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VOLTAGE CONTROL
To protect the IGBTs of the AC unit, the voltage across them must not exceed
600V. Filter Capacitor C09 is charged from the positive and negative rails via
diode V05. Measure the voltage between XA:5 (+) and XA:8 (- - ),
The voltage over C09 is controlled by the monitoring circuit, which uses
transistor Q301 and resistor R03 for discharging. Adjust discharge with trim
potentiometer R302 so that the mean voltage level does not exceed 400V.
Voltage at discharge capacitor C09 at 200A (AC welding)
Version 1 of AP07
To protect Q301 and R03 from overload, a PTC resistor
(R317), of the same type as ST02 on previous page, is
fitted on the transistor. When the voltage across R317
rises due to high temperature, IC6 is activated and the
input to the error monitor IC1 goes low (0V). The
threshold level for the voltage across R317 is 5.1V.
Version 2 of AP07
To protect Q301 and R03 from overload, a temperature detector (R317) is
fitted on the transistor. When the voltage across R317, testpoint TA1, rises due
to high temperature, IC6 is activated and the input to the error monitor IC1
goes low (0V). The threshold level for the voltage across R317 is 5.6V, it can
be measured at testpoint TA2. Trimpotentiometer R35 is adjusted at the factory
to set the voltage at TA1 to 4.77V 0.5V when the machine is cold.
As a last protection, in case the voltage control does not work, the maximum
allowed voltage is adjusted to about 580V with R301. If the voltage is too high,
IC6 supplies an error signal to IC1, which stops the machine.
Note: The voltage supply to the voltage control comes from the IGBT drive
supply +17V/3 and GND3. GND3, is connected to the machine negative rail.
0V for the supply voltages (+5V and +15V) on this board is not connected either
to GND3 or to the machine electronic zero (0V), which is connected to the
positive rail.
ADJUSTMENT PROCEDURE
All machines and circuit boards are adjusted when delivered from the factory.
The threshold levels may be checked and readjusted as follows:
WARNING: Take great care: if you do something wrong here, you may
destroy the IGBTs.
1. Disconnect the supply to the HF unit AP13, by disconnecting wires 021 and
041 from terminal XT11. See the wiring diagram.
cdte1de1
- - 48 - -
.
V--LIMIT+
R317 fitted on Q301
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