Protecting long wires from EMI (TIG inverter project)

use slow Hi Z logic

put RC filters on each line with the series R's located near the shield and the shunt c's grounded to logic ground

Mark

I am going to have the inverter circuit, with heatsink, in the back of the TIG welder (mostly for proper cooling, there is no other place to put it). Separated from the back by a steel wall (not quite reaching to the bottom), there is a front compartment where HF and the inductor unit live.

The controls, such as the duty cycle (penetration vs. cleaning) pot and the 11 position frequency switch, will live in the front of the welder. Basically next to the inductor and HF unit. The small wires will go from it to the back of the welder.

The HF unit consiste of a double spark gap and high voltage transformer and the capacitor.

I am concerned that they could be subject to interference from the HF unit and everything else.

1. Are my concerns justified.

1. I plan to twist the wires. Is that going to be enough to protect my circuits.

thanks

Are you going to be able to use the HF when your circuit is fitted? I would have thought not, since that kind of voltage isn't going to do it any good, and won't make it through the IGBT circuit. I would temporarily disconnect the HF unit whilst your circuit is connected. If you do run the HF with your circuit fitted, put your circuit in a metal box (a tin can will do, or you can buy something nicer looking), and use shielded cables e.g. RG174 coax or better still, a cable with a single shield containing all of the wires that go to the gate driver board. Keep the wires well away from the HF unit. The main thing will be to consider the loops that you are forming, and minimise the area of these loops. Expect trouble with the HF on: wrong operation and blown ICs should not be surprising. If you can post a photo of where you want to put your circuit in relation to the HF unit, that would be useful.

Chris

It is currently my plan to use HF. The HF transformer would be after my inverter.

I do not have a photo, but my circuit would be after the inductor, then there is HF transformer, tig torch and work.

Ok, I know what circuitry you want, but a photo of the physical location of the various parts inside the welder might be useful in determining where the new parts can go with some hope of it working. I haven't looked at your site much so maybe there already is one.

Chris

Could you rescan your schematic, it's not readible.

Chris, some pictures are here (for now. I will move them soon)

I do wish I wasn't drinking coffee when I saw your follow-up to those pictures. You owe me new keyboard. ;-)

You know, I think that my welder is kind of cute on the outside.

The photos you see were made after I spent at least 15 minutes or even more vacuuming it.

It's amazing how it could work, while holding a few lbs of dust, grit, and dead insects.

Thanks. I am sorry, I tried to make it readable as a jpeg.

It was impossible to make readable at regular screen resolution. I tried many things.

The only way to read it is to open the PDF file (referenced on that page) and go straight to page 66, and then use at least 200% zoom. 400% is even better. I put everything together (my drawing, PDF with schematic, page number etc) at

I will be happy to provide more photos, measurements etc, if you feel that it would help with getting some answers.

I was complaining about that scan as well. We all know how to zoom, you don't need to tell us that. But after zooming, the drawing's printed names and numbers can't be made out because your resolution is too low, hence my request for a rescan. Or you could simply extract page 66 from the manual.

I extracted page 66 for you, at very high resolution, each image is over 1 MB in JPEG format. The page is split into two images.

Here's my drawing of where the inverter will be placed on the schematic. Physically, it will be in the back section of the welder, where the transformer, SCRs, and the fan are located.