Ghetto "HF start" on MMA welder?

[xfrankie]

Wall of text ahead, please bear with me as i explain.

I am very much a noob with welding, and i have an old transformer stick welder with bad characteristics. Electrode sticks down rather than igniting the arc. Very difficult to start. Low-ish current welding is essentialy impossible.
But once the arc burns, its not that difficult to keep going.

So, you know HF start on TIG welders? Press a button, high voltage shoots a spark through the welding gap, the welder dumps the main welding current through the already-ionized gas and keeps the arc going.

Can it not be done on a stick welder?

Yes it's not a good idea, yes it's likely going to shock me, yes it might kill me and hurt the whole way through... Im not asking about safety here. How much safer is TIG HF anyway?

So, imagine:
Put a cattle-prod-like circuit between stick holder and ground clamp. Great, now the current flows back and forth through the welder's transformer secondary winding.
Put a high power diode (bridge rectifier) onto the cables to block it.
--If the "HF starter" current is DC, then it would be forced right through the welding gap.
--If it's AC, then one half-wave would go through the transformer, the other half-wave is blocked and goes through the welding gap.



The diode in the picture are two paralleded 200 Amp bridge rectifiers, chinese-rated at 1600 Volt. Thus the spark-inducing voltage needs to be lower. Lets say 1 kV or so. Else it might shoot through the diode and not through the welding gap.
1 kiloVolt should produce a spark of about 1 millimeter if memory serves.

So, position electrode stick 1mm above surface, press momentary switch to get the initial spark, arc starts, welder main power takes over to keep the arc burning, continue welding as usual...

There should be very little voltage rise on the transformer secondary, since it's low resistance winding, and the spark generator circuit would be current limited (at like 40-100 mA). So no damage to the transformer...

Would this 'work', or am i missing something important?

Pls no replying 'git gud' or 'get new welder'...

 

[stan.distortion]

Have a look how the HF works on older transformer TIGs. It's actually incredibly simple, just a short coil of damn thick wire (part of the output lead iirc) and a thing that makes sparks right beside it. A cattle prod or similar would probably work ok, maybe a car ignition coil on a trembler circuit, all sorts. I'd looked into the same years ago, iirc there where lots of DIY examples around and there's no need to directly connect to the +/- leads.

No reason it should cost a lot to turn a cheap stick plant into a decent TIG and even have AC for aluminium etc. but I'd strongly suggest seeing what inverter units are available, they're getting well within the price range of the DIYer and both the improved efficiency and additional features make them a no-brainer imo.

 

[Overclocker]

arc pig

 

[xfrankie]

arc pig

Well im glad i googled that before replying, at first i thought you really disliked my choice of welding method hahaha.
Nice to see im not the first one to think of this solution.

@stan.distortion

Thanks for bringing this to my attention. Feeding high voltage across a spark gap of RLC resonator gives me some new ideas how to electrocute myself in a more exciting manner.
And it also might work as a HF without direct connection.
Well, time to order some parts...

 

[stan.distortion]

arc pig

Well im glad i googled that before replying, at first i thought you really disliked my choice of welding method hahaha.
Nice to see im not the first one to think of this solution.

@stan.distortion

Thanks for bringing this to my attention. Feeding high voltage across a spark gap of RLC resonator gives me some new ideas how to electrocute myself in a more exciting manner.
And it also might work as a HF without direct connection.
Well, time to order some parts...

Glad to help Could be worth having a quick look at florescent light ballasts, I've never really understood how they work but I know they can be used as a fast and reliable spark-maker and they seem to be more or less the same thing as the HT box on my ancient transformer TIG here (clearly labelled a F.A.R.T. box ).

I can't say don't do what you're trying, I'd try to do the same myself but I can't stress how much better off you'd be getting a cheap inverter unit instead (with a good reputation of course!). Even the really simple stuff like being able to set the AC offset at-will is a huge bonus and the peak output is much higher than transformer units when you're bound by the limits of a single phase supply. That last point alone is worth the cost imo, especially if you ever plan to do anything with aluminium.

EDIT: Just had a quick read on RLC circuits, still don't understand the damn things but I'm guessing you're also going to need a damn great capacitor in there too. I had to replace the one on that transformer TIG a few years back, the type used was a doorknob capacitor 3300 pf 10kv.