Can someone explain the large variances in arc voltage to maintain a .06 distance via THC

[chadmjohn]

This is more of a general understanding question regarding arc voltage on our cnc tables.

My plasma cutter is a 45 amp everlast, it works 'decent' for cnc but not great. Everlast does not publish any cut charts. In getting it dialed in via straight line test I have it working well but when I compare my settings to, say hypertherm, the recommended arc voltages for any given cut are significantly higher for the hypertherm than my setup uses.

This isn't a troubleshooting question, my unit is working as expected. I'm more wondering about the large difference in voltages.

Electricity being what it is, the same voltage should be required to bridge a given airgap regardless of equipment.

For example, the powermax 45, cutting 16g mild steel it's 249ipm at 128v for a .06" torch height. (per the chart I pulled from powermax).

For the same material I'm running 175ipm at 92v. I get good, dross free cuts on the straights with minimal on curves / corners.

If I set my machines THC for 128v, it's over an inch above the material. At 92v I get my expected .06".

Can anyone explain to me why there is such a HUGE difference in voltages?

[acourtjester]

I cannot say for sure but the design of the torch with the placement of the actual tip from where the voltage is emitted is most likely different. When I first started with Plasma CNC I used a Everlast PM256 Tig with plasma built in on my first table. Then moved to a Longevity 80I plasma unit on another table, their voltages were different. If memory serves me right they were about 100 volts with the THC (Proma). Be it as it may you will need to use what works for you system to get the results you want.

[djreiswig]

Tom is correct. The arc gap is measured from the electrode to the material. The further the electrode is from the material the higher the voltage is going to be.
Incidentally, as the hafnium in the Hypertherm electrode wears, the arc voltage climbs slightly causing the thc to lower the torch slightly. That is why some systems use arc sampling to reset the voltage to account for this.

[chadmjohn]

Thanks for the replies thus far, but i think maybe I haven't worded my question clearly.

I don't have a problem I'm trying to correct, my table is running fine, my THC works fine. This is more of an academic question.

For any given distance, a certain voltage is required before an arc can form. This has nothing to do with plasma cutting, it's just basic electrical principle.

So, 'on paper' every system should have a pretty similar arc voltage at a .006" torch to material height. Small variances would be expected based upon the quality of the connection to the work piece, electronics and their slight variance, etc. but this would only account for a small fluctuation in arc voltage, likely as small as +/- 2 volts.

But the hypertherm chart (only chosen as an example) uses an arc voltage almost 40 volts higher than my cutter creates at a .006" height.

It may be that I need to call a plasma cutter manufacturer to get something like this answered as it may be 'quite deep' into the design and function of plasma cutters.

also, hypertherm uses such different consumables, it could be they have an overall longer arc where some of the distance of the measured arc voltage is further inside the torch head than my everlast has (basically hafnium to orifice distance may be longer in the HT than the everlast).

So, basically, it complete geek inquiry

[robertspark]

I believe it is a power function, and arc power density

if the arc is narrow, for the same power, the voltage will be higher for a broader arc the voltage will be lower

the relationship between voltage and power are machine dependant.

hypertherm (in my opinion and from my observation following review of manuals) provide a lot more information on their plasma cutters

to take the example machines you have given.

hypertherm powermax 45 (non XP), on pdf page 18 it lists the power of the machine as 132V at 45A, which is 5940W cutting power density.
https://www.google.com/url?sa=t&source= ... ccqZuzskNc

the powermax45xp on pdf page 21 lists the power output of the machine as 145V at 45A which is a cutting power density of 6525W
https://www.google.com/url?sa=t&source= ... sNHKOBntZe

and the everlast 52i (I could not find a 45A rated machine), pdf page 10 lists the power output as 50A at 100V which is a power density of 5000W
https://www.everlastgenerators.com/site ... a30fc0.pdf

and finally the Razorcut 45 on pdf page 10 lists the output rating on pdf page 8 as 45A at 96V so a power density of 4320W
https://razorweld.com/wp-content/upload ... al-web.pdf

given all of the numbers are at 45A (ok except for the everlast 52i) the lower the voltage you will find as a wider arc and I suspect kerf.... like using a blunter axe


note I don't work for any manufacturer or in the industry and I may be talking out of my rear but that is how I suspect it is likely to work

[acourtjester]

AS Robert points out due to the close to similar amps out the voltage is not the same for different plasma units. From Google
"The formula for calculating wattage is: W (joules per second) = V (joules per coulomb) x A (coulombs per second) where W is watts, V is volts, and A is amperes of current. In practical terms, wattage is the power produced or used per second. For example, a 60-watt light bulb uses 60 joules per second"

[robertspark]

it's also worth looking at the duty cycle comparisons when you look at those same pdf pages listed.

duty cycle is the amount of ON (cutting / running) to OFF (cool down) time in a 10 minute cycle.

60% duty cycle is therefore 6 mins of run time and 4 of cool off time .... 40% is 4mins of run time to a 6 min cool down time.

it wasn't relevant to the OPs question.... but it's interesting to compare machines and apples with apples....

over stretching / running a machine longer than it's duty cycle won't help out it's longevity. also check your air compressors as they have a duty cycle too..... that is also why I run 2 compressors at the same time so they can share the load.

[adbuch]

This is more of a general understanding question regarding arc voltage on our cnc tables.

My plasma cutter is a 45 amp everlast, it works 'decent' for cnc but not great. Everlast does not publish any cut charts. In getting it dialed in via straight line test I have it working well but when I compare my settings to, say hypertherm, the recommended arc voltages for any given cut are significantly higher for the hypertherm than my setup uses.

This isn't a troubleshooting question, my unit is working as expected. I'm more wondering about the large difference in voltages.

Electricity being what it is, the same voltage should be required to bridge a given airgap regardless of equipment.

For example, the powermax 45, cutting 16g mild steel it's 249ipm at 128v for a .06" torch height. (per the chart I pulled from powermax).

For the same material I'm running 175ipm at 92v. I get good, dross free cuts on the straights with minimal on curves / corners.

If I set my machines THC for 128v, it's over an inch above the material. At 92v I get my expected .06".

Can anyone explain to me why there is such a HUGE difference in voltages?

OK. I guess I didn't read it over close enough last night. I somehow thought you were referring to the same machine, but under different circumstances - and were looking for an explanation of arc stretch vs. voltage as it applies to thc (digital torch height control). Now I understand that you are comparing two entirely different cutters with entirely different electronics, power supplies, torches, consumables, etc. This is probably the same reason that some different manufacturers list different cut heights, pierce heights, etc. for the same metal thickness and similar current settings/cut speeds. In other words - Manufacturer A has different settings than Manufacturer B for the exact same cutting scenario. The specific design of each machine dictates the best settings for each machine for specific cutting situations.
David

[chadmjohn]

I believe it is a power function, and arc power density

if the arc is narrow, for the same power, the voltage will be higher for a broader arc the voltage will be lower

the relationship between voltage and power are machine dependant.

hypertherm (in my opinion and from my observation following review of manuals) provide a lot more information on their plasma cutters

to take the example machines you have given.

hypertherm powermax 45 (non XP), on pdf page 18 it lists the power of the machine as 132V at 45A, which is 5940W cutting power density.
https://www.google.com/url?sa=t&source= ... ccqZuzskNc

the powermax45xp on pdf page 21 lists the power output of the machine as 145V at 45A which is a cutting power density of 6525W
https://www.google.com/url?sa=t&source= ... sNHKOBntZe

and the everlast 52i (I could not find a 45A rated machine), pdf page 10 lists the power output as 50A at 100V which is a power density of 5000W
https://www.everlastgenerators.com/site ... a30fc0.pdf

and finally the Razorcut 45 on pdf page 10 lists the output rating on pdf page 8 as 45A at 96V so a power density of 4320W
https://razorweld.com/wp-content/upload ... al-web.pdf

given all of the numbers are at 45A (ok except for the everlast 52i) the lower the voltage you will find as a wider arc and I suspect kerf.... like using a blunter axe


note I don't work for any manufacturer or in the industry and I may be talking out of my rear but that is how I suspect it is likely to work

That makes perfect sense. I had, sort of in the back of my mind, guessed better cutters, like hypertherm, had a better arc form and that may be a contributing factor but didn't want to taint my question with supposition.

The way you called out power density though, that make a great deal of sense, wattage delivered to the material!

Thank you!

[robertspark]

No problem, happy I could help

Some guys like hypertherm (I have one too), and there also seems to be a fair few users of Thermal Dynamics too as an alternative.

https://www.thermal-dynamics.com/tdus/e ... series.cfm
https://www.thermal-dynamics.com/tdus/e ... /index.cfm

Unfortunately they didn't have a "45" just a "40" and "60", but if someone was trying to use the list below to choose a machine, then you probably want to be aware of Thermal Dynamics as an option.

If you are in the UK then Oxford Welders + RTech (same as everlast) are also options worth considering their arc power density (actual output power).

https://www.oxfordwelders.co.uk/plasma.html
https://www.r-techwelding.co.uk/welding ... sma-cutter

Unfortunately. like all the other manufacturers their information is thin / sparse compared to hypertherm + the power densities also are lower than hypertherm (I don't think I've ever seen any manufacturer with a higher or equal output voltage for same / similar output amperage than hypertherm).