Thread: Mig welding Stainless Steel tube and Sheet

I looked into HF a few years ago. i wondered why it was called HF and not HV or EHT even. EHT, like you used to get in a TV, is DC, the HF is an AC voltage. I think this is a safety thing, where DC voltages are a bit more nasty to you. The other reason is its easier to filter out a high frequency signal so it doesn't damage the welder itself

If I am nowhere near an earth and accidentally zap myself, I have seen sparks going into my finger thinking that should hurt, but could barely feel it. Yet if your hand is leaning on a welding table and the earth isn't too good onto the workpiece, you can get a big jolt. its all to do with how much current is behind the voltage. i think the big metal table acts an an electron sink, even if its not directly connected to the welder. You will appear as a capacitor, well that's my theory anyway.

In fact, in my welder it was a very simple circuit that had a supply voltage applied to it 50 times a second. Every time the voltage was applied, it caused an oscillating decaying signal, about 16khz from memory. The oscillating voltage was multiplied up by a coil and a points gap same as a car spark plug in the old days.

I have a generic chinese welder of the everlast variety. It would draw a spark of 50mm when i got it. After a while I had a fault whereby the HF voltage got back through the output filters and took out my fred diodes in the switchmode stage. I could trace a line of damaged components all the way back on one leg. I closed the points up so it would only arc across about 15mm, I reckon the extra gap was causing too much stress on components necessarily and it took out a filter component. I'm pretty sure that the HF gets switched off as soon as DC current starts flowing and its pulsed in time to your ac, so I'm not sure its going to do you much harm since its off most of the time.
Regarding vehicles, I've heard a lot of people say hf is a risk to cars. The usual advice is to disconnect your battery, but to me, you've just disconnected a massive capacitor that will absorb any high frequency voltage. Still, I've seen funny things happen with batteries so maybe its best to stick to the advice. best of all is to remove the electronics I suppose.
I "heard" of someone who had a new cellphone which came with an intermittent fault. the shop wouldn't accept it back as it never happened when demonstrating. So the person zapped the phone with HF from his welder. I was surprised how much it took to kill a phone. With the case on, it could not be harmed, even on the exposed terminals. In the end the case had to be unscrewed and even generally zapping the circuit board did not kill it. it took a concentrated effort directly onto the cpu pins for a fair while to finally kill it. This is just a story, no-one would ever do this for real of course, but if someone wanted to, you'd need to be careful not to leave etch marks from the arcing. remember what i said about how the current is less if you are nowhere near an earth? Definitely don't sit it on an earthed welding table for instance. Even an unearthed welding table is enough of an electron sink that you can etch a metal surface. Start with several books thickness away from the table and give that a go. This is why I tend not to worry too much about welding on a car though.

Hino trucks publish a lengthy procedure, 5 plus pages in fact that must adhered to if any w r lding is done on their trucks and Volvo construction equipment decree that apart from disconnecting the battery, all ECU's must be disconnected.
Did you realise that a Volvo rubber tyred loader has 4 ECU's? Neither did I until a welder at a neighbouring plant welded on the bucket without disconnecting the battery. All 4 ECU's fried and a repair bill north of $30,000 not counting downtime! Boy was I careful when I had to work on ours.

Apparently the HF part of TIG also does nasty things to digital hearing aids.

Originally Posted by Gavin Newman

Apparently the HF part of TIG also does nasty things to digital hearing aids.

That's worth knowing as my father wears hearing aids and I would hate to inadvertently fry them. It makes sense, but I hadn't actually considered it
There is something of a question regarding TIG welding and the male reproductive system. I don't know if it is the electromagnetic emissions (which would stand to reason, given the effects radar has in this area) or some other facet of the process. Maybe we need lead lined, leather undies to protect our future prospects?

Originally Posted by Karl Robbers

That's worth knowing as my father wears hearing aids and I would hate to inadvertently fry them. It makes sense, but I hadn't actually considered it
There is something of a question regarding TIG welding and the male reproductive system. I don't know if it is the electromagnetic emissions (which would stand to reason, given the effects radar has in this area) or some other facet of the process. Maybe we need lead lined, leather undies to protect our future prospects?

Lead lined, leather undies - kinky...

With my hearing aids setting me back just under $10k I leave them off whenever I'm in the workshop now, that also has the beneficial side effect that I can't hear she who must be obeyed when she calls me from the house (or so I tell her).

I already have to be careful when my father visits as he has a pacemaker and the MIG and TIG are not good for those either according to his cardiologist.

Any spark will cause a broad band of electromagnetic radiation. The rf energy will get absorbed by anything it perceives as a resistance, which includes your body. For non-ionising radiation, the safety standards are based on your bodies ability to dissipate that heat. Your eyes will absorb heat due to the fact they contain water and also their size (particularly in microwave range as the wavelength is close to the diameter of your eye) and since there is no blood flow, the heat will not dissipate quickly. Your reproductive parts are similar.
There will not be a lot of energy in an HF spark, I'd be more scared of your cellphone which is much more concentrated into a narrow band. Although there is still no proof of non-ionising radiation causing you any damage except through heat, I think most RF engineers will tell you that if you are concerned, don't use a cell phone. NI doubt anyone without a financial interest will tell you its safe, or otherwise.
I'd say that welder HF, being a pulsed rf signal at 50Hz, is very dangerous to pacemakers, which are producing tiny electric pulses to keep your heart beating at close to 50Hz. It's not the radiation that's the problem, its the interference with the frequency of the very thing its trying to do. Its likely to make your heart beat irregularly.