# a welding question



## Bonez (Feb 24, 2006)

disclaimer: moderators feel free to move this thread if you feel it is in the wrong area

I go to school at clarkson unversity. My friend approached me the other day b/c i am the official eletronics guru in my area of housing but his question stumped me. For one of his classes he needs to make a simple (key word simple) battery operated portable TIG welder. He is being provided with the tig welding head and all the associated connectors for the gas. The machine needs to be able to roll around for his class and make a bead. He was thinking of using a large capacity car battery and hooking up the TIG nozzle to it for the power source. From my understanding (and correct me if i am wrong) it requires 50-80 amps to TIG weld and the voltage is not that important. (ive seen people arc weld with two car batteries in series out on a 4-wheeling trail) Would anyone know how to design a high powered circuit to limit the current coming from the car battery to only 50-80 amps. Thanks in advance if anyone can help me (and dosent think im crazy for asking this question)


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## jtice (Feb 24, 2006)

I have seen it down with one or two car batteries.
and a bread toasters heater coil ran inline with the wire to the tig.
The coil acts as a buffer to take some of the initial jolt.
And eats up some excess power.

Hooking the batts directly to it works, but I think its really hard on the batts.

~John


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## gadget_lover (Feb 24, 2006)

I'm talking off the top of my head, so feel free to disregard.

First you need to double check the parameters to make sure of the voltage and amps. Then you can create a control circuit.

I seem to recall that older units used carbon rods as big resistors to limit current. Somewhere I read about a "saltwater variable resistor" that was used for high current control. 

You said simple 

Daniel


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## Bonez (Feb 24, 2006)

thanks for everyones quick responses. i am somewhat familiar with the design of electronic circuits (i am an engineering and managment major with a concentration in electrical engineering (so not full ee) so i have some idea of circuits). I was concerned though that with the amount of power going through the circuit, no matter how i design it i will fry the resistors and other components. with 50-80 amps going through the circuit at 12 volts that is approx 500-800 watts, which is way above the ratings for even high power (5-20watt) resistors. The carbon rods sound interesting though as i'll bet they have a high internal resistance and would not be too hard to heat sink. I hope that my friend is provided with several nozzles so we can test various strategies  I may have to resort to the old beg a professor for their expertise, but most of the professors are engaged in their research and have little time to be bothered :help: 

Any idea on circuit design would be greatly appreciated!! (if only to make me look smarter, which sometimes can be hard) I wish he'd asked me a flashlight question..........


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## CNC Dan (Feb 24, 2006)

you need to add some controlable resistance to the circiut to limit current.

You can find large power resistors if you know where to look. OR, you can make your own. The steel strapping that is used to hold cargo to pallets is a good choice.
You will need to make good conections, and find the right length by trial and error.
Remember, the arc will have its own restance too, so the limiting resistor doesn't have to be as high of a value as you might think. If you clean all the paint off the steel strapping you can use a pair of vice grips to clamp your wire on at the proper spot.
You can fold the strapping in a "zig zag" to reduce the space it takes up, but be mindfull of the heat produced. A fan may be needed.


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## jpfaff (Feb 24, 2006)

You've sparked my curiosity... TIG(Tungsten, Inert, Gas,) Where is the gas?? Otherwise it would be a simple SMAW weld or shielded metal arc weld. I work as a carmen on the railroad, repairing rail cars daily, welding everyday. Without gas 
your just stick welding...


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## Bonez (Feb 24, 2006)

the origional idea behind this post was for my friend who was told by his 400 level materials and welding class teacher that he needed to make a portable TIG welder for class. He has to weld a frame (for the requirements of the class which is primarily welding) and then they are supplying the gas and the TIG tip and the connectors. He just needs to figure out on his own time how to get enough current to the tip from batteries. The frame will be put on wheels to be a portable TIG demonstration. All it needs to do is be able to strike an arc and lay a bead on a sheet of metal. It does not have to work for more than 30 seconds and recharge time does not matter. The teacher needs something portable for the class because he was injured in a shop accident and so is making all of this years class projects something to help him out. The thing that is making this complicated is the fact that the school does not want to buy another TIG welder (to just strap on the cart.... that would be the easiest) but they have alot of extra parts for the TIG welders that we already do have, so the challenge for my friend is to make a makeshift TIG welder from the tip, the gas and car batteries. I dont envy his challenge, its gonna be tough. He was just looking to me for circuit help, but the largest circuit i have ever designed or worked with was dealing with far less than 50-80 amps. 


I may have confused everyone with the idea of a rolling demonstration. My friend also has to make a feeder for a piece of metal that will move the metal by the fixed tip while it is laying the bead or whatever TIG welding does (unfortunatley i have never TIG welded, all my friend told me was that he called a manufacturer of machines and they told him 50-80 amps and the voltage does not matter as much as the current, they said it could be done with 12v) So all i know is the specs of the circuit that he wants me to design so i thought i'd see what information the "community" could come up with. I know that this is a vague request, and i also know of the kindliness and dedication of the people on this forum, so i figured i could glean a bit of information and ideas from some of your ideas and some more information from my limited knowledge. Boy... if you guys actually come up with a working idea i doubt he'll believe me that i got my inspiration from the great people on a _flashlight_ forum. Maybe i can create another convert...........


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## jpfaff (Feb 24, 2006)

Thats a MIG welder and not TIG.. I dont mean to push ,but I have experience in both. I went to a vocational school for electronics, as well as, currently I'm a welder.. Give me exactly what you need. Several thing I know. A power supply. Equipment provided.. Task at hand.. Things we know.. Maintain amperage.. From car batteries.. How to store the energy and maintain it?? Capacitors?? And yet it trickle a certain amount. Rectify by transformer??


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## jpfaff (Feb 24, 2006)

Some key points:
1) Somewhat mantain voltage. If it suffers, so does amperage
2) Keep a somewhat constant amperage for 30 seconds off of car bats.. If he didnt state which car battery you must have, get or create a NiCad.. A lead acid battery gives 55 amps while a nicad is 155.
3) Did he say anything about recharging?
I think I can help..
My email is [email protected]
I'd rather talk to you on a personal level..


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## Bonez (Feb 24, 2006)

jpaff,

PM and email sent!!


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## Luna (Feb 24, 2006)

TIG is a constant current process. You need approx 1 amp per .001 of material. Lets assume that he is not going to do Aluminum. This means he can go with a simple DC power supply. You can tig with CV but it isn't the best way to go (I once mounted a tungsten in a MIG tip and ran Argon just to play with the idea). Car batteries can easily provide 300amps plus, so if he wants to cheat, 2-3 batteries in series an resistor (AC light bulb) might suffice. He wont need that much power though. I say a 80 amp would be perfectly fine for a proof of concept. If a quasi CC device is wanted then that is easy too. 

Establish the limits and I can help more just in case. How thick of material will be needed. A cheap Tig torch can be found at Harbor Freight so all he will need is the gas/reg and consumables once he builds the PS.


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## James S (Feb 25, 2006)

> he was injured in a shop accident



This accident wouldn't have anything to do with improvised and dangerous shop equipment would it?

The ideal way to limit the current might very well be the transformer from a regular welder! If you have an older arc welder the transformer in it can be used as a coil to limit the DC. For AC projects like stupidly huge tesla coils and such arc welder coils are regularly used to limit current from transformers that would otherwise melt all your gear.

though you could do it with just 1 batt probably, 2 in parallel will offer more available current without being so hard on the batteries. 

But I'd say that 30 seconds might just be all the duty cycle that you get without the coil melting and the batteries exploding due to excessive out-gassing or something.

Make sure your cart is big enough to properly strap down the gas cylinder to. Lugging that around carelessly is probably more dangerous that exploding batteries.


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## Bonez (Feb 25, 2006)

I fully understand that this would be a dangerous device since he is going to be rigging a TIG torch...... but then again im just the messenger that was asked to design a current reduction circuit..... oh well :sweat: 

Thank you everyone for all your ideas and help. Hopefully with all the knowledge provided i can advise my friend on at least a way that will get him an A on the project, if not actually make the rolling automatic welding demonstration that the teacher wants.

James: thank you for your suggestion that the cart be large enough to accomodate the cylinder for the gas. My friend has the design of the cart mocked up in CAD and i will make sure that his plans include more than enough space to *safely* (key word) include the gas cylinder. I also forgot about the variable transformer for a standard arc welder (probably because i am not familiar with welding equipment) I will run that suggestion by him and jpaff (who has graciously said he will also help me out) and see what we can come up with. Pictures of this rig when he finishes it by the end of the semester should sure be interesting. I just hope the pictures dont end up being exploded batteries and a puddle of molten metal.................. 
Once again :thanks: for everyones input. Everytime i post a question here on the forums (and read responses to everyone elses questions) i am time and time again amazed at the level of knowldge and willingness to help people that exists in this great community (i know i say this alot in my limited number of posts so far, but with todays society the way it is right now, this is an amazing community of caring folks) You guys rock :rock: :rock:


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## Prototype3a (Feb 25, 2006)

I hate to rain on anyone's parade but transformers don't work with DC. They are AC only components. Don't forget that you're gonna need some solenoid valves for the argon/helium and some sort of "contactor" to essentially start and stop the welding circuit. I may be able to help as well as I've done quite a bit of tig welding and am familiar with the theory behind it. My e-mail is [email protected]


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## James S (Feb 25, 2006)

I wasn't thinking that you could use it as a transformer :laughing: but the secondary coil would make a really big resister to limit the current. Might be easier and safer just to use a thrift shop toaster inline with it, or if you can find an old cal rod from a water heater or even an element from an old electric stove. I see a trip to the junk yard in your future!


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## MoonRise (Feb 27, 2006)

Take a complete TIG welder and put it on a cart. Get a honking big DC-AC inverter and a bunch of deep-cycle lead-acid batteries and put them on another cart. Wire up batteries to inverter, and run welder off of the inverter's AC.

No duct tape involved and mostly safe.

Another option is to run the welder off of a generator.

Want portable all-in-one? Just buy an engine-driven welder.

Want more info about TIG welding? Search the web (hint: Google for "Lincoln welder" and "Miller welder" and then look on their sites for info about TIG welding).

Can you weld with one or two car batteries and some wire? Sure, but it's not the prefered way to weld, that's why companies make welding machines and people buy them.

Regarding the amperage used in TIG welding, it all depends. For thin/small stuff, the amperage used will be in the single-digit number of amps (2 to 5 amps). For bigger stuff, more amps are used. You need shielding gas (that's the "IG" in TIG, stands for Inert Gas). TIG can be DC or AC, but there seems to be a high-frequency overlay to help stabilize the arc as well as some current control to limit blow-out.


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## Luna (Feb 27, 2006)

Prototype3a said:


> Don't forget that you're gonna need some solenoid valves for the argon/helium and some sort of "contactor" to essentially start and stop the welding circuit.



Not necessary. You can run hot (like stick), scratch start and use a mechanical valve on the torch body. Certain isn't gonna have me wanting to get rid of my inverter Tig, but it works. 

You should be able to scratch up an arc with around 14-19volts with Argon. 


If the car batter isn't what you want, build a regular ol' constant current IGBT supply. HIFreq is only necessary if running AC or you want non-contact arc starting. Plus it really feels good when you forget to ground then work piece 

(seems some are forgeting this is a school project, not a production welder design)


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## Prototype3a (Feb 28, 2006)

Continuous hi freq overlay on AC is only required to maintain the arc when a sinusodial ac is used. I have a Dynasty 200dx and it outputs squarewave AC so hi freg is only needed for starts (if so desired). Ya I remembered the valve type torches after I posted the other day. Never used one though.


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## Luna (Mar 6, 2006)

Prototype3a said:


> Continuous hi freq overlay on AC is only required to maintain the arc when a sinusodial ac is used. I have a Dynasty 200dx and it outputs squarewave AC so hi freg is only needed for starts (if so desired). Ya I remembered the valve type torches after I posted the other day. Never used one though.




Even better is your dynasty puts out asymetrical waveforms, not just squarewave. One nice adavantage of an inverter design with a microcontroller, until it comes time to replace the system board. 

Try AL without the HF. It will be frustrating or at least it is to most people. I use HF but lift arc is fine for ferrous materials to me. Remember, I'm one of those idiots that likes to O/A thin (0.025) aluminum so to cause me frustration is not an easy task


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