DIY Tig

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A while back I asked about adding DC to my AC buzzbox which I've done by adding a full wave rectifier from Miller. This works great for stick welding but when attempting to TIG with it most times the arc won't stay going. I know why this occurs, because I don't have a choke after the rectifier, but what I don't know is what size choke should I use ...  Any educated guesses ?thanks.
Reply:Jack, you need some capacitance as well as a choke to smooth out the DC.Burdens surplus center sells some heavy chokes and they are shown in the on line site.  Sorry, I don't have the URL, but I'm sure you'll find it in nanoseconds.Appreciation Gains You Recognition-
Reply:www.surpluscenter.comStangnetShop Full Of Stuff. Joey
Reply:I bought a choke from surplus center about a month ago but it turned out to be a big air wound coil which I didn't even bother hooking up. does anyone have specifics on how much choke is needed ?franz, the full wave recitifier I got from miller has some capicators built into it. pretty neat piece I'll try and get a pic of it.edit: this is the part I ordered.http://www.surpluscenter.com/item.as...tname=electric
Reply:Jack,  this onehttp://www.surpluscenter.com/item.as...tname=electricAppreciation Gains You Recognition-
Reply:Jack, what you have is a choke, and you're right all it is is a big coil of wire.
Reply:Jack, I will try to measure the value of the choke I have in my setup tommorrow. It is the same one that was used with the 200 amp bridge rectifier, came out of a 14volt, 200 amp battery charger. I don't use any capacitors.
Reply:Originally posted by Franz Jack,  this onehttp://www.surpluscenter.com/item.as...tname=electric
Reply:Jack, I measured my choke and it is .35 milli-henry. The coil winding is about 6" high, 5" wide, and 5" deep. The wire is probably flat stuff since it is rated at 200 amps. I took some pics and will post them.
Reply:thanks for the info Mike, any idea what it weighs ?I'm told that's a fairly good indicator of one's usefullness. the one I ordered from surpus center didn't weigh 2-3 lbsany ideas of sourcing a good sized choke ? I could order the piece from Miller but it's like $70 - jack
Reply:I just leave the HF going all the time and its impossible to extinguish the arc without lifting it  way off the work.  I'm using an AC welder with a bridge rectifier, and no choke.  A friend did some welding with it and used DC with no HF (after starting the arc) and it worked fine for him.  Very quiet arc when its only DC.Someone said to me that chokes on DC welders need a tap for a high and low current range, as one choke does not fit all.  Makes sense, as chokes stabilize current.  I kick myself for throwing out a junk DC welder a couple of years ago.  It had a choke, but I think someone burned out either the transformer or rectifiers.
Reply:Interesting. I read something similar the day before yesterday about leaving the HF going all the time but haven't had a chance to try it with my setup. Is there any downside to using the HF all the time ? - jack
Reply:It could cause the arc to wander, but I have not found that to be the case, even when welding an inside corner.  It is noisier as well.  Shouldn't do any harm to the HF unit.  It runs all the time if you weld with AC.
Reply:Jack, my choke is at least 30 lbs.
Reply:You could use a timer to make the HF start only, rather than constant, just like was done on the 1960s vintage machines.On DC, the only time you need HF is starting the arc.Constant HF will keep the tungsten cleaner, and you shouldn't experience arc wandering if the tungsten is clean and properly balled.Appreciation Gains You Recognition-
Reply:Ok. I'll give it a try this weekend Franz.A friend of mine recommended the timer for the HF start only also. - jack
Reply:I've run across alot of potential methods for shutting off the HF on a timed basis. What do you guys recommend ?
Reply:What is your source of HF?
Reply:a standalone HF box
Reply:Ok, so it has no provisions for timing.  Personally, I wouldn't worry about it.  DC tig with HF running is fine (anyone please feel  free to pitch in and disagree), just noisy.If you really don't want the HF running all the time, why not mount a momentary N/O switch on your torch to turn the power on while you start, then release the switch once you are going?I put a pushbutton on my torch to start the gas and HF timer.  Saves gas I figure.  I get everthing lined up, helmet down, then press the button and welding starts.  This was a feature of the Miller / Airco HF-15 box, either touch start or switch start.  I like the switch, so I can set the torch down and it shuts off when the timer runs out (1 set it for 10 seconds) and start it only when ready.  I never understood the touch start feature, as touching the live tungsten to the piece (there is no disconnect of power) seems like a poor way to start the process.  If I wanted to touch the tungsten to the piece, why bother with HF start?If I set the box to DC mode, gas and spark flow only when you press the switch, then the HF spark drops out once it senses you have struck an arc (due to the voltage drop of the constant current supply).  The gas continues to flow as you weld, then shuts off 10 seconds after the arc is broken.  It senses an arc by knowing the open circuit voltage is higher and will close or open a 24 v relay (biased thru a variable resistor and a diode bridge).
Reply:I've tried to win one of those HF-15-1WG's on eBay but the bidding keeps going to high.It doesn't sound like you're using constant HF with DC though - jack
Reply:hey, Maybe one of you guys can answer a question I can't seem to figure out the answer to:A Miller HF-251D-1 box has a 14 pin foot/hand control input on the front and a 5-pin input on the back. I've read the .pdf file but can't figure out if the foot control would only control the amperage if the welding source had the 5 pin connection to the Miller HF box  or if it would control the amperage from any power source ? - jack
Reply:Originally posted by morpheus I've tried to win one of those HF-15-1WG's on eBay but the bidding keeps going to high.It doesn't sound like you're using constant HF with DC though - jack
Reply:Originally posted by morpheus hey, Maybe one of you guys can answer a question I can't seem to figure out the answer to:A Miller HF-251D-1 box has a 14 pin foot/hand control input on the front and a 5-pin input on the back. I've read the .pdf file but can't figure out if the foot control would only control the amperage if the welding source had the 5 pin connection to the Miller HF box  or if it would control the amperage from any power source ? - jack
Reply:Originally posted by Tim The HF-251D-1 does not in itself control the welding current, it simply is in and out for the welding current thru the HF coupling transformer for whatever output the welding power source supplies.  The plugs are likely just to integrate the controls through the HF-251D-1.Originally posted by Tim I leave the HF switch on AC position, so that it keeps the HF running as long as their is an arc.If you ever see an HF-15-2-WG or 4-WG the 220 or 440 volt models don't be afraid to buy them. The can be easily converted to 110 volts simply because they have an extra transformer in them that steps it down to 110.  But the 110 model can only run on 110 as it lacks the extra transformer.
Reply:You just need lugs on the ends of cables to connect up to those posts.  My tig torch cable is a one piece, so the brass adapter that the hose screws into is on one of those lugs.I'm using flattened copper pipe with holes drilled in the ends as a bus strip to connect my rectifier unit to the input of the HF unit.I would imagine that in the DC position, you would get HF until it senses the welding arc, then the HF would drop out.  In the AC position, it probably buzzes out HF at all times that the unit is turned on.  I guess there is no sense in using a timer if there is no control over gas or water.
Reply:How did you wire the rectifier in?