Interference from welder

[metal pig]

Hi to all

This is in regards to a non-Hobart welder but I am sure it is a pertinant question no matter wat the manufacturer is.

I have purchased a V160T TIG welder and am experiencing some degree of electrical interference on the AM radio in the house when the welder is used in the garage. It is worse when using the stick welding function even when not performing any welding. Just merely changing over the function switch changes the level of interference.

I have added an earth rod next to the garage and linked the mains earth in the garage switchboard to it.

Would you recommend adding another lead directly from the weldment to the Earth rod?

Would you also suggest adding a ferrite ring to the mains supply lead with the lead running supply through it or looped once through it?

Any other thoughts on how to approach this issue for domestic and neighbourly harmony.

Thanks

Metal Pig

[Al T.]

Your problem sounds like it is traveling through the air. AM is amplitude modulation, any rising or falling magnet wave will affect AM. FM, frequency modulation, should not be affected.

To eliminate waves from leaving your work area, you might need to build a copper screen enclosureto all sides, top and bottom. All screens should be grounded to each other and at several points to ground. I'm not sure about the grid size of the screen. That comes into play if you are generating RF at a certain frequency.

Anyone else got an idea?

[John Stuckey]

If you are interested in building a "copper grid tent" you could get information and see what one looks like by finding a shop that repairs/tests radio transmitters. Motorola repair facilities come to mind. A public safety official can tell you where they get their radios repaired.
John

[Ed Heimbach]

Easy solution is to put some bypass capacitors on both the input and the output of the welder. I've used small mica caps rated at 500 volts for this. If you need more info on this do a google search on electronics shielding, good luck.

[Main]

Unfortunately todays radios have very poor filtering. Most AM radios have an internal ferrite bar antenna. Try turning the radio 90 degrees to see if it reduces the noise. That would be the easy fix. Next step is to find where the RFI, EMI is being radiated from. Remove the welding leads(possible radiating antenna) from the machine and turn the welder on. Do you hear the interference? If so, get some shielded coax. Connect the center conductor of the coax to the outside case of the welder and run the other end to earth ground. Connect the shielded braid of coax to seperate earth ground. Take the welding leads and make a tight coil about 6 inches around using five or six turns in the cable as close to the welder as possible. You can use a coffee can or similar object to form the coil. Tape coil tightly. This will create an RF choke in the cables and help reduce the leads from radiating RF. This is the down and dirty cheap way of doing things. One more thing you can try. Do you know any amateur radio operators (hams)? They deal with RF problems on a regular basis and usually like the challange of solving problems like this. Good luck and keep us posted.

[metal pig]

Thanks to all for your suggestions

I will work through some of these ideas and I will let you know how I get on.

Ed, in regards to your idea of putting some bypass capacitors on both the input and the output of the welder. Do you mean for them to be in series with the cables or 'across' the cables, one for input, one for the output?

Main, the interference still appears to be current when the cables are disconnected so I will initially pursue the idea of some sort of Faraday cage around the machine. I am intending to build a trolley to hold the machine, bottle, cables and ancilliary equipment in a tidy and mobile manner so potentially I could include something along these lines in the design. Once I have that done I will also be able to minimise the amount of putput cables that are trailling across the floor as well.

Does the cage need to be made of copper or is that requirement related purely to the conductivity of copper?

Once again thanks for the suggestions.

Regards

Ralph Price

[Al T.]

metal pig,
Copper is used because of its conductivity, shorts out that noise to ground faster than higher resistance metal.

I never thought about putting the cage around the welder, that might work too without all the expense of building a welding room inside a RF cage. But there is a good chance that all the RF noise is coming from the Arc itself.

The capaciter question you had, use 3 caps, one between the two cables and one cap from each cable to chasis ground(earth ground). Don't put the caps in series with your cables, current can not go thru'em.

I hope you get it solved!

[metal pig]

Hi Al

thanks for the rapid reply.

I will try the cage only around the machine initially for convenience. Could it be copper sheet rather than mesh?

Any thoughts on the microfarad size of the capacitors?

Thanks

Ralph Price

[Main]

metal pig
You can use copper, steel or aluminun for the material. Basically what you are making is an antenna to capture the radiated signal and sending it to earth groung. I`m sure copper sheeting would work but screening might be easier to work with. The recommendation of capacitors is probably the easiest to work with.
I should of thought of this before. Have you tried a different radio? Some radios have better filtering than others. Do you get the same interference on your automobile radio when its parked in the yard?

[BillC]

Metal Pig,

If you try copper sheet make sure you allow sufficient airflow to cool the power supply.

Main and Metal Pig,

Turning the radio around or moving it is no longer an option unless Metal Pig lives miles away from any other people. The FCC says it is the responsibility of the source of the RFI to shield, filter, or cease operation...

[Main]

Bill C
Metal Pig is from New Zealand so the long arm of the FCC doesn`t reach that far. But lets just say for sake of example your equipment was interferring with your neighbors. If you were a nice Guy (and I`m sure you are) you would try to resolve the problem within reason. But and this is kind of a grey area you could just say tuff cookies and do nothing.

Taken from the FCC site..."The two most common causes of interference are transmitters and electrical equipment. Communication systems that transmit signals (transmitters) are capable of generating interference; these include amateur radios, CBs, and radio and television stations. Electrical interference may be caused by power lines or electrical equipment in your home".

It also goes on to say..."Transmitter interference is normally caused by the actual design of the (interfered-with) equipment itself. Many manufacturers do not protect internal wiring with adequate shielding or sufficient filtering, so the interfered-with equipment is susceptible to receiving unwanted signals - interference".

So in a nutshell its not my fault that my neighbor happens to own lousy designed, elcheepo, piss poorly filtered receiving equipment that would pick up static if I happen to scuff my feet on the carpet.

Just my 2cents worth. no flame intended. I`m just having one of those days.

[lranch]

EMI

Hello Metal Pig.

EMI can be quite a problem some times, however with regards to an AM reciever, just walking across a shag carpet will produce "noise". I myself have damaged a modem and a Kenwood reciever with one of my tigs, my fault, grounded to table instead of work, should have reground tungsten when hard started, was playing mp3s on winamp (long patch cables) knew It would get me some day. However, the interesting thing about your situation is you seem to experience EMI with machine at idle (power on, not welding!). This would suggest that the source of your noise (bear in mind I do not have a mental image of your machine) is either an exceptionaly crappy transformer, or, with any luck, a fan on it's way south. In your post you said that switch settings will affect degree of noise. I would suggest you disconnect rig from power, pop covers, and take a look at trans. Check for: clean/tight connections and direct trans case ground to equipment ground. Also, disconnect fan motor and power machine (just turn on don't hit pedal). Am interested to see what, if any difference you encounter. Please be very careful.

[Roger]

To fix your EMI problem get new metal shop building with metal window screens. Just because my wife wouldn't believe that doesn't mean it wouldn't work.

[BillC]

Originally posted by Roger
To fix your EMI problem get new metal shop building with metal window screens. Just because my wife wouldn't believe that doesn't mean it wouldn't work.

Good thinking Roger! I will have to try that one out on my wife!