CNC Plasma cutters, DIY, building info and guide
09 Feb 2019 20:28 #126090
by tommylight
Replied by tommylight on topic CNC Plasma cutters, DIY, building info and guide
Just uploaded the toma_THC config for version 2.8pre of Linuxcnc at it's original thread, with some more info and updates and much easier to edit.
forum.linuxcnc.org/plasma-laser/34978-th...-with-how-to?start=0
Also working on other versions of THC anything and everything. Need caffeine badly !
forum.linuxcnc.org/plasma-laser/34978-th...-with-how-to?start=0
Also working on other versions of THC anything and everything. Need caffeine badly !
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05 Mar 2019 01:08 #127740
by tommylight
Those 2 terms do not go together. If i remember correctly when watching your videos you had a pilot arc one, not a blow back one. I just can not know if it was a HV or HF/HV type pilot arc. Please do correct me if i am wrong.
There is so much confusing and plain wrong informations about pilot arc and everything related to HF HV plasma etc, that i am baffled ! How did that happen? Where was i when that happened? Who allowed that to happen? ......
Oh nevermind, internet is slowly but surely becoming the worst place to get proper informations, just sifting through that makes the head hurt.
Do i sound a bit grumpy ?
Scratch start = the torch has to physically touch the material it is cutting to strike an arc
Blow Back = has a partially moving nozzle that when pressed against the material it shorts to ground and as it is released it strikes and arc.
Pilot arc = has the means to strike an arc all on it's own even when far from material and more importantly it can maintain that arc for some time without touching or moving any torch parts. This makes it very reliable and that is why almost all expensive ones have one of two types of pilot arc, and this is why cheap Chinese ones insist they have pilot arc although most of them do not.
The implications of using a pilot arc are far from simple and it takes quite a bit of explaining so i will try a short version:
there has to be some provision inside such power sources to protect the rectifier inside, the rectifier can not be disconnected and connected again after a successful arc transfer as that would cause much more trouble etc etc.
Then there are 2 types of pilot arc start systems the HV or High Voltage and the HV/HF or High Voltage and High Frequency
The HV uses a transformer to raise the voltage to some 10 to 20 thousand Volts ( this is why the protection above mentioned ) and use that voltage to strike a maintainable arc between the electrode and the nozzle. This is done at 50 or 60 Hz frequency so it is much easier to isolate and causes less interference to other equipment.
The HV/HF is a bit different as it also changes the frequency of that high voltage to several KHz, hence the inherent eagerness to induce itself on anything and everything around it at some fairly long distances.
Now some more info about the interference caused by plasma power sources:
They all make interferences ! ALL! Some more some less, but for us who use them with CNC machines the most important thing regarding the two types we use, namely the HV and the HV/HF types is : NOT IMPORTANT, it absolutely is not important what of the two types you have, they are very reliable and work perfectly well given the proper grounding and shielding.
As a reference of why they are the same in terms of interference, is the fact that the HF is a bit harder to isolate, but the HV makes much stronger interference. That can be easily verified by checking the power usage of the ignition system : The HV type use roughly 80 to 150 Wats of power for the arc while The HF one uses 30 to 60 Wats.
I think this was enough for tonight, thank you all for everything, going to grab some ZZZZZZZZZZ now.
Replied by tommylight on topic CNC Plasma cutters, DIY, building info and guide
Both of these have pilot arc (blowback) starting.
Those 2 terms do not go together. If i remember correctly when watching your videos you had a pilot arc one, not a blow back one. I just can not know if it was a HV or HF/HV type pilot arc. Please do correct me if i am wrong.
There is so much confusing and plain wrong informations about pilot arc and everything related to HF HV plasma etc, that i am baffled ! How did that happen? Where was i when that happened? Who allowed that to happen? ......
Oh nevermind, internet is slowly but surely becoming the worst place to get proper informations, just sifting through that makes the head hurt.
Do i sound a bit grumpy ?
Scratch start = the torch has to physically touch the material it is cutting to strike an arc
Blow Back = has a partially moving nozzle that when pressed against the material it shorts to ground and as it is released it strikes and arc.
Pilot arc = has the means to strike an arc all on it's own even when far from material and more importantly it can maintain that arc for some time without touching or moving any torch parts. This makes it very reliable and that is why almost all expensive ones have one of two types of pilot arc, and this is why cheap Chinese ones insist they have pilot arc although most of them do not.
The implications of using a pilot arc are far from simple and it takes quite a bit of explaining so i will try a short version:
there has to be some provision inside such power sources to protect the rectifier inside, the rectifier can not be disconnected and connected again after a successful arc transfer as that would cause much more trouble etc etc.
Then there are 2 types of pilot arc start systems the HV or High Voltage and the HV/HF or High Voltage and High Frequency
The HV uses a transformer to raise the voltage to some 10 to 20 thousand Volts ( this is why the protection above mentioned ) and use that voltage to strike a maintainable arc between the electrode and the nozzle. This is done at 50 or 60 Hz frequency so it is much easier to isolate and causes less interference to other equipment.
The HV/HF is a bit different as it also changes the frequency of that high voltage to several KHz, hence the inherent eagerness to induce itself on anything and everything around it at some fairly long distances.
Now some more info about the interference caused by plasma power sources:
They all make interferences ! ALL! Some more some less, but for us who use them with CNC machines the most important thing regarding the two types we use, namely the HV and the HV/HF types is : NOT IMPORTANT, it absolutely is not important what of the two types you have, they are very reliable and work perfectly well given the proper grounding and shielding.
As a reference of why they are the same in terms of interference, is the fact that the HF is a bit harder to isolate, but the HV makes much stronger interference. That can be easily verified by checking the power usage of the ignition system : The HV type use roughly 80 to 150 Wats of power for the arc while The HF one uses 30 to 60 Wats.
I think this was enough for tonight, thank you all for everything, going to grab some ZZZZZZZZZZ now.
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05 Mar 2019 05:14 #127752
by jmr
Tommy: once You get some sleep please tell me if you have seen one of these in any machines:
Thanks
Replied by jmr on topic CNC Plasma cutters, DIY, building info and guide
Ok, so chinese "cut40" has its own category: HV with no pilot arc = with just one wire going to the torch (or the antenna) = noisy as **** when the spark has nowhere to jump. With one wire there is no way to have a pilot arc - unless you hack it and add another wire to the nozzle. This works a little bit but certainly the heat input is too big for the nozzle. The same thing happens when people drag the nozzle on the material. I imagine it would work better if there was a return wire from the nozzle with some kind of current detector on it, to allow only very little current to flow when the pilot arc is on. Once the arc jumps to the material the current would ramp to normal value - isn't it like this in more expensive models with pilot arc? Is it possible to use such cheap power source with different kind of torch like the air switch type (is that the blowback?)?
Pilot arc = has the means to strike an arc all on it's own even when far from material and more importantly it can maintain that arc for some time without touching or moving any torch parts. This makes it very reliable and that is why almost all expensive ones have one of two types of pilot arc, and this is why cheap Chinese ones insist they have pilot arc although most of them do not.
The implications of using a pilot arc are far from simple and it takes quite a bit of explaining so i will try a short version:
there has to be some provision inside such power sources to protect the rectifier inside, the rectifier can not be disconnected and connected again after a successful arc transfer as that would cause much more trouble etc etc.
Tommy: once You get some sleep please tell me if you have seen one of these in any machines:
Thanks
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