high frequency and other questions

[lostcause]

ok, i've been using stick and wire feed welders for 20+ years, but i've never had any training or kept up on technology. i've been pretty close to buying a new machine, but it's a lot more of a complex decision than it was a few years ago, and i don't want to shoot myself in the foot (or wallet).

the latest thought that popped into my head was from pure luck. i was reading something and it mentioned high frequency plasma cutters not being suitable for cnc operations. i intend on building a cnc plasma table at some point this year, but i'm not at that point yet, so it didn't really seem to be an issue, or so i thought. i had also heard the high frequency terminology tossed around with tig welding, but also that's something i have never learned or tried, so it again didn't seem to be an issue.

now as i look at new welders, many of them are capable of multiple processes: mig/tig/stick, tig/stick/plasma. is it likely that some, many, or most new welders are going to have a technology in them that will interfere with the operation of a computer nearby? which technology specifically should be avoided for each type? for plasma i have seen hf, hf start only, pilot arc, for tig i've seen hf, and i don't remember what else. anyone got a good breakdown on what will and won't work with a computer nearby?

 

[Mark @ Everlast]

Lost,

HF is like a pet tiger. Tameable, but then go ask Sigfried and Roy.

All tigs have a high frequency if they weld AC. Transformer machines have a HF that runs continously to keep the welding arc energized as the AC reverses polarity so the arc won't extinguish. Most inverter welders, at least all that I am familiar with only use it at start to initiate the arc. The switching frequency of the MOSFETS or IGBT electronics is fast enough that no extinguishing of the arc happens. Many DC only machines offer a touch free HF start along with the lift start function as well.

Now, with that said, HF capable machines have "drain" for HF on the case of the units. Its usually labeled with a ground symbol..which is exactly what it is. It is not to be hooked back into the electrical system!!! Rather a separate wire should be run to an outdoor metal stake or ground rod that is in moist soil. This give the HF that collects in the case a place to drain away. It won't soak up all of it, but in many cases it provides adequate protection. I dare say you MIGHT find one out of every 10 machines hooked up though. The adjustment of the point gap where the HF is generated also affects the amount of HF that strays into the work environment.

HF units, especially small ones can be shielded with faraday type cages that absorb almost all the frequency. Lines can be further shielded. LARGE plasma cutters use HF only and it is successfully operated with CNC machines because of the shielding that is done.

Our smallest IGBT plasma unit (PowerPlasma 50) does not use HF to start the cutting arc, rather it has a special moving tip that creates necessary spark to ionize the air as it is blown backward away from the interior wall of the nozzle. Our other units have HF start, but it is only for a split second. We have several customers running their HF plasma cutters with a CNC table. But they typically have the unit sitting at a distance, the "ground bolt" hooked up or they use a contact start to initiate the arc with the HF disabled. A few of these customers infrequently experience a slight "glitch", but they aren't concerned as long as it is only momentary at start.

Personally, my computer sits next to my Tig and plasma welders/ only separated by my office wall. Never had one problem...yet.

 

[Mark @ Everlast]

Here is a short video of an Everlast Customer from
Costa Rica using a HF machine on a CNC hooked to a computer, just to prove its possible.

YouTube - Corte Plasma Infratel 01.wmv

 

[AlanB]

I will add a side note that I believe is relevant.

When I fire off my HF on my TIG in my new barn, you can hear the GFCI's trembling. Took me a bit to figure out what it is, but I think that it points to it can erratically effect the electric, and if it is doing that, I would believe it could occasionally cause a computer to glitch.

Sounds like Mark has the details on specific machines so I would tap that resource.

May be unrelated but will add in that I know my dad spent a lot of time working with the phone company on Grounding issues and they ended up doing a lot of separating and joining of various "grounds" of equipment to eliminate and prevent issues between the phone company equipment and the power sources and in their case (Florida) Lightning strike issues.

Good luck with your setup that sounds neat.

Just curious where are you in Maine, my mom and dad came from Waterville, Fairfield and many of the family still live there.

 

[yomax4]

Most Plasma units have gone away from HF for all of the reasons mentioned above. AC Tig units have HF for AC Tig. HF will raise cain with Computers, CNC and sometimes phones. The Plasma units I sell (20 - 500 amps ) are either non HF or have Shielded Leads to prevent HF contamination of your electricasl system. Good luck with your Plasma Table.. You will enjoy it..:thumbsup:

 

[wdchyd]

Lostcause,

Our shop has several Miller Tig HF welders and CNC Lathe, CNC Mill, and CNC Plasma Table, several computers in offices, all within a 100' radius....no problems with HF Welding or Plasma table or computer interference.....

Years ago we were co-renting with another company that had a Lincoln Idealarc AC/DC/HF Tig and it did funky things to anything with a circuit board in it, (Computers, alarm system, radios, digital watch).....I wonder if it was the "Grounding" that was the problem but I think it was the old style welder....when somebody was welding alum with AC/HF you could see small components on PC Boards frying right before your eyes......weird....:confused2:

Never had that happen since 1986 when we moved out and bought a new Miller AC/DC/HF Tig.....Maybe newer welders are no problem?:confused2:

 

[Mark @ Everlast]

Newer, inverter welders or plasma cutters (that have HF start) only run to initiate the arc, then cut out. The older units ran a continuous overlay of HF so the arc would not extinguish when the half cycle reversed polarity.

Point gap settings, cable length, condition, and arrangement all factor into HF emmisions.

Also the ground provision that is on every HF unit that I can think of can effectively deal with most issues....but it is as I said earlier, seldom used until there is a problem.