| Electronics > Projects, Designs, and Technical Stuff |
| Open HV Probe 40kV |
| << < (5/26) > >> |
| tggzzz:
--- Quote from: MasterTech on April 21, 2019, 11:40:16 am --- --- Quote from: tggzzz on April 21, 2019, 11:27:10 am ---It only contains dissipation factor and dielectric constant. Those are useful for assessing capacitance and HF losses, but have zero relevance to operation at 40kV. --- End quote --- Actually 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 --- End quote --- I 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 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. |
| bd139:
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. |
| beanflying:
--- Quote from: tggzzz on April 21, 2019, 11:27:10 am --- --- Quote from: beanflying on April 21, 2019, 10:33:06 am ---The Ultimaker data does contain electrical properties and goes toward what DaJMasta mentioned about actual datasheets on Filaments. --- End quote --- It only contains dissipation factor and dielectric constant. Those are useful for assessing capacitance and HF losses, but have zero relevance to operation at 40kV. Hence my statement that "The ultimaker data contains nothing relevant to this discussion". As stated it was meant for DaJMasta not you specifically as mentioned but IGNORED by you to score a supposed point about what they don't include --- Quote ---Far from being an 'poorly understood properties' but perhaps 'needing more study' is appropriate which is the broad NON Conclusions about aging and extended use they made. If you take there figure of 33kV/mm as a best case the tip of my design is @ 210mm away from the hand gaurd. So 170X my proposed maximum would be needed in theory be needed to get it to breakdown. The PLA would need to be compromised dramatically for 40kV to be an issue. --- End quote --- Engineers 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. --- End quote --- As 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? |
| beanflying:
--- Quote from: bd139 on April 21, 2019, 11:54:14 am ---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. --- End quote --- Even 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. |
| tggzzz:
--- Quote from: beanflying on April 21, 2019, 11:56:46 am --- --- Quote from: tggzzz on April 21, 2019, 11:27:10 am --- --- Quote from: beanflying on April 21, 2019, 10:33:06 am ---The Ultimaker data does contain electrical properties and goes toward what DaJMasta mentioned about actual datasheets on Filaments. --- End quote --- It only contains dissipation factor and dielectric constant. Those are useful for assessing capacitance and HF losses, but have zero relevance to operation at 40kV. Hence my statement that "The ultimaker data contains nothing relevant to this discussion". As stated it was meant for DaJMasta not you specifically as mentioned but IGNORED by you to score a supposed point about what they don't include --- Quote ---Far from being an 'poorly understood properties' but perhaps 'needing more study' is appropriate which is the broad NON Conclusions about aging and extended use they made. If you take there figure of 33kV/mm as a best case the tip of my design is @ 210mm away from the hand gaurd. So 170X my proposed maximum would be needed in theory be needed to get it to breakdown. The PLA would need to be compromised dramatically for 40kV to be an issue. --- End quote --- Engineers 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. --- End quote --- As the study I added was based on a using a Prusa Mk2 What is the difference in my 'homebrew' printing to their 'Homebrew'? --- End quote --- How the hell should I know?! If anything, it is up to you to determine that the prints are comparable. --- Quote ---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? --- End quote --- Please don't advance strawman arguments. I have asked questions. To me, the responses have not been answers. --- Quote ---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? --- End quote --- You 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 would far rather use that than a homebrew probe. But hey, it is your health, not mine! |
| Navigation |
| Message Index |
| Next page |
| Previous page |