Plasma Cutter Common Loss of Arc issues

[suttoncnc]

Can you more experienced operators list from most probable to least probable the causes of loss of arc during operation?

I am using a Longevity 42i plasma cutter cutting 16 gauge at 100 ipm and 26 amps. Voltage is 110 with new consumables. Twice during a large job I lost the arc and the machine stopped. Not a huge deal, just have to cycle the "Run-Set" switch on the plasma cutter and the arc starts back and Mach continues the job. I really am at a loss as to what the reasonable causes can be.

Thanks in advance. I would be almost totally lost without this great site.

Scott Sutton

[icmplasma85]

1. Shoulda bought a hypertherm.
2. Distance from plate - if youre running too high you could lose arc.
3. Bad ground - if you dont have a good ground to the plate you will lose arc. Try putting ground clamp directly on plate you are cutting.
4. Could be a contaminant on the plate? Oil, dirt, etc?

Also, what cnc machine do you have?

[Shane Warnick]

1. Shoulda bought a hypertherm.
2. Distance from plate - if youre running too high you could lose arc.
3. Bad ground - if you dont have a good ground to the plate you will lose arc. Try putting ground clamp directly on plate you are cutting.
4. Could be a contaminant on the plate? Oil, dirt, etc?

Also, what cnc machine do you have?

All of these. Number 4 will make #2 happen. Rust, contaminants, or cutting right on the edge of the plate will cause the impedance to change and if your height control is using arc voltage feedback it can cause it to think it is too low or too high and climb or dive the torch and make the arc go away.

Could also happen if you get a drop in air pressure, if it drops below the min level even for an instant the torch may extinguish the arc but by the time you get around to looking at the panel to see if there is an error, the pressure is back up. I have chased that demon once or twice.
Shane

[jimcolt]

If you are cutting thin material with a lot of details....and your machine acceleration is sluggish...then you can get arc blowout. This is caused by the material burning away very quickly and the machine is moving too slow (slowdown in accute corners, etc). Use a smaller nozzle (I don't think there is one for your plasma...Hypertherm has Finecut nozzle) and lower power as well as increasing your machines acceleration rate can solve this.

-momentary low air pressure
-momentary loss of work ground

Jim Colt Hypertherm

[suttoncnc]

After reading all the responses (much appreciated) I still could not determine a root cause of the issue and the problem continued. Yesterday I needed to cut a lot of parts for a customer and the torch cutoff was really bad. I hooked my oscilloscope up to the torch start output from the CANDCNC controller and the problem became apparent. The signal for torch start was dropping out for about 15 milliseconds during cutting and the torch would extinguish when that happened. I inserted a 47uf capacitor across the output wires and the problem went away but now the torch took about 1 second to shut off after the controller signal normally went away because the capacitor was recharging back to the 15 volt state. I kept dropping the capacitor value all the way down to 2uf and the problem went away completely. No more torch issues and it cuts off within 20 milliseconds of the signal turning off when it is supposed to.

I do not think that this is a controller problem, but rather a problem with noise being induced within my wiring system. Also i think that my Plasma Cutter may be overly sensitive to this phenomenon. My plasma cutter is likely the very source of the noise itself. Anyhow, I am posting this just in case someone else has been struggling with this issue. Without a scope it would have been very difficult to figure out. If anyone has this issue and needs more detail on the fix you can PM me or I can post detailed pics of the capacitor installation.

Scott

[m79b01]

I seem to have similar issues and would greatly appreciate pics of your fix. I am going to try a UPS first, but if that doesn't fix my issue this looks like it might. Thanks for the info.

[suttoncnc]

I would hold off on the UPS unless its money already spent, bets are this is the issue for you as well. One correction, I put a 1uf cap in and not a 2uf cap. I changed several out until I found the correct value. Here is a link to the ones that you need, I happened to have had an assortment in the shop that I could pull from.

http://www.ebay.com/itm/10-x-1uF-35V-Ra ... 3365053a48

You only need 1 of them but if your system still has torch off issues you can add another on top of the first to double the capacity. It will not hurt the system to put too high of a value in but it will cause torch off delays when it gets too high. Tantalum capacitors are polarity specific so be sure to use a meter so you can determine the positive and negative wires on the 2 torch switch wires. You will need to have the plasma cutter powered up but NOT firing the torch to find the negative and positive wires. When you first connect the capacitor the torch may fire for just a second, this is normal as it indicated the capacitor is charging up the the off torch voltage state. Other capacitors may work but tantalums are great for bypassing in electronic circuits because they are relatively fast. Just simply loosen the 2 wires and run the cap leads under the wires and re-tighten.

CAP INSTALLATION.JPG

[m79b01]

Thank you for the help and info. I will repost after setup and some testing.

[Rftek]

I am trying to solve this same issue with Hypertherm45XP and Langmuir firecontrol.

Did you happen to try a ferrite choke before this?

I thought my loss of arc was wet air, but with new dryer
And (relatively) fresh consumables same problem.

I’ll try your 1uf tantalum and report back

[acourtjester]

Don't forget air pressure, if you drop below a level of about 80 PSI at the plasma unit it will lose the arc. Put a gauge at the rear of the hypertherm to see what happens when cutting.

[adbuch]

Tom brings up a good point. Sufficient air pressure is critical to the operation of your cutter. Also check for loose connections on your wires that monitor your arc voltage.
David

[weldguy]

I am trying to solve this same issue with Hypertherm45XP and Langmuir firecontrol.

Did you happen to try a ferrite choke before this?

I thought my loss of arc was wet air, but with new dryer
And (relatively) fresh consumables same problem.

I’ll try your 1uf tantalum and report back

You should not need to add a capacitor, I suspect something else is the problem. Tom's advice is great about air pressure.

Sounds like your aware of wet air being an issue, adding a dryer is great but not an instant fix since your torch lead, plasma cutter, and air line after the dryer could still be contaminated and have moisture in low lying areas of the torch lead, air lines etc. A few hours of dry air operation should clear this out.

Do you see any errors codes on the 45XP when the arc goes out?

[Rftek]

I solved my arc loss issue, it was due to loss of air pressure. Adding a regulator at the Plasma helped tremendously.
Now I occasionally have a issue with arc not starting,
watching the gauges (regulator input, regulator output) it looks like the regulator itself is not maintaing flow at 80PSI.
The input air pressure is rock solid but the output is dipping below 80. When that happens is when (I believe) the arc is not firing to start.

[acourtjester]

You can increase the line air pressure to about 100 PSI or maybe be sure the inside diameter of the air supply line is big enough so you don't drop in pressure when cutting.

[adbuch]

As Tom said, may be larger air lines are in order. I run 3/4" copper from the compressor around the shop and out to the machine shop. In the machine shop, I drop down to 1/2" hard line to the refrigerated dryer/regulator, and then 3/8" id flex hose to the cutter. If you are using a mini regulator, make sure it is rated for the cfm requirement of your cutter.
David