Time ago i was trying to pick a plasma cutter for my unfinished cnc. I read trough loads of material but i had no experience.

I wanted one which has very low amps so i can cut thin metal as i read that you need like 3A/mm and too much power is problem. So I picked one capable of 5-25A which seem good quality. Later i found out i could have buy a bit stronger, and it wouldn't be really an issue. but that is different story.

Problem i realised after talking to some experienced people here was that my cutter doesnt have an HF. And they where telling me that HF is must!!! otherwise you have to touch material to start the torch and you destroy loads of material when the arc goes off or the arc doesnt even start when touching rusty part of the material.

But i thought, to overcome extinguishing the arc you need Pilot Arc, so the arc can still burn when the torch is not touching the material.

And i thought having pilot Arc is just different technology used and it will start nicely without the HF. but again i was told on the forum that they didnt hear about plasma with Pilot Arc without HF, but my was like that. And i was bit depressed as my plasma was ordered but didnt arrived yet and i couldn't try it, and i was 100% sure i did mistake at this stage.

I thought i will have to touch material to start the arc and then i can cut just fine even mesh as the pilot arc will keep the torch on for few seconds.

Reasons i wanted to avoid HF (high frequency circuit to start the arc) : vikipedia: ". This method has a number of disadvantages, including risk of electrocution, difficulty of repair, spark gap maintenance, and the large amount of radio frequency emissions. Plasma cutters working near sensitive electronics, such as CNC hardware or computers, start the pilot arc by other means."
...also i am i dont know if this is always true but HF plasma cutters i come around where 360V and i wanted 220V supply voltage.

So when my plasma arrived i found out it can start in the air and there is no need for HF. It always started the arc, there was no failure ever.
So i thought ok it works, there is probably some mechanics in the switch when i press it, it does press some internal parts to start the arc. So i thought i will do some mechanical switching to press the switch on torch.

At the end from curiosity i did open it and the switch was only to close 12V circuit. So if there is some mechanics starting the spark it wasnt related mechanically to the switch.

I made simple relay to switch the contacts (as i was afraid if there is high voltage) from the torch and all worked perfect. so at the end there wasnt HF needed. I used Telwin Tecnica Plasma 31

Also, this is informative so you know it is possible. Ive seen the contact switches used on HF machines without special connector for signal, so i tried the same approach here. Of course do not do these kind of thinks if you are not experienced, there is always risk of electrocution and i am not responsible for any damage.

Hope i cleared few thinks up here as when i needed it i got confused answers. Also be aware this is feature of the plasma i ordered so i cannot guarantee it is the same at all pilot arc non HF plasma cutters. Someone else can clear that up maybe.


One addition on the next page-->

Step 1: Small Addition

Jut in case you dont wana disable hand usability of your torch by removing the button and you like another way to risk electrocution i added two images of opened inventor.

1. Image First, two arrows pointing to brown and blue cables. Thats are the cables going from your torch same Voltage as described earlier and then connection to opto-couplers on the board. So you can attach here your cables. Which when closed they will turn on the plasma.

2. Image Two, two black cables, one with yellow sleeve. Seriously, do not even go near them if you do not know the dangers of this kind of machines. Even the capacitors might be charged long time after machine is off so no running with screw driver around the board... , just do not risk. But these are the connections you would use for THC height controller to read the voltage from the arc.

Be carefull! and do not risk!


I'm sure people will find that useful, thanks for sharing.

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