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Open HV Probe 40kV

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mnementh:

--- Quote from: beanflying on April 21, 2019, 10:33:06 am ---The Ultimaker data does contain electrical properties and goes toward what DaJMasta mentioned about actual datasheets on Filaments.

Far from being an 'poorly understood properties' but perhaps 'needing more study' is appropriate which is the broad NON Conclusions about aging and extended use they made.

If you take there figure of 33kV/mm as a best case the tip of my design is @ 210mm away from the hand gaurd. So 170X my proposed maximum would be needed in theory be needed to get it to breakdown. The PLA would need to be compromised dramatically for 40kV to be an issue.
--- End quote ---

Okay... here's my concern: First, not so much about being unsafe as PLA is an organic material; two of the oldest, most commonly used HV insulators for the last century are phenolic resin and Bakelite, both of which are organic materials. The problem here is not JUST the properties of material... what would give me concern is the likelihood of surface contamination that cannot be readily removed.

All HV test equipment I've ever used came in a mirror-smooth finish; and this is for a reason: part of the "preparation before use" of any such probe is to wipe it down with alcohol or similar solvent to ensure no conductive path to the user if something has been smeared or splashed on the probe between uses. Even the arc-brakes are made so that if you soak a rag in alcohol, you can get near-absolute coverage of the surface between the discs with minimal effort.

Obviously with FDM, this is not the case. The nature of the surface almost guarantees that any contaminant that gets on the surface of the probe will be difficult, if not impossible to remove. This is a use-case where it is the manufacturing process itself is contraindicated, not JUST the material, which unless you personally test with a number of the most popular filaments, and then continue curating those results, you cannot say with even reasonable certainty that your constructed part is even remotely safe for ANYONE TO USE. Even you.  ;)

The problem you face is not YOUR use case... YOU are smart enough to know not to use this where lethal combinations of HV and current capacity exist. The problem is the dumbasses who outnumber us 10:1. There will always be dumbasses who want to play with dangerous shit... and the barrier to entry is availability and cost of tools that make playing with that dangerous shit possible.

By posting this experiment as a project, you make available to those dumbasses a tool that it would APPEAR is as safe as those commercially available products that cost much more... but can easily be fabricated on a 3D printer, then populated with anything (resistors, wiring, coathanger, pour it full of jello) said dumbasses want to stick inside it...


[SOAPBOX MODE]

Right now, the cost of entry here is the time and patience and ability to create the thing in some CADD program. That by its nature will require that anyone wanting to play with it has some technical skill and knowledge of some sort. This is one of those projects best played close to the vest, and kept to yourself.

Do the world a favor. Don't do the world THIS favor.  ;) Don't make it EASY for dumbasses to make this "tool" which will likely kill them if misused; because it most likely WILL be misused by some damned fool.  :-\

[/SOAPBOX MODE]

mnem

bd139:
This is my problem:

mnementh:
Yes, but that particular predilection does appear to be a "bd problem", irrespective of the particular instrument being used.  :-DD

mnem
 :-/O

BravoV:
If probe's body surface contamination is a serious issue, includes easy to clean surface, wonder if PTFE rod is used to build probe's outer body will help ? PTFE dielectric strength average around 500 kV/cm, cmiiw.

Random image from google

ArthurDent:
A commercially made HV probe I had was designed safely. The disc on the front of the hand grip was metal and connected to a metal tube or sleeve that went the entire distance inside the hand grip and this was connected to the metal braid of the coax probe lead that was grounded. Using this setup you were holding the plastic grip but there was a complete metal barrier at ground potential between your hand and the resistor and HV. I would not want to use a probe made just with plastic and no protection.

I had a 10Kv adjustable lab supply and I made the output lead for that using the same idea. Even though the output lead was rated far higher than 10Kv, I put a metal braid around the wire and some heat shrink tubing over that to make my own HV coax.

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