I wouldn't bother, have a look at the R-Tech range of welders, they have a small dc tig plant for not much money, three year warranty. They are chinese, but very good. Also have a look at doubleboost's channel on youtube.

Hi, the old company where I used to work, over ten years ago now, just purchased a TIG torch, a HF unit and an add on rectifier and just coupled it up to one of the AC welders, it also allowed it to be used for aluminium welding, by not using the rectifier. This was of course, when TIG welding started to become popular. It worked then, so no reason not to work now, but the biggest issue you would maybe find now is a stand alone HF unit at a reasonable cost.

Regards Nick.

I don't think HF units are made any more these days, as modern inverter sources with built-in HF are so cheap – probably little different from the cost of an HF unit. The "HF unit" includes the various functions you need to convert an AC or DC source to TIG. Several decades ago, TIG equipment was new and very expensive, so HF units were developed to give an alternative solution based on existing welding sources.

As mentioned, for TIG you need a constant current (CC) source ie possibly a stick welder. In the old days, AC sources could be little more than a (variable current) transformer, so AC was easier to generate than DC. These days it's the other way around – inverter sources will produce DC output and converting that back to an AC output adds cost.

The old HF units contain a spark generator and a coupler (high frequency high current transformer) to inject this high frequency, high voltage onto the output to the torch. That enables the arc to start without having to touch the electrode to the work, which would risk contaminating the tungsten. Generally, once the arc is established, the spark generator is turned off if you are running DC, whereas it's helpful to leave it running for AC welding.

The other function generally included is the gas control – and water if you have a high current, water-cooled torch (typically for over 150A or so). So there is generally a couple of solenoids, one for the argon and one for water. To control these you need a switch on the torch (or a foot pedal) and ideally a timer to continue the gas for a few seconds after stopping the arc. Ideally this switch would also control the welding source….

Doesn't sound much but these features are the basic difference between a simple constant current source and a TIG welder. The main feature missing from this approach is any form of remote current control, eg the ability for the operator to turn the current up and down (and on and off). You'd need some sort of contactor to turn the welder on and off at the very least.

If you plan to weld steel you should rectify the output. HF units work with DC or AC. If you don't rectify the output, half of the output power (heat) will end up in the torch. Also bear in mind that you need pure argon (or argon helium mix). The argon – CO2 mix used for MIG is not suitable.

True enough, you could have a go at making your own HF unit if you have a stick welder. But it will be very crude and take a fair bit of effort. Apart from proving that it can be done, it won't be a very productive use of your time. At the very best, if you managed to find an HF unit for free or very cheap it may get you started and then you may be able to decide if TIG is for you. I used to have an HF unit but threw it way because nobody uses them any more…

Murray

Thanks Muzzer and Nick

Probably stick them on Ebay on the next clear out.

The arc welder has aluminium wire in the transformer, it's rated at 200 amp but I don't know for how long. I think this means it's not a proper one. I suspect the OC voltage wasn't high enough to drive the TIG box

Cheers Michael.