanced. This can stress the Inverter and Stator. If an
SCR module is found to be faulty, then the Inverter and Stator must also be verified.
1. Isolate the compressor power as described
in the “Electrical Isolation of the Compressor”
section of this manual.
2. Remove the Soft Start.
3. Remove the AC Mains Input bus bars, snubber
capacitors and DC bus to isolate the SCRs from
the system.
4. Using a multimeter set for diode
measurements, place the black (-) lead on
terminal 1 of the SCR and place the red (+)
lead on terminal 3. The measured value should
be between 0.3V and 0.45V. See Figure 36 for
terminal locations.
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