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Posted by on May 5, 2008, 12:13 am
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On Sun, 4 May 2008 21:04:24 -0700, "Jon Danniken"
>"Mechanical Magic" wrote:
>>
>> Jon,
>> For ultra thin materials, DC/HF may work, reverse polarity IIRC.
>>
>> But for sheet metal on up, nope.
>>
>> There is a VERY significant swirl on the puddle caused by the AC, that
>> moves crap to the edge. On many settings, it is almost invisible,
>> depending on the machine.
>
>Thanks, Dave, I appreciate that. Didn't know that about the puddle, either,
>so I'll watch for that.
>
>Alrighty then, so a squarewave would be the easiest waveform to make, would
>that be a sufficient enough selection of waveforms, and what frequency range
>would be most useful?
>
>Jon
>
Square wave AC with variable duty cycle is best. More negative cleans
better, more positive penetrates better, from what I remember. Almost
needs to be an inverter unit to do this.
** Posted from http://www.teranews.com **
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Posted by Jon Danniken on May 5, 2008, 12:31 am
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clare at snyder dot ontario dot canada> wrote:
> On Sun, 4 May 2008 21:04:24 -0700, "Jon Danniken" wrote
>
>>Alrighty then, so a squarewave would be the easiest waveform to make,
>>would
>>that be a sufficient enough selection of waveforms, and what frequency
>>range
>>would be most useful?
>>
>>Jon
>>
> Square wave AC with variable duty cycle is best. More negative cleans
> better, more positive penetrates better, from what I remember.
Thanks, Clare, I appreciate it. A duty cycle control shouldn't be too hard
to put in there, if I'm feeding them anyway.
Brings up another issue though, I'm guessing the waveform will need to swing
from positive to negative, and not just dance around above the work
potential. Hmmm, I'll have to think about that one.
Jon
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Posted by Randal O'Brian on May 5, 2008, 1:19 pm
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> clare at snyder dot ontario dot canada> wrote:
>> On Sun, 4 May 2008 21:04:24 -0700, "Jon Danniken" wrote
>>
>>>Alrighty then, so a squarewave would be the easiest waveform to make,
>>>would
>>>that be a sufficient enough selection of waveforms, and what frequency
>>>range
>>>would be most useful?
>>>
>>>Jon
>>>
>> Square wave AC with variable duty cycle is best. More negative cleans
>> better, more positive penetrates better, from what I remember.
>
> Thanks, Clare, I appreciate it. A duty cycle control shouldn't be too
> hard to put in there, if I'm feeding them anyway.
>
> Brings up another issue though, I'm guessing the waveform will need to
> swing from positive to negative, and not just dance around above the work
> potential. Hmmm, I'll have to think about that one.
>
> Jon
The commercial inverter welders I 've seen use a transistor H bridge between
the DC output and the work piece to get the AC output. The technology is
the same as a VFD but single-phase only. A microprocessor would seem to
make it fairly easy to vary both freq. and pulse width as needed.
Randal
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Posted by Jon Danniken on May 5, 2008, 5:53 pm
Please log in for more thread options "Randal O'Brian" wrote:
> "Jon Danniken" wrote:
>>
>> Thanks, Clare, I appreciate it. A duty cycle control shouldn't be too
>> hard to put in there, if I'm feeding them anyway.
>>
>> Brings up another issue though, I'm guessing the waveform will need to
>> swing from positive to negative, and not just dance around above the work
>> potential. Hmmm, I'll have to think about that one.
>>
>> Jon
> The commercial inverter welders I 've seen use a transistor H bridge
> between the DC output and the work piece to get the AC output. The
> technology is the same as a VFD but single-phase only. A microprocessor
> would seem to make it fairly easy to vary both freq. and pulse width as
> needed.
Thanks, Randall, I appreciate that. When I was looking at inverters the
other night (from Clare's suggestion), I was contemplating a two-mosfet
jobby, such as this:
http://engr.nmsu.edu/~etti/spring97/electronics/cmos/IMG00006.GIF
Since I haven't built an inverter of any type before, what would be the
advantage of going with an H bridge?
Thanks,
Jon
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Posted by David Billington on May 5, 2008, 6:27 pm
Please log in for more thread options Jon Danniken wrote:
> "Randal O'Brian" wrote:
>
>> "Jon Danniken" wrote:
>>
>>> Thanks, Clare, I appreciate it. A duty cycle control shouldn't be too
>>> hard to put in there, if I'm feeding them anyway.
>>>
>>> Brings up another issue though, I'm guessing the waveform will need to
>>> swing from positive to negative, and not just dance around above the work
>>> potential. Hmmm, I'll have to think about that one.
>>>
>>> Jon
>>>
>> The commercial inverter welders I 've seen use a transistor H bridge
>> between the DC output and the work piece to get the AC output. The
>> technology is the same as a VFD but single-phase only. A microprocessor
>> would seem to make it fairly easy to vary both freq. and pulse width as
>> needed.
>>
>
> Thanks, Randall, I appreciate that. When I was looking at inverters the
> other night (from Clare's suggestion), I was contemplating a two-mosfet
> jobby, such as this:
>
> http://engr.nmsu.edu/~etti/spring97/electronics/cmos/IMG00006.GIF
>
> Since I haven't built an inverter of any type before, what would be the
> advantage of going with an H bridge?
>
> Thanks,
>
> Jon
>
>
>
Not sure if it will help but I posted the schematic of my Hitachi
inverter TIG to the dropbox a couple of years ago
http://www.metalworking.com/dropbox/HitachiInvTIG.gif and
http://www.metalworking.com/dropbox/HitachiInvTIG.txt .
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