Saturday, December 19, 2009

Finished Dual Pulse Welder

The oscilloscope photo above shows a 12.6 Volt, 5Ms and 15.1Ms weld. Both pulses and the charge times is measured between the two purple lines and is 189Ms which is more than 5 welds per second at this setting.


  1. Why does the energy after each weld peak, taper off instead of cut off sharply back to zero? -Mike

  2. Mike, the bottom turn of the wave is when the Mosfet turned off and the solid up line zoomed in looks like a "S" that lay on its side and that's when the charging Mosfet turned on to start the charge. Go look at a Mosfet switching waveforms. I have no idea what you are talking about "going to zero"

  3. Hi Fritz,

    i designed an ultra efficient powerful power section and are waiting for your control pcb, when do you plan to release it please ?


  4. I see. The vertical going part of the trace is recharging, not further discharging. I thought there was still a slow discharge occurring with the slight voltage rise. Got it. -Mike

  5. Mike asked regarding the oscope photo:

    "Why does the energy after each weld peak, taper off instead of cut off sharply back to zero?"

    I see the turn on of the first pulse with a rise time at ~3ms. It then decays linearly to '0' over a period of ~34ms. The second pulse then fires with a rise time of ~8ms and again a linear decay to baseline of ~57ms.

    I think Mike's question, as mine is, is why the slow decay time rather than a sharp cutoff when the IRF's are snubbed? As I read elsewhere, the first pulse width should be fairly square and somewhere on the order of around 6-7ms to clean and then followed by a second reasonably square pulse in the order of 15ms to weld.

    In the photo, it would almost look like we are looking at a capacitive circuit element slowly discharging down to ground. But, there is no telltale 'glitch' a few ms into conduction indicating the IRF's are shutting off.

    Hope that makes sense and what am I missing?


  6. Fritz said...

    Ok, let me help you Meaux: At the bottom of the display you will see "CH1 5.00V" that means that every block vertically is 5V.
    On the left(middle) there is a red arrow with a "1" in it. This arrow is 0 volt.
    This is the actual capacitor voltage while doing a dual pulse weld. On the left going to right the voltage over the capacitor is 12 to 13V and then at the vertical "T" line the weld starts and the capacitor starts to discharge to about 6V. At this point the mosfets are turned off and the graph goes up and then down (ringing when the mosfets turn off) and then slowly over a 25Ms period going up again. This going up back to 12 or 13 volts are when the capacitor is charging. When it reach the set voltage the second pulse is fired. You are confusing this wave with the square wave on the Mosfet Gate.

  7. Thanks Fritz.

    I was erroneously thinking the oscope was looking at the output of the welder, not at the cap itself.

    Thanks for the explanation. Makes sense now.



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