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Econotig: Partial Flame Control (50%-100% only)

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  • #31
    https://patents.google.com/patent/US5187428A/en

    Thanks for the mention to the patent number. I googled it. Interesting read.

    "As will be explained below, air gap 208, in conjunction with the physical dimensions of magnetic core 102, determines the gain of the amplifier effect, thereby determining the minimum and maximum output current of transformer 100."

    "Any ideas why the low end power would be so high?"

    Your question was running around in my head and when I read this, my head already spinning from all the mad science explanation to things, I asked my self if that statement was a clue to the answer?





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    • #32
      Yeah, I read thru the patent too, a lot more technical details from a lot I've come across which was really nice in this case.

      If you were to tweak the air gap distance (not likely on this behemoth), or insert a material that has a different permeability, I would imagine you could possibly change the reluctance on the shunt leg and so change the gain of the main transformer? I'm assuming that this was all tuned at the factory and nothing has changed since as it is quite a solid structure, so what else might have changed? Would something cause a change in impedance of the primary, secondary, stabilizing (Z1), or blocking (Z2) coils that would have impact on current output? In the service manual, it does say that Z1 "smooths current from main rectifier in DC mode and limits output in low AC setting"...

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      • #33
        I've read it three times today. I'm still wrapping my mind around it.
        To make more sense of it I'd have to print pages, blow up diagrams to enhance visuals, get out the high lighters and a note pad with pencil then spend some serious quiet time studying.

        I agree that patent held a wealth of information and does offer a much better explanation then I've ever received on the subject of how they make welder magic happen.

        I've seen and wondered about welding issues that appeared electrical function related but without knowledge of such things could only speculate on the reason behind them. Blame the board and wash hands of it is rapidly becoming there's a reason and I can figure it out maybe?

        Reading that patent took some of the mystery away and replaced it with a greater knowledge, understanding and appreciation, to what goes on inside the box, things on the board, and appearing on the schematic with why they do.

        While not able to offer up much past moral support, encouragement, I apologize for any distraction from the path to that solution. Following along and paying attention just the same.









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        • #34
          Reading page 10, lines 16-20, it seems like the shunt coil only conducts in one direction (unbalanced for gtaw), which is why Q13 is a thyristor (one direction conduction) instead of a triac (two direction like in figure 4). Q13 is used to short across the shunt coil. I would guess R52-R53-C35 is the Snubber for Q13, with D22 and D20 the voltage clamp. When the shunt voltage AC cycle goes negative, D21 is forward biased, which activates Octocoupler OC1, that energizes Q11, which energizes Q10, that discharges C22 through R46. The voltage across C22 drops to the voltage across R46, which is based on the amperage control settings (long resistor divider network). When the shunt voltage again goes positive, Q10 is turned off, which allows C22 to charge through the amperage control settings resistors (R57, panel potentiometer, pedal potentiometer, R41), until it's voltage is high enough to forward bias Q12 and optocoupler OC2. OC2 forward biased triggers Q13, which shorts the shunt coil. The amperage control settings and the R57 potentiometer control how long it takes for C22 to charge high enough to trigger OC2 and Q13.

          RC9-4 voltage should vary over panel and pedal settings as the duty cycle of the optocoupler OC1 LED varies with shunt driver timing. RC9-3 should be a constant voltage at about 7.5V.

          What did you measure the shunt voltage when the coil was disconnected? Does it get to 430VAC?
          Last edited by jjohn76; 11-18-2019, 09:04 PM.

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          • #35
            Edit, looking at the tech manual, page 23, the shunt winding seems reverse biased, so it switches on the negative AC cycle instead of the positive AC cycle like mentioned above. Either way, I think the timing comes down to the time constant set by capacitor C22 and the variable resistance from R57-panel amperage potentiometer-pedal amperage potentiometer-R41. If the voltage measured at RC9-4 doesn't vary over the entire range set by the panel and pedal, then either that potentiometer is off, or one of the components in that chain is out of spec.

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            • #36
              Good catch on the unbalanced output waveform statement in the patent, it caught my eye as well, but then I wrongly dismissed it thinking it wouldn't apply since I was dealing with DC. Obviously it does apply since it is the only power output adjustment for both AC and DC on this machine.

              Also, I follow your logic and I believe your assessment of the shunt control circuit is correct. To answer your question about the shunt coil voltage, the highest I measured with the DMM was 370VAC with the leads disconnected.

              After fine tuning R57 a bit more tonight, I have much more useable pedal travel. It isn't 100% utilized, but it is much more than it was, I'd say close to 80%. By adjusting R57, you can move that 80% "band" earlier or later in the pedal travel, so I set it a bit biased towards the high end as it made it a little more friendly for thin materials. So, now 0-15% of pedal travel is minimum output, 15-95% is variable output, and 95-100% is maximum output. Good enough for me... Think we can close the books on that!

              I still feel like the minimum amperage is a bit higher than what it should be, but I'll have to measure it someday to know for sure. I tried some 20ga (0.036") steel test parts tonight and was able to work with them, it was not pleasant, but it did work out ok as long as I went quickly enough. I know 20ga is listed as "difficult" for this machine, so maybe I've just maxed out the capabilities on the low end, but using a different Econotig years ago (the machine I learned on) it did not seem to be as hard as this one...

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              • #37
                Glad it worked out! It almost sounds like part of the shunt windings are shorted together, which limits the effective windings by about 17% (370VAC instead of 430VAC). That could be the reason why you're not seeing the entire amperage adjustment. Either that or the gap has somehow adjusted (alignment or spacing), but this is far outside my understanding...
                Last edited by jjohn76; 11-20-2019, 07:27 AM.

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