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Learned about an HF welder today

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amdx

Jan 1, 1970
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I learned something interesting today, that is probably common knowledge to
most welders. I have a friend that welds, mostly on marine equipment. He
came to me wanting a switch installed on his tig torch to help him tig some
anodized aluminum. He has an HF251-D1 high frequncy unit and a Trailblazer
302.
I found a schematic for the High frequency unit, but was a bit perplexed as
I couldn't locate any semi conductors that I thought would be used to
generate a high frequency. Well, later in this process I found
out that the thing operates like a tesla coil with a spark gap to create the
high frequency.

Now, in order to figure this thing out I wanted to see it operate, So the
welder went on to show me and
it would not work. He could not get any high frequency arc. He said it
worked fine last night, Ok, "so what did you change"? He had added about 70
feet of cable, OK, so let's take that cable out. So now the HF works fine,
It turns out the cable was wound up making an inductor that would not allow
the HF to operate properly. Once the cable was straighted out it worked
fine.
So.. the HF unit uses a spark gap to create HF and you can't coil the wire
and use an HF unit.
I thought it was interesting.
Mikek
 
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Shaun

Jan 1, 1970
0
Robert Baer said:
And the FCC is going nuts wit all of the gruesome RFI complaints.
Spark gap transmitters are almost 100 percent illegal now.
"Almost"? if that was the only to transmit an SOS in a life-and death
situation, then it is "just" barely acceptable (but do not do that again).

Bullshit!

Hobbyists operate tesla coils and it is legal as long as you don't get too
many neighbours complaining. They also operate in museums and at shows.
Also some medical electrosurgery units that are still in use today use a
spark gap.
 
F

F Murtz

Jan 1, 1970
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Pintlar said:
Years ago when I was working on the MinuterMan 2 missile sites we had a
dozen or more big diesel 400+ amp welders up on the ridge of the 'Launch
Control Center' hole.
There was mucho feet of very heavy cable (over 100') coming down to the
'eggshells' that were the inside forms for the launch control capsules.
The excess cable was coiled up at the welders in about 4' diameter circles.
When a welder struck an arc (1/8" 7018) those coils would jump from the
magnetic force generated.
********************************


I once saw a dc welder(bullet shaped vertical thing with motor and
generator vertically) the leads were wrapped round the whole thing and
someone started welding, the whole thing blew up and made a hole in the
roof of the shed,
 
W

Warren

Jan 1, 1970
0
Shaun expounded in
Hobbyists operate tesla coils and it is legal as long as
you don't get too many neighbours complaining. They also
operate in museums and at shows. Also some medical
electrosurgery units that are still in use today use a
spark gap.

I still have my Model-T 6V Ford ignition coil, that I bought
on ebay (I was hoping then to interest my son in electronics).
I haven't operated it in a little while ;-)

When I was young, I had made an HF coil using a paper towel
cardboard roll form, and an outer coil of a dozen turns or so.
There was a HV cap involved to cause it to resonate.

I'm not sure what the output freq was, but it was fun drawing
sparks to your hands. Being HF, it would only tickle slightly.

I'd love to know what the lowest minimum frequency for human
tolerance of HF HV arcs is.

I once knew a guy that claimed that he'd test TV HV power
supplies by arcing the transformer +HV lead to his fingers
(approx 15.7 kHz). I've never had the guts to try it.

Warren
 
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