"BobH" wrote in message
...
Grant Erwin wrote:
Back when I was working as an electronics engineer in San Jose,
California (heart of Silicon Valley) I came up with a design for this. It
was a chip which produced variable PWM waveforms. I planned to use power
Darlington transistors to go between the CMOS logic chip and the gates of
beefy SCRs. I got as far as simulating the whole design in a mixed signal
simulator.

Then I found out what the failure mode of SCRs is. About the same as hand
grenades. Did I want this in my house? No.

I scrapped the design, never looked back.

Now the power devices will probably be Insulated Gate Bipolar Transistors,
but the failure mode is the same. 240VAC Rectifies to over 300VDC and a
multi-horsepower drive will need many amps of DC supply capability. I have
built some smaller drives and from that my advice is:
A) keep a CO2 fire bottle handy.
B) always wear safety glasses.
C) never leave the room with a prototype energized.
D) buy lots of spare transistors and drivers.
E) don't try to build with point to point wiring, parasitics will kill it.
F) keep a CO2 fire bottle handy.


In the few commercial VFD's I have played with programmability was never
in short supply. Figuring out all the programability they gave you was
tough enough.

That said, doing it is still one of the best ways to learn about a new
area of technology. I have been kicking around the idea of designing and
building an inverter welding machine for a while. It would not replace my
commercial machine for a long time, but it would be a heck of a project. I
wonder if argon puts out fires as well as CO2? (grin)

Bob


Saftey is a main concern, so i will be expermenting at reduced power levels
and gradualy step up the power. I did download some schematics from
esab for thier inverter welders. Learned a lot from studing thier
schematics.

Heres a link to esabs document library:

http://www.esabna.com/html/downloads...rc%20Equipment

Best Regards
Tom.