TIG HF coupling transformer

tcmtech said:

The spark gap and 500 pF capacitor need to be switched around with each other.

Also the AC side driver circuit with the single triac and capacitor is still terribly inefficient design that dumps a huge amount of RF noise directly into you home power lines when its running.

Lastly if its not superimposing the HF on the work leads you need to have proper blocking and bypass circuits on your leads between the high current DC source to stop the HF from feeding back to the diodes and to give it a path to follow from one work lead to the other.

Click to expand...

Yea, all of the schematics have the spark gap like you are suggesting and the cap where the SG was. I will test that configuration.
I'm really just trying to get the HF to induce into another wire at this point.......any wire and then I can build from that. But when I do the final wiring and install it in the machine, I will have the nessicary blocking and Bridge ?? capacitors to complete the circuit before my diodes.

dr pepper said:

Mine uses a stack of about 10 ferrite torroids inside the coils, about 25mm x 15mm x 10mm.
And H.T. comes from a car ignition coil, as the weld set is vehicle engine driven.
Opposing spark plugs is a cool idea.

Click to expand...

Thanks man. I had read that you werent supposed to use resistor plugs, and if anyone thinks that might have a bearing on the outcome, Ill get some non resistor plugs. Im gonna check ebay for some ferrite beads

Mobius said:

I'm really just trying to get the HF to induce into another wire at this point.......any wire and then I can build from that. But when I do the final wiring and install it in the machine, I will have the nessicary blocking and Bridge ?? capacitors to complete the circuit before my diodes.

Click to expand...

Have a look again at post 26 and think about what C3 from that schematic I linked to is doing. That 10uF 600 volt non polar capacitor between the two leads is there for a reason.

Same with the physical components (and their values) of the circuit being laid out in a specific way as well.

Electronics circuits and systems are not something you can just toss together any old way you feel like all while ignoring the specifications and values of each component.

I cant find the original article the page might have been taken down, the ferrites are the size I mentioned but they dont say what type of material they are, your probably better off with some inteference suppression cores, I have about 20 turns primary and secondary.
They are not expensive if you stuffed as many in that will fit in what you have it will improve things.
Resistor plugs will reduce the spark, as the resistance will affect the Q of the tank coil, still might not be so bad an affect to make the thing useless though, my circuit uses 5mm T-in plated drill bits cut down, but you could probably use some tig tips for the job.

dr pepper said:

I cant find the original article the page might have been taken down, the ferrites are the size I mentioned but they dont say what type of material they are, your probably better off with some inteference suppression cores, I have about 20 turns primary and secondary.
They are not expensive if you stuffed as many in that will fit in what you have it will improve things.
Resistor plugs will reduce the spark, as the resistance will affect the Q of the tank coil, still might not be so bad an affect to make the thing useless though, my circuit uses 5mm T-in plated drill bits cut down, but you could probably use some tig tips for the job.

Click to expand...

OK, so, putting ferrite inside the trans would help the flux? transfer ? or at least make it more efficient? Say no more, Ill start collecting them. Does it really matter if they are configured like yours (a series of doughnuts stacked into a tube) or smaller beads / toroids inside the tube I have. Or does it just make it more efficient?
I think I am going to try some non resistor (racing ) plugs on the gaps because I want to try to use that stand I machined for them if I can.

tcmtech said:

Have a look again at post 26 and think about what C3 from that schematic I linked to is doing. That 10uF 600 volt non polar capacitor between the two leads is there for a reason.

Electronics circuits and systems are not something you can just toss together any old way you feel like all while ignoring the specifications and values of each component.

Click to expand...

OK, I have looked at C3 on post 26 and let me make sure Im thinking about this correctly. The capacitor (c3) provides a pathway for the HF to go through to complete the HF circuit without exposing it to the diode / rectifier bank or any other harmful sh*t that could be damaged by the HF.
The HF would "prefer" to go through the Capacitor short
The HF would "avoid" going through an inductor like a coil of several turns / loops of the weld cable?
If these 2 are correct then what I am trying to do is simply achieve a spark in the secondary winding of the transformer, Just like Dr Pepper and others did with their Mock ups, just to prove to myself that it works. At that point, you bet I will put the proper caps and an inductor to protect my diodes because I dont want to replace them.
If, on the other hand you are telling me that it wont induce the spark/HF into the secondary of the transformer WITHOUT the caps like C3, then Ill start buying caps and building, but I still have to ask how the others do it without the caps in the circuit, understanding full well that when they change from "proof of concept" secondary HF spark to installing it in the welder that they will need caps like C3
Understood, but if it was designed by a man, then it can be duplicated by a man, and then modified by a man

Mobius said:

OK, I have looked at C3 on post 26 and let me make sure Im thinking about this correctly. The capacitor (c3) provides a pathway for the HF to go through to complete the HF circuit without exposing it to the diode / rectifier bank or any other harmful sh*t that could be damaged by the HF.
The HF would "prefer" to go through the Capacitor short
The HF would "avoid" going through an inductor like a coil of several turns / loops of the weld cable?
If these 2 are correct then what I am trying to do is simply achieve a spark in the secondary winding of the transformer, Just like Dr Pepper and others did with their Mock ups, just to prove to myself that it works. At that point, you bet I will put the proper caps and an inductor to protect my diodes because I don't want to replace them.

Click to expand...

Yes thatis correct. The high voltage HF signal superimposed on the low voltage high current needs to have its own path to follow that does not go through the diodes and the diodes need some degree of protection to keep it away form thiem since they are not designed to work with high frequency or high voltages.

Mobius said:

Understood, but if it was designed by a man, then it can be duplicated by a man, and then modified by a man

Click to expand...

Yes, but to make modifications to something to improve things you have to actually know and understand why the first person who made it did it the way they did.

Putting ferrite in will multiply the flux by the permeability of the ferrite, which can be 1000's, in theory the coupling between pri and sec shouldnt chabge, but due to non perfect windings the coupling will most likely be a heck of a lot better with the ferrite.
Doesnt really matter which way you put the ferrites in the core, but its imprtant they are all the same way, if you put a torroid in one way and another at 90 degrees bad things will happen, mine is arranged like a pack of polo mints, if you know what they are, if you look in one end you can see right through.

OK,
Thanks for the help.

dr pepper said:

Putting ferrite in will multiply the flux by the permeability of the ferrite, which can be 1000's, in theory the coupling between pri and sec shouldnt chabge, but due to non perfect windings the coupling will most likely be a heck of a lot better with the ferrite.

Click to expand...

Unfortunately you may also change the resonant frequency plus inductive characteristics of the coupling coil assy far enough as to not be so easily blocked or ignored by the low voltage high current components of the circuit.

Large power diodes tend to be fairly good at ignoring system noise MHz range even if it has a substantial voltage and power level behind it but they may not be so forgiving to the same system noise voltages and power level when that noise in now down in the 10's - low 100's of KHz with high inductive pulse effects from a spark discharge circuit driving it.

Back in the early days of plasma cutter tech many models of certain brands used such a method of arc striking and it was well known to blow out the HV diodes in the power supplies if the HF coupling coil got too much metallic dust in it and the resonant frequency went too low.
The large 100+ amp 1000 - 1400 volt silicon power diodes totally ignored the MHz range frequencies but if things got down to far below that they would short out the dies due to HV breakdown because the diodes semiconductor dies equivalent capacitive impedance was not low enough at those frequencies to keep the HF HV signal attenuated enough.

Tcm yes thats correct, a 0.1 class x or motor start cap should be across the high current supply to short the Hf into the load, indeed without it the Hf probably wouldnt even get to the load.
Frequency aside, the voltage from the Hf is probably enough to kill a power diode, they usually only take 200v or so.
There is an amount of suck it & see with the resonant freq, but then all we want to do is make a spark.

Gentlemen, Thanks for all the help and replies. Sorry I have not had time to complete this project as I have been busy with work. I hate to report no success with the HF transferring through any kind of transformer. In other words, this circuit:

**broken link removed**
makes a serviceable HF arc, but I have been unable to get it to jump / induce from the primary side to the secondary side of a transformer. So, I will not be able to use it to start / maintain the arc. Here are some of the transformer configurations that I have tried:

with zero success. Could this HF signal not want to transfer through a transformer like the Neon sign transformer that I tried first for some reason. Any other alternating current would have already gone from primary to secondary with any of these transformers.
I did switch the spark gap and the 500 pf (510pf) cap in the diagram per TCMs request. I hate to do it, but I might have to walk away from this thing for a while so it dosent accidentally become airborne and hit a concrete wall. This shouldnt be this hard.... Im missing something.

I have been playing with flyback transformers lately and got this one working.

Simple Flyback Driver - Step by Step Instructions


I was just now getting one to work with a 555 timer. Thinking about your post, I remembered a high voltage diode from a microwave transformer. I wired it in series with the flyback output and got a 1/2" spark one way & nothing the other way. Could we wire this directly to the plasma cables in opposite polarity?

I don't know how long the H.V. diode will last.
If the flyback output is DC, does it even need the extra diode?

We could use the output good signal to turn this off making it momentary.

ClydeCrashKop said:

I have been playing with flyback transformers lately and got this one working.

Click to expand...

Thanks, that looks a lot simpler that what Im trying to build, simpler is better, but will this HV go through a transformer to be induced into the other side, the high current welding cable? what do you think? if so, Im gonna get on craigslist and get an old tube TV with a flyback this week

Lets wait to hear from members that know a lot more than I do.

I got one new flyback on eBay that I couldn't make work. Then I got a dozen used ones on eBay for $20.00. Seven of them worked easily.

The output can be lethal but is it any different than a high frequency 15KV ignition coil?

tcmtech said:

The high voltage HF signal superimposed on the low voltage high current needs to have its own path to follow that does not go through the diodes and the diodes need some degree of protection to keep it away from them since they are not designed to work with high frequency or high voltages.

Click to expand...

Are we back to worrying about this problem?

OK good idea. If I remember correctly the reason they said the NST HF wouldnt pass through the transformer was because it was in the megahertz range and your flyback HF is in the Kilohertz range? so it does look good

My frequency meter is a little erratic measuring the low side of that circuit but it averages about 200 kHz.

ClydeCrashKop said:

My frequency meter is a little erratic measuring the low side of that circuit but it averages about 200 kHz.

Click to expand...

Thx, according to some of the older posts that should go through the coupling trans.
Have you guys ever heard of the theory that the only stupid question is the one thats not asked? well here goes. How about this:
HF 20-Apr-2017 19-44-22.pdf

I just tested it and it works, it has no direct connection to allow the High current in from the welder, and it does away with that damn coupling transformer.
If it is possible to use this in this configuration, Im still gonna use your flyback design instead of the one I have..... the spark on that thing was very good

OH OK this will just start welding between the 2 center spark gaps.... Damn

OK, If anyone still has any interest in this project, I finally got it working. I used a kit:

**broken link removed**

This includes everything I needed to add HF start to my welder. This guy was very helpful and he will sell parts of this kit as well. His kit does what the arc pig does for less than a third of the price. He also offers another kit to add a foot pedal control as well. So, for about 100 bucks, my old ac welder trans and a bank of diodes, I have an economy TIG welder. I have not got the welder completed but the DC works, the HF works and the coupling coil in his kit is rated for 400 amps.
Im just finishing the polarity switch and if anyone is still interested, I can post pics of finished product. Once again thanks for the help everyone.

Thanks Mobius

I ordered one. Now I just need a TIG torch & Argon cylinder to go with it.

Clydecrashcop,
I got everything but the tank off of ebay.... good deals, I can send u links if you want. Do yourself a favor and get at least a 80 to125 cu ft cylinder of argon,they really dont cost anymore to fill and if you buy a used one they are just as cheap to buy the cylinder.

Great to see you sorted it.
If your going to use this a fair bit a pre made kit that has all the bugs sorted out is a good way to do it, it'd have most likely cost you more with all the bad prototypes.
You can get really cheap tigs with hf locally, 200 amp for 125 quid, but they need a bit of sorting out before use, and they wont be anything like as robust as an old arc transformer set.