Re: [CAD_CAM_EDM_DRO] Off topic, inverters / rectifiers

on 2001-07-15 06:05:41 UTC

> info.host@... wrote:
>
> > Hello,
> >
> > Since so many of you on here know a lot about electronics I was
> > wondering if you could explain something for me. I an thinking about welders
> > and how MIG sets, the cheaper ones, have a number of preset current
> > settings. But on DC TIG welders with an inverter they have an infinite
> > control of current through a thyristor. Are the cheaper MIG sets controled
> > by a rectifier that just cuts off the top of the ac waves and sticks it on
> > the bottom?
>
> No, most MIG's, especially the cheap ones, are AC. There is no rectifier.
>

I have never seen a Mig that wasn't DC and all used a rectifier to get there.

Garry

> > If that's what a rectifier does then how is the inverter
> > different? I have seen bridge rectifiers and understand they use the four
> > diodes in that 45 degree pattern to cut the waveform up. I'm sorry it's off
> > topic but you are the people I'd expect to know about this.
>

> An "inverter" welder has a big recitifer that converts input power to
> about 340 V DC, and then has a set of power transistors that chop the
> DC up into roughly square-wave AC at 25 KHz or so. This is then run through
> a roughly 20:1 step-down transformer and a full-wave rectifier.
> This then produces the DC output, which is electronically regulated for
> proper voltages and currents. For "square-wave" TIG, this is then
> followed by an electronic switch that flips the polarity of the electrodes
> at a low frequency (a few hundred Hz) for the required duty-cycle
> to keep the electrode clean.
>
> So, an inverter welder is quite different from a rectifier. The other
> difference
> is that the power transformer, operating at 25 KHz instead of 60 Hz, can
> be almost 400 times smaller and lighter!
>
> Jon
>
>
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