ETD790 DC speed controller repair scope:
ETD-790/37A 37A 500V Reversible ETD-791/37A 37A 500V Irreversible
ETD-790/80A 80A 500V Reversible ETD-791/80A 80A 500V Irreversible
ETD-790/110A 110A 500V Reversible ETD-791/110A 110A 500V Irreversible
ETD-790/150A 150A 500V Reversible ETD-791/150A 150A 500V Irreversible
ETD-790/180A 180A 500V Reversible ETD-791/180A 180A 500V Irreversible
ETD-790/300A 300A 500V Reversible ETD-791/300A 300A 500V Irreversible
ETD-790/400A 400A 500V Reversible ETD-791/400A 400A 500V Irreversible
ETD-790/500A 500A 500V Reversible ETD-791/500A 500A 500V Irreversible
ETD-790/700A 700A 500V Reversible ETD-791/700A 700A 500V Irreversible
ETD-790/850A 850A 500V Reversible ETD-791/850A 850A 500V Irreversible
The ETD 790 and 791 series devices are three-phase fully digital DC speed controllers with a maximum operating voltage of 500 Vac and an operating current of 850 A.
With a frequency range of 45-62 Hz, it can be used to control the speed and torque of a motor.
By employing different external dimensions, the device's current can reach up to 9000A.
Speed controllers can be divided into two types: unidirectional (791) and bidirectional (790).
A unidirectional speed controller is used to control the speed and torque in only one direction, while a bidirectional speed controller can be used to control the speed and torque in two directions.
When using a bidirectional speed controller, true four-quadrant control of the motor armature is achieved through the use of a fully controlled anti-parallel thyristor module. During braking, the motor's energy can be rapidly fed back to the power grid.
The speed controller comes standard with an adjustable excitation module for adjusting the motor excitation current or field weakening control. The speed controller is controlled by a 32-bit microprocessor on the ETD 10.07.0 control board. The control board can be used for both unidirectional and bidirectional speed controllers.
The functions of a microprocessor include: master control, interface with external devices, and diagnostics. These functions can be summarized as follows:
Given a signal generator, it can provide various combinations of signal outputs;
PID (Three-Phase Controller) speed regulator;
Current pre-control regulator with motor resistance and inductance calculation functions;
The auxiliary PID function block is freely configurable.
Two layers of protection (alarms and warnings);
Keyboard configuration and display functions on the control panel;
External communication functions are implemented through RS232, RS422 and RS485 serial ports;
It has an embedded CAN fieldbus, and different fieldbuses can be selected through different modules.
The signal processing circuit is completely electrically isolated from the power supply, the circuitry connecting the control board, and the digital input and output circuits.
Differential inputs can be used to simulate a given input in order to ensure ideal anti-interference performance.
There is a set of LED displays on the lower left of the control panel, which are used to display the status of each digital input and output.
ETD790 DC Speed Controller Fault Analysis:
Fault symptom: LCD screen is black (but the power supply to the baseboard is normal and the indicator lights on the front panel are flashing).
Fault Analysis: There are two possible causes for the LCD black screen: one is an abnormal 5V power supply; the other is that the program initialization failed to execute properly. Initially, the input waveform of the 80C196KC crystal oscillator of the microcontroller was observed with an oscilloscope and appeared basically normal, but there were intermittent sudden drops in oscillation amplitude (intermittent period of about 5ms). The microcontroller's I/O output data was also intermittently interrupted (no data status and consistent frequency). Therefore, the faulty circuit points to whether the 5V power supply and the microcontroller's reset signal are normal.
The results indicate that the reset pin should normally be at level H, but instead it was a single pulse. This pulse clearly caused the intermittent interruption of I/O output data. The +5V power supply also intermittently dropped to 4V, suggesting a possible short circuit due to component damage at this intermittent frequency. This caused the microcontroller's reset to fail. Therefore, the microcontroller's power monitoring and reset protection signal was specifically removed from the MAX825 chip's power-on function. A short circuit fault (ULN2003 overheating) appeared. Replacing it with a new ULN2003 resolved the issue and enabled normal power-on.
