Open HV Probe 40kV - Page 1
Forum section: electronics / projects

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 03:14:13 am
content: Reason HV probes are either rubbish from the usual asian suspects or what I consider way OTT on price for what little they contain.While this is starting out as a 3D Print type of project the options for what goes inside and what you use the enclosure for can be far more wide ranging. The design is optimised to avoid needing supports when printed is the main reason for so many parts.Currently I am printing the first sample one and tweaking the design as I go but as you see it is a close clone the Pintek and some others on the commercial market.Version 1: 40kV maximum rated 990Mohm divider against a 10Mohm Meter for a 100:1 divider. Plan is to make up the 990 MOhm Resistor with 500, 400 & 90 MOhm Ohmite Slimmox 1%https://au.mouser.com/datasheet/2/303/res_slimmox-1265542.pdf. Fairly easy to change around from that if you want but the three of them will fit in the long tip barrel easily attached to a 5mm knurl nut in the final tip section to screw the metal probe into. These three cost circa $22 USD from Mouser so add that to a few other bits and for around $40-50 you will have a 1% 40kV HV Probe.Version 2: Something in a lower kV rating but with far better bandwidth for possible Scope use.? Thinking circa 2-3kV and 1-2MHz? Totally open to circuit options and ideas and I have added a slotted mount into the handle to take a 20x80x1.6mm PCB.Version 3: Chicken Stick for playing with Neon and MOT Transformers just because it's fun and it should be safe fun lest your internal smoke come out.Version X: Up to you lot. Possible self contained probe like the older Heathkit one with a built in meter in the handle?When I have a print that works and screws together I will drop the STL's here for others to try out most likely later today as I am onto the 2nd Red barrel section already and so far so good.

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 05:54:51 am
content: What material are you using?Is it in any way hygroscopic over time?Can oils/grease/etc lodge on the surface and be difficult to remove?At 40kV it might be necessary to be careful of those points, but those questions are worth what you pai for them.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 06:11:55 am
content: Quote from: tggzzz on April 21, 2019, 05:54:51 amTrue of fairly much all plastics and especially with HV. Regardless of commercial or home made care with oils and water is a must do. I am planning to use PLA on mine but ABS would be fine too, PETG I have never seen any tests done on it but it is better with moisture then PLA for example but I am uncertain of it's electrical characteristics.The couple of youtube videos below are worth a look. There is also some on Lichtenberg Figures and dumbasses with MOT's but playing with salt water and HV is DUMB if you don't know what you are doing.With Version 1 for example if used properly your hand will be 60+mm away from an Earth referenced point and further away than that to any HV so unless you are being rained on with salt water fairly safe.Long term keep it clean and dry and if in doubt print another.https://youtu.be/-_LJXKLgIYchttps://youtu.be/ZqXQRq8As1o

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 06:25:56 am
content: Quote from: beanflying on April 21, 2019, 06:11:55 amThe fabrication technique may also be relevant, in particular the body will not be smooth and will not be solid. Both of those may trap undesirable water/oil/etc.QuoteI always have doubt, so that wouldn't help me!Sorry, I don't feel like spending 40 minutes of my remaining life looking at those videos. (Especially since almost all yootoob vids are talking heads and I can speed readmuchfaster than I can watch videos)

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 06:35:26 am
content: For comparison, here's my 40kV meter. Tip to disc is 13cm, disc diameter is 7cmI picked it up cheaply, and haven't had occasion to use it at more than a too small fraction of its rated value.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 06:56:25 am
content: Quote from: tggzzz on April 21, 2019, 06:25:56 amYou wanted information and some details then dismiss without reviewing and then trust in antique secondhand equipment of unknown originAlso fairly insulting to regard w2aew as a talking head for a start and Kerry is far from one either.

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 07:11:59 am
content: Quote from: beanflying on April 21, 2019, 06:56:25 amIt came directly from an industrial calibration facility, and is visibly in a good condition. I cannot foresee using it on more than 20kV (i.e. CRT voltages).So yes, I would trust that more than a homebrew fabrication using materials with poorly understood properties.For amusement, I did make a handle for a Tek HV scope probe (using SLA), but only on the grippable side of the disc; the probe was safe to use without that part of the handle (apart from dropping it!).QuoteI didn't dismissthem. I did say I'm not prepared to spend 40 minutes looking at their videos. After all, it may be interesting to you but is only of passing interest to me.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 07:26:47 am
content: So in passing with NO evidence to back your claims about 'poorly understood properties' used 3D printing materials when offered some ACTUAL testing of those materials using FDM you still dump on the process and materials?PLA along with ABS are very well understood materials as is PETG. Please let me know how you arrive at 'poorly understood properties'?

author: DaJMasta
author_rank: Super Contributor
timestamp: April 21, 2019, 07:29:28 am
content: It's a neat project but I would be worried about choice of plastic as well - namely in disclaiming that you really need to verify the exact plastic you're using to print the parts and clean them thoroughly before assembly. There is a gigantic variation in available PLAs, and especially at these voltages, even the choice of pigment could degrade the dielectric breakdown voltage quite considerably.Yes, by putting that much plastic between you and the high voltage, a lot of things are covered, but with commercial probes they have the advantage of being able to mold their probe housings around known, tested materials produced in a very controlled environment, which is exactly the opposite of a home 3d printer putting together a neat project. I have little doubt that with the right choice of materials you can make a safe probe, and I'll go as far as to say that most standard plastic filaments should do the job.... but I know for sure that some will not, and this is dangerous enough that it's not worth the risk unless you can test your specific material used to be sure.Perhaps there are filament manufacturers that actually have electrical breakdown voltages on their datasheets, and perhaps it's "safe enough" for your own use, but I really think there should be a reminder that emphasizes that not all filaments are the same so that unless you can buy a rated filament and use it within specification or you can test it and verify yourself, that you shouldn't just DIY this one on whatever filament is lying around.Come to think of it, though, maybe there's a high voltage insulator tubing or something you could cover the divider with that would make much of the worry about breakdown voltage of the plastic away, or even some sort of high voltage rated potting material.

author: Zero999
author_rank: Super Contributor
timestamp: April 21, 2019, 07:39:58 am
content: Also note that the input impedance of most meters isn't that well controlled. I've found it can differ significantly from the stated 10MA x10 oscilloscope probe should be much better though, as it will be designed with a definite 1M 'scope input impedance in mind.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 07:47:36 am
content: Quote from: Zero999 on April 21, 2019, 07:39:58 amAgreed about the impedance all of my handhelds vary off the 10MOhms on lower ranges. It was part of the reason to go with 100:1 and use the highest range setting available. My testing matches what Allan found in the video above on the lower ranges but on the highest ranges they are very close.For anything above main frequencies I would expect a fairly major error hence looking toward something for lower kV and compensation as a different option.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 07:53:20 am
content: Quote from: DaJMasta on April 21, 2019, 07:29:28 amThere would be room for putting a glass sleeve around the resistors until you get to the Earth and meter tap connection. The Resistors I am looking at will all be contained in the single long section as will the terminations so at that point the highest voltage at a full 40kV in will be 400V with 70mm of plastic between the user and that point.Edit Avoid BLACK would be a good start re pigments too as it is likely carbon based.

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 08:24:22 am
content: Quote from: beanflying on April 21, 2019, 07:26:47 amI refer you to my first and subsequent posts (with myemphasis), and I am content to let others decide whether I am "dumping on process and materials"...What material are you using?Is itin any way hygroscopic over time?Canoils/grease/etc lodge on the surface and be difficult to remove?At 40kV itmightbe necessary to be careful of those points,but those questions are worth what you pai for them.The fabrication techniquemayalso be relevant, in particular the body will not be smooth and will not be solid. Both of thosemaytrap undesirable water/oil/etc.QuoteThe fabrication technique can be as important as the material, especially for uses like this.

author: tautech
author_rank: Super Contributor
timestamp: April 21, 2019, 08:43:39 am
content: Version 2 suggestion.1000:1 probe of say 5KV design rating and along the lines of Pintek's 8KV probe.Far less unwieldy than a 40KV jobbie and offers significant voltage headroom over 100:1 probes.Example:http://www.pintek.com.tw/files/pintek/HVP-08-front.pdfImage for comparison to ordinary probes:https://youtu.be/W30AqcDQL18?t=18But hey we need be careful with projects like these and those that follow themmustknow they do so at their own risk........but hell, if Joe Smith can make a 1000:1 probe for monitoring his 15KV pulse gen then with care and understanding others with the capability could too.Joe's journey down the HV probe rabbit hole:There are a few more for those that want to hunt them out.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 09:27:03 am
content: And some more 'actual evidence' and a studyStudy of electrical properties of 3D printed objectsandhttps://www.sciencedirect.com/science/article/pii/S1876619616000565Data on PLA (brand specific)https://ultimaker.com/download/74599/UM180821%20TDS%20PLA%20RB%20V10.pdfThe only downside would appear to be surface contamination and that to a degree is true of any materials regardless of process.

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 10:01:11 am
content: Quote from: beanflying on April 21, 2019, 09:27:03 amA couple of quotes from the first reference that would concern me w.r.t. this application (my emphasis):The dielectric strength measurement wasdifficult tocompletedue to thesurface dischargesthat occurred duringthe increasing of the voltage. Therefore the relativelyhighobservational errordistorted the measured data. However,thehighestobserved value of dielectric strength for PLAwas about 33 kV/mm.However, several problems could occur, when usingPLA in insulating systems. This material is derived fromcorn starch and so it is biodegradable,unstable in time. Themechanical and other propertiescould change verymarkedly during aging. The solutioncouldbe also thedevelopment of proper additive to suitable adjustment ofthe PLA properties.Generally, animprovement of the electrical properties ofthese materials is required, for example by adding someadditives to the base material.The ultimaker data contains nothing relevant to this discussion; I'm not sure why you referenced it.QuoteOf course. The degree is the key point; professionally produced products wiill have characterised the materials and processes, and won't be constrained to use whatever fits in their machines.My first boss told me a story... He was using a screwdriver around the neck of a TV CRT, and after a while he got a hell of a belt from it. After looking carefully for the cause, he found there was an almost invisible oil track/film onpartof the screwdriver's stem and handle.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 10:33:06 am
content: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 11:27:10 am
content: Quote from: beanflying on April 21, 2019, 10:33:06 amItonlycontains dissipation factor and dielectric constant. Those are useful for assessing capacitance and HF losses, but havezerorelevance to operation at 40kV.Hence my statement that "The ultimaker data contains nothing relevantto this discussion".QuoteEngineers base their designs on worst case specs, not best case specs.I gave an example of how smooth and solid metal and plastic could be dangerously compromised. Hombrew 3D printing is worse in that it has non-smooth surfaces with problems stated in your reference. Add to that any porosity and aging, and who knows what the worst case properties might be.But hey, it is your heart, and it is up to you to do with as you wish.

author: PartialDischarge
author_rank: Super Contributor
timestamp: April 21, 2019, 11:28:46 am
content: Quote from: beanflying on April 21, 2019, 10:33:06 amWell not really. I'm not going to position myself for or against the use of PLA but let me clarify some terms.Breakdown is measured across a material and not over the surface. The latter is surface tracking which is highly dependable on humidity and roughness and on the material in question. Some materials are tested for CTI (comparative tracking index) for that reason in some materials used in power equipment.Now, breakdown can measured at DC or at 50Hz,and it makes a huge difference. That same paper he measured in the video with a dc breakdown of >1kVdc would break down at 200Vac easily.Most importantly and less known is that for anything high voltage (>10kV) conductivities, permittivities and the distribution of the field lines are of utmost importance yet ignored by mostly everyone.At pure DC, high voltage only cares about conductivities along its path and will create resistive dividers as a result. At AC material permittivities do matter and capacitive dividers are formed. If a high er material is inserted as an insulator at a certain point near a high voltage conductor for example, field lines will be expelled to the outside, and if that outside is air, the concentration of field lines may create breakdown in this space, something with goes against the idea that inserting a good insulator in a high voltage path is always positive.Chapter 2 in this interesting book talks about thishttps://www.academia.edu/30766171/High_Voltage_Engineering_Practice_and_Theory

author: PartialDischarge
author_rank: Super Contributor
timestamp: April 21, 2019, 11:40:16 am
content: Quote from: tggzzz on April 21, 2019, 11:27:10 amActually the dielectric constant is the top 1 or 2 most important specification or any material used in high voltage, since it dictates how the field and equipotential lines will be distributed, the capacitances that you mentioned. Since most HV applications are for power line frequency this has been extensively studied, the most typical being an air void inside a high er dielectric (due to a problem in epoxy injection in a bushing for example). This will create arcing inside the void (acting as a very small capacitor) which will create UV light, which will destroy surrounding walls, which will create cracks, conductive paths, etc ,etc

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 11:50:45 am
content: Quote from: MasterTech on April 21, 2019, 11:40:16 amI stand corrected; thanks for the clear explanation. I now have to fall back on my statement "...but those questions are worth what you pay for them"However, since there are so many parameters (e.g. frequency, porosity, surface texture) involved, I don't see how the dielectric constant can give anyuseful predictiveinformation 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.

author: bd139
author_rank: Super Contributor
timestamp: April 21, 2019, 11:54:14 am
content: Just a point on PLA, the actual conductivity varies with temperature and the surface can have pin prick holes in it which are enough for HV to creep out. This is one application where (quality) injection moulding is essential unfortunately. Any failure could escalate pretty quickly!HV is terribly unpredictable as well. My first proper zap was trying to build an HV probe for TV anode. I did this with some PVC tubing with stacked carbon composition resistors in it and filled with epoxy. The HT decided it was quite happy to go around the probe entirely because it wasn’t clean.You can probably “megger” a finished probe but I’m not sure I’d trust it hands on ever.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 11:56:46 am
content: Quote from: tggzzz on April 21, 2019, 11:27:10 amAs the study I added was based on a using a Prusa Mk2 What is the difference in my 'homebrew' printing to their 'Homebrew'?The fear argument and scenarios you keep repeating without facts and data are a warning at most (which I am aware of and acknowledge) and I await you to show me some numbers that the design is or will be unsafe and not your imagined remote maybe's?BTW have you 'tested' that old cord and probe on your HV Tester? Or are you happy to place yourself at risk with an unknown plastic and cable that may or may not have broken down to an unknown degree with age?

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 12:05:26 pm
content: Quote from: bd139 on April 21, 2019, 11:54:14 amEven if the HV found a path out of any flaw in the probe tip as mentioned the ground potential end of the resistors string will be 70mm from the user. It will be about 100 to the end of the first Resistor which at 40kV input will still only be at 4kV. Assuming the probe isn't contaminated 70mm Airgap is a lot of safety even if something does go to poo electrically.

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 12:11:49 pm
content: Quote from: beanflying on April 21, 2019, 11:56:46 amHow the hell should I know?!If anything, it is up to you to determine that the prints are comparable.QuotePlease don't advance strawman arguments.I have asked questions. To me, the responses have not been answers.QuoteYou know the answer to that, because I have already stated "... haven't had occasion to use it at more than a too small fraction of its rated value".However, given its apparent condition, I wouldfarrather use that than a homebrew probe.But hey, it is your health, not mine!

author: PartialDischarge
author_rank: Super Contributor
timestamp: April 21, 2019, 12:25:25 pm
content: Quote from: tggzzz on April 21, 2019, 11:50:45 amOh 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.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 12:42:48 pm
content: Quote from: MasterTech on April 21, 2019, 12:25:25 pmMost 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.

author: Zero999
author_rank: Super Contributor
timestamp: April 21, 2019, 01:37:42 pm
content: 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.

author: PartialDischarge
author_rank: Super Contributor
timestamp: April 21, 2019, 02:13:00 pm
content: 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 20000Vhttps://www.imdb.com/title/tt6105406/

author: bd139
author_rank: Super Contributor
timestamp: April 21, 2019, 02:18:29 pm
content: Ah that dude. On the other end of a bear shaped capacitor as well. quite horrifying that one.

author: mnementh
author_rank: Super Contributor
timestamp: April 21, 2019, 05:06:45 pm
content: Quote from: beanflying on April 21, 2019, 10:33:06 amOkay... 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 isthe 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

author: bd139
author_rank: Super Contributor
timestamp: April 21, 2019, 05:48:52 pm
content: This is my problem:

author: mnementh
author_rank: Super Contributor
timestamp: April 21, 2019, 06:43:12 pm
content: Yes, but that particular predilection does appear to be a "bd problem", irrespective of the particular instrument being used.mnem

author: BravoV
author_rank: Super Contributor
timestamp: April 21, 2019, 07:15:20 pm
content: 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

author: ArthurDent
author_rank: Super Contributor
timestamp: April 21, 2019, 07:54:16 pm
content: 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.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 21, 2019, 08:29:01 pm
content: 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

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 09:53:56 pm
content: Quote from: Zero999 on April 21, 2019, 01:37:42 pmCertainly 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.

author: beanflying
author_rank: Super Contributor
timestamp: April 21, 2019, 10:06:37 pm
content: Quote from: joeqsmith on April 21, 2019, 08:29:01 pmI 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.

author: mnementh
author_rank: Super Contributor
timestamp: April 21, 2019, 11:17:23 pm
content: 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*

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: April 21, 2019, 11:21:24 pm
content: 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

author: tggzzz
author_rank: Super Contributor
timestamp: April 21, 2019, 11:35:02 pm
content: Quote from: wasyoungonce on April 21, 2019, 11:21:24 pmIt is easy to dream up things thatmightwork. Where 20-40kV is concerned, any techniques need to be predictable and repeatable.

author: beanflying
author_rank: Super Contributor
timestamp: April 22, 2019, 12:13:50 am
content: Quote from: mnementh on April 21, 2019, 11:17:23 pmThere 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 generalhttps://youtu.be/RAOw0mHQRvk

author: mnementh
author_rank: Super Contributor
timestamp: April 22, 2019, 12:35:08 am
content: 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 tenand 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!"mnemA little knowledge is a dangerous thing.

author: beanflying
author_rank: Super Contributor
timestamp: April 22, 2019, 12:48:57 am
content: And NO or BAD Knowledge is WORSE and even MORE DANGEROUS

author: 0culus
author_rank: Super Contributor
timestamp: April 22, 2019, 01:00:29 am
content: Quote from: beanflying on April 22, 2019, 12:13:50 amLet'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.

author: mnementh
author_rank: Super Contributor
timestamp: April 22, 2019, 01:35:49 am
content: Quote from: beanflying on April 22, 2019, 12:48:57 amI'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,mnemTEA time!

author: beanflying
author_rank: Super Contributor
timestamp: April 22, 2019, 01:52:47 am
content: Breathing is dangerous in particular if done in the path of an oncoming Red Bus on SundaysWe 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 MOTinfotainmentvideos for example have multi million views

author: mnementh
author_rank: Super Contributor
timestamp: April 22, 2019, 02:55:36 am
content: 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*

author: beanflying
author_rank: Super Contributor
timestamp: April 22, 2019, 02:56:14 am
content: Quote from: joeqsmith on April 21, 2019, 08:29:01 pmReally interesting series of videos and a lot of workI 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 DatasheetAustralian Source

author: joeqsmith
author_rank: Super Contributor
timestamp: April 22, 2019, 03:55:25 am
content: Quote from: beanflying on April 22, 2019, 02:56:14 amI'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.Quote from: beanflying on April 21, 2019, 10:06:37 pmThe 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/0thOfk4I3qsIf 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=PLmj4qMKo6w6etRqmdffwfg9JqIeAR0tzLDave'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.

author: beanflying
author_rank: Super Contributor
timestamp: April 22, 2019, 04:24:02 am
content: Funny I watched Dave's video #85 again this morning as it came up in a search. People are worried about PLA and this one is maybe a touch less safe out there for the masses to watchI have no qualms about the maker of it being safe after seeing what else he plays with but it lacks for most.I will grab some dope at some stage but opt for an epoxy clear coat over the hot end of the 40kV probe based on that. Also checked and based on your videos there is plenty of diameter for a secondary thin wall PLA/Kapton Taped inner tube for the Resistors and any above ground terminations to sit in the tip barrel (14mm bore but fitted with a 13.5x12.7 wrapped tube).Just reprinting some bits including the handle after increasing the thread pitches on the parts so they screw together without needing any post processing.Shown in the photo is four parts screwed together. Other than removing the Brim (Flashing) from the prints they are as the came off the printer (Ender Pro).

author: vk6zgo
author_rank: Super Contributor
timestamp: April 22, 2019, 05:24:30 am
content: Back in the day, EHT probes were quite expensive, & the users paid due care & attention to the useandstorage of them.For this reason I would trust an old HV probe. (After, of course, checking it thoroughly for physical damage.)Most of the old style ones are made from hard polystyrene, which, if looked after well, maintains its voltage rating over many years.I do remember seeing one probe machined out of solid Perspex, but that was an outlier.Most HV probes were used to look at TV set EHT, which although it has lots of voltage, cannot source enough current to do much harm.Transmitter HT supplies are another kettle of fish, but most full size TV or Radio Broadcast Tx have their own built-in metering for such supplies, so even at such a site, the HV probes didn't get that much use.3D printed devices are not as homogenous as cast or extruded plastics, but whether that is a problem, or not , I don't know.

author: tautech
author_rank: Super Contributor
timestamp: April 22, 2019, 05:39:51 am
content: Quote from: beanflying on April 22, 2019, 04:24:02 amThis is key IMHO ^^^The handle should just be a vessel to enclose the construction of safe innards.If, and only if the printed materials can be proven to be safe against leakage or flash-over may they be used in any insulation capacity.We can never be sure someone with the printer files and a printer won't use an unsuitable filament.

author: beanflying
author_rank: Super Contributor
timestamp: April 22, 2019, 07:06:21 am
content: Quote from: tautech on April 22, 2019, 05:39:51 amAll things are possible you and can now get fairly easily get Conductive PLAhttps://www.proto-pasta.com/pages/conductive-plalaced with Carbon. Anyone making an electrical safety probe with it would truly deserve their Darwin AwardThere is other options out there but Styrene (ABS, HIPS etc) or PLA are clearly the better and easier to use options.With switching to a secondary tube it is in theory possible to remove the metal tip from having direct contact to the outer shell as it could be mounted onto a stronger inner tube without major changes. A flanged end at the rear of the inner sleeve would hold it in place then carry the probe tip forward. It would only need the first two tip sections modding to make this possible.BUT The downside to this is it would allow the possible ingress and entrapment of liquids or dirt between the inner and outer unless maybe a teflon encapsulated o-ring or seal of some sort was added. Adding more parts with finer tolerances and complexity would maybe not increase overall safety. Like replicating all the parts used in Joes probes it pushes the design beyond most or you may find people cutting cornersSample Inner sleeve done and wrapped with Kapton, I will drop the diameter another 0.4mm so a second or third layer can be added easily. New Handle section is on the printer with the PCB mounts and latest revisions. Will be in Clear PLA as I am short of Black at present.

author: 0culus
author_rank: Super Contributor
timestamp: April 22, 2019, 07:28:20 am
content: Nice work, bean!Reading over the conversation in this thread, I gotta agree with bean that open designs are overall better. Idiots will be idiots, so let's stop wringing our hands over what they might do. If it's not playing with large electrical potentials, it will be high powered fireworks, thermite, binary explosives, dumbass lifted pickups, and more. So, put proper disclaimers with it and if someone does something stupid, it's their own damn fault. I'd far rather have open and accessible designs than none at all.

author: tggzzz
author_rank: Super Contributor
timestamp: April 22, 2019, 08:21:44 am
content: Quote from: beanflying on April 22, 2019, 07:06:21 amPLA and many thermoplastics are hygroscopic to some extent. Unless proven otherwise I would assume that would change the electric properties over time, e.g. it becomes more conductive.I have not seen (because I haven't looked for) any measurements indicating whether or not that would be sigificant in this application.

author: beanflying
author_rank: Super Contributor
timestamp: April 22, 2019, 10:12:38 am
content: H2O (pure) has a far greater dielectric strength than air for example and any amount of moisture absorbed will be more or less pure due to its origin. Discussion of moisture in filament is generally due to the issue of what there is creates steam when used to print something. There is no figures I am aware of re changed electric or physical data over time but is is massively hard to get even very high voltage to pass through pure water due to a lack of ions. Mine for example once a month maybe is the use case my HV scope probe will get over 1kV and I have meters already up to that point so maybe a silica pack and vac bag it.If anyone is still concerned then styrene options are always there but they then come with some common solvent based issues (acetone in particular). That will include the Vintage ones vk6zgo mentioned a few posts back.With accelerating/composting PLA for example both high heat (70+C) and high moisture with limited oxygen is needed. UV can effect some pigments. Refound some practical outdoor testing of PLA prints from Angus @ makersmuse in the Australian weather. Bear in mind a lot of these pots are SINGLE LAYER (0.4mm wall) I am printing @ 6 layers with 40% infill where needed.https://youtu.be/qqNfa_zExRU

author: mnementh
author_rank: Super Contributor
timestamp: April 22, 2019, 06:15:28 pm
content: That picture makes me cringe; no less than that video we were just discussing.I'm not hand-wringing. I'm pointing out clear and obvious hazards in publishing the stls for this.The intended manufacturing process and material simply and clearly are NOT fit for the intended purpose. Add to that the proclivity of dumbasses to just snurch and not read instructions, and the bottom line is that publishing these STLs is ethically the same as leaving a loaded gun lying around on the intardnet.I'm not the only one here who can clearly see the clear and present danger this project represents; you discount those dangers at your own peril.I've said my piece; I'm done here.mnem"Good luck! And may your god go with you."

author: tggzzz
author_rank: Super Contributor
timestamp: April 22, 2019, 06:39:03 pm
content: Yes and yes.And I too remember Dave Allen fondly

author: beanflying
author_rank: Super Contributor
timestamp: April 22, 2019, 09:10:39 pm
content: For those who actually take the time to watch Angus's video in my last post will know the SINGLE LAYER vase mode prints suffered mechanical damage and are not the result of open air environmental, water or UV exposure. PLA needs very specific environmental conditions to breakdown without those conditions it is far from bio-degradable as numerous scientific studies have shown. Google it and do some reading of the scientific papers.If your doubts are still with PLA then use ABS or HIPS like the commercial probes use and put up with its shortcomings like all materials have. Without having seen one in the flesh Pintek appears to still be using ABS based on it's cleaning warning against solventshttp://www.pintek.com.tw/files/pintek/HVP-40.pdfPLA on the other hand is not effected by most solvents.Part of the idea of this being open was to work on ideas and to improve the safety of the design and in a small way try and redress some of the youtube bs 'designs' that have little to none.

author: ArthurDent
author_rank: Super Contributor
timestamp: April 22, 2019, 11:24:48 pm
content: I am somewhat baffled at the endless discussion of possible failure modes of different plastics, methods of construction, or maintenance issues that could cause injury or death while no one seems to be paying any attention to how this safety issue has been solved for decades.As I said in post #34, the simple safety solution is to have a complete ground potential between you and the HV resistor built into the probe handle. Below is a drawing of the Tektronix 6015 HV probe showing the grounded tube they used around the end of the HV resistor. In the video link it shows the same idea in a Fluke probe of having the closest thing to the HV be a grounded shield and not your hand at minute 3:10.

author: tggzzz
author_rank: Super Contributor
timestamp: April 22, 2019, 11:44:20 pm
content: Quote from: ArthurDent on April 22, 2019, 11:24:48 pmAppropriate materials and appropriate construction are not mutually incompatible.Do you need both or is either sufficient on its own?Personally, in this case I thinkbothare highly desirable - I wouldn't want to rely on either alone.

author: ArthurDent
author_rank: Super Contributor
timestamp: April 23, 2019, 12:01:56 am
content: tggzzz - "Appropriate materials and appropriate construction are not mutually incompatible."I don't see anything wrong with any of the plastics used and I didn't mentioned that as a problem. What I am confused about is how the safety issue is being ignored when it has been solved ages ago. Everything can possibly fail, I just don't want that failure to take me with it.

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 12:50:48 am
content: Sigh, the Spaghetti monster paid me a visit overnightOn the plus side all the threads work well as do the PCB slots. The modded inner tube now takes four layers of spiral wrapped Kapton and would probably take a fifth.Re the outer shield it is certainly possible to make rolled copper sheet then soldered is the obvious one or you could design around a standard hard drawn Copper pipe size. The downside to it is in terms of usability as the probe diameter will need to be increased making it awkward in more cases. The Scope test point I needed to measure last week was already fairly tight and only 2kV so I could have butchered something up to get it done.I see no reason not to use the base handle and lower sections and then screw a different tip section to it. It may actually be of benefit to do that in the case of the higher frequency version to add some noise shielding as well?If we can move on a little:PLA and ABS are both good insulators - PERIOD !PLA as some sort of magic water sponge is BS and it doesn't breakdown rapidly even when immersed in water without microbiological activity as well.PLA as a rapidly Bio-Degradable Plastic in open Air is BS unless someone finds me ACTUAL SCIENTIFIC EVIDENCE to prove otherwise?Dirt Contaminants and Grime are the enemy so the probe outer needs to be easily cleanable (smooth) so an Epoxy Coating should be added to the 3DP surface.Operator Safety is paramount as it always was. Lets work to improve it where possible.

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 01:41:04 am
content: Quote from: ArthurDent on April 23, 2019, 12:01:56 amJust slowed the video right down you linked and took a screen cap. Some of the commentary about spark gaps and the circuit is wrong and the parts he tried to reference simply hook over the shield on the barrel section as shown. The question if someone that has one can check is how far into the barrel on the Fluke does the shield go? Also the LV end of the Resistors is back right at the operators handIn the case of the Resistors I am looking at and the layout of my design it sees that point 65-70mm up into the barrel.

author: ArthurDent
author_rank: Super Contributor
timestamp: April 23, 2019, 04:02:17 am
content: I was only using that video to show how the Fluke probe was constructed and not anything else, although his using pill bottles for insulators is a nice touch!When the metal piece the coax is crimped into is pushed into the front part of the probe, the end of the resistors look like they are almost an inch inside and the two metal tabs on either side of that piece makes good contact with the two metal threaded halves and pretty much enclose any live parts inside the tube. All metal shell parts and the coax shield inside the handle are at ground potential. At 1000:1 the maximum voltage at that end should be less than 40 volts so it should be fairly safe as long as it is connected to a meter. I assume the second (ground) lead going to the resistor assembly is to a safety resistor across the output to limit the maximum voltage if there is no meter connected.I don't know how far the shield goes inside the front part of the probe but the drawing of the Tektronix probe shows that that one goes about 3/4 of the distance to the tip. The coax connects to the end of that assembly with a BNC connector and that probe is assembly is sealed. To achieve the full voltage rating with the Tektronix p6015 (non "A" version) you had to open the sealed assembly and pour freon in it. The "A" version used more environmentally friendly silicone oil. I had used one of the old versions and they worked well but were a pain to maintain.

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 06:58:40 am
content: Had a look at the space within the current tip and roughed in the planned Resistors as per the cutaway below and have shown the maximum voltage and distance from the hand. There would be room to allow a thin copper tube perhaps covering up to 1/2 way into the 90MOhm resistor. Inside that tube would still be the multilayer wrapped PLA tube already made. Another option would be some tinned copper sleeve which I already have from some RFI shielding, it could easily be expanded over the last section of inner tube then soldered onto the common Earth/0V wires.I most likely won't see the Resistors this side of the coming weekend so plenty of time to tweak and remake a section or two.** I am getting 90, 400 and 500 MOhm resistors so it will be 100:1 not 1000:1

author: PartialDischarge
author_rank: Super Contributor
timestamp: April 23, 2019, 08:00:32 am
content: Quote from: ArthurDent on April 23, 2019, 04:02:17 amThe workings of the p6015 series are different, it is a compensated oscilloscope probe and the shield is not there for safety but to 1) isolate the internal high impedance resistor from external fields, and 2) create a internal cylindrical volume where fields are controlled and HF compensation can take place.I do not think the fluke dmm probe has the resistor covered but theres an easy way to know. Connect the probe to an oscilloscope using a banana-bnc adapter with vert scale set to 10mv/div. Now grab the probe top part with your hand and see if you can see a 50Hz signal in it. Given the thin diameter of this probe I do not think it has this part shielded.It is mostly forgotten that any high valued resistor is a 50Hz nice pickup.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 23, 2019, 08:13:16 am
content: Quote from: beanflying on April 22, 2019, 12:13:50 amI also noted he determined the series resistor value on a low voltage range.I seem to remember that many DMMs have lower internal resistance on such ranges, with the high range resistance around 10/11M .As far as I know, my old Fluke 77 has the high value on all ranges, but ! may be wrong.

author: bd139
author_rank: Super Contributor
timestamp: April 23, 2019, 08:14:19 am
content: Fluke 7x and 8x meters have variable impedance on each range. It's "around 10-11 meg" and varies from meter to meter and range to range. This is one reason I originally bought a Keysight U1241C as it has constant across all ranges. Shame it otherwise sucked.

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 08:19:18 am
content: Quote from: bd139 on April 23, 2019, 08:14:19 amIt is mentioned and tested in W2AEW (Alan's) Youtube video I put up back on page one closest to 10MOhms at the highest range. Also confirmed on the 121GW it is closest to 10MOhms on the highest range. Partly why I opted for 100:1 over 1000:1

author: vk6zgo
author_rank: Super Contributor
timestamp: April 23, 2019, 08:24:37 am
content: Not that it matters with commercial probes, because you always use the highest range.Many older probes were designed initially for VTVMs which do maintain the same input impedance .That said, I have even seen ones designed for use with AVO Model 8s.The most interesting ones came complete with their own display, in the form of an "Electrostatic voltmeter".

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 08:28:58 am
content: Quote from: vk6zgo on April 23, 2019, 08:24:37 amInteresting Pintek is still making a version of something similarhttp://www.pintek.com.tw/product_detail/landersound/index.php?Product_SN=19263&Company_SN=6002&Product_Site_Classify_SN=17071Making something similar with a modded handle wouldn't take a lot mainly a case of sourcing a good quality movement. The Digital one given cheap DMM's I wonder about even more

author: vk6zgo
author_rank: Super Contributor
timestamp: April 23, 2019, 09:44:45 am
content: Quote from: beanflying on April 23, 2019, 08:28:58 amI have used one like in the first picture, but the Electrostatic ones were different again.The display unit was remote at the end of an insulated lead like the DMM/VTVM with a normal one, but the electrostatic meter had a light source & optical system which projected the meter position onto a wide curved display screen on the front of the unit.The cases of these units were painted flat silver, & had a strange curved "streamlined "shape,which, together with the probes, gave them very much a 1960s "Doctor Who" appearance.I don't remember seeing them used, & now, I wish I had taken a photo of them, just for their "weirdness coefficient"!

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 09:57:06 am
content: There is some odd ones out there.Having a trawl for Capacitive and higher frequency dividers and came across this (Page 15)http://hparchive.com/Catalogs_Specialized/HP-Catalog-195x-UHF-Equipment.pdfMy 427A Manual also mentions the 11039A (was 452A) Capacitive Divider but I cant seem to find it in any details on it. HP also seem to have had a preference for dropping a 1MOhm resistor across the probe to get to their 1000:1 for their resistive ones which would help with the meter variations.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 23, 2019, 10:55:45 am
content: Here's the electrostatic meter I referred to (3rd pix down), along with a lot of other oddities.https://sites.google.com/site/squirrelsanonymous/scientific-laboratory-instrumentsI used the HP 11042A along with a 410c to check the output power on TV transmitters of up to 2kW ( from memory).

author: ArthurDent
author_rank: Super Contributor
timestamp: April 23, 2019, 12:18:52 pm
content: While not a 'probe' in the usual sense, this HV resistive oil-filled divider I picked up for $1 at a fleamarket works if used with great care and proper termination.

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 12:51:57 pm
content: Cool old tools.I will resist adding them to my Evilbay searching 'for now'Finally off the printer after last nights random issue. I suspect it may have come loose from the print bed and made the Z axis skip up so this one was printed with a Raft and Brim (3D nerdishness) to help it stay stuck to the bed without any other supports. Empty like this it is just over 200g in weight and balances just in front of the Black hand guard. Bit more Cleanup and Epoxy coating next.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 23, 2019, 01:50:15 pm
content: Looks nice. Testing it will be fun.. I think I would just try your other parts with a car coil and see how it behaves. You should be able to get 40KV pretty easy this way.This is another antique HV meter. I think it can read up to 100KV.

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 02:03:50 pm
content: I think the PS on my small Laser Cutter is 15-20kV and I have a Neon transformer that will be over 12kV and I can run it up to over 1kV on my Calibrators first so soft start then get something more to getmedievalJoeQSmith on it

author: joeqsmith
author_rank: Super Contributor
timestamp: April 23, 2019, 02:10:38 pm
content: A 50/60Hz neon sign transformer would be a good one to try. I wouldn't even assemble with the resistors. Maybe just put the wires on on the two ends. You could attempt to measure the current through it. Obviously a bit more risk. Anytime I play with these, I do it remotely..

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 02:38:11 pm
content: What is your thoughts on a Uni-T 210E measuring current on 10kV Plus wiring?oror

author: joeqsmith
author_rank: Super Contributor
timestamp: April 23, 2019, 03:33:09 pm
content: I think if you are measuring mA+ leakage current through your plastic parts, something major is wrong!!With your 12KV neon sign transformer, that would only be 12M and your plastic parts would dissipate 12 Watts! Then again, my math is not great so double check.

author: BravoV
author_rank: Super Contributor
timestamp: April 23, 2019, 04:44:07 pm
content: Quote from: beanflying on April 23, 2019, 02:03:50 pmReally tempting, as I just acquired recently a NOS 15kV neon transformer too, thanks for sharing these.

author: ArthurDent
author_rank: Super Contributor
timestamp: April 23, 2019, 09:10:46 pm
content: Warning! If I recall correctly, a neon sign transformer that has an output above about 7.5KV has a secondary that is centertapped and the centertap is grounded to the metal base. If you plan to use a neon sign transformer, then check it out to see if this is the case. I don't have a neon sign transformer but check it out before you power up the transformer. Oil burner igniter transformers may be centertap grounded as well. If you have a c.t. transformer and connect your meter common lead to one of the transformer terminals you could have a big problem.Google it for more info. Also trying to disconnect the c.t. and ground one of the output terminals can cause transformer insulation failure

author: vk6zgo
author_rank: Super Contributor
timestamp: April 23, 2019, 11:41:39 pm
content: I'd like to have one of these:-https://www.ebay.com.au/itm/L-M-Ericsson-Pty-Ltd-Trimax-Division-Model-52C-Ionisation-Tester-Type-G1B-/202602664145Just about everywhere I worked had one, so there were plenty around.The eBay one is a bit too costly for me, though!Grays Online auctions have one, too, but they always insanely overprice everything.

author: beanflying
author_rank: Super Contributor
timestamp: April 23, 2019, 11:51:25 pm
content: Quote from: ArthurDent on April 23, 2019, 09:10:46 pmYou are correct at least in the case of mine about the centretap. While that information is available fairly easily it might be a good idea to add some additional appropriate safety information/links on HV probe use and safety but there are a lot of testing cases to cover. There is also a lot of bad information out there to try and counter

author: beanflying
author_rank: Super Contributor
timestamp: April 24, 2019, 04:01:16 am
content: Just a few design details on the handle end. Currently takes 80x20mm PCB's with plenty of room above the board location and is setup for a small cable gland on the bottom. I might change the sizing and part for it as some idiot used a 13x1.25mm thread pitch on this oneCreating non standard threads in Fusion is a PITA!

author: joeqsmith
author_rank: Super Contributor
timestamp: April 24, 2019, 04:31:12 am
content: I was thinking just start by applying the signal across the two ends of an empty probe body and see if you can measure any current through it.If you have an electrometer, maybe try and measure it that way.Yes that shield on my probe is there for noise andpreventcoupling to any stray objects. It has nothing to do with safety. Even the GDTs are not there for safety. My only concern is to protect the scope's front end.

author: beanflying
author_rank: Super Contributor
timestamp: April 24, 2019, 05:08:25 am
content: Really Quick and dirty test at 1kV AC and DC uncoated and uncleaned after being handled trimmed/sanded etc by me without gloves. Poor leads and poor techniqueDC 0.00mA @ 1kV.AC @50Hz 1kV 0.00mAAC @1kHz 1kV 0.24mAGiven the setup that stray current may be coming from elsewhere into the 121GW other than via the Valhalla. That said the Valhalla needs a Cap replacement and a proper going over and I haven't hooked up my Micsig HV probe to look at the wave at higher voltages. My 344501A and 34461A are not back from Keysight Cal yet (should have them next week). May is Recalibration and testing month for the fleet.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 24, 2019, 12:50:34 pm
content: DC 0.00mA @ 1kV.AC @50Hz 1kV 0.00mAAC @1kHz 1kV 0.24mAYou lost me. The meter's switch is set to A/mA and the leads are connected to the Volts input.If I assume that everything was setup correctly when you took the actual measurements, with the 1KHz@1KV signal, if you just removed the red wire from the probe body as shown and let it rest on the wooden stool, does the current drop?I made some posts about testing some capacitors for leakage. One problem I ran into was how much my test jig would leak (the colored boots). Ended up floating them from the case with some Teflon. With you working in the 40KV level, I assume you are going to have some head room. Maybe double that? You may find that the materials cause an error in your measurements.https://www.eevblog.com/forum/testgear/using-low-voltage-levels-to-test-hv-capacitors-leakage-current/25/

author: beanflying
author_rank: Super Contributor
timestamp: April 24, 2019, 01:00:52 pm
content: oops brain fart due to being in a rush grabbed the meter off the bench and forgot to swap. Tomorrow job I will have some free time and do it properly

author: joeqsmith
author_rank: Super Contributor
timestamp: April 24, 2019, 05:45:49 pm
content: This makes more sense. Look forward to the actual numbers. At 1KV, I am expecting the 121GW not to detect any thing but you never know.

author: kony
author_rank: Regular Contributor
timestamp: April 24, 2019, 07:13:58 pm
content: Someone notify the Darwin awards commission, they might get a special serial entry brought you by the open source community (TM).No, NO, and FUCK NO to the material and manufacturing selection for the insulator of the probe. Having dealt with reliability of manufacturing processes of 20kV PSU assemblies in the past, I am very painfully aware of how deep the rabbit hole goes to even start thinking about passing the design for production after several iterations of debug and validation of BOTH the design and manufacturing process. And you are attempting to get this out in a way such everyone can wing it with the leftovers just lying around? Gotta be shittin me! I am sorry, but I am not sorry for my languague, it is fully apropraite for the magnitude of the possible consequences this can have.OP, do you have a single fucking clue about the E field distribution on the probe insulation, what air pocket inclusion or surface defect or grit contamination will do to it? Sensitivtity to moisture, long term stability of the plastic (selection of which you, BTW, have absolutely zero control over)? Corona resistance of the material should partial discharge occur - and what certanity is there it won't avelanche in the degradation? How about air gaps in the insulation to the center isntalled divider or elsewhere - do you at least understand what relative permitivity discontuinuity implies for local electric field magnitude?Can you imagine the consequences of some poor bastard using such thing handheld on hard power supply?

author: beanflying
author_rank: Super Contributor
timestamp: April 25, 2019, 01:46:02 am
content: Moving right along to some actual practical testing and data. Two Coffees this morning after a 4.30am Possum Roof visit, wiped the seat and Neon Transformer over with IPA, probe as per yesterday uncleaned etc. 121GW plugged into the mA jack and had the correct range selected** I do have an issue with the Valhalla it seems on the 1kHz range it is clearly spraying noise as I was getting a current reading with the 121GW unconnected as per the pics below.Feeling a little brave for the inner smoke on the 121GW I broke out the Neon Transformer to raise the stakes a little. 6+kV to Ground and 0.0000 mA so I am feeling happier about where I am heading. Forgot to take any snaps of in on the Fluke but Zero @ 1kV DC.Photos remind me I must clean up and repaint the outside of the Neon.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 25, 2019, 03:07:24 am
content: Looks like a nice old transformer.You could try using the uA range as well. Can you go across the output of the transformer instead? You could also try a shorter distance. Maybe try going through the sidewall of the case.

author: beanflying
author_rank: Super Contributor
timestamp: April 25, 2019, 03:36:55 am
content: Transformer is an Allanson 277V, 60Hz, 15kV, for anyone playing along at home (Running nominal 240-250V in my case)I have started prepping the Probe for Epoxy coating so no more testing for a bit. Floating a decent DMM that far above ground was worrying me so I didn't. I do have a couple of old Victor 86B's with mA and uA ranges that I care quite a bit less about so maybe I will look at that when the coating is done.Having a look at what ArthurDent raised I think I will extend the inner tube further toward the handle by a bit at a reduced diameter again and add some Tinned Copper Sleeve and bond it to the Earth and LV connection to the meter to it. Belts and braces a bit but it certainly cant hurt.I have ordered some more PLA which should be in tomorrow and I have planned to print a second one as a Chicken stick for the Neon Transformer with HV cable going in right at the tip part of a Lanthanum TIG electrode (longer barrel again). While I am going I can do a second barrel with multiple points to connect to along the Barrel.Easy to add these as small raised knobs or holes/divots to help connect to? Let me know what may work best?For interest I have attached some cutaways of the actual Sliced Gcode for the upper Barrel. It was 6 inner and 6 outer layers and it is well down into the tip before there is any infill/voids. They could be eliminated easily if it looks like being an issue with a simple setting change to the infill from 40% to 100%.

author: tggzzz
author_rank: Super Contributor
timestamp: April 25, 2019, 06:23:42 am
content: Quote from: kony on April 24, 2019, 07:13:58 pmSome of us have tried asking pointed questions, and been rebuffed, and bowed out of the discussion.

author: beanflying
author_rank: Super Contributor
timestamp: April 25, 2019, 07:29:50 am
content: I chose to roll past Mr Fuck this that or the other before as he offered no factual information to back up spurious claims that would be true of HV probes commercial or otherwise in the hands of a numpty. If we use this thinking anyone who spends money on evilbay or aliexpress and buys Probe X can injure of kill themselves and that's ok?It is really simple SHOW ME EVIDENCE of the material or process not being suitable. When offered video of the material being tested under HV for breakdown you didn't watch and then went on again without looking further for yourself. You chose to dimiss the people as 'Talking Heads'. When offered further information about the material you went on again with no evidence to back up your claims about it.QuoteI have done some additional research into moisture and all plastics absorb water to a greater or lesser degeree with Teflon being a bit of an exception. The ABS for example used in a lot of these probes commercially will hold water in the order of 0.2-0.3% based on my reading and for PLA it seems to vary but at around the 0.4-0.6% range is what I have read and all plastics absorb more moisture as the Temperature rises. What have you done and what did you find?You have sought at every possible point to add zero constructively to the project and only tell the world it cant and shouldn't be done because you say so.As I thought may be obvious by now I have a set of files ready for release that work and quite deliberately haven't and won't be generally releasing them until I am happy that tests carried out be me and hopefully a few others independently give more confidence in the design.

author: The Soulman
author_rank: Super Contributor
timestamp: April 25, 2019, 09:33:58 am
content: Quote from: beanflying on April 25, 2019, 07:29:50 amEngineers are used to it being the other way around.

author: beanflying
author_rank: Super Contributor
timestamp: April 25, 2019, 09:57:30 am
content: Quote from: The Soulman on April 25, 2019, 09:33:58 amWhich is why it is up here and being tested against what available evidence there is and open for others to have their input. Science and Engineering are not based on who can hurl the loudest and most frequent abuse or post non evidence as fact.PLA being a relative newcomer is worthy of additional scrutiny and as I have mentioned before there is always ABS which is a more known material.

author: kony
author_rank: Regular Contributor
timestamp: April 25, 2019, 02:37:24 pm
content: Defend your design, not your ego && faith, OP. The burden of prooving the due diligence being done for the design is on your side.If you provide something that ressembles design calculations and documentation, I am fully willing to provide more detailed constructive feedback, but right now I don't even see any signs of understanding of the fundamentals.

author: HighVoltage
author_rank: Super Contributor
timestamp: April 25, 2019, 03:20:34 pm
content: Nice design !I would not worry too much about the insulation material. I have seem commercial HV probes with PVC insulation tubes and they are just working perfectly and are safe. Almost any good insulator material would work, as long as you keep the distance to your high voltage spot large enough.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 25, 2019, 06:08:02 pm
content: Some time ago, we had bought some sort of plastic to machine some parts from. These parts were used in a high voltage application. Once they were made and installed, we noticed that the system was having a problem. The new plastic parts were presenting a decent load. I pulled the remaining raw stock and sure enough, it was fairly conductive at DC. The properties of the plastic chosen wouldn't have suggest it would behave this way. In the end, we bought another slab of the same material and it was fine. I never took the time to dig into why that one lot had a problem. Something in the mix. I can only think of one case like that in my entire career.Most of the commercial probes similar to what is being shown will state in their manuals that they are for CAT I only. For my own personal use, pretty much everything it CAT I and very low energy. Fairly low risk for the most part and certainly something I am willing to accept.Back to the scheduled program...

author: beanflying
author_rank: Super Contributor
timestamp: April 26, 2019, 01:22:23 am
content: Quote from: kony on April 25, 2019, 02:37:24 pmPlastics vary electrically even engineered or injection molded ones and generally have upper and lower limits. As such no I have not done definitive calculations, in particular as there is limited data on PLA would fairly pointless. I have not seen upper and lower limits even for Engineered PLA just 'typical' or Calculated from Experiment. So Empirical evidence is what I am basing this design on using what limited data has already being linked in this thread. As I have said happy to look at EVIDENCE or Data if anyone has any.Moving along again as I am not a huge fan of drumsticks and random lumps of wood from the corner of the garden shed with nails in the endA first pass of a High Voltage Corona probe. Lanthanide Tungsten (DO NOT use Thoriated ones!) Electrode, Ceramic insulator, HV rated cable. I have gone this way to increase physical separation to the hand to the HV and any resulting Arcs. Base of the Electrode is 300mm from the Hand.And no you can't eliminate the second long barrel and shorten the design they are different Thread diameters.WARNING Even if you are a Dumbass don't play with Microwave Oven Transformers with any stick or probe. Unregulated MOTS Kill !

author: vk6zgo
author_rank: Super Contributor
timestamp: April 26, 2019, 03:58:19 am
content: Quote from: The Soulman on April 25, 2019, 09:33:58 amMaybe in modern times, but Engineers were, in the past, very much in the forefront of finding what materials were most suitable for such use.This was mainly using real world tests, so most of the evidence of "what works" comes from as much empirical testing, as from any knowledge supplied by the manufacturers of the materials.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 26, 2019, 04:24:48 am
content: Quote from: joeqsmith on April 25, 2019, 06:08:02 pmThere are many interesting properties of various materials, which sometimes seem counter intuitive.An FM transmitter broke a porcelain standoff insulator in the driver stage.The real part was forever away in Norway, so I dug around & found a piece of what looked exactly like PTFE, & fashioned a new one.Turning the Tx on, it came up OK, but after a few minutes dropped in power markedly.On investigation, the insulator now looked like a "Cocoa Pop".Whatever it was, it wasn't PTFE!At home, later, I found a suitable porcelain insulator in a box of some National HRO receiver parts, so the beast was returned to service.(A short interval for vintage Radio fans to burn me in effigy!).Cad plated steel screws usually don't fare well in RF environments,(both MF & VHF), & there are reports of Nylon getting quite hot in the same environments.

author: beanflying
author_rank: Super Contributor
timestamp: April 26, 2019, 04:35:29 am
content: Quote from: vk6zgo on April 26, 2019, 03:58:19 amSome of us also went through the Victorian Technical School system before it was Kennettedso we learned a large bunch of practical hands on Engineering method as well as Maths and Science before getting to Uni.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 26, 2019, 06:08:33 am
content: Quote from: beanflying on April 26, 2019, 04:35:29 amYeah, the WA Tech School was good value, too.In fact, I think that was where I saw the EHT probe machined out of solid Perspex that I referred to earlier.The main "Perth Tech" that I went to was an old building in St George's Terrace, Perth.To get to the Electronics section, you walked through that building, down a lane between a bunch of Ex WW2 transportables & some weatherboard buildings, where all sorts of stuff went on, from training cooks, to running a massive steam engine for the guys doing "Heat Engines 1 & 2".(Steam would come out of the gutter)In another building there was "hands on" use of a fair sized Radio Transmitter.(We did Semiconductors Lab in the same building, & a uAmmeter carefully set up to read base current would go full scale if the guys next door fired up the Tx)At the other end was a red brick building, in the sub-basement of which Electrical Engineering had a large quantity of rotating plant, & ancillary test equipment, again, "hands on" for students doing the relevant courses.From there it was up two flights of stairs to where we had our lectures.You really felt like you were learning stuff there, none of this "monkey see, monkey do" crap!

author: joeqsmith
author_rank: Super Contributor
timestamp: April 26, 2019, 01:42:34 pm
content: Quote from: beanflying on April 26, 2019, 01:22:23 amOf course the cap can get you as well. Just a quick search, many are attempting repairs, one some guy burning wood and one a kid trying to replicate a YT video.https://www.wkyc.com/article/news/local/lorain-county/teen-dies-from-homemade-science-experiment/145431142https://www.northjersey.com/story/news/passaic/passaic-city/2017/08/24/passaic-man-killed-after-being-electrocuted-while-fixing-microwave/596748001/https://www.union-bulletin.com/local/local-man-electrocuted-using-dangerous-wood-art-process/article_daf59a2a-3420-11e7-8508-c7eb2f3dc175.htmlhttps://www.brownsvilleherald.com/news/local/man-fatally-electrocuted-while-repairing-microwave-oven/article_d0749396-3b1a-52f3-9201-65bce57008b3.htmlhttp://www.walb.com/story/19823265/update-deadly-microwave-was-not-plugged-in/https://dailyegyptian.com/21717/archives/student-dies-in-microwave-electrocution/https://www.cdc.gov/niosh/nioshtic-2/20026141.html

author: beanflying
author_rank: Super Contributor
timestamp: April 27, 2019, 02:58:46 am
content: So many needless ones and that is just the tip of the list. Lichtenberg wood burning is just asking to die unless you are very knowledgeable and well set up. For those that haven't seen it done High Salt content water and HVOT but on the grounds it is my Topic. NST Jacobs ladder Saddle (will suit any 4" wide units) and slide adjustment for the electrodes. 50+mm minimum Vertical separation to any metal parts. Two small inverted heatsinks to make sure any heat is kept from the PLA mounted on two pairs of sliding mounts. Could easily be mounted on a board away from the NST too. About 1/2 way into the main saddle on the little Ender Pro.The Corona Probe version is ready for a test too but I am tied up for the day but will get to it later maybe.Edit Added photo. Starting to get the bits arranged for the inner of the voltage divider probe. Ohmite Resistors as discussed earlier and Tinned Copper sleeve.

author: beanflying
author_rank: Super Contributor
timestamp: April 28, 2019, 07:52:00 am
content: 24 Hours of print time later the NST Jacobs Ladder Saddle is finished, tested and works as planned. I did try attaching on the front fin to Earth but didn't get any current reading which is to be expected as it has more isolation due to the ceramic insulator at the tip and increased distance. The slides on the saddle allow for shorted to 20mm+ of gap which won't jump without the probe.Nothing new learned in particular just a few more safer/nicer bits than I used to have added to the kit. I will be stripping the probe shown down for the same epoxy coating treatment as the divider one. The NST Saddle will likely get the same treatment and time to repaint the NST outer shell.** All Test Gear in the shack was unplugged during this playing.https://youtu.be/Qx7eH9snu3U

author: Helix70
author_rank: Unknown
timestamp: April 28, 2019, 09:41:27 am
content: I work on MV switchgear products for the outdoor market. We rapid prototyped a housing using fdm printing using abs. It's dielectric withstand was terrible. It isn't the abs that's the issue, its the partial discharge due to the air trapped in the print.I certainly would not hand hold a probe that was printed to the same dimensions as a proper vacuum molded silicon HV probe ( MV actually), I wouldn't trust it.My two cents.

author: beanflying
author_rank: Super Contributor
timestamp: April 28, 2019, 09:48:41 am
content: Quote from: Helix70 on April 28, 2019, 09:41:27 amDo you have any figures on that? Were you using a Hipot tester or what for your testing would be interesting? ThanksSort of relevant too if you believe it was air causing the issue was your enclosure printed with walls thick enough to allow infill? As shown a page back the barrel tips have virtually zero infill until well back from the tip other than any under extraction (poor setup) that may occur.

author: Helix70
author_rank: Unknown
timestamp: April 28, 2019, 10:10:40 am
content: We have a 110kv capable transformer/capacitor in a chamber that we use for power frequency and partial discharge. We also tested at our lab in Germany for BIL of 170kv. Basically our magic number is 50kv for power frequency testing, and the partial discharge was really bad. Due to the size, our infill was not 100%, so yes that is not good, but even 100% infill will lead to bad partial discharge performance. That's why everyone in the industry uses silicon. HV stresses are just not good.We ended up flashing over and blowing a hole in the side of the printed housing at about 75kv, but that's another story.

author: beanflying
author_rank: Super Contributor
timestamp: April 28, 2019, 11:04:24 am
content: Thanks for the extra information it's fairly hard to come by and first handWent and got my fairly ordinary Victor out of storage which I should have done before getting started on this project. The sections as tested have a chunk of 40% infill in them and are from the probe I was playing with in the video above. 5kV test on 200GOhm range.Anyone with serious test gear and a printer and who is interested in punishing some bits PM me. Or even anyone in Oz PM me and I will post you a printed set to abuse.Edit some dummy forgot the picture. 200+ Gohms at 5kV

author: PartialDischarge
author_rank: Super Contributor
timestamp: April 28, 2019, 04:04:59 pm
content: Quote from: Helix70 on April 28, 2019, 10:10:40 amfor MV or HV use things have to be pressure casted or vacuum filled, no other optionQuoteThat's to expect. That's why I pointed in an earlier post that the kind of probe designed here would be ok only for low energy sources and to be used for small periods of time, because partial discharges are no problem for short term use, since it takes months or years for faulty materials to fail due to partial discharges.QuoteSiliconeis mostly used in outdoor bushings for its superiority in non-stickiness to dirt, which is a problem in porcelain, and can not be casted as silicone rubber, when grading rings or other components are present inside the bushing.By volume however I'd say that most MV 'stuff' (interior and exterior) uses epoxy.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 04, 2019, 02:30:16 am
content: Have you made any further progress on your probe?

author: beanflying
author_rank: Super Contributor
timestamp: May 04, 2019, 02:38:17 am
content: Life has been in the way.Will assemble the Divider insert and take some pics of it as I have all the bits needed. The Probe front end itself is now epoxy coated and I have a few more Rolls of Black so I will reprint the handle end as I have tweaked some of it internally.

author: ArthurDent
author_rank: Super Contributor
timestamp: May 06, 2019, 05:49:35 am
content: Here are some photos of the old HV probe I mentioned in post #34 to show the construction details. In the photo that shows the metal shield on the handle you can see that the address has no ZIP code, which I recall happened around 1962, so that somewhat dates the probe. I believe the rating of this probe is 20KV.The first two photos show the various parts and will give you an idea how they fit together. The shield of the probe cable securely contacts the brass tube that slides inside the entire handle. The small spring goes in the hole near the front of the handle to contact with the brass tube and you carefully hold it compressed while you slide the finned guard with the metal shield that the other end of the spring contacts with into position, then screw the front half of the probe into the handle. When the brass tube and the inner lucite insulating tube are seated all the way inside the handle there is about 0.75 inch of this inner lucite tube that slides inside the front lucite half of the probe so there is pretty good overlap and you won’t have a path for breakdown at the front of the grounded brass piece. So the way this probe is designed there is a complete metal shield between your hand and the HV. If there was an arc-over the grounded shield would protect your hand.An interesting side note is that I went to a hamfest this past weekend and just before I left, at the last table I checked, was a Fluke 80K-40 HV probe brand new in the sealed plastic. The price was much higher than on eBay so I left without it.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 19, 2019, 12:04:17 am
content: Quote from: beanflying on May 04, 2019, 02:38:17 amAbandoned your efforts? I would sill like to see a few pictures of the coated parts.

author: Kosmic
author_rank: Super Contributor
timestamp: December 10, 2019, 04:30:55 pm
content: I did some non-scientific electrical tests with a PLA filament. Connected 1.2 cm of filament to my Genrad 1644. Tested a 1Kv on the Tera Ohms range. The filament wasbeforehand washed with IPA and gloves were used for manipulations.- At room temperature I was reading 1000 TOhm (pretty much the limit of the instrument)- Now heating the filament at 100C at almost no effect.- Heating at 200C I saw a very little drop in resistance.- Now at 300C for some time the filament was starting to melt and resistance dropped to something like 750 TOhm.I was expecting a drastic change of electrical characteristics at high temperature but in the end, it was pretty moderate.

author: Kosmic
author_rank: Super Contributor
timestamp: December 10, 2019, 04:43:18 pm
content: In comparison, with a similar piece of PTFE I can't detect any resistance (infinite) and heat do not really affect the results.

author: trobbins
author_rank: Frequent Contributor
timestamp: December 11, 2019, 04:24:34 am
content: I was a bit surprised that some simplified testing of the solid insulation resistance of significant sections of a probe didn't appear until post #115. But even that 5kVdc test, as shown by the photo, appears to be poorly configured. Testing should I suggest be about wrapping foil around one surface region, and the other relevant surface region - whether that be for checking creepage as well as bulk resistance as shown, or by making an internal surface that coats the inner tubing, or about covering the entire handle region. Foil wrapping was the standard technique for testing PD and breakdown of telephone handsets in days of yore - certainly for Telstra and EPR issues.I would think the advantage of 3D printing would be more towards a lower kV probe, but with designed-in shielding to allow experimentation for flat compensation out to kHz plus range, as that is where the commercial probes get expensive for DIYers. Designing in protective earth tubing, and even an additional redundant earthed handle would similarly seem to be worthwhile, plus some compartment allowance for compensation parts and additional protection parts such as MOVs to shunt any fault to redundant protective earths.

author: tautech
author_rank: Super Contributor
timestamp: December 11, 2019, 04:33:38 am
content: Quote from: trobbins on December 11, 2019, 04:24:34 amYet if someones scope is inadvertently floated due to a poor or NO mains earth there would be no protective gain.Better to use the foil wrap test you suggested and so prove there is no HV leakage.

author: james_s
author_rank: Super Contributor
timestamp: December 11, 2019, 05:40:45 am
content: I think some perspective is needed when evaluating this sort of thing. Would I use a home made 3D printed HV probe to measure the primary of a distribution pole pig or a 50kVa 150kVp xray transformer? Heck no, but for the sort of hobby HV stuff most of us are likely to encounter? Sure, why not? I played with CRT flyback transformers and neon sign transformers for many years using various scraps of plastic and strings of 1/4W resistors before I got a proper Fluke HV probe. It is seriously over-engineered for typical hobby stuff but it came in handy when I wanted to measure the output of MOTs and later the 4160V output of a pole pig we were using to power a HV series streetlighting regulator used for testing some products I was involved in. These sort of not only high voltage but high energy things is where it's worth splurging on the real deal.

author: trobbins
author_rank: Frequent Contributor
timestamp: December 11, 2019, 12:10:43 pm
content: Quote from: tautech on December 11, 2019, 04:33:38 amI am a fan of redundant protective earth connections. Extra effort, but making any such measurement requires a set of precautions when setting up.