High Freq interference

[MikeR]

Much like Choppers question. Some of you may remember asking to see pictures of my positioning table. I haven't forgotten, but I refuse to take pictures of something that doesn't work!

The first few times I used the table, I had it sitting on my welding table, which is 4'x8'x1/2" plate on 3x3x1/4 angle. I had no problems whatsoever with it. Just recently I built a stand for the positioning table so I could sit in a comfy chair and use it. Now I'm having much trouble with the HF.

The positioning table consists of a 90volt DC gear motor, run with a thing that converts it from 110vac to 90vdc, and it also has a foot switch on the 110 side, another on/off switch 110v, and a clockwise/counterclockwise switch 110v. Oh, and it also has a speed control doo-hicky in the same box as the two switches and the votage converter thing-a-ma-jig. The box is plastic, and the bolts that mount it are isolated via rubber grommets.

So now, I'm all comfy in my chair, got all my aluminum pieces spotless, I set the speed for the table, strike the arc, and off it goes. With the arc on, the table goes faster than the max it normally has through the speed control.

I tried to ground the whole thing to my welding table, thinking that some of the RF / HF would get absorbed into it, but all that did was make it run fine, then JERK!, then run WAY too fast, then fine, then JERK JERK!!

WAKE UP!!

My question is: How do I fix this?? Is there another ground I can run? Is there a cover I can use to isolate the motor? I'm only gonna post pictures of this contraption if it works! Any help would be greatly appreciated.

[Sberry]

If I understand this right,, you may need to pipe the wiring going to it,, shield it.

[MikeR]

110v or 90v side or both? What kind of pipe?

[Sberry]

This could get complex but shield everything you can with metal and make sure the controller is in a metal box. The DC wire may be the most sensitive. Then, if that doesnt work you may need to put some capacitors between the motor leads and ground. I know they often use something called feed thru caps and you can get at automotive. We need electric engineer here.

[Sberry]

I re read the post. Cover the controller box with metal first. It should have been in metal box for this project. Then conduit the wiring. As a guess I would have to say the box cover might be most effective,, obviously that effects the speed. Cover it with a couple layers of aluminum foil for testing and make sure the foil is grounded.

[MikeR]

But everything was wired the same when it was sitting on my welding table. What's changed?????

[Sberry]

Maybe the way the table was reflecting or something,, who knows, read back to addtion to last post about foil.

[Franz]

What changed? You acheived the perfect RF circuit between the welding cable and the solid state speed control.
Unfortunately, TIG he freq is usually broad spectrum RF, so it's hard to acheive detuning the RF path via distance.
An alternative might be to run the TIG leads overhead to the positioner, sometimes simple solutions work, other times they don't.

[atucker]

You might try plugging the positioning table into a GOOD computer surge suppressor. That might filter out any RF/noise that is coming thru the power line. We're getting too many solid state devices in this world that want to talk to each other, whether they should or not .

Allen T.

[Wood-N Steel]

stray HF

This sounds like you are working at the shop where I work same problem with a set of positioning rolls we purchaced.Talked to original manufacture and several electrical engineers. Not one had a definite and precise answer. I would suggest you put it back on the welding table try again if it works there figure out the difference
?? Torch cable running to close to controller lines
?? Torch cable laying on bench or not
?? Torch cable wrapped around lazy boy recliner


We use our positioners for wire feed now so I dont have pissed off weldors.

[Hobart Expert Rock]

MIKER...........HF RADIATES 50' IN ALL DIRECTIONS........... IF YOU CONTACT A PHONE COMPANY THEY HAVE RF SHIELDING CONDUIT TO RUN PHONE LINES AND COMPUTER LINES THRU.......... HF IS NOTHING MORE THAN A RADIO FREQUENCY.......... SHIELD, GROUND, ISOLATE.............

I ONCE SEEN IT TURN ON A OVERHEAD CRANE VIA THE CABLE HOLDING THE PIECE BEING WELDED ON.......... THE OPERATOR (WELDOR) WAS SO USE TO THIS THAT HE JUST WALKED ALONG AND TIG WELDED FOR 11 FEET UNTIL HE GOT TO THE END OF THE TORCH........... THEN MOVED THE CRANE BACK TO ORIGINAL POSITION AND STARTED ALL OVER AGAIN........... HE CONFIDED IN ME THAT AFTER 3 WEEKS OF THIS IT WAS GETTING TO BE A PAIN IN HIS BACK SIDE.................. ........ 20 TON OVERHEAD CRANE................ KINDA LIKE PIPE LINE WELDORS WHO CAN LIGHT A CIGARETTE AND DRINK COFFEE AND NEVER STOP WELDING..................TRUE STORY.................ROCK.
[email protected]

[ventureline]

Try tying the ground and electrode cables together over the first 3 ft after leaving the welder. This tends to disipate the HF, so that it doesn't effect other items like controllers, computers and phone lines

[MikeR]

Thanks guys, all good suggestions. I haven't had time to try them out yet, but need to soon. Just wanted to let you know I'm listening.

[MikeR]

hmmmm........ listening?