CNC Plasma cutters, DIY, building info and guide

tommylight wrote:
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.

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?)?

Tommy: once You get some sleep please tell me if you have seen one of these in any machines: image missing http://www.profelectro.info/wp-content/uploads/motorCircuitoImpresso4.jpg
Thanks

I suspect different terminology in different parts of the world makes this confusing. I think the blow back is another way of igniting a pilot arc.

This is the torch I have and its both pilot arc and blowback according to ESAB.
www.esabna.com/us/en/products/plasma/tor...mechanized-torch.cfm
It certainly does not need to touch the material to start the pilot arc.

Utilizing a blowback start, and an electronically controlled pilot arc,
Blowback starting mechanism to initiate the cut, which eliminates high frequency interference from the starting circuits

I have seen some other high frequency pilot arc machines. For example, my neighbour at work recently purchased a Hypertherm Maxpro 200 which is high frequency pilot arc start which falls into Tommy's definition.

www.hypertherm.com/en-US/hypertherm/longlife/maxpro200/

The ignition console is attached to the outside of the rear panel of the power supply enclosure. The ignition console uses a spark-gap assembly. The ignition console converts 120 VAC control voltage from the power supply into high-frequency and high-voltage pulses (9–10 kV) to initiate the pilot arc at the torch electrode-nozzle gap. The high-voltage, high-frequency signal is coupled to the pilot arc lead.

jmr wrote:
Tommy: once You get some sleep please tell me if you have seen one of these in any machines: image missing http://www.profelectro.info/wp-content/uploads/motorCircuitoImpresso4.jpg
Thanks

No, but sure looks like the internal coil of very slim motor with no metal core. Interesting, i wonder what is the efficiency of such things?

tommylight wrote:

jmr wrote:
Tommy: once You get some sleep please tell me if you have seen one of these in any machines: image missing http://www.profelectro.info/wp-content/uploads/motorCircuitoImpresso4.jpg
Thanks

No, but sure looks like the internal coil of very slim motor with no metal core. Interesting, i wonder what is the efficiency of such things?

I found some general info: www.motioncontroltips.com/faq-servo-pancake-motors-work/
There was also article in some old technical newspaper (1960~?) that was readable online. When searching for pancake motor I got a lot of confusing info, so maybe this term is not very specific. On aliexpress it was even related to ordinary permanent magnet DC motor. Today there are the AC motors of similar kind, but reversed - the neodymium magnets are on the rotor. Those can be found in electric Toyotas, its just a few kilos for ~40kW of power. Not sure about efficiency, but i may have seen a number around 80%
It's not that I would ever want to pay for a new one, but they can be found in piles of other thrash in the scrapyard, with just the brush holders broken off. Look out for them:woohoo:
I may be able to send you one if there is enough of them so you could try it in some monster.
Unfortunately I still don't know where to use them best, but they should be good for a laser or plasma. I will try to take some photos, I believe some of them were made in France, I have also Polish copies (licensed or pirated, not sure which way...). Inner and outer connections on the rotor were electron beam welded. 1kW or 1.5kW with forced cooling is around 26cm in diameter and ~8cm in height plus shaft. Smaller shaft is on the back to connect the tach or encoder. Acceleration is crazy, torque possibly too. I need to solder another servo driver with some heavy fets and big PSU.

[quote="tommylight" post=127824
No, but sure looks like the internal coil of very slim motor with no metal core. Interesting, i wonder what is the efficiency of such things?[/quote]

To be very specific it looks like the rotor of the Lynch motor.

en.wikipedia.org/wiki/Lynch_motor

Checked that last night, interesting, especially the nearly 90% efficiency ! It uses brushes, lots of them. No more brushes, if i can help it.