Electronics > Projects, Designs, and Technical Stuff
Open HV Probe 40kV
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beanflying:

--- Quote from: Zero999 on April 21, 2019, 07:39:58 am ---Also note that the input impedance of most meters isn't that well controlled. I've found it can differ significantly from the stated 10M

A x10 oscilloscope probe should be much better though, as it will be designed with a definite 1M 'scope input impedance in mind.

--- End quote ---

Agreed 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.
beanflying:

--- Quote from: DaJMasta on April 21, 2019, 07:29:28 am ---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.

--- End quote ---

There 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.

tggzzz:

--- Quote from: beanflying on April 21, 2019, 07:26:47 am ---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?

--- End quote ---

I refer you to my first and subsequent posts (with my emphasis), and I am content to let others decide whether I am "dumping on process and materials"...

    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.
    The 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.


--- Quote ---PLA along with ABS are very well understood materials as is PETG. Please let me know how you arrive at 'poorly understood properties'?

--- End quote ---

The fabrication technique can be as important as the material, especially for uses like this.
tautech:
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.pdf

Image for comparison to ordinary probes:
https://youtu.be/W30AqcDQL18?t=18


But hey we need be careful with projects like these and those that follow them must know 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.
beanflying:
And some more 'actual evidence' and a study Study of electrical properties of 3D printed objects

and

https://www.sciencedirect.com/science/article/pii/S1876619616000565

Data on PLA (brand specific) https://ultimaker.com/download/74599/UM180821%20TDS%20PLA%20RB%20V10.pdf

The only downside would appear to be surface contamination and that to a degree is true of any materials regardless of process.

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