Open HV Probe 40kV

[PartialDischarge]

However, since there are so many parameters (e.g. frequency, porosity, surface texture) involved, I don't see how the dielectric constant can give any useful predictive information as to the maximum voltage that such a probe could withstand. I presume measurements would have to be done, and I would be surprised if many amateurs have appropriate equipment.

Oh yes it totally does, again because it defines how field lines will distribute, and they determine when breakdown occurs. HV is a very smart and will not condone mistakes. Once you have a mechanical design with all the elements in place, you have to study the thickness and breakdowns of the materials in question (air is also a 'material' here). These elements create capacitors and each one has its limit at AC.

A 40kv unshielded probe like the one here is not that difficult to design (as long as the resistive element is well chosen) because distances are big, the distance between the hv pole and ground is huge and the 'usage time' is going to be low.

Also not talked about is this: what kind of 40kV are we talking about? because not all 40kV are created equal.I would not use *any* kind of these probes (even commercial ones) on a distribution 40kV power line. The energy here is very high and makes things more complicated.

[beanflying]

However, since there are so many parameters (e.g. frequency, porosity, surface texture) involved, I don't see how the dielectric constant can give any useful predictive information as to the maximum voltage that such a probe could withstand. I presume measurements would have to be done, and I would be surprised if many amateurs have appropriate equipment.

Oh yes it totally does, again because it defines how field lines will distribute, and they determine when breakdown occurs. HV is a very smart and will not condone mistakes. Once you have a mechanical design with all the elements in place, you have to study the thickness and breakdowns of the materials in question (air is also a 'material' here). These elements create capacitors and each one has its limit at AC.

A 40kv unshielded probe like the one here is not that difficult to design (as long as the resistive element is well chosen) because distances are big, the distance between the hv pole and ground is huge and the 'usage time' is going to be low.

Also not talked about is this: what kind of 40kV are we talking about? because not all 40kV are created equal.I would not use *any* kind of these probes (even commercial ones) on a distribution 40kV power line. The energy here is very high and makes things more complicated.

Most definitely not for high energy mains testing. I posted a link to the Ohmite Resistors planned in post Number 1 from memory. Also this option is unlikely to see use above mains frequencies as accuracy will go down the tubes. Typical use is in CRT testing and maybe Neon or similar Transformers are most likely the upper limit at 15kV?

Unless a containment of some sort allows tracking to occur the material seems up to the task. I am considering epoxy filling the tip where the resistors will sit but it won't add much in the way of safety over the air gap and distance along the probe from the users hand.

[Zero999]

I wonder if adding a suitable lacquer will help with the poor finish created by the 3D printing process? I imagine some kind of polyamide would be ideal.

[PartialDischarge]

Some thoughts about the energy of high voltage sources. I have been zapped many times by some low energy kV sources, like power supplies and 2 or 3kV CRT rails. While it hurts, meh, its no big deal.
Now, a guy named Eduardo Garcia was electrocuted by a power line, only 2.4kV . There is a documentary (available in torrents ) with graphic real images and it is just unbelievable what it did to him, lost an arm and a lot of flesh in the body. And this is only 2400 freaking volts, most medium voltage lines in Europe within cities are 20000V

https://www.imdb.com/title/tt6105406/

[bd139]

Ah that dude. On the other end of a bear shaped capacitor as well. quite horrifying that one.

[mnementh]

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.

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. 

mnem
 

[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.

[joeqsmith]

A fun project to work on, especially if you want any sort bandwidth out of it.   

I made a few attempts at making my own KV+ low energy probes.  The last someone dubbed the burrito probe for some reason or another.    This repair video shows what it looks like today and I talk about some of what I would change if I make another.  Not sure it will be much help.    Good luck.     

https://youtu.be/kWOe803atvg

[beanflying]

I wonder if adding a suitable lacquer will help with the poor finish created by the 3D printing process? I imagine some kind of polyamide would be ideal.

Certainly can be externally coated post printing. As contamination would seem to be the main concern of others over time an epoxy coating would work well on the PLA. Easy to do and I have plenty on hand.

[beanflying]

A fun project to work on, especially if you want any sort bandwidth out of it.   

I made a few attempts at making my own KV+ low energy probes.  The last someone dubbed the burrito probe for some reason or another.    This repair video shows what it looks like today and I talk about some of what I would change if I make another.  Not sure it will be much help.    Good luck.     

https://youtu.be/kWOe803atvg

I will have a good look at your few videos Tautech linked too. One of the reasons to roll this probe was even a simple Calibration point of a 20MHz Scope last week was out of the range of gear I own. Having some bandwidth over a simple resistive divider would see it getting more use.

[mnementh]

Please understand... my primary concern here is the "open" part of this project. As soon as you put that label on something, the fuckwits start to come out of the woodworks. Building it for yourself is one thing; sharing the blueprints online is something I'd consider to be roughly akin to all the imbeciles sharing plans for 3D-printable firearms, all of which are far more likely to kill the user than anyone more deserving such fate.

I've committed numerous Darwin-award-worthy acts of stupidity with HV transformers; my grand-dad started me early helping him wind a 3KV transformer for a 160m transmitter when I was 10. 

There's a reason I don't document the details of those adventures publicly; and as anyone in the TEA will tell you, it isn't embarrassment because I have not so much as a single shred of it left in my being.

mnem
*tzzzt*

[wasyoungonce]

How’s about gel coating the probe to increase issues isolation and reduce probes ability to ingress contamination.  If gel will not adhere....even better.  Use the 3D printer in negative and use the parts printed as fibreglass moulds.  FWIW

[tggzzz]

How’s about gel coating the probe to increase issues isolation and reduce probes ability to ingress contamination.  If gel will not adhere....even better.  Use the 3D printer in negative and use the parts printed as fibreglass moulds.  FWIW

It is easy to dream up things that might work. Where 20-40kV is concerned, any techniques need to be predictable and repeatable.

[beanflying]

Please understand... my primary concern here is the "open" part of this project. As soon as you put that label on something, the fuckwits start to come out of the woodworks. Building it for yourself is one thing; sharing the blueprints online is something I'd consider to be roughly akin to all the imbeciles sharing plans for 3D-printable firearms, all of which are far more likely to kill the user than anyone more deserving such fate.

I've committed numerous Darwin-award-worthy acts of stupidity with HV transformers; my grand-dad started me early helping him wind a 3KV transformer for a 160m transmitter when I was 10. 

There's a reason I don't document the details of those adventures publicly; and as anyone in the TEA will tell you, it isn't embarrassment because I have not so much as a single shred of it left in my being.

mnem
*tzzzt*

There is a counter argument to that non discussion of potentially hazardous projects given the mass idiocy on youtube with a simple search on High Voltage. Discussion here in the open is educational, imformative and generally carried out by people with a greater level of understanding than the potential Darwin Award Winners.

The maths in this one is generally ok but the practical is horrifying as are the comments below it in general

https://youtu.be/RAOw0mHQRvk

[mnementh]

Yes... and as obviously Darwin-Award-worthy as that video is, (cringeworthy too); it is just the tip of the iceberg for some of the stupid out there. At least that moron knows what heat-shrink tubing is.

I remember a video about one fuckwit who strung together 90 9V batteries; that is high enough voltage and high enough current capacity to stop the human heart, and he was playing around with it striking arcs for a firestarter using strands of telephone station wire.   

The problem is NOT with your intent, or your level of knowledge... it is with the TL:DR takeaway that fuckwits will gain from it. You can tell them 10 times that this is dangerous, explain in great detail how and why, but once their eyes glaze over, they'll hear one word in ten and then only the explosive "action words". 

The only thing they'll take away the above mentioned video is "String 90 9V batteries together and you can play with lightning! This guy did it and didn't die!"

mnem
A little knowledge is a dangerous thing.

[beanflying]

And NO or BAD Knowledge is WORSE and even MORE DANGEROUS

[0culus]

*snip*

The maths in this one is generally ok but the practical is horrifying as are the comments below it in general
*snip*

Let's start with that multimeter he's using. Those things, if they are fused at all, usually have glass fuses and are only really safe for very low voltage DC protected by a current limited supply. 

[mnementh]

And NO or BAD Knowledge is WORSE and even MORE DANGEROUS

I'm not saying don't discuss... that's what we're doing here. What I'm saying is keep your dangerous prototype blueprints to yourself; an hour after you post them here, one of those crazy Russian house-burning nutbags will be printing one to hook up to a microwave oven transformer.

For sure, anything in this vein you devise that can be printed via FDM is just plain dangerous, for a dozen reasons we've described very clearly. 

Cheers,

mnem
TEA time!

[beanflying]

Breathing is dangerous in particular if done in the path of an oncoming Red Bus on Sundays 

We will have to agree to disagree about releasing STL files as it offers a major safety improvement over what is generally available to individuals. How they get released should be in this thread stream (Not in the opening post) and with the express understanding that people have read the discussion to that point.

The enclosure is not dangerous but how it is used that presents issues. Letting the Gene pool only be exposed to bad solutions or really sub standard ones raises the risk of Electrocution. The King of Random's MOT infotainment  videos for example have multi million views 

[mnementh]

Yeah, but you're talking about adding to the pool of BAD information out there.

What you propose is to release plans for a protective testing device that is inherently not fit for its intended purpose. To an uneducated public who has no idea how or why it's inherently not fit. 

Even if you make it and test it successfully, your test sample is far too small to reasonably declare it safe, for the same exact reasons as that fuckwit with his heat-shrinked resistors on a HFT Meter.

All for the sake of avoiding paying for a tool that is readily available on eBay for $30.

Please don't.

mnem
*Lit*

[beanflying]

A fun project to work on, especially if you want any sort bandwidth out of it.   

I made a few attempts at making my own KV+ low energy probes.  The last someone dubbed the burrito probe for some reason or another.    This repair video shows what it looks like today and I talk about some of what I would change if I make another.  Not sure it will be much help.    Good luck.     

https://youtu.be/kWOe803atvg

Really interesting series of videos and a lot of work  I will go back over them when I get around to the higher bandwidth option.

Did you completely stop using the Super Corona Dope and if so any reason? I see it is made up in part with xylene and a few other ene's but how does it stand up to repeated cleaning with IPA? I have found a localish source for not to many peso's for it so I can give it a test for adhesion on PLA.

Link to Super Corona Dope Datasheet
Australian Source

[joeqsmith]

Really interesting series of videos and a lot of work  I will go back over them when I get around to the higher bandwidth option.

Did you completely stop using the Super Corona Dope and if so any reason? I see it is made up in part with xylene and a few other ene's but how does it stand up to repeated cleaning with IPA? I have found a localish source for not to many peso's for it so I can give it a test for adhesion on PLA.

I'm glad you are enjoying them.  The dope will come off with IPA and other solvents.  It can be easily damaged with a finger nail.  I clean the parts, then apply the dope.  I'm not aware of a better product for this sort of application and will continue to keep it in my bag of tricks.     

One of the reasons to roll this probe was even a simple Calibration point of a 20MHz Scope last week was out of the range of gear I own. Having some bandwidth over a simple resistive divider would see it getting more use.

The response on my 40KV probe isn't very good.  It took some effort to tame it as well as I did.  Having the GDTs built in and using the two 40KV resistors (to handle a single point failure),  I have no concern about using it with any of my scopes.     

Of less interest, I did demonstrate a few simple low end, low voltage, low energy differential probes.  I don't think these were part of my HV probe playlist.  The last one I made on some perf board from scrap parts I had.   It's pretty funny to look at.   It does have some decent BW for being such a mess.         
https://youtu.be/0thOfk4I3qs

If you can keep your single ended probe within a dB from DC to 20MHz, I would say you have done a VERY good job!   

Beyond the obvious advice, like keeping parts CLEAN and keeping your source to a safe level a few things to consider.   While experimenting,  I suggest making some sort of protection circuits for when things go wrong.  No point in blowing a scope channel or your spectrum analyzer's front end.  Even some Citel GDTs and attenuators may save you a big repair bill.     Keep in mind what you want to measure in the future and minimize the loading effects.   While toilet paper rolls,  aluminum foil and other things laying around the house can look stupid, they can provide a lot of insight into how things will behave with little time invested. 

I followed this guy's channel until he stopped posting.  He did a series on AC high voltage probes as well that you may find of interest.   He was after a differential setup.   Here you can see them in operation.  The probes are the soup cans: 
https://youtu.be/cogG29Z7wrc?list=PLmj4qMKo6w6etRqmdffwfg9JqIeAR0tzL

Dave's friend also walked through an AC probe.  I attempted something similar to this but my skills were too lacking to get it to work as good as my toilet (shitter) paper roll and some aluminum foil.