I am redoing my welder by installing a new 3 phase rectifier. To get a picture of what it is like, see here:
I am using a three phase firing system by PCTI. A diagram of hooking it up is provided above in a PDF file.
Note that according to PCTI, they wired current control to have input from a 100 mV shunt, which is what I have (a 100 mV, 200 A shunt).
I think that I connected everything properly. I use a simple divider as a 5 V voltage transducer on the schematic.
Some thing sare working, for example the voltage adjustment pot seems to adjust voltage, but see below.
The voltages that the current setup is capable for are from 0 vdc to
150 vdc.
My problems are kind of strange:
- When I look at voltage with a analog voltmeter (in my welder), sometimes at higher voltages above 80 volts, the meter pointer becomes "wobbly" and unstable. For instance, it could be fluctuating between about 82 and 90 volts. Sometimes it would not do that. It seems to depend on whether I moved the potentiometer quickly or slowly, if I adjust the pot slowly, there seems to be less wobble. I will experiment more tonight.
- Sometimes when I move the pot to desire voltage higher than about
100 V, the firing system "faults" and displays a "fault" signal.
- This system can produce current, however, when I desire max current, it produces just a few amps (like 2-5A), and not the full
200A output. Another tidbit is that before I hooked the current feedback from the shunt, it was capable of producing full current (probably limited by transformer) and made a lot of sparks at contact.
Some of the things that I will explore tonight:
- Double check that my divider for voltage feedback is correctly done.
- Maybe the voltage feedback needs to be a little stabilised, such as by adding a capacitor and a resistor or some such?
- The current regulation seems to be a separate problem. Maybe my regulator is factory configured for 1 mV or another small value feedback by mistake (like I said, they said it is configured for 100 mV). If so, that would be an easy fix with a little divider to divide
100 mV to become 1 mV or some such.
This would be surprising, but not bad, as I would be able to reuse my
400 amp shunt if I desire to go to higher amperages than 200A.
So... Has anyone here "debugged" such control systems?
thanks
i