Resistance of an arc in ohms

admin

I'm looking for help to determine the actual reistance of a welding arc, as if it were just another resistor in a resistor network or voltage divider, (series circuit), etc. I realize that arcs can be created at any V above a certain threshold.The problem I'm running into is all the references I've read so far, reason from the point of the supply, but that doesn't help me to calculate ohmic value of the arc. If you told me the arc resistance was zero, a short circuit, even that would help, because I could design with other circuit elements based on that, but what's killing me is the ambiguity of the arc itself.The point of this is I'd like to build a welder, rather novel design concept, doesn't use a transformer so the formulas for transformers are no help (am well familiar.) Not owning a functional welder at the moment doesn't let me measure the Resistance at a work-piece or I'd do that. I just want to know how to calculate the value of R across the arc with other known resistances in the circuit. Thanks in advance.
Reply:Just a guess from an hvac contractor, but wouldn't the arc resistance, if any, be negligible making the are like a flame rectification circuit? Sent from my iPhone using Tapatalk
Reply:I graphed it out at one time.As I remember it depended on the size of the ionized channel (amps) and was non linear.I believe it started at about an ohm at 20a and dropped to about 1/10 ohm at 100a,after that it was fairly constant.This is from memory so I may be off.You should be able to graph it yourself using the volts amps curves listed for various welders.
Reply:No.Have you heard of this guy Ohm and his law?In SMAW and GTAW, you use a CC power source, so arc voltage varies a lot, as does resistance (since resistance is largely a factor of arc length).In GTAW, you use a CV circuit which controls the arc length, and with a relatively constant current, the resistance is relatively constant.
Reply:I believe air has a high resistance but once its ionized (arc), resistance drops close to zero. I would think ion gases like: Helium, Neon, Argon, Zenon etc have low resistances as they have there valence band filled.Other than that, what Papaasmurf, Bluewelders and rlitman said. rlitman kinda threw a curve in there with CC and CV tho.
Reply:An arc is a complex beast electrically speaking. It cannot be described by a simple resistance. At its simplest, it can be modeled by two voltage drops, one at the anode and one at the cathode, in series with a non-linear resistance. This resistance is influenced by current, arc length, atmosphere, composition of electrodes, and other factors.The design of arc welders is a fine art, even for engineers with years of experience in the field. While I wish you the best of luck in designing a new type of welder, it will be an uphill battle, especially without some knowledge of the physics of the arc, and of mathematical modeling of circuits.JohnA few weldersA lot of hammersA whole lot of C-clamps
Reply:Welder without a transformer?  Here's one Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:It is as simple as ohms law. Measure the current with a shunt resistor, and measure the voltage across the leads at the arc, not back at the welder. ohms law, there's your resistance... and the resistance obviously changes a lot as you weld...Welding/Fab Pics: www.UtahWeld.com
Reply:Originally Posted by MinnesotaDaveWelder without a transformer?  Here's one
Reply:One minor detail they forget to mention, a welder with no isolation from the power line will KILL you.
Reply:Originally Posted by BlueweldersOne minor detail they forget to mention, a welder with no isolation from the power line will KILL you.
Reply:I bet you that it is also UL approved.    Did you see any actual welding in the video???   How in the  fwak do you control the amps?????
Reply:That Atom welder is awesome, only a 110V line right to the panel and conveniently they give you that heavy duty little pouch for your belt to protect you from the 1000 amp output. Truly Amazing. Last edited by 70Challenger; 04-15-2014 at 04:31 PM.Millermatic 135Craftsman 7 Hp 80 Gallon           2 stage compressor
Reply:Originally Posted by 70ChallengerThat Atom welder is awesome, only a 110V line right to the panel and conveniently they give you that heavy duty little pouch for your belt to protect you from the 1000 amp output. Truly Amazing.
Reply:Neat,run 1000 amps through yourself,and there will be no dental records.
Reply:You people have so little faith! They couldn't sell it if it weren't safe. Besides you can't say it on the internet if it isn't true.
Reply:Originally Posted by Willie BYou people have so little faith! They couldn't sell it if it weren't safe. Besides you can't say it on the internet if it isn't true.
Reply:Originally Posted by BilldacatMy wife claimed that water gives her heart burn...WTF...She googled it.  so it must be true!
Reply:Originally Posted by MinnesotaDaveHey, it's perfectly safe to stuff a random wire into an open panel and then use earth ground to complete the circuit...no really...it's safe
Reply:Originally Posted by Oldendum I'm certain it meets Undertakers Labs specifications.
Reply:Originally Posted by BlueweldersOne minor detail they forget to mention, a welder with no isolation from the power line will KILL you.
Reply:Originally Posted by germetenThere are knock-offs to the Atom Welder, one called the Powerwelder (also in the Phillippines, posted on Youtube) show guys welding with their hands in and around buckets of water. "It's Amazing!" Fact is there are bare-foot people using it (or was that glass-blowers in India) as the videos clearly show, and trusting their lives to whatever operative principles it uses, even if it doesn't pass US standards."Atom welder" aside, is this true of ALL welders? (i.e. No isolation will knock you dead?) For example, what if I have no isolation, but I do have capacitive (Xc) current limiting? I'm thinking of making a welder from an old garage spring, it has enough turns to work as an autotransformer, so long as current is kept within reason. (Not to say what might happen if the cap blows.)
Reply:Originally Posted by BilldacatI would say that your are FWAKING NUTS!!!
Reply:If you could keep the current through the circuit to less than 1/10 amp, it probably wouldn't kill you.You will find welding with less than 1/10 of an amp pretty difficult.
Reply:Originally Posted by BlueweldersIf you could keep the current through the circuit to less than 1/10 amp, it probably wouldn't kill you. You will find welding with less than 1/10 of an amp pretty difficult.