[rchavez101]

Hello everyone I am new to this sight although I have been reading for quite some time. I recently purchased a Everlast plasma cutter that is High Frequency. I read that High Frequency cutters are hard to make compatible with a CNC table due to possible damage to the PC. Can anyone give me more information on this. Is it true or something that is not all that big of a deal. Please let me know what I can do if I was to take this route or is it not even worth trying to do. Thanks for the help.

[jimcolt]

There are hundreds of thousands of Industrial cnc plasma machines in the world that all use high frequency start plasma systems, as virtually all plasma systems above 120 Amps are high frequency start. These industrial machines use cnc controllers (many are PC based) that are industrially hardened to withstand the high frequency from plasma and other sources as well as all kinds of electrical line fluctuations.

Almost all low cost, entry level, and "do it yourself" cnc machines use a standard, off the shelf PC (personal computer) as the machine controller. These computers were designed to sit in a clean office, with stable power and no electrical noise.

So, it would definitely be a gamble to install any high frequency based plasma on a cnc machine that uses a PC as the controller.There is better than a 90% chance that the high frequency/high voltage starting energy that is used to ionize the air in the plasma torch will couple to one or more of your motor, drive, or control cables and will either cause you to reboot the computer often, or cause damage to the computer or drives.

There have been a few limited cases where extra care was taken on the design and installation of a PC based machine where a HF start plasma worked acceptably, but those cases are rare.

It is best to use a plasma with non high frequency start, also known as "blowback start" (a Hypertherm invention) for this type of machine. Most modern design air plasma systems use this technology today.

Jim Colt

[rchavez101]

Thanks for the repsonse Jimcolt.

[flyinwilly]

Jim is correct that HF start machines cause problems to your PC but there are ways around it. I just completed my table and I use a CUT40D from Gianttech which is the same type of machine that Everlast sells. I've had to use shielded cable, a good earth ground for the cutter and table (8' rod and les than 10' of ground cable), chassis grounds on the PC, and move the PC about 20' away from the table and cutter. So after all of this, the table and pc work great , no problems at all. There is one exception and that is my pendant. If I am 10-12' away from the table, it works great. If I get closer than that, it stops working until I removed the USB cable from the PC and then reattach it. I have a 20' cord on the pendant so it acts like a very nice antenna. Also, I ran the limit and home wiring in EMT conduit which also provides some protection.

You can get around the RF interference but it takes some diligence and attention to detail. Miss any one thing and you're screwed.

So after all of my work to get it working with my HF start machine, I am now looking at the PM45. It's beyond my budget right now but maybe next year.

Good luck with your build.

Willy

[jimcolt]

I can pretty much guarantee you can make almost any machine work with a high frequency plasma. Here are a few things you would need to consider doing:

1. All motor and drive related leads need full shilding and twisted pair connectors. The shields should all be connected back to a star ground point at the driven ground rod.
2. Torch leads need to be shielded (outer cover with braided metal shield) that should be grounded only at the high frequency generator end.....back to the star ground point. The rest of the leads must be isolated from any machine metalic parts....preferably inside a plastic non conductive powertrack.
3. Chassis of plasma power supply (with high frequency generator should be mounted away (as far as practically possible) from the PC, and should be grounded directly to the star ground point.
4. PC should be as far away from the plasma power supply, should get its AC sourced through an uninteruptible power supply with surge protection. PC chassis should be grounded directly to the star ground point.
5. If a remote wired pendant is used, it should have a shielded cable, also grounded to the star ground point.
6. The gantry of the cutting machine should be grounded to the star ground point.
7. The torch carriage and z axis slide should be grounded to the star ground.
8. The computer monitor should be connected to the computer with a shielded cable. The mousealso needs to be shielded.
9. There should be some sort of optical isolation between the plasm I/O and the control box for the I/O.

Note, each ground wire to the star ground needs to be separate.....no "daisy chaining" as this can create ground loops.

The work ground from the plasma should be bolted directly to the star ground (no welding clamp)

The cutting slat bed should be connected directly to the star ground as well.

The star ground point should be right on the ground rod, or within about 6 feet, any extra cable length should be shortened, no cables on the machine should have any coiled extra length.

This is the minimum that should be done on any cnc installation with a high frequency plasma.....this often, but not always, eliminates electrical noise interference problems!

I have worked with these issues for many years in the field. There were a few installations where we never completely solved the noise issues.

On the latest technology industrial machines the plasma and motion connections to the cnc control consist of 2 small fiber optics cables as well as a single ethernet connection.....there are no longer any noise issues with this setup!

Jim Colt Hypertherm

[Mongkol]

Thanks Jim,
The information is very useful.

[pinjas]

All this has put my mind at ease.

I've been considering purchasing a plasma cutter with blow back design and they seem rather costly.

I've been TIG welding a transformer style welder for some time and I can always hear the high frequency on the radio when I start to weld.

I've got a 8 foot ground rod right behind my garage so I think I should be pretty well set assuming I follow all these guidelines, at least in the sense of not having HF destroy or prohibit.

[pinjas]

I am hoping for some opinion or perspective on this idea. PowerPlasma 50 - Multi Purpose Units, Diesel Generators, Welders, Arc Tig Mig Welding Equipment, Plasma Cutters I am comparing the benefits of using this plasma cutter versus something else that uses a high frequency pilot arc and grounding the heck out of everything I can. It almost seems like I'd end up spending a lot of the difference on wire, shielding, cables, and lets not forget the time it would take to add all that in.
It looks like the cheapest I can find a blowback plasma cutter is around 700 dollars (price I was told over the phone). Would it be wise to go with a blowback plasma for 700 instead of a pilot arc plasma cutter for around 550?
Plasma Cutter Plasmacutters plasma cutting equipment plasma torch,plasma arc You can see on this chart where it notes the non-hf start.

[CPierce18]

When I got my 52”x96” cnc plasma table running, I had a 25 year old Hypertherm Max20 I was cutting with. After 2 or so months, the transformer went in it and I ended up buying the PowerPlasma 50. Great machine I think.

I have it sitting on a shelf, right next to my pc and I have no interference issues. I also spent about $100 on shielded wire for my motors just in case, but all my limit & home switch wiring is just plain doorbell wire. So far in the 6 months I’ve had it running, it I haven’t had any interference problems with the PowerPlasma 50. Table & gantry are grounded thru an 8’ grounding rod 6-8’ away.

I had the same thoughts as you when I was in the market for a new plasma cutter. Save some cash and chance it, or spend a few extra bucks on something without HF. Glad I picked the non-HF. If I were you, go look in your in your seats and see if you can find some extra change to get the non-HF PowerPlasma50.

Thickest I’ve needed to cut so far was ¼”. Cut no problem. Haven’t tried the thicker stuff yet. I need to upgrade to a 40-50amp breaker.