Review Request for Arc Volt Sensor Schematic

I use the filter for a couple of reasons:
1. environmental noise
2. I don't trust cheap plasma cutters to output clean DC

I see a couple of capacitors and resistors as cheap insurance against potential future problems.

I want to be able to confidently support cheaper options like Lotos LTP5500CNC. That's the one I have. It works fine and is a small fraction the price of a Hypertherm.

I actually looked at supporting HF start machines in the past. I just couldn't justify the cost and effort.

edit:
The values are placeholders, i usually use 2x470K to 2x1M for the side resistors and adjust the value for the middle one depending on what i can find.

I've added the SPI isolation. The whole thing is now fully isolated.

 

@  tommylight  Really interesting. Thanks.

Edited previous post to reflect resistor values, as the drawing is just a wiring example .

In what way do you see 2x50k as a better way than 1x100k?
You get voltages in the 50-60V range to THCAD.

With one 100k, and recognize that ground is really close to ground on the 5V rail,
you only get a few volts in after the voltage divider.

I thought about that on my card.
 

Only what is in red has 100V (well, -100V) and thereabout, the rest is 5V max.
I made some distance between torch voltage and copper as you can see in the read.

I always excuse myself by saying I am not an electric engineer, so I can be wrong.

Regarding filter, I have a digital lowpass filter with 10 Hz pole frequency in the controller. No hardware filter.
Linuxcnc has a "lowpass" hal filter component so it can be done there also.

I used the Herocut equivalent to the Lotos. Worked fine.I live in a place where we only can have 16A, absolutely max 20A, 230V at home.
I couldn't use all the 55A, the fuse blew all the time. I replaced it with a Herocut HC8000, three phase 400V 16A. I can now max out
the plasma cutter. But the compressor need to run off the petrol generator, it's too much with that one on one phase too.

 

Hakan wrote:

In what way do you see 2x50k as a better way than 1x100k?

 

Keeps the high power stuff more isolated in case of wire break/short, making it much safer.
I always put those 3 resistors on the plasma source of in a box behind it.