TIG welder hf start circuit

shortbus

Joined Sep 30, 2009
8,060
He did kind of go overboard on his design, but you can pick and chose the things you need from something like that.

As far as a OBIT you might want to check with a Grainger's supply for one. Might save some money on shipping if you order one through them and don't have to have it fast, it could just come in with other things they order. Looked on their website and they have stores in Hi.

Sorry I couldn't get you up and running, but if you need help, this is a good forum.
 

Thread Starter

Rick A

Joined Jul 30, 2010
31
I'm going to ask my friend for an OBIT because he used to be in the HVAC business and may have something lying around. I try to avoid paying retail for anything!

It does seem to be a good forum; some forums aren't very welcoming to folks who aren't knowlegeable going in. I'm grateful for your willingness to deal with me on that basis. I'll be back as soon as I've rounded up some more hardware.

Rick A.
 

GeorgeB

Joined Aug 26, 2012
1
I'd like to try this one: http://www.yoreparo.com/foros/files/hf15.gif, but I'm a bit confused. The circuits I've found all show a lamp dimmer or equivalent to control output, but all I see here is R3, which looks like just a variable resistor. Input is 120v AC, T1 is an auto ingnition coil...Here's a similar circuit that didn't work for me (got a weak arc at the welder electrode but it didn't start the welding current.)
http://www.casano.com/projects/hfstart/index.html
Thank you for any advice.
Rick - I was interested to find your post because I've been working on a similar HF start unit. Here's my experience, for what it's worth. I'm a DIYer with an interest in electronics, but with no formal training or anything.

I'm basically using the casano circuit as in your link, but with a few minor changes which borrow concepts from the Miller circuits. My prototype works a treat, and makes it very easy to start the arc when I hook it up to a transformer-based AC welding machine. The circuit shown in the yoreparo link looks to me like one of the Miller circuits. If so, T1 is not a car coil - it's a custom made transformer which goes from 110VAC up to about 3KV. I stuck to the Casano approach by using a light dimmer and motor run capacitor, which drives a car coil. My changes to the Casano design are (a) that I'm using simple steel nails to make two spark gaps. They hardly get warm, let alone melt so i can't see how tungsten or anything special is justified (b) I'm using only 2 spark gaps like Miller, rather than 3 gaps like Casano (c) I'm using an air coupled output coil like Miller, rather than a toroid ferrite like Casano. The ferrite should provide a greater transfer of HF energy but it will probably lead to a reduction in your main welding current. (d) I added suppression components at the end of the circuit like Miller/yoreparo but I'm still not prepared to run the risk of hooking up my HF start unit to the sensitive electronics of a DC inverter welder.
 

Thread Starter

Rick A

Joined Jul 30, 2010
31
George:

I haven't looked at this thread for awhile so didn't know you'd posted. Like you, I put together a circuit that makes an impressive little lightening bolt, but doesn't get it into the welding current. Per Shortbus's advice, I scrounged an OBIT to replace the coil/dimmer circuit. It puts out 10k volts, more than enough for this application. I completely understand your reluctance to expose your welder to that kind of voltage without the proper protection. I know; I've already fried two rectifiers. Someone on another forum was suggesting a suppression cap across the rectifier outputs, but referred to an ordinary low voltage, low mfd cap. At my very limited level of expertise it seems like it would need to be something that would handle the high voltage, like a doorknob cap. I'd love to simply use an ordinary motor run cap, but don't want to sacrifice another rectifier. Anybody have any thoughts? Thanks.

Rick A
 

Thread Starter

Rick A

Joined Jul 30, 2010
31
Hi, Shortbus:

Glad to see that you kept up with this thread- you seem to be the most helpful guy on the forum.

I'd thought about a hv diode, but it seems that it'd have to be in the welding current wire between the rectifier and coupling coil and wouldn't tolerate the high amps.

The other link you provided offers a ray of hope, though. He said the microwave cap failed at 10.5kv; don't know if they all would do that well. I only need to energize the hv circuit momentarily for welding steel, so the cap may last awhile. They're free anyway (I beg discarded microwaves from the local recycler- saves him the cost of shipping them away.)

Thank you for the info and I hope to be back soon and tell you that your suggestion bore fruit.

Rick A
 

shortbus

Joined Sep 30, 2009
8,060
Thank you for the kind words, but many here don't share your sentiment. Hope you have good out comes with the welder.

I had another link for you but changed browsers and can't find it now. But in a nutshell he was using a 1:1 ratio for the HV transfer. And several others said it worked better for them.
 

Thread Starter

Rick A

Joined Jul 30, 2010
31
I've wrapped my coupling xmfr at about a 1:1 ratio per info I've gleaned from various forums.

I wired it together today with a microwave cap across the rectifier outputs and fried another rectifier (I'm experimenting with cheap 50a bridge rectifiers and welding current on the lowest setting - not a really painful loss.) I wonder if a bigger resistor between the hv xmfr and the coupling xmfr would cut down the hv current more and render it a little less destructive?

I wish I understood what I''m doing! I have the feeling that someone knowlegeable could glance at this and tell in just a minute what I'm doing wrong. We'll get it eventually, though.

Rick A
 

shortbus

Joined Sep 30, 2009
8,060
What is the voltage rating on your rectifier? If you trying to do this with a standard square bridge rectifier I don't think you'll have much luck. The reverse voltage rating of what ever diodes you use has to be higher than the voltage of the HV.

Instead of a bridge rectifier the type of diodes should be the ones that have a bolt thread, commonly called a "stud mount diode".
 

Thread Starter

Rick A

Joined Jul 30, 2010
31
I don't remember the voltage rating offhand, but I know it's considerably higher than the 30-40v of the welding circuit. Nowhere near the 10kv of the hv circuit, though. I initially built the rectifier out of six 50a square rectifiers in parallel. It worked OK for DC stick welding and scratch-start TIG- the trouble started when I tried adding the hv. So I shelled out for four 300a stud mount welder diodes, figuring they'd handle about anything, but I managed to fry one of them with the hv. The next attempt was back to a 50a unit and the lowest welder current- just for experimentation. Killed it, too. Now I'm reluctant try the hv again until I'm SURE I have the rectifier protected.

I noticed on another forum (4hv.org) a guy was describing a choke with two coils wound counter to each other to filter out the hv. Any knowlege of that? Thanks.

Rick A
 

THE_RB

Joined Feb 11, 2008
5,438
Can you please post a schematic as GIF or JPG?

For decoupling I would use the ignition coil itself, it's secondary of 50kV or so could be connected to the welder leads through a MW cap and resistor. Anything the welder produces back into the secondary when welding would be attenuated about 4000 times when it comes out the 12v primary. So on the 12v primary side all you need is a good high current high voltage transistor or FET, and maybe an RC snubber.
 

Thread Starter

Rick A

Joined Jul 30, 2010
31
http://4hv.org/e107_files/public/1302453905_3414_FT112240_hf.jpg

RB: This is the circuit the guy developed. He said he wound half a dozen turns each on the opposite sides of a E-I xmfr core. I'm not sure it's necessary, though- I've found a number of hv curcuits on the web and they all show just a cap across the rectifier leads.

Your suggestion may not apply- I'm using an OBIT, not an ignition coil. It turns 110v AC into 10kv. Actually, I played around with it today and actually got it to work. My errors must have cancelled out! The only thing I did different that I can think of was removing the ferrite core from the coupling coil. I had made it that way per this design: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?112240.0#post_113103 but I noticed the coupling coil in the Miller HF-15 I'm copying has an air core. Wish I understood what I'm doing, but it does work!

Rick A
 

shortbus

Joined Sep 30, 2009
8,060
I too wondered about using a core in the coupling coil. The few tigs that I've seen inside of had air core coupling coils. But then I'm far from being an "expert" on this stuff.
 

THE_RB

Joined Feb 11, 2008
5,438
My apologies, I did not realise you wanted to get DC from the welder and thought you just wanted a HF addition to start the arc.
 
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