Welding -- what to do about HUGE 2" arcs

When I say that it failed, it did not fail as in "died", it shut itself down with a FAULT LED indicator. Which is a good thing. It has a built in detector of phase imbalance, which could happen if power drawn exceeds the capacity of my phase converter.

i

A couple HV diodes, resistors and capacitors to make a low pass filter (you only want the welding buzz (or DC), not the hash the arc makes) and envelope detector. Toss on a voltage divider (to put it in terms a comp can handle), add a comparator with pot to vary trigger voltage and send the now detected signal to your shutdown thingie.

Oh, and some clamping after a resistor, so you don't blow caps or other stuff. Voltage spikes are fun.

I'm guessing this doesn't have to be very fast at all, as long as 100ms could be considered acceptable? Should be pretty easy then.

But really, you're COMPLAINING about 2" arcs? I've got to see this.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

I think that I understand about LP filter, but what do you mean by envelope detector.

Absolutely. I could as well throw a zener in there.

Sure. Maybe 50 ms, but there is no need to be fester than that.

I played some more with welding tonight. If I withdraw the electrode quickly, there is no problem at all. It is when I pull it away slowly, then I see the unbelievable 2" arcs.

It is unreal, I have never seen anything like that. Not that I can claim great life experience.

i

How about a foot pedal? Like standard tig. Btw..if I set my control on Local rather than remote..when tigging I can get the HV to run at least 1.5-2" when I draw away from the work. I had to turn down my HV a fair amount when doing a weldment that I coulnt use the foot pedal on (no torch mounted controller)

Gunner

"If thy pride is sorely vexed when others disparage your offering, be as lamb's wool is to cold rain and the Gore-tex of Odin's raiment is to gullshit in the gale, for thy angst shall vex them not at all. Yea, they shall scorn thee all the more. Rejoice in sharing what you have to share without expectation of adoration, knowing that sharing your treasure does not diminish your treasure but enriches it."

- Onni 1:33

I think that you have a good point, that with a remote control it will not be as much of an issue (not that it is a show stopper now). I will definitely do remote control soon.

i

Peak detector- think AM demodulation (hence envelope detector). Just a diode into a capacitor, with another resistor and capacitor to add the RC delay, and an RC in front of the diode to slow transients.

Hmm, you have HF start right? A notch filter might not hurt, even with the slow front end of this circuit.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Oh, I see. Thanks. I had some very educated opinions that what I have (big arcs) is not a bad thing as it could let me weld over dirty spots and such -- and that all that I should do about it is pull electrode away quickly when I am done with a bead.

Yes, I have HF start indeed.

I have not yet wired it up.

i

2" arc at how many amps? When I borrow my friends tig, we usually use HF start and it arcs at about 3 CM out at a maybe 100 mA, then as you get close to the work the arc thickens into the normal welding arc. Maybe you have it close to being right?

Steve Roberts

Not sure how many amps, but if I recall correctly (I did look at dials, but in haste and mostly at the voltage dial), it was at about

100 amps.

Maybe, indeed, it is close to being right.

i

It is a DC welder ? Yes, DC makes arcs this long.

Rene

--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

Yes, it is a DC welder.

i

take a picture of it :)

Colin =^.^=

Try something small and simple like a Crouzet Millennium II - the programming is done with logic blocks on screen, and downloaded to the device. They have analog inputs (0..10V) and PWM outputs too.

Steve

But a 2" arc is not at all normal for a DC stick welder.

You could try implementing DROOP so that the current drops to a low value at a reasonable voltage.

DROOP lets you taper off the heat into the weld puddle by pulling the rod away slowly, to prevent craters and crater cracking, without resorting to manual current control via footpedal or torch potentiometer as in TIG.

The right amount of DROOP is what you want, not constant current or constant power. DROOP. Adjustable DROOP.

With enough DROOP, the arc will be substantially cooler at 1/4" and go out at around 1/2" to 3/4" at the most, way longer than the 1/8" arc you should be welding with.

The straight poop - DROOP DROOP DROOP.

If that dosen't work, try DROOP.

Did I mention DROOP yet?

If you don't like DROOP, you can call it DIG, BOOST, or SUPER DELUXE EXTRA SPECIAL DC STICK WELDER AUTOMAGIC OPTIMAL CURRENT PROFILING. Just make sure current increases when voltage drops and decreases when voltage rises by enough for a controllable arc.

Thanks Glen. I appreciate it. What do you think about implementing a feedback based not on current, but on power (current x voltage), it should not be too difficult with a couple of opamps and analog multiplier like AD633.

i

Reduce the max voltage as soon as a current flows. That would be a limit on the max pulsewidth then.

Rene

I think that would be a nice experiment, but that there is probably a reason most welding machines use linear current vs voltage control, or piecewise linear current vs voltage. This is actually easier to do, only a few op-amps required, but it will require a bit of care so that the droop control does not significantly change the welding current at the normal arc length voltage, which would probably be in the 25 to 30 volt range. You could check this with a data logger or a second person to watch the meter while you weld.

So you want to convert welder current and voltage signals to a range within the signal capabilities of your op-amps, and do a bit of simple analog math as described in for example

to compute the current set point for your controller. I'm sure a search will turn up a ton of info on analog computers, but George Philbricks "Computing Amplifiers" is a real classic.

You can implement all sorts of I/V curve modifications like this including power control, but I still recommend starting with droop.

Sorry about the DROOP rant :-).

That is an excellent idea. In this case he is using a standard controller which wants a DC voltage limit signal, which can be reduced when current is above some threshold, in the same analog computer which implements droop and whatever other effects he wants to try.

Glen, do you think that a microcontroller based control solution would let me kill many birds with one stone? to do droop, tig timing, plasma cutting timing, etc etc?

If so, any suggestions for something simple? I could spend some bucks (not too much) if it saves me time and wiring efforts.

i