Add on HF box for inverter ?

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Hi I posted this question on another forum but would like a second or third opinion before I hook this up to my welder. I have been looking for a factory TIG add on module for my Powcon 300 MST but have had no luck finding one. Last week I was at a garage sale and bought a Craftsman add on high frequency box. I have used these in the past on transformer and engine driven welders but not on inverter. I use the Powcon mostly for MIG and stick but It would be nice to use it for TIG. Will using the high frequency box harm the Powcon welder in any way? I have used the Powcon for scratch start and with the factory RT10 that's on my other Powcon MS 200 and it works very well for TIG. Thanks for any help with the compatibility between these.Andy
Reply:Since the HF piggy backs to the output I don't see any problem.   I think Mac has a powcon.  He can maybe give a more definitive answer.DennisThermal Arc 185-TSWMillermatic Challenger 172VictorO/AAtlas Craftsman 12 by 24 LatheEsab PCM-875Wholesalem Tool Mill-Drill
Reply:Originally Posted by Tailshaft56I think Mac has a powcon.  He can maybe give a more definitive answer.
Reply:Without knowing the supply schematic and part specs, and not knowing the voltage of the HF box, it would not be responsible to answer.The HF output has little effect on the winding-based supplies.  The HF does not pass through the windings.  But the output terminals of an inverter supply are sometimes connected directly to the output transistors.  Maybe not so good for the type of waveform the HF box supplies.  Unless the welding supply was designed for it, or the HF would not damage it.Maybe the welding power leads pass through the HF box.  And the HF box has diodes for reverse voltage protection.  I can see that.  One or two forward voltage diode drops does not amount to much. I am unfamiliar enough with a large enough cross-section of welders to be of much help. - Jim
Reply:Hello Astuch!Many moons ago, in my former life (prior to my liver transplant and prior to teaching) I used to work as a technical sales rep for an "indy" welding distributor in the New York City Metro area... We were one of the first distributors of those "Powcon'" inverters in our region - back in 1983 if I remember correctly but, I'm probably not!Btw, I teach for a living now so, I'm not endorsing or putting down this welding equipment...Anywho, the model 300SMT is a DC only CC/CV power source... In other words, unless you have an engineering background in electronics, one cannot produce AC output from this power source so, if you're attempting to GTA welding on aluminum with a HF box hooked up to the Powcon 300SMT, the end result is a CC output of DC w/HF which will not weld the same as opposed to AC w/HF continuous...Some of the newer generation of Welding inverter type power sources offer the capability of welding both with DC and AC output... However, since these power sources produce an adjustable square wave output, the need for HF is NOT necessary at all... Overall, it's a good machine but, not of the type to use with a HF box attached to it for GTAW of Aluminum...I hope this helps!P.S. "Watch out for those ceramic inductors that were known have cracks on them which caused many a malfunctioning power source which were hard to diagnose as being defective initially when troubleshooting them!"                                  BIG TIME SAFETY TIP!!!"Also, Make darn sure that the heat sinks are neutralized prior to working on those power sources in order to prevent someone from being shocked - meaning yourself or anyone else, by those primary and secondary capacitors discharging a whole lot of E-juice into one's soul!"Respectfully,SSBN727Last edited by SSBN727; 06-11-2006 at 04:13 AM."Run Silent...  Run Deep!!!
Reply:I just assumed he wanted a non-contact HF arc-starting method, but SSBN is correct if the goal was something else.
Reply:Hi MAC702!No problemo!  Btw, Good to see you here also!!!  Same goes for JTMcC!!! Respectfully.SSBN727"Run Silent...  Run Deep!!!
Reply:The powcon tig (300st) units generally use the capacitor starters for tigging steel...not, HF.  However, to get the best answer, you probably should just call Arc Products at 1-800-770-0063.  They service these units and have techs that can answer this definitively.http://www.arc-products.com/powcon/index.htmlSmithboy...if it ain't broke, you ain't tryin'.
Reply:Hi GuysThanks for the help. I just want to use this setup for steel / SS, noncontact DC TIG not AL. I have other TIG welders that I use for AL work. The Powcon has a spool gun that I have used for AL MIG when I have to (only a few times in the 15 years I've owned the welder). This welder is small, light,portable and can be hooked up to different power supplies. So it is perfect to take to the job when I have to, so I would ike to use it to it's full potential. I have bought parts from Arc Products in the past and they have been very helpful. I have asked them what I feel are easy technical questions about Powcon and Oxo stuff in the past and have never gotten very good answers. The question is I feel more about the Craftsman Box than the Powcon welder.  I know Powcon made at least 3 different add on TIG boxes that would work with this welder but these might have used different starting methods. I was hoping for an answer like ( yes, I run mine setup like that all the time and have no problems) or (no, I did that one time and it blew up the welder)Thanks for the helpAndy
Reply:Originally Posted by astuchI was hoping for an answer like ( yes, I run mine setup like that all the time and have no problems) or (no, I did that one time and it blew up the welder)Thanks for the helpAndy
Reply:Hey Astuch!Where in Pittsburgh do ya live?I live in Robinson Township by the Intl. Airport...Those Powcon SMT's if I remember correctly, Have pretty good DC GTAW arc starting capabilities via capacitive discharge that should be adjustable...Now I do'nt know exactly what accessories you  may have with your power source but, if you want to e-mail me@: [email protected] and if our schedules do'nt conflict, I'd be happy to take a look at what you've got to work with.Respectfully,SSBN727  "Run Silent...  Run Deep!!!
Reply:I have heard of arc starting with those peizo dohickies that are used to start the flame on gas grilles and stuff, but I have never seen a working layout of how it's done.  Seems like it would have to be pretty simple.  Might be something to look into.Smithboy...if it ain't broke, you ain't tryin'.
Reply:astuch, whatever experience you have had with tech support from Arc Products before, it never hurts to ask your new question from the people who SHOULD know or MIGHT know the answer.  At least they should have access to a schematic of your Powcon, which is a big part of the battle.  Same goes for Craftsman, but I seriously doubt you will be able to reach anybody who knows the answer there.  But what's the downside of asking both?Neglecting for the moment the question of why you want to use the HF unit with the DC inverter source, I believe that the serious question is whether either the Powcon or the HF unit have an effective LC (inductor/capacitor) filter between the HF transformer, where the high voltage is injected into the welding circuit, and the expensive, voltage sensitive parts of the inverter.  Schematics or tech support for both units should answer that question.Such filtering does not require huge component values (capacitance and inductance) because the frequency of the injected high voltage is very high.  Thus, a low inductance (but high current) coil in series with the DC output of the inverter and a low capacitance in parallel with the DC output could effectively block the high voltage/high frequency from reaching the very expensive IGBTs or MOSFETs or the rectifiers in your welder.Without seeing the interior of, or a schematic of, the HF unit or the welder, I can't say whether such filtering is provided, but it is highly likely that it is.  For one thing, Craftsman would get a black eye if they went around destroying thousand dollar welders with their hundred dollar add-on.  For another, the HF unit probably needs such a barrier at it's input to effectively feed the HF to the torch instead of dissipating HF energy into the welder guts.Regarding use of the HF unit with a DC source, presumably you want it for non-contact arc striking, but don't need it thereafter?  It wouldn't be too difficult to come up with a current sensing device that turns off the HF unit when welding current rises above some adjustable threshold.  I think this was an approach used in some commercial machines, but I'm not sure.  The welding current sensor could be electronic, such as with a Hall Effect sensor in the magnetic field of the output conductors, or electro-mechanical, as with a relay having a coil of only a few turns of very heavy copper wire or copper bar that the welding current passes through.  The relay would pick up at some threshold welding current and break power to the HF unit.I'm not suggesting that this is a desirable combination of equipment, but if you want to do it, it would not be too difficult to make it do what you want.awrightLast edited by awright; 06-12-2006 at 02:16 AM.
Reply:Hi Awright!I know for a fact that these PowCon 300SMT's DO NOT have Protection from HF feedback into the circuitry based on prior personal experience and, based on the former company's (Cyclomatic out of California) recommendations and warnings about attempting to produce or engineer such an attachment to the PowCon 300SMT system...In other words: If anyone attempts this, the warranty is VOID but ,since that's a mute point currently - Life is full of risks so, "give it a whirl" because, who's to say that these days you ca'nt come up with a way of making it work although for the life of me, I cannot understand why??? Especially if the power source already is equipped with a capacitor discharging arc starting circuit which the last time I checked, negated the need to have HF starting in the first place, and the capacitor discharging circuit is supposed to be adjustable on that power source.;Btw, I used to service quite a few of these puppies back in the day!!! I've also seen the "Guts" of the newer, more current technology inverter type power sources that do have either IGBT's (Insulated Gate Bipolar Transistors) or MOSFET's (Metal Oxide Semiconductor Field Effect Transistors) in them but, that's another story on another post... These older design PowCon's had an early version of an IGBT and more than one of them - which was actually more like an advanced type of SCR (Silicon Controlled Rectifier) of the "hockey puck" type design. Bottom line is that something is "amiss" with this power source if one is having a hard time arc starting without the addition of High Frequency assistance because, an independent HF arc starting attachment should not be necessary to use with this power source in order for it to start properly without "scratching" the "Wulfram" (German word for Tungsten) electrode to the joint.... Astuch just needs to locate qualified personnel to service his PowCon power source. Many Moons ago, I used to be one of them!   Respectfully,SSBN727  Last edited by SSBN727; 06-12-2006 at 05:32 AM."Run Silent...  Run Deep!!!
Reply:Just to add to my previous post, The power source in question already has an output frequency that's much, much higher than 60 hertz because, that's what  these particular inverter type power sources of this model do!   For example: If you ever heard these "puppies" run, you would be able to hear how high - the frequency really is niside the power source!!! Am I right astuch??? Sounds like a high pitched screaming sound if I remember correctly???  Even though the HF output is much less than what is being "generated" inside before the ouput terminals, the HF output @ the terminals is absolutely much higher than 60 hertz!!! It's more like around 200 to 500 hz depending on what your output current and closed circuit voltage is set to and other factors such as arc length, etc...This time I know I'm correct because, some things in life you do'nt forget!!! Especially the first time I ever tried out one of these PowCon's myself and heard that horrendous sound while welding!!!   Respectfully,SSBN727 Last edited by SSBN727; 06-12-2006 at 06:13 AM."Run Silent...  Run Deep!!!
Reply:I have the 300ss and the 300sm and both of mine squeals when you use them for stick.  I thought there was something wrong with the first one I got, the first time I used it.  SSBN727 is right...if you have only welded with a 50-60hz transformer welder, the powcon sound is not something you will easily forget.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Hi GuysIt's Great to have all of this info and help from so many nice people. Here are some links to photos of the HF box and Powcon welder. http://i80.photobucket.com/albums/j161/astuch/HF001.jpghttp://i80.photobucket.com/albums/j161/astuch/HF002.jpghttp://i80.photobucket.com/albums/j161/astuch/HF003.jpghttp://i80.photobucket.com/albums/j161/astuch/HF004.jpghttp://i80.photobucket.com/albums/j161/astuch/HF005.jpgYes as SSBN727 and Smithboy wrote the 300MST puts out a squeal when in use and ticks when on but no arc is struck.As I wrote above I just wanted a way to use the welder for TIG with some type of none contact start. I have used only HF start, lift start and what I think is high voltage start to do this in the past on other welders. IF there is a better way to do TIG with this or other welders please let me know.If this welder already has a way for noncontact arc start as SSBN727 pointed out I will not need the HF box. I am going to try and get with SSBN727 for some hands on help with this. In the HF box there are only a few partsSPST switch to turn off the 115v supply115-3500 step up transformerSpark Gapresistor2 capacitorsand what I think is a transfer coil?These last two parts might be what awright wrote about in his reply and used as filters.I really don't have any electronics background and thats one reason I was asking this in the first place. I was going to call Arc Products for there opinion after I got some help here and on other forums. I'm also going to call Sears and see if I can get a manual for the HF box that might help. Thanks again for all the helpAndy
Reply:Yeah.  That's a pretty simple HF unit.  I used the same unit with a Craftsman buzz box 40 years ago.  It worked, but it was a pretty crude setup.  I did manage to make a few aluminum boxes for special equipment.The operation of such a unit is quite simple, but I won't go into detail here because I believe the question is now moot if you get your internal start circuit serviced.The capacitors are for HF filtering, but it's not clear from the picture that there is any filtering in the HOT lead from the power source unless there are two terminals in the vicinity of the ground lead.  What is the small twisted wire from the hot input lead passing behind the TIG Torch receptacle connected to?  Is there one capacitor on the hot input and one on the ground input?  How about another picture showing the inside of the connector panel a little clearer?Good luck getting your starter fixed.  Sounds like it may just need a tuneup.awright
Reply:From the image below, the very large pass-through inductor is on the right.  The HF signal from the starter is filtered by that inductor winding, and does not appear at the transistor outputs of the welding supply.The pass through for the POS and NEG welding supply leads are also clearly visible.  It looks obvious from the image that the high voltage starter signal is injected 'downstream' of that inductor.  And in the second image, is the labeling for the weld cabling pass-thrus.  Though the 'torch input' cable is out of frame camera right.Seeing what is shown in the images, I would hook it up.  But as the much more experienced have posted here, the supply you have already has a 'BBQ starter' (piezo is a capacitor discharge, sorry for the slang) built in. And getting that repaired is a good choice. - JimLast edited by MotoFab; 06-12-2006 at 03:31 PM.
Reply:I believe the Powcon inverters operate in the range of 800-5000hz which produces what I consider to be a nice audio feedback while TIG welding.  I'm pretty sure that HF starters operate at around a few Mhz.I've seen the Powcon schematics and they don't have any protection from HF.  With some electronics knowledge it would be pretty simple to construct an RF filter.I'd like to come up with a decent non-contact start circuit for the Powcon myself as my power supply (400SM) doesn't have the capacitive discharge of the "T" models.  A piezoelectric starter would probably work, but those things develop a tremendous amount of voltage which I'm not sure would be healthy for the SCRs or the rectifier diodes in the power supply.-Heath
Reply:Hi awrightI do not have the HF box in front of me right now but I will get a better photo of it soon. If I remember right the twisted wire runs to the resistor that is right under the capacitors in the photo (hard to see in the photo). The other end of the resistor is attached to one of the capacitors.As for the internal start circuit, I don't think this welder has one. I know that SSBN727 said that it has one but I have no knowledge of it. There is a setting for scratch start TIG another for CC and Two for CV/MIG. I am now wondering if the "Scratch start" setting is really a Powcon term for lift start or some other type of starting method? ThanksAndy
Reply:Hi halbrittI knew that the T in the MST300  was for TIG but I didn't know that this welder had any starting method. The welder may not be broken, it might just be operator error on my part and I won't need the HF box. So what settings should be used to use the starter? Should I have it set for CC and when the foot pedal is pluged in It will know to use the auto start? ThanksAndy
Reply:I'm not certain about the "T" power supplies, but I'm pretty sure that had a capacitor discharge starter.  I know the Arcon units do, which is the company that is currently building similarly (identically) designed power supplies.  In fact, they're still using SCRs.The 300ST supplies that I've seen have a switch on the front panel to turn on the arc starter.-Heath
Reply:Hi Astuch!Definitely  have your machine set to CC (Constant Current) because, that's for SMAW=Shielded Metal Arc Welding (Stick), & GTAW=Gas Tungsten Arc Welding (TIG) processes... If the power source is set to weld in the CV (Constant Voltage or otherwise known as CP=Constant Potential) mode, that power source is set for the GMAW=Gas metal Arc Welding (MIG) & FCAW-G=Flux Cored Arc Welding -Gas shielded processes...  On this power source, if the process settings are'nt compatible with the process that you're attempting to use, the power source will not work properly so, make sure that you have all of your "Ducks in a row"...Sort of like a preflight checklist that pilot's use before "Taking Off" It's a shame that you do'nt have the instruction manual for this power source because they used to have really good instructions on the proper operation of the power source so, to make you feel a little bit better for what it's worth, all this time you were flying kind of "Blind" and that's no fun for anyone including myself  If you're going to weld Mild stl. or Stainless then make sure that your TIG Torch cable is connected to the Negative (-) terminal on the power source, and your work cable (some people like to call it the "ground" cable which is an incorrect description) connected to the Positive (+) terminal on the power source... Double check to make sure everything on the power source is set correctly... turn off the power source and check to make sure you have the correct gas shielding for TIG welding which is straight Argon and not an argon /CO2 mix or a tri-mix that's normally used for MIG welding...Connect the Foot pedal to the correct terminal on the power source, Turn the power source back on, open your gas cylinder, set your flow rate,  make darn sure that your work lead is making VERY GOOD contact with whatever you're going to weld, then see if the equipment will work the way it's supposed to, and let us know how it turns out... Good Luck!!!P.S. Man,   is that HF attachment unit ever dirty inside!!!Someone please clean that dust out and check out the sufaces of those HF points to see if there's any pitting or corrosion of any sort!!!  P.P.S. Ohh yeah Astuch send me an e-mail if ya want to meet so you can get this "puppy" welding the way it's supposed to and no charge because, for myself -it's been awhile since I've seen one of these but, for all you other folks, I used to go all around the greater NY,NJ metro area demonstrating and servicing this equipment and, the 300SMT was my Demo model so, it'll be like "a blast from the past"!!!Respectfully,SSBN727   Last edited by SSBN727; 06-13-2006 at 01:51 AM."Run Silent...  Run Deep!!!
Reply:MotoFab, I have to disagree with you about the function of the "coil" on the right of the photo.  If you look closely, you will see wires to the primary of that transformer (not coil, which implies a single winding inductor) from the spark gaps, and two heavy copper strap conductors forming the secondary of the transformer bridging from the hot input lead to the hot output receptacle.  This is a series HF injection transformer, with it's primary excited by the almost instantaneous transition from a few thousand volts to near zero volts at the instant that the air in the gaps (between the tungsten buttons clamped in the copper bars in the middle of the photo) ionizes.The few thousand volts supplying the air gaps come from the line powered, double winding transformer on the left of the photo.  The output transformer is a variant on a Tesla Coil, in that the HF output is the oscillatory response of the transformer in combination with some stray or discrete capacitance to the impulse excitation as the air gap breaks down.  One aspect of the device that I don't understand is where the capacitance to create the oscillatory response is located.  Perhaps one of the two capacitors clearly visible performs the function of the "tank" capacitance required for oscillation.Since, by my interpretation, the transformer on the right is the HF series injection device, it cannot also be the filtering device since it is the source of the HF.  That leads me to believe that at least one of the two capacitors is a rudimentary filter to keep the HF out of the power supply AND/OR is a solid point from which to launch the HF into the hot lead to the torch.  While looking at the photo, I wondered why the input wire from the power supply was not filtered, but I suspect that the small wire running from the hot input lead to the area of the capacitors just be connected via the capacitor to ground, which fulfills the two functions I was describing (shunting HF to ground to protect the power source and providing a solid (AC ground) for the HF injection.  It would be possible to improve the filter at the hot input lead by adding an inductor and capacitor to form a "pi filter," which is more effective than a simple capacitor to ground.Halbritt, I suspect the frequency of oscillation is a lot higher than, "...about a few MHz," but without some data on component values or a 'scope on the output (with extreme care to protect the 'scope from the HV), it's hard to predict.  The larger the difference between the inverter frequency and the HF unit frequency, the easier it is to block the HF from the welder and provide a launching point for the HF.  Astuch, since you seem to believe that your unit may not have the arc starting circuit, if you want to work on a welding current-sensing setup to cut off the HF unit once the arc is established, let us know.Have fun.awrightLast edited by awright; 06-13-2006 at 01:45 AM.I'm staring at the schematic for the 400SM and I do see a couple of capacitors that both shunt to ground that occur in the schematic after what I know to be the output capacitors.  Unfortunately, no values are listed, so I can't say for certain, but it does look to me like my unit has what could be protection from both HF and high voltage DC (there are some resistors in the circuit as well).I'm not sure where I got the impression that HF arc starters operated in the realm of a few Mhz.  I doubt it's much more than that.  Being an amateur radio licensee, I've always just thought of "HF" as those frequencies between 3 and 30 Mhz.  I've also personally never heard of a spark gap transmitter that has operated at anything greater than 5Mhz.I'd like to build a capacitive discharge arc starter for DC TIG.  I wonder if anyone has any clever ideas?  I was thinking of doing something like a Marx generator.-Heath
Reply:Heath, I'll defer to your radio experience on frequency.  But it would be interesting to see the HF on a scope, eh?  Perhaps using a small search coil as a probe and gradually approaching the welding cable until you see a clear signal.A Marx generator would be an interesting project, but I think you would run into reliability problems with the multiple spark gaps.  By the way, have you seen the website of the guy in the U.K., I think, who has posted a lot of pictures showing his Marx generator experiments?  VERY dramatic, and he's covered a lot of the R&D ground work for do-it-yourself builders.  I wish I could give you the link, but I changed my computers a few months ago and didn't transfer the info.  If interested, try googling it.  I think it was something like Tom's or Mikes High Voltage site.But my intuition is that, while fun, the Marx generator approach is overkill for the task at hand and that a more conventional spark generator with an IGBT, mosfet, or fast SCR and a spark coil running off 12 or 24 volts would be more controllable and reliable.  In particular, I think that a conventional spark generator could more easily reach higher spark discharging repetition rates which may be desirable when you don't get a welding arc on the first discharge.  Additionally, you need a moderately high voltage source to feed the Marx generator, since you have to have a high enough voltage to break down each spark gap.  uh...or does each breakdown add to the trigger voltage of each stage in the rest of the string?  I don't remember.  So it gets a little complex.  But workable!awrightLast edited by awright; 06-13-2006 at 04:26 AM.
Reply:It'd probably be simple enough to use a frequency counter near the HF starter to figure out the frequency.  I doubt it'd be necessary or desirable to use an oscilloscope.  HF starters are noisy suckers.One can build a marx generator using avalanche transistors rather than spark gaps.  I was thinking of using transistors with a breakdown voltage above welding voltage and below OCV and powered off of the welding supply.-Heath
Reply:Hi SSBN727I think you might have misunderstood me, I didn't need help setting up the welder for TIG. As I said in my first post on this topic I have been using this welder (and others) for  TIG for many years. I might have been born at night but it wasn't last night. What I was asking was which of the two CC mode setting will give me the non contact arc starting.The first CC setting is (scratch start TIG) the second is just( CC). As I wrote it might be that Powcon has a different meaning for scratch start than I do. I will try and use the welder for TIG sometime this week and post back with an update.Good write up on the TIG setup. I emailed you about getting togetherThanks Andy
Reply:Heath, that's a neat idea.  Automatically shuts off the Marx generator when an arc is struck.  I never saw a Marx generator using avalanche transistors - always a series of spark gaps.  But is it easy to find avalanche transistors the fire below 80 volts?  I suppose it would be, since there are plenty of type with lower voltage ratings.  But you are probably going to have to do the selection yourself to get an array of avalanche transistors that fire at about 75 volts because I think most transistors rated for avalanche use fire above 100 volts, don't they?.  The idea gets more intrigueing the more I think about it.  My last venture into avalanche transistor applications was coming up with a laser diode pulser about 30 years ago.Still, isn't that going to require a pretty large number of stages to get several thousand volts to start the arc?awright
Reply:I found a Zetex FMMT413 with a breakdown voltage of 50V that I thought could work.  Granted, I've only begun contemplating this, and a marx generator with avalanche transistors is something that I haven't really seen documented but rather just mentioned in passing.  I'm still trying to figure out a clever way to couple the marx generator to the welding supply, while also charging from the welding supply, and not running welding current through the marx generator.With regards to the output voltage required to start the arc, there'll be argon present which has a much lower breakdown voltage than air.  I believe air starts to break down around 700V depending on conditions.  I've also read that argon (at one bar) breaks down around 300V.  There's a lot of complicated math that could be done to determine what kind of voltage is required to jump a gap of a given distance in the presence of a given gas at a given pressure, but the end result of the prediction isn't particularly accurate, which leaves empirical testing and that's where the fun is anyway.  If I do this, I'm guessing 20 stages at about 50 volts per stage minus losses, so something between 900-1000v.Before I get into this, I'll do some testing with a simple voltage multiplier to see what kind of voltage I really need to jump a spark across a gap in argon.-Heath