Lair Of The Multimedia Guru

September 20, 2018

Testing high voltages

The chinese negative ion generator i used in 3d-printer-particles-air-pollution made me a bit curious about what voltage it outputs. The page from the seller mentions several different values, 2-5kv, 5-8kv, 5kv and other things. So one wonders what it actually is. This sadly cannot be directly tested by just using a normal DMM as its a bit outside the supported voltage range of the average DMM. High voltage probes for DMMs exist but even chinese ones seem to cost at least ~70€ and i wouldn’t trust them safety wise. So lets make one for 1€ which we can trust to be unsafe.
We start out with a inappropriate high voltage probe enclosure, which we disassemble and remove the unneeded parts:

The innards of our HV probe is simply a 90MΩ resistor, which will together with the internal 10MΩ resistance of the DMM form a 10:1 voltage divider, extending its input range.

Lets try:

1470V, hmm
Checking what output saftey resistance this device uses:

It seems its something around 20MΩ, maybe 2 10MΩ resistors ? Its potted so no easy way to tell exactly. But this changes our output voltage estimate as now our probe effectively is 110MΩ instead of 90MΩ. That raises it to 1764V, but it still feels a bit lowish to me. Also the 120MΩ to ground would draw 15uA, which could pull the voltage down by an unknown amount. This ionizer thing after all is not intended for producing any current.
To test for this we can use a higher value resistor. I do have a 1GΩ resistor (though it cost more than 1€), with it we get:

Aha, 4270V, so the 15uA does in deed quite significantly pull the voltage down. Now with 1GΩ we still pull 4uA here so this is likely still a too low estimate. Sadly i do not have a higher value resistor ATM.
What remains is to check that the 2 HV probe setups actually work at all, we must test this as we cannot be sure the DMM behaves as expected in this setup.

Both produce expected values at a 1kV test input, the voltage appears to be slightly below 1kV though.

at a 500V test input the value matches much better indicating that indeed the 1kV test output seems lowish

disclaimer: high voltage is dangerous, do not play with it or replicate anything described above. If you do anyway you do so at your own risk.

Filed under: Electronics,Off Topic — Michael @ 10:39

September 10, 2018

Copyright EU #4

In 2 days (on 2018.09.12) The next vote on the copyright directive in the EU Parliament will occur.
Resources about the draft, which IIUC will be voted on are available on If you live in the EU and feel that this proposal is bad you can use to contact your representatives.
There are also 252 proposed amendments, iam not sure these will be voted on or not (i thought they would but the timeline seems too tight to really do that).
Also there will be EU parliament elections in a few months. If you live in the EU and care about this, check how the parties voted on this directive and other directives that may affect you before you vote on who you want in parliament. Politicians of all parties are very dishonest, only by looking at past actions can one with any accuracy predict what they will actually represent. No politician would ever say they intend to vote in a way that the audience of the moment dislikes.

Filed under: Uncategorized — Michael @ 18:04

September 9, 2018

3D printer particles / air pollution part2

When i experimented with measuring the amount of particles from my 3d printer, i noticed the majority originated from when the heat-bed was turned on. I had cleaned the inside of the printer roughly before, so this was slightly odd. More investigation shortly later revealed the cause though.

The use of tinned multi-core wire without ferrules. Why it was done this way you may ask? Because between the incomplete and poor official documentation, the consumer made videos of how to assemble it and my plain lack of knowledge about how multi-core wire with and without solder behaves in this case. This way of connecting the wires seemed sound enough and there also where no ferrules included with the printer kit.
That said if you did connect high current wires in a similar fashion, you probably want to consider redoing it with ferrules or in another reliable way, like directly soldering to the board or soldering a solid core wire onto the multi-core as an intermediate. Also keep in mind iam a programmer not a expert for this so do your own research if failure of a connection could have some real consequences.
My printer is fine, the heat-bed also didn’t behave erratically or anything. And i never trust/trusted it anyway in terms of safety to ever run it without someone being at home, so in my case it was impossible for this to cause any real harm. But i still didn’t expect that …

I didn’t had any fitting ferrules, so the way i fixed it was to take some terminal connector thingies, which when one cuts half of each off are basically ferrules. I also didn’t had a new terminal block that was rated for enough amps to replace the roasted one. I will properly replace these once i have proper replacement and have time. Quite likely next time that printer needs some kind of “service”.

Filed under: 3D printer,Electronics — Michael @ 17:09

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