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Registered Member #2885
Joined: Thu May 27 2010, 10:11PM
Location:
Posts: 11
Hi guys I'm new to this forum but not welding, I decided to add a pedal, tig torch and HF arc stabilizer to an old lincoln AC 225 buzzbox lying in the shop at work.
I'm basing my HF box off of this website and diagram:
It looks like it uses part of the circuit on the HVwiki ignition coil page here
Today I picked up a lamp dimmer, ignition coil, some welding cable and did some local searching to find out where I can get a motor start cap tomorrow.
Talking to the nearest electric motor shop that sells start caps the smallest they sell is 4 uF @370V, next step larger is 5 uF @ 440 V and only goes up from there in both voltage and capacitance. How small is "a few" when the same page says that going too big can result in overheating the coil? How much difference would small power supply fan blowing over the ignition coil body make?
Since I plan on using this setup to weld aluminum I need this to be able to handle at least 10 minutes of solid "on" time as the arc stabilizer will be on from before the arc is initiated until I'm done with the welded joint.
Since excessive HV is going to cause a straying welding arc I'd much rather start small and have a wide range of adjustment. Is 4-5uF at lower voltages a problem that I should shop ebay for instead or will that value be OK?
Also, just another thought that came into my head while planning the build of such a device...I see a lot of guys use multiple spark gaps of 1/4"-3/8" pure solid tungsten for spark gaps at considerable expense, and information unlimited sells fan-blown spark gaps that can handle big loads and keep them cool. Why doesn't, or has anyone tried chaining automotive or marine spark plugs together as a cost-effective and easily adjustable way of making a spark gap? The ones I'm picturing are the mercury marine engine plugs that are "flat" and have a non-adjustable distance between the outer ring and the center electrode
Are there any good (cheap) vendors I should be aware of to get a large ferrite core from? Most of what I could find on ebay was way too small in diameter & thickness for the #4 welding cable I intend to use.
Thanks for the help. I'll post pics of my progress after I start putting things together.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Greenbuggy wrote ...
Why doesn't, or has anyone tried chaining automotive or marine spark plugs together as a cost-effective and easily adjustable way of making a spark gap?
I've sawed up a few automotive sparking plus in an attempt to use them as trigger electrodes in centre-triggered gaps, but haven't got far enough with it to report on here.
Jitter spread would be a likely problem with your gaps-in-parallel proposal.
Registered Member #2885
Joined: Thu May 27 2010, 10:11PM
Location:
Posts: 11
Proud Mary wrote ...
Greenbuggy wrote ...
Why doesn't, or has anyone tried chaining automotive or marine spark plugs together as a cost-effective and easily adjustable way of making a spark gap?
I've sawed up a few automotive sparking plus in an attempt to use them as trigger electrodes in centre-triggered gaps, but haven't got far enough with it to report on here.
Jitter spread would be a likely problem with your gaps-in-parallel proposal.
I hadn't considered gaps in parallel, my thought was to put them in series. Any thoughts on the 4-5 uF cap?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Here's a reference to a similar project, posted here a couple months ago (search the forum for tig welder).
Klugesmith wrote ... Here's a project on a welders' forum that strikes some chords with topics popular here.
These guys have been refining a fancy homebrew TIG welder. A block diagram appears under Complete System Drawing.
For sustained 100+ amperes at moderate voltage and frequency, they start with a basic current-limiting stick welder (buzz box). Its output is rectified, filtered, then switched with IGBT bridges. See 100- and 200-A power stage drawings.
As a high-frequency arc starter, they are using a variant on SGTC. A little NST drives a resonant sparkgap-capacitor-inductor loop. The coupled secondary winding is a few turns of the main welding cable. See Arc Starter drawing.
The makers seem to be experienced TIG welders with the requisite knowledge of EE. Their arc starter/stabilizer is practically identical to the one in your reference, except they use a neon sign transformer instead of lamp dimmer & ignition coil. Here is the schematic, but you should also read the commentary and look at the pictures on main page.
I wonder if a circuit using -your- schematic would trip a GFCI breaker, because of ign-coil secondary current in the white (groundED = neutral) wire. If so, the 2000 ohm resistor could return to white instead of green (groundING conductor).
Registered Member #2885
Joined: Thu May 27 2010, 10:11PM
Location:
Posts: 11
Klugesmith wrote ...
I wonder if a circuit using -your- schematic would trip a GFCI breaker, because of ign-coil secondary current in the white (groundED = neutral) wire. If so, the 2000 ohm resistor could return to white instead of green (groundING conductor).
I considered adding a 220-110V stepdown transformer I've got lying around to the welder to provide power to the HF box and to the chiller for the water cooled tig torch. I don't really like the idea of having to plug in 3 cords to use the welder.
I have seen the DIY tig welder before, and while I like the idea the lack of updates since 2006 scares me a bit. Also I'm not sure how he's controlling the intensity of the NST, without a way to turn down the HV the arc will be wandering all over the place as well as posing a risk to the weldor.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Greenbuggy wrote ...
Klugesmith wrote ...
I wonder if a circuit using -your- schematic would trip a GFCI breaker, because of ign-coil secondary current in the white (groundED = neutral) wire. If so, the 2000 ohm resistor could return to white instead of green (groundING conductor).
I considered adding a 220-110V stepdown transformer I've got lying around to the welder to provide power to the HF box and to the chiller for the water cooled tig torch. I don't really like the idea of having to plug in 3 cords to use the welder.
I have seen the DIY tig welder before, and while I like the idea the lack of updates since 2006 scares me a bit. Also I'm not sure how he's controlling the intensity of the NST, without a way to turn down the HV the arc will be wandering all over the place as well as posing a risk to the weldor.
I'm afraid I don't have any experience of TIG welding to share with you, and don't understand what an ignition coil in series with a light dimmer and a capacitor has to do with it, except make it much less safe than it was before.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Greenbuggy wrote ... I have seen the DIY tig welder before, and while I like the idea the lack of updates since 2006 scares me a bit. ... Also I'm not sure how he's controlling the intensity of the NST, without a way to turn down the HV the arc will be wandering all over the place as well as posing a risk to the weldor.
Please be sure to come back and share your results with us!
Lack of updates since 2006 could mean they got it right already. Electronic component technology doesn't advance THAT fast, except for silly computer and wireless parts.
The makers claim:
With the new circuit which is taken from a welder handbook, the spark gap / cap primary winding increases the dangerous and unsafe frequency from 60Hz (coming out of the Neon trans) to around 1Mhz at the primary of the coupling transformer. ... This circuit works really well with lots of power at a good (safe / skin effect) frequency, I have touched it to make sure The arc is about 6mm long and very strong.
You get the same HF benefit with the ign-coil circuit. I guess you could use a suitable dimmer on primary of NST if that's what you had lying around.
Registered Member #2885
Joined: Thu May 27 2010, 10:11PM
Location:
Posts: 11
Proud Mary wrote ... I'm afraid I don't have any experience of TIG welding to share with you, and don't understand what an ignition coil in series with a light dimmer and a capacitor has to do with it, except make it much less safe than it was before.
Sorry if I didn't explain that one well.
The ignition coil/light dimmer/capacitor part of the circuit is the high voltage, high frequency, low current primary side of a transformer arrangement designed to infuse high frequency into the welding cables coming off of an old stick welder to make it work as a tig machine.
This is necessary when welding aluminum to ionize the air between the tig torch and workpiece, as "scratch starting" leaves nasty bits of tungsten in the aluminum which degrade the quality of the weld. So basically, it will help me to strike an arc without actually touching the torch to the alumicraft canoe I'm planning on welding a crack shut on.
Maybe a few of you can help me with my next batch of questions, which will help me construct the transformer arrangement.
I've seen a couple of build threads & pics on hackaday and CNC zone, and most of the homemade arc starters I've seen have used a primary 8-12 ga wire with welding cable as the secondary. Several are wrapped around a piece of PVC pipe or something similar, a couple I've seen have a ferrite core of some sort.
Is there an advantage/difference to having it wrapped around a ferrite bar core vs torroidal ferrite core vs a double-E core as would be found in a larger transformer or MOT? From wiki the only good explanation I can find is that the toroid shaped core is likely to have less EMI.
I have a pretty beefy transformer I stole from work that powered 480Vac sodium bulbs that shorted the primary and blew up, I stripped all the copper off it and think that would probably make a good core if its suitable. Approx dimensions are 7"x4"x2". I have some #12 ga wire lying around that I was contemplating using for the primary and the secondary will be #4 welding cable.
I understand the relation of loops of wire as having to do with the desired change in voltage, but I'm curious what difference the amount of loops have to do with it if the voltage can stay the same....most of these that I've found build pics of appear to have a 1:1 ratio however some have 5 loops others have 20-30
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Greenbuggy wrote ...
The ignition coil/light dimmer/capacitor part of the circuit is the high voltage, high frequency, low current primary side of a transformer arrangement designed to infuse high frequency into the welding cables coming off of an old stick welder to make it work as a tig machine.
I still don't follow how this arrangement is intended to generate high frequency - except for harmonic noise voltage created by the triac as it slices steep cliffs off the rolling mains-frequency sine waves. Perhaps you could explain?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
If you put ferrite in the HF transformer, it should be a bundle of rods, or something with an airgap. If you used a toroid or an ungapped E core set, the welding current would probably saturate it hard, and it would be no better than an air core.
But then you can argue that if welding current is flowing, the arcstarter has already done its job and doesn't need to work any more.
The answer to "how many turns" - as many as you can tolerate the IR drop of in your welding circuit. The more turns, the better the HF will get coupled.
Mary: The TIG arc starter is basically a Tesla coil. And you can use the ignition coil/lamp dimmer thing as the power supply for a Tesla coil, you just substitute it for the neon sign transformer in the regular TC/arcstarter circuit. I assume this is what the original poster plans to do.
The capacitor will probably need to be smaller, I doubt an ignition coil can charge as much capacitance as a NST can.
You'll probably be able to adjust the HF intensity by twiddling the dimmer, but it will also change the point in the cycle where the arcstarter fires. If your welder's output voltage is passing through zero at that point, results could be dismal.
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The start of a tig arc stabilizer/starter
The arc is about 6mm long and very strong. 