You really need AC to weld aluminum. Do you have a TIG torch? There's no way to weld aluminum without it, unless you do it in a glove box filled with argon.
There are ways to add an HF system to a stick welder. Basically, you build a heavy-duty Tesla coil, with a neon sign transformer, spark gaps and an air-core resonant transformer. The secondary of the transformer is just a few turns of welding cable around the Tesla coil. There should be plans somewhere on the net for such a thing. If you are not very competent with REALLY dangerous electrical gear, this could be a real hazard. It also will likely wipe out any TV or radio reception for blocks.
Several posters have built these things. In fact, there is a recent post with a neon sign transformer shown in photos (you have to register to see the photos).
The HF setup is after the transformer and after the diodes. It is also after the DC welder choke. These kind of help with the arc stability. A capacitor is placed across the leads, and a large coil of heavy wire is placed in series after the capacitor. This coil is coupled to a coil of thinner wire, which is excited with a resonant spark gap oscillator. The oscillator is powered by a low frequency AC or a DC power source, and looks a lot like the primary circuit of a Tesla coil.
Not too bad. I can think of a lot more dangerous electrical gear. There have been some recent posts on the above mentioned group by someone who claimed to get a working stabilizer with several milliwatts of HF. Commercial units like the Miller use about 100 watts, and as a result, the primary circuit poses a shock hazard. Microwave ovens, large capacitor banks used for pumping ruby rod or NdYAG lasers, and high voltage powerline thyristor converters seem much more dangerous.
As for the RF emissions, as long as the Q of these circuits is fairly high, their interference is narrow band. Most homebuilders shoot for about 1 MHz. The claims of TV interference are usually caused by backflow along the power lines, and can easily be dealt with by means of HV side chokes, or AC line filters in reverse. In fact, if you are backfeeding that much power, you will probably burn out the gate driver resistor on the FET (if you are using a DC supply). Mine has two iron cored pye wound RF chokes in the HVDC bus to stop backfeeding. It seems to work. There is a small AC line filter as well.
Several posters have built these things. In fact, there is a recent post with a neon sign transformer shown in photos (you have to register to see the photos).
The HF setup is after the transformer and after the diodes. It is also after the DC welder choke. These kind of help with the arc stability. A capacitor is placed across the leads, and a large coil of heavy wire is placed in series after the capacitor. This coil is coupled to a coil of thinner wire, which is excited with a resonant spark gap oscillator. The oscillator is powered by a low frequency AC or a DC power source, and looks a lot like the primary circuit of a Tesla coil.
Not too bad. I can think of a lot more dangerous electrical gear. There have been some recent posts on the above mentioned group by someone who claimed to get a working stabilizer with several milliwatts of HF. Commercial units like the Miller use about 100 watts, and as a result, the primary circuit poses a shock hazard. Microwave ovens, large capacitor banks used for pumping ruby rod or NdYAG lasers, and high voltage powerline thyristor converters seem much more dangerous.
As for the RF emissions, as long as the Q of these circuits is fairly high, their interference is narrow band. Most homebuilders shoot for about 1 MHz. The claims of TV interference are usually caused by backflow along the power lines, and can easily be dealt with by means of HV side chokes, or AC line filters in reverse. In fact, if you are backfeeding that much power, you will probably burn out the gate driver resistor on the FET (if you are using a DC supply). Mine has two iron cored pye wound RF chokes in the HVDC bus to stop backfeeding. It seems to work. There is a small AC line filter as well.
Thanks for all the good info here guys. I do appreciate your taking the time to answer. I am checking everything out.
I would like to stay away from the tesla stuff. I saw a cat that got tied up with a tesla coil once. Not a pretty sight. That was enough to stop messing with it.
I did like that attachment for a DC machine. I might look into that. Does the gas take the place of the HF? Or do you still need the HF?
This whole thing started as a hobby and has developed into a part time job LOL. One guy has already dropped off a pickup truck load of steel. So much for a day off for a while.
Maybe I had better leave well enough alone on this machine It has paid for itself many times over. I made a couple of spare transformers but even though I tried, I haven't been able to burn one out yet, only burn up a lot of rod.
I might start over on another one though with the gas attachment as long as I don't need the HF. If I need the HF, I think I will stick with a factory made version..
The only problem is that now that I have this part time welding work, I don't have much time to play. I don't need the extra work but I hate to say no when somebody needs something done. I would rather be building something I want to build.
OK, thanks again for everything and if somebody would comment on whether I need the HF with the gas I would appreciate it.
Gas is always needed when TIG welding, argon, helium, or an argon/helium mix. You can TIG weld steel with DC- and without HF, but you want to use AC to TIG weld aluminum, and you need HF to stabilize the arc when using AC.
It is possible to TIG weld thin aluminum using DC+ and no HF, but the torch will get very hot very quickly since the majority of the heat goes to the tungsten when using DC+. You'd need to use a large tungsten, and preferably a water cooled torch, if you try DC+ welding aluminum.
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