1. Home
  2. Electronics Design
  3. Strange control problem -- 3 phase "firing system"

Strange control problem -- 3 phase "firing system"

I am redoing my welder by installing a new 3 phase rectifier. To get a picture of what it is like, see here:

formatting link

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:

  1. 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.

  1. Sometimes when I move the pot to desire voltage higher than about

100 V, the firing system "faults" and displays a "fault" signal.

  1. 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:

  1. Double check that my divider for voltage feedback is correctly done.

  1. Maybe the voltage feedback needs to be a little stabilised, such as by adding a capacitor and a resistor or some such?

  2. 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
Reply to
Ignoramus11506
Loading thread data ...

I have a feeling that my controller is not configured the way I expected. I think that it is supposed to sense current from a 0-0.0015 volts shunt, and not from a 0-0.050 volts as I expected (and asked).

Will try to make a little divider cur input from current shunt and see if it helps.

i
Reply to
Ignoramus11506

Because it current limits at a lower current than you expected? The ratios your current limit is off do not agree with the above figures, you could be on the wrong track here. Are you sure the controller does not have a foldback current limit?

I looked at the new diagram ...

Marginal stibility from your controller, you need to turn the gain down or better yet learn how to properly adjust all of your controller parameters.

More issues with the unknown controller ...

Yes, and I started by verifying all control inputs and proceeded systematically through the controller to the gate drives. Do you have a controller schematic and adjustment procedure?

Reply to
Glen Walpert

Yes, and not only it current limits, it also fails with overcurrent LED coming up, if I get current above 5A (approximately).

I am not sure. I called their engineer this morning (did not want to do it yesterday before gathering more data).

He suggested to try running the welder without any current regulation (RSH+ and RSH- connections jumpered). I will do it today running through a low ohms resistor (0.4 ohm 200 watt).

Yes, there are some trimpots that possibly could be adjusted. It is discussed in the page for the regulator board.

I added PDF manuals that I have, to my page with pictures. You can check

formatting link

(three other documents are also available).

Yes, it is in Regulator.pdf. I think that I will try what theiur engineer suggested, that is, to get higher current with current control disabled (using the big resistor). If that gives me higher current, for instance 25 amps, I will know that I have an issue with current control.

From the document:

``fourth from the left is the current feedback control. this sets the maximum current output. CW decreases current. ''

Thanks Glen. I am optimistic, this controller is likely good, but perhaps needs some adjustments.

i
Reply to
Ignoramus6482

Another line of thought is that the controller assumes that the low side (negative) is grounded, this is related to the voltage sensor input. Voltage sensor is not differential, according to their engineer.

So, I think that I can also try to firmly ground the low side and see if it would make any difference.

If it does help, then I can probably think about redoing the voltage sensor input. I'll see tonight.

igor

Reply to
Ignoramus6482

Did not make any difference. Even more strangely, reversing the + and

- side of the current shunt output, still did not make a difference, very puzzling.

i
Reply to
Ignoramus1014

OK, another guess... I found two pins on the firing system that are marked OVSET and OCSET that are not mentioned in the manual that I have (someone from that company emailed it to me).

The manual does not quite match the system, there are two more internal trimpots not mentioned, and I think that the manual also does not mention this OCSET pin. It is blank in the manual.

Some mentions of OCSET pins in other systems like this

formatting link

seem to be quite related and explanatory of my problem, which is that OC trips at lowest currents. Maybe I need to supply some voltage to OCSET. I will call their expert on Monday to discuss this, I think.

i
Reply to
Ignoramus1014

Sounds like you are on thr right track, the correct manual should be a big help :-).

Reply to
Glen Walpert

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.