Re: [CAD_CAM_EDM_DRO] Off topic, inverters / rectifiers

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.

> 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