Hacking the Harbor Freight TIG

Hi,

Has anyone really hacked the HF TIG set they sell for 200 bucks ? I bought one in the last few weeks, and have been very pleased with it. Like others have said though, it needs remote control of welding current, to which end I amm buying a pedal and getting some connectors. An HF start is also going in. I have also got an (untested) solution to the nasty crack of the input caps charging on first plug in, which is probably mainly an aesthetic touch more than anything.

Of course, a proper hack would add ramp-in and out, but I haven't the time to play with that yet.

If there is any interest, I'll set up a little forum for discussion. somewhere. Since HF don't provide any sort of decent service support (and I have imported mine into the UK in anycase), I'll create a list of alternative components (probably better rated too), for when the inevitable happens.

My welder is happy on 230V 50Hz by the way, for anyone in the UK who feels tempted to try 150 quid on a TIG set.

Steve

Steve, I would be very interested in seeing the progress (and photos) of such a project. By the way, do you want to buy an arc starter, or to build your own?

i

I found an on-line reference which I am following up, which uses a neon sign transformer and a Tesla arrangement, with an aircoupled transformer to add in the HF. It looks feasible to build, and has a good degree of supply isolation. A neon sign transformer will deliver a lethal shock, so isolation is very important. I would prefer to use a tiny flyback transformer, but I have only just deci ded to fool around with the thing, so I have no topologies in mind yet. Safety is paramount.

Steve

Yep. By the way, I have some 9,000V franceformers for sale and also some 3/16" tungsten electrodes, which you can cut into small pieces for the spark gap.

Actually, 30 mA transformers were designed to give you a good chance of surviving, hence the low amperage rating. It's not "safe" to shock oneself with them, of course, and one could die, but there is a decent chance of staying alive. It's a good idea to make safety paramount in your project.

Also, be mindful of RF interference produced by HF, high voltage equipment. It is a serious issue and in the jurisdiction of the FCC.

i

I have lots of tungsten bits and pieces - old tool tips, Heavy TIG electrodes, etc. etc. Thanks. What kind of transformers have you got

10mA through the heart can kill, and AC is worse than DC. I am not taking any chances !

BTW what does the HT in a uwave kick out ?

Not in Europe it isn't....

Steve

see the spark gap in action

i

Thanks for the link Igor. Where are you anyway ?

Steve

Having had a browse around your site, why not just use a cheap microcontroller to do your square wave/PWM generation ? Easy to get adjustable ranges without a mess of analogues components, easy to extend the functionality ?

Steve

I am in the USA (Illinois). If you are in the UK, you can probably find a better local deal that does not involve international shipping. Also you'd need a 220V transformer, being in the UK, I suppose.

i

Are you talking about the TIG inverter project? If so, I already made the square wave generation circuit, using XR2206 chip. $3.69 per chip. It adjusts both frequency as well as percentage of negative and positive in every cycle.

i

I am curious, how does this Harbor Freight welder start the arc without high voltage high frequency?

i

Same way any MMA welder starts, a little arc, low voltage low current, and a sod to start on thin (hence low current) sheet.

Steve

Steve, I have to admit that I did not understand what you said, sorry.

i

Any time I would unintentionally "scratch" work with tungsten, it would firmly stick to it.

i

I prefer the term 'lift start'. You just touch the tungsten to the metal, lift it, and wait three seconds or so for the current to ramp up to the full setting. Easy as pie, and I have never had an issue with electrode contamination from it, (although I do contaminate the tungsten too often anyway).

I have a Daytona MIG Pocket Pulse 100 Tig welder, (which I believe is a relabeled Cebora), that has no HF and a lift start, and it works well for me. That said, I do wish I had a way to control the output with a foot pedal or torch mounted control to ramp down at the end of the weld, so I am interested in that aspect of this hack...

Sign me up as interested in any mods you come up with.

I haven't opened the case yet. Does anyone know the resistance of the pot used for current adjustment? I'd like a pedal, or possibly torch control add-on. That'd be especially nice when terminating welds. At present I pull-away until the arc extinguishes, and then quickly move the torch tip back to the work area (in what's now darkness) in an attempt to keep the post-flow gasses heading to the hot spot.

I've been practicing a bit with my HF tig unit, and it works quite nicely. I have done a fair bit of stick and O/A welding, but tig is new to me. I suppose not using a fancy commercial tig unit first helps somewhat. It certainly does a much nicer job on 409 stainless than I could attain with my O/A unit.

What's the availability of replacement cups like? Any chance they are reasonably standard?

Roger.

I downloaded the diagram from the link pointed out earlier and checked it over, and these were my conclusions:

The frequency that drives the output transformer is most likely set up on the main board. If you could figure out what controls that frequency, you could skip the output diodes and that will be your AC output, and override the original frequency control. I don't know how to keep the HF from feeding back through the diodes when in DC, considering the space on the machine, other than adding a switch to take them out of the circuit. Simply having a second set of output terminals wouldn't do the job. There could be some bypass caps around the diodes, but that would have to take some thought, obviously, once you know all the other variables. A pair of 555 timers, or a 556 dual timer, IIRC, is enough to provide you variable frequency and duty cycle, so just needs the section to drive the output. If you could control the frequency from the main board, as noted above, but the duty cycle would have to be controlled afterwards. If you replaced the diodes with SCR's, and some logic circuitry to prevent both a short if both sides are on at the same time, then you could do both with the output diodes, be they SCR's, IGBT (which I think they already are,) or whatever device you prefer. This way your could skip the above bypassing of the diodes and just use them to provide the frequency (although likely square wave, with whatever smoothing the HF transformer adds.)

For a tig welder that is small, with a small transformer, the frequency may well be extremely high.

You can see how it is done in my welder

HF transformer

-----------------------------|-------|---/\/\/\/\/\/\/\------ tig torch-- |( | | |) |recti | |( Simply having a second set of output

the problem with 555 timers is, it is hard to control frequency and duty cycle separately.

I actually made a timing circuit which fully works, based on XR2206 chip. Here I can control frequency with a 11 position switch switching the caps, and duty cycle with a regular pot.

I am not sure what you mean here. If you want to make adjustable frequency, then you have to rectify first and chop later, no? The power transformer is made for a particular frequency. Am I mistaken?

i