I like how you straight talk about a subject rather than to feel you have to add a bunch of flare to entertain. If a person likes electronics and science then there is the entertainment. The education without games.
5:29 The blue, pink, green , purple or "Metallic" ESD bags are in fact totally non-conducting (are a isolator), exact the same as a normal plastic bag, but they have the abbility not to create static electricity and keep static electricity out of the bag. But once again, once a static charge is inside the bag, it remains there. If you place a component that carry a static charge inside a ESD bag, the component stay charged. This is the case with all semi-transparant ESD bags. Only the black ESD bags are slighty conductive, and these can slowly discharge a static charged component and keep it discharged. The black ESD bags contain carbon. Regarding the mesh arround the meter, this acts like a Faraday cage. It's the same as a person would stand inside a metal cage, and where high voltage is connected to the outside of this cage. The high voltage would not to flash over to the person. This is also how the metallic suites work that high voltage technicians use. Regarding the cage experiment with high voltage, there are pictures of that experiment on the www , where a person sitting on a chair inside the cage is reading a book/magazine, while a Tesla coil is creating major sparks to the outside of the cage.
"The blue, pink, green , purple or "Metallic" ESD bags are in fact totally non-conducting" and "Only the black ESD bags are slightly conductive". Thank you for that - I had read somewhere the that the pinkish ones had very think film metal coating but I guess not. You sure explained why I could not detect any non-infinite resistance with the ohmeter. I wonder whats in those bags to reduce static creation? I have seen some of the videos of HV techs in mesh suits being delivered to power lines on helicopters. Amazing job - but not something I would ever want to do! I'm planning a couple Faraday cage videos sometime .....
Just tried a black anti-static bag. You were so right - could even measure the resistance of the bag surface. And tried it around the voltmeter. No as good as the aluminum mesh - there was around a 2V variation around the 40V reading, but still a massive improvement over the uncovered voltmeter where readings jump from 40 to 80V. Here is 20 sec clip (unlisted, unnarrated) showing the results ruclips.net/video/YjP2q5bc96o/видео.htmlsi
The anti-static bags and anti-static plastic foam "peanuts" used for cushioning are conductive when given sufficient electric field strength. A quick test applying 10 kV from end-to-end of a white "peanut" about an inch long showed no current but the same test using a green "peanut" of similar size showed a current of 10 nanoamps.
@@analog_guy Interesting! I have seen pink ones conduct as well (as one might hope). Maybe conduct is a bit of strong term as 10nA is hardly anything, but enough to bleed static charge.
@@ElectromagneticVideos Yes, the pink ones behave like the green ones. There is just enough conductivity to rapidly remove or adjust any charge on the colored "peanuts". Since the white peanuts tend to accumulate negative charge due to their place in the triboelectric series, if they are placed on an electrode which is subsequently charged to a very high positive voltage, they will remain there, typically for quite a few seconds, until enough negative ions accumulate on the surface. In contrast, the pink and green ones will fly away immediately as they rapidly acquire charge from the electrode. I don't know if the additive in these colored "peanuts" also materially alters the triboelectric positioning.
I suppose it's a bit like the guard traces seen around op-amps and other sensitive circuitry on PCBs particularly high precision measurement instrumentation
I hadn't thought of that - great point - your absolutely right. In some of those circuits - particularly the very high impedance ones - even the tiny leakage from nearby traces can be an issue unless you protect it with guard traces.
Yet another great video, Dr. Jones! I was wondering how that problem would be resolved. Great info on the static bags as well, including the excellent comment by @BjornV78 about the different types of bags. I had believed the same thing you did about the metallic coating or metallic content. Thank you for all the planning and materials and efforts you put into this. Very educational.
Thanks Michael! Pleased I did find a solution to the issue - at least the measurement problem had a silver lining (or maybe Aluminum lining in this case :). I'm sure I read somewhere that nickel(?) was used to coat the reddish pink plastic bags. Who knows! It was great that @BjornV78 and @emilalmberg1096 where able to correct me on that and steer me towards the black bags. If you didnt see my response to their comments, I uploaded a 20 sec video showing the black bag as a voltmeter shield: ruclips.net/video/YjP2q5bc96o/видео.htmlsi
There is a trick to look through the window of a microwave oven. It's similar to the metal mesh. Move your head left and right slowly. But I'm sure everybody knows this.
I think a bit of edge sharpening in the camcorder made the mesh harder to see though in the video. It was easier to see in real life. But thanks for the tip on how better to see if you can move your head (or camcorder!).
Hi. Having built my bench isolation transformer, I know that electricity wants to go back to its source. So then why is there a corona even when the HV transformers' secondaries are isolated from ground?? Where is the electricity trying to go? Birds aren't affected by this. Why is your meter?
I wonder if this is due to the fact that ground is so close to the DMM? The further away from ground the better is might get possibly? Excellent question!
As @ThriftyToolShed said, great question! The HV secondaries in this setup actually have their neutral to connected to ground and the entire table that everything is sitting on (actually a table saw bench) is metal and grounded. So the electricity is trying to to get to anything that is grounded. But even if the secondary was not grounded, you would still get a corona type effects happening. What happens is there is an electric field from anything attached to one side of the HV secondary to everything attached to the other side of the secondary. If both sides of the secondary were big flat parallel plates 10cm apart, we could easily calculate the field strength : field = 10kv/10cm = 1kv per cm. When you have points - sharp edges, the field lines curve in around the sharp point and the field goes way up because the electric flux gets concentrated at the point (I'll do a more detailed video on this sometime). Bottom line, the field strength gets so high that depending on polarity it can effectively eject electrons into the air and ionize air molecules that way, or tear electrons away from the air molecules. So the electricity forces itself into the air by charging molecules. Eventually the charged molecules touch something (or each other) and release the charge. Birds - will they probably feel a tingle and hear the corona fizz when sitting on HV lines. Sometimes you can hear the fizz from the ground when a long distance HV line. As long as the its just the micro amps going into the bird and being emitted around the bird as corona, no problem. But if the bird is big enough to narrow the gap between power lines to the point where an arc forms, thats the end of the bird. Its does happen, often when larger birds sit near insulators.
Your right about being near the ground making things worse - the electric field goes up. But even far from ground you can still get corona discharge. See my response below (above?) to @d46512.
Great solution to an unusual problem. Once you think about it, you can imagine corona discharge within the multi-meter shuttling charge between adventitious capacitors (circuit board traces, probe jacks, etc. and then off to ground) to give the jumpy readings you observed. Reminds me of an issue I had when running a high voltage pinwheel. The first time I fired it up next to my (steel) kitchen table, I noticed a regularly timed spark between the table and my Variac, which was sitting on the table but insulated from it by plastic feet. The corona discharge from the pinwheel was charging the (well insulated) table up until the air between the table and the (grounded) case of the Variac broke down. Adding a ground strap to the table solved the problem. Of course, I was also being charged up when the pinwheel was running which made touching the table or Variac a bit annoying, but my capacitance is relatively low so this was no worse than a typical static shock.
You know, your kitchen table spark sounds a lot like what I observed - the voltmeter reading seemed to go up and down - some maybe a very similar mechanism - something accumulating a charge and then it being discharged. Its funny we dont think of things like a kitchen table being well insulated but they can be. Even dry wood is a good insulator. What were you using to generate HV? From the charging effect I would guess something with a DC output?
@@ElectromagneticVideos Interesting, RUclips seems to have deleted my initial reply, which included a link to my web-site showing some pictures of the set-up. Yes, I was using a DC supply. To be specific, it was a 2-phase, 4 stage Cockcroft-Walton multiplier with a +80 kV output at about 8 mA. The metal sphere tipped legs of the table were separated from a linoleum covered floor by plastic scuff protectors and the wood-framed house has been drying for 140 years or so.
@@robertlapointe4093 Wow - I would be fascinated to the see the photos. Could you try posting the link again? If it is somehow being removed, please email me the link. (Email is in the "More about this channel" under the "View email address" button.
@@ElectromagneticVideos No luck putting links, or even partially broken links in comments, or getting your e-mail. I am beginning to think YT is just tossing all of my comments.
@@robertlapointe4093 Thats strange - always what triggers spam or other algorithms they use. To email me, (and I will describe it here so spam bots dont get it) take the name of my channel , remove spaces and write as all lower case, followed by the at symbol, followed by gmail dot com. Lets hope this doesn't trigger some sort of junk removal bot.
Corona discharges in the multimeter, clearly odd problems! If I've understood correctly, the metallic and black bags are conductive, while the pink ones can't create charges, the blue ones I don't know. Something for you to try!
@BjornV78 had a similar comment about bags. Be said everything other than black was no conductive. I;ll have to measure some others that I have and see if any have a resistance that is measurable with a normal multimeter. I thought they were all slightly conductive but clearly got that wrong!
Just tried a black anti-static bag. You were so right - could even measure the resistance of the bag surface. And tried it around the voltmeter. No as good as the aluminum mesh - there was around a 2V variation around the 40V reading, but still a massive improvement over the uncovered voltmeter where readings jump from 40 to 80V. Here is 20 sec clip (unlisted, unnarrated) showing the results ruclips.net/video/YjP2q5bc96o/видео.htmlsi
The cheap voltmeter is probably only approved for up to 300V AC. You have to think about whether the plastic of the housing provides sufficient insulation. There are voltmeters for higher voltages, but these are more robust and also more expensive. Voltages over 100V AC are certainly not playable by inexperienced users.
If that! Although it has a 750V AC range, I would not trust it on anything above a few hundred volts. The insulation of this voltmeter would definitely not withstand 10kv. Even better insulation that did may not solve the issue as capacitative effects of the AC could still get through. I know they make clip on ammeters for use on HV power lines. Would be interesting to see how they are constructed - maybe with a metal plating on the inside of the plastic case?
Very clever i might add, way to use a typical DMM in a way not approved by the manufacturer and certainly against the CAT ratings, which range fron I - IV with IV being most resistant, and reflects the ability to withstand transient voltages without an arc flash occurring inside the meter, which in a higher voltage, low impedance circuit such as outside at or close to the meter base in a 277/480V 3ø for those in the US, or worse, 347/600 3ø for those in Canada/some areas in the US, could be the last measurement you live to take since such an event would essentially turn into a direct short across the test leads. Many things can cause transients such as a lightning strike even some miles away can induce voltages possibly reaching several kV , riding down the power lines to the building and the risk level decreases with increasing distance from the service entrance, hence the importance of choosing a meter with the appropriate CAT rating, your life could depend on it. Your demonstration because of the impedance and limited available short circuit current even at 10kV, scares me a lot less than troubleshooting in a live 277/480V panel in a large commercial building.
Yes! And that multimeter is fine for home applications but not much more. You make an interesting point about lighting. I'm always surprised anything can survive a lightening strike - even pole transformers with external lighting protection. Years ago one summer lighting hit the pole mounted transformer near my house. Amazing nothing nothing when bad in my house. Even the transformer survived after the protection device was reset . Two weeks later lighting hit the same transformer. The time the transformer failed and had to be replaced. (And it hasn't been hit since). Unfortunately the transformers for the 10kv demo are not current limiting enough - somewhere in the 15mA max limited current rating or so. So I have a dead mans switch setup to make sure I cant be anywhere within reach of it when its powered up. Live panels with almost unlimited current available - scary!
What you built was a "Faraday Cage" for the meter. Great for keeping RF energy in or out of your device. Yes, I know it was just 60 Hz, but this also works for anything at very high voltages, like in this application. Play safe. Now, how about magnetic fields on old CRTs. LOL I am thinking about transformers in the room below. A very old story. Also, fluorescent lights just above the CRT. Both true examples. The first was in a large building, and the other was on a submarine.
Sometimes autocorrect does the funniest swaps - it should be "Faraday Cage" :). I didn't want to get into the details of Faraday cages in this video since the main purpose of it here was in this case to raise the electric potential immediately around the meter to the same potential as the meter to prevent corona on the the meter . "magnetic fields on old CRTs" are you referring to how things can be shielded from magnetic fields? The equivalent of a Faraday cage made with high permeable magnetic material will do it. Many CRT color TVs had a mu-metal shield in the cabinet around the from part of the tube for that reason. If you want to see a CRT exposed to a 60Hz field, see my video on demagentizing : ruclips.net/video/mGK8oYdEqyE/видео.html
@@ElectromagneticVideos Very True, Thanks for catching that. will fix. "Faraday Cage" There was a system that had that, it was called the "Tempest System" that costed a bit more and was used by the military. At the time (late 80's), seen that many times.
@@wrongmouse1658 I remember the tempest computers! Never used one myself, but they were notoriously expensive if I remember right. There must be some equivalent standard today with all the potential electronic eavesdropping and disruption.
@@ElectromagneticVideos Word Processor - CPT, Model 8100, circa 1982. There was a tempest version of that one. Also, a version of CPT with a "S" suffix for submarines. You know, if it did not fit thought the hatch, you could not get inside. LOL
@@wrongmouse1658 I guess that makes size a pretty strict requirement :) I had to google CPT Model 8100 - never heard of it - 1982 was when I started university and was the time when various home computers like Apple etc were becoming widespread. I'm guessing as dedicated word processor, if I ever did see a CPT, I never paid any attention to it.
Unfortunately not - this is not measuring the voltage to ground - its measuring the voltage (about 40V) across a resistor where both ends are about 10kV above ground. The problem with measuring the voltage from a Van de Graaff generator is the max current the machine can supply is usually in the micro-amp range probably at 100kV or so depending on the machine. The low current makes it hard to use something like a voltmeter because even with sufficiently high voltage dropping resistors, the current drawn by the meter would bleed off the charge faster than the machine can replenish it. The high voltage from a Van de Graaff makes it possible to use electrostatic repulsion in a meter to measure (high) voltage while drawing almost no current. See en.wikipedia.org/wiki/Electroscope
@@ElectromagneticVideos Thanks. I've always wondered how that might work. Now my mind is going the other way wondering if those little "leaf repulsion" instruments (the electrostatic meter, which again my mind is foggy of its name)... wondering how small a voltage they can measure - a battery? Hmmm. Wish I was in a lab right now. I've got a hankering to walk around on carpet holding one of those. I guess these days we'd just use a FET or better a BiFet opamp for sensing fields. I dunno.
@@schitlipz The electrostatic meter is a (gold leaf) electroscope. Easy to make - just cut two strips of Aluminum foil 1cm x 4cm, put a hole close to the ends of each, and hang on a hook shaped metal wire in a small jar or bottle. You should easily be able to detect the type of static charges we get on clothing etc in the winter. As to how low a charge they can detect, I'm not sure what the practical limit is. The thinner and lighter the metal strips, the more sensitive. Gold leave is used because it can be made incredibly thin. I'm guessing 500V or 1kv is the minimal practical voltage that can be detected with an electroscope. Anyone know? A MOSFET would be the perfect thing for measuring charges at low voltages - if you can protect the input to a max voltage less than what would damage the oxide insulation lager. Maybe a NE-2 lamp would do that without drastically lowering the input impedance. I think the issue would be having the max input V so low. Maybe a combination of a MOS device for low potentials and an electroscope for higher ones?
@schitlipz and @ElectromagneticVideos. Electrostatic voltmeters measure high dc voltage and require no current (except for teeny tiny leakage) from the item being measured and except for a bit of initial current to charge the capacitance of the meter. Unfortunately, I have never seen one that measures into the hundreds of kV range. Such a unit would be large to avoid corona discharge but could be built in principle. The vintage electrostatic voltmeters work like an electroscope except they typically use electrostatic attraction to pull a moving vane closer to a fixed vane. They require no other source of power. A pointer is attached to the moving vane and swings over a mirrored scale to give a very accurate indication of the voltage. Sensitive Research Instrument Co. used to manufacture these. There were a number of units with various full-scale readings. I saw units from 100 V full scale up to 25 kV full scale. They had the additional advantage of working just as well on ac, being true RMS responding. The ac source that is being measured needs only to supply enough reactive current to charge the meter capacitance which is on the order of 100 picofarads or so. Modern electrostatic voltmeters include an adjustable high voltage source and a field sensor that rides on the high voltage. Feedback from the sensor is used to control the meter's high voltage such that the field becomes zero, assuring that the meter's high voltage matches the high voltage being measured. The meter measures its own high voltage using a conventional resistive voltage divider feeding a conventional electronic voltmeter. In this way, the current to operate the voltage divider is supplied by the meter and no current is required from the item being measured. A company called Advanced Energy makes instruments of this type, reading up to 20 kV. A company called Ross Engineering Corp. makes specialized equipment for voltages as high as over one million volts. The voltage of a Van de Graff generator can be measured approximately by measuring the arc length between electrodes of known diameter, referring to a table or graph of arc length as a function of voltage and electrode diameter. For this information, look up Jochen Kronjager for instance. Another way is to use a conductive sphere hanging on an insulated line to transfer charge from the generator to a charge-sensitive amplifier whose output voltage is being measured. This requires a calculation of the effective capacitance of the transfer sphere when it is in contact with the top electrode of the Van de Graff generator. (Not the same as the self-capacitance of the sphere. A bunch of math is required. See a paper by John Lekner.) Another way is to use a capacitive voltage divider consisting of a high voltage low capacitance capacitor (such as a Leyden jar) in connected series with a low voltage high capacitance capacitor and measuring the voltage on the low voltage capacitor with a charge sensitive amplifier, such as an operational amplifier with picoampere level (or less) input current. The open end of the high voltage capacitor is connected to the top electrode of the Van de Graff generator and the open end of the low voltage capacitor is connected to the base of the Van de Graff generator. Both capacitors should have dielectrics (such as polypropylene or polystyrene or teflon) that exhibit low dielectric absorption and virtually no leakage for best accuracy of results. If both capacitors start at zero volts and there is no leakage current, the total charge will be equal on the two capacitors when they are charged by the generator. The voltage on the high voltage capacitor is equal to the voltage on the low voltage capacitor times the capacitance of the low voltage capacitor divided by the capacitance of the high voltage capacitor. The voltage of the generator is the sum of the voltages on the two capacitors. As stated by @ElectromagneticVideos, another way is to use a resistive voltage divider, but to keep the current low such that you are measuring close to the open circuit voltage, the high voltage resistor needs to be up in the terohm range and must be capable of standing off the generator voltage without breakdown. Such items are expensive specialty items and must be kept very clean to avoid surface leakage.
@@analog_guy Thank you so much for this detailed explanation of HV measurement. It never occurred to me that an electroscope device would measure RMS - in hindsight, it obviously has to, but like so many things, its only obvious once you know the answer. Also never knew about the adjustable voltage + field sensor technique. How clever. You did such a wonderful write-up on this subject would you mind if I copied it to the Community table of this channel so it gets preserved? I find there is no easy way to find things in the comments and it would be to bad if what you wrote got lost.
Hopefully someone from the UK can confirm this. but from what I understand the use of ring circuits in UK wiring was to reduce the amount of copper wire needed in homes that were built around and after WWII when materials were scarce. The skin depth at 50Hz for copper is about 1cm, so for any wire of smaller radius than that, it has minimal effect, and of course wires in homes as way smaller than that.
With the ring intact you are effectively doubling the wire cross section supplying the outlets. If you ran it as a radial circuit you'd use more copper to do the same job, so it was essentially a cost and materials saving move. Quite a few electricians in the UK state they prefer to do radial rather than rings for various reasons, not least being the risk of a fault in the ring splitting it on one or more conductors and having high load on one side exceeding the rating of the wiring.
@@retrozmachine1189 Thanks for that extra info! I wonder if rings are still installed in new places, or if for reasons like what you stated everything is done with radial wiring? I suppose one could make a double breaker much like the Canada/US 240V ones but in this case connect them to the same phase and use the double breaker to cause a trip if if more than half the total current goes though one or the other side of the ring. Might be the thing to do if copper values continue to rise!
I like how you straight talk about a subject rather than to feel you have to add a bunch of flare to entertain. If a person likes electronics and science then there is the entertainment. The education without games.
Thanks! I try and keep things down to earth and in an understandable way.
Added a Faraday cage to the voltmeter...brilliant! Same thing those line workers wrap themselves in when flying up to work on the high voltage lines.
Yes! There sure are some spectacular videos of them working on HV lines.
5:29 The blue, pink, green , purple or "Metallic" ESD bags are in fact totally non-conducting (are a isolator),
exact the same as a normal plastic bag, but they have the abbility not to create static electricity and keep static electricity out of the bag.
But once again, once a static charge is inside the bag, it remains there.
If you place a component that carry a static charge inside a ESD bag, the component stay charged. This is the case with all semi-transparant ESD bags.
Only the black ESD bags are slighty conductive, and these can slowly discharge a static charged component and keep it discharged. The black ESD bags contain carbon.
Regarding the mesh arround the meter, this acts like a Faraday cage. It's the same as a person would stand inside a metal cage, and where high voltage is connected to the outside of this cage. The high voltage would not to flash over to the person. This is also how the metallic suites work that high voltage technicians use. Regarding the cage experiment with high voltage, there are pictures of that experiment on the www , where a person sitting on a chair inside the cage is reading a book/magazine, while a Tesla coil is creating major sparks to the outside of the cage.
"The blue, pink, green , purple or "Metallic" ESD bags are in fact totally non-conducting" and "Only the black ESD bags are slightly conductive". Thank you for that - I had read somewhere the that the pinkish ones had very think film metal coating but I guess not. You sure explained why I could not detect any non-infinite resistance with the ohmeter.
I wonder whats in those bags to reduce static creation?
I have seen some of the videos of HV techs in mesh suits being delivered to power lines on helicopters. Amazing job - but not something I would ever want to do! I'm planning a couple Faraday cage videos sometime .....
Just tried a black anti-static bag. You were so right - could even measure the resistance of the bag surface. And tried it around the voltmeter. No as good as the aluminum mesh - there was around a 2V variation around the 40V reading, but still a massive improvement over the uncovered voltmeter where readings jump from 40 to 80V. Here is 20 sec clip (unlisted, unnarrated) showing the results ruclips.net/video/YjP2q5bc96o/видео.htmlsi
The anti-static bags and anti-static plastic foam "peanuts" used for cushioning are conductive when given sufficient electric field strength. A quick test applying 10 kV from end-to-end of a white "peanut" about an inch long showed no current but the same test using a green "peanut" of similar size showed a current of 10 nanoamps.
@@analog_guy Interesting! I have seen pink ones conduct as well (as one might hope). Maybe conduct is a bit of strong term as 10nA is hardly anything, but enough to bleed static charge.
@@ElectromagneticVideos Yes, the pink ones behave like the green ones. There is just enough conductivity to rapidly remove or adjust any charge on the colored "peanuts". Since the white peanuts tend to accumulate negative charge due to their place in the triboelectric series, if they are placed on an electrode which is subsequently charged to a very high positive voltage, they will remain there, typically for quite a few seconds, until enough negative ions accumulate on the surface. In contrast, the pink and green ones will fly away immediately as they rapidly acquire charge from the electrode. I don't know if the additive in these colored "peanuts" also materially alters the triboelectric positioning.
I suppose it's a bit like the guard traces seen around op-amps and other sensitive circuitry on PCBs particularly high precision measurement instrumentation
I hadn't thought of that - great point - your absolutely right. In some of those circuits - particularly the very high impedance ones - even the tiny leakage from nearby traces can be an issue unless you protect it with guard traces.
Yet another great video, Dr. Jones! I was wondering how that problem would be resolved. Great info on the static bags as well, including the excellent comment by @BjornV78 about the different types of bags. I had believed the same thing you did about the metallic coating or metallic content. Thank you for all the planning and materials and efforts you put into this. Very educational.
Thanks Michael! Pleased I did find a solution to the issue - at least the measurement problem had a silver lining (or maybe Aluminum lining in this case :).
I'm sure I read somewhere that nickel(?) was used to coat the reddish pink plastic bags. Who knows! It was great that @BjornV78 and @emilalmberg1096 where able to correct me on that and steer me towards the black bags. If you didnt see my response to their comments, I uploaded a 20 sec video showing the black bag as a voltmeter shield: ruclips.net/video/YjP2q5bc96o/видео.htmlsi
There is a trick to look through the window of a microwave oven. It's similar to the metal mesh. Move your head left and right slowly. But I'm sure everybody knows this.
I think a bit of edge sharpening in the camcorder made the mesh harder to see though in the video. It was easier to see in real life. But thanks for the tip on how better to see if you can move your head (or camcorder!).
Hi. Having built my bench isolation transformer, I know that electricity wants to go back to its source. So then why is there a corona even when the HV transformers' secondaries are isolated from ground?? Where is the electricity trying to go?
Birds aren't affected by this. Why is your meter?
I wonder if this is due to the fact that ground is so close to the DMM? The further away from ground the better is might get possibly? Excellent question!
As @ThriftyToolShed said, great question! The HV secondaries in this setup actually have their neutral to connected to ground and the entire table that everything is sitting on (actually a table saw bench) is metal and grounded. So the electricity is trying to to get to anything that is grounded. But even if the secondary was not grounded, you would still get a corona type effects happening. What happens is there is an electric field from anything attached to one side of the HV secondary to everything attached to the other side of the secondary. If both sides of the secondary were big flat parallel plates 10cm apart, we could easily calculate the field strength : field = 10kv/10cm = 1kv per cm. When you have points - sharp edges, the field lines curve in around the sharp point and the field goes way up because the electric flux gets concentrated at the point (I'll do a more detailed video on this sometime). Bottom line, the field strength gets so high that depending on polarity it can effectively eject electrons into the air and ionize air molecules that way, or tear electrons away from the air molecules. So the electricity forces itself into the air by charging molecules. Eventually the charged molecules touch something (or each other) and release the charge.
Birds - will they probably feel a tingle and hear the corona fizz when sitting on HV lines. Sometimes you can hear the fizz from the ground when a long distance HV line. As long as the its just the micro amps going into the bird and being emitted around the bird as corona, no problem. But if the bird is big enough to narrow the gap between power lines to the point where an arc forms, thats the end of the bird. Its does happen, often when larger birds sit near insulators.
Your right about being near the ground making things worse - the electric field goes up. But even far from ground you can still get corona discharge. See my response below (above?) to @d46512.
Great solution to an unusual problem. Once you think about it, you can imagine corona discharge within the multi-meter shuttling charge between adventitious capacitors (circuit board traces, probe jacks, etc. and then off to ground) to give the jumpy readings you observed. Reminds me of an issue I had when running a high voltage pinwheel. The first time I fired it up next to my (steel) kitchen table, I noticed a regularly timed spark between the table and my Variac, which was sitting on the table but insulated from it by plastic feet. The corona discharge from the pinwheel was charging the (well insulated) table up until the air between the table and the (grounded) case of the Variac broke down. Adding a ground strap to the table solved the problem. Of course, I was also being charged up when the pinwheel was running which made touching the table or Variac a bit annoying, but my capacitance is relatively low so this was no worse than a typical static shock.
You know, your kitchen table spark sounds a lot like what I observed - the voltmeter reading seemed to go up and down - some maybe a very similar mechanism - something accumulating a charge and then it being discharged. Its funny we dont think of things like a kitchen table being well insulated but they can be. Even dry wood is a good insulator.
What were you using to generate HV? From the charging effect I would guess something with a DC output?
@@ElectromagneticVideos Interesting, RUclips seems to have deleted my initial reply, which included a link to my web-site showing some pictures of the set-up. Yes, I was using a DC supply. To be specific, it was a 2-phase, 4 stage Cockcroft-Walton multiplier with a +80 kV output at about 8 mA. The metal sphere tipped legs of the table were separated from a linoleum covered floor by plastic scuff protectors and the wood-framed house has been drying for 140 years or so.
@@robertlapointe4093 Wow - I would be fascinated to the see the photos. Could you try posting the link again? If it is somehow being removed, please email me the link. (Email is in the "More about this channel" under the "View email address" button.
@@ElectromagneticVideos No luck putting links, or even partially broken links in comments, or getting your e-mail. I am beginning to think YT is just tossing all of my comments.
@@robertlapointe4093 Thats strange - always what triggers spam or other algorithms they use. To email me, (and I will describe it here so spam bots dont get it) take the name of my channel , remove spaces and write as all lower case, followed by the at symbol, followed by gmail dot com. Lets hope this doesn't trigger some sort of junk removal bot.
Corona discharges in the multimeter, clearly odd problems!
If I've understood correctly, the metallic and black bags are conductive, while the pink ones can't create charges, the blue ones I don't know.
Something for you to try!
@BjornV78 had a similar comment about bags. Be said everything other than black was no conductive. I;ll have to measure some others that I have and see if any have a resistance that is measurable with a normal multimeter.
I thought they were all slightly conductive but clearly got that wrong!
Just tried a black anti-static bag. You were so right - could even measure the resistance of the bag surface. And tried it around the voltmeter. No as good as the aluminum mesh - there was around a 2V variation around the 40V reading, but still a massive improvement over the uncovered voltmeter where readings jump from 40 to 80V. Here is 20 sec clip (unlisted, unnarrated) showing the results ruclips.net/video/YjP2q5bc96o/видео.htmlsi
The cheap voltmeter is probably only approved for up to 300V AC. You have to think about whether the plastic of the housing provides sufficient insulation.
There are voltmeters for higher voltages, but these are more robust and also more expensive.
Voltages over 100V AC are certainly not playable by inexperienced users.
If that! Although it has a 750V AC range, I would not trust it on anything above a few hundred volts.
The insulation of this voltmeter would definitely not withstand 10kv. Even better insulation that did may not solve the issue as capacitative effects of the AC could still get through. I know they make clip on ammeters for use on HV power lines. Would be interesting to see how they are constructed - maybe with a metal plating on the inside of the plastic case?
Very clever i might add, way to use a typical DMM in a way not approved by the manufacturer and certainly against the CAT ratings, which range fron I - IV with IV being most resistant, and reflects the ability to withstand transient voltages without an arc flash occurring inside the meter, which in a higher voltage, low impedance circuit such as outside at or close to the meter base in a 277/480V 3ø for those in the US, or worse, 347/600 3ø for those in Canada/some areas in the US, could be the last measurement you live to take since such an event would essentially turn into a direct short across the test leads. Many things can cause transients such as a lightning strike even some miles away can induce voltages possibly reaching several kV , riding down the power lines to the building and the risk level decreases with increasing distance from the service entrance, hence the importance of choosing a meter with the appropriate CAT rating, your life could depend on it. Your demonstration because of the impedance and limited available short circuit current even at 10kV, scares me a lot less than troubleshooting in a live 277/480V panel in a large commercial building.
Yes! And that multimeter is fine for home applications but not much more.
You make an interesting point about lighting. I'm always surprised anything can survive a lightening strike - even pole transformers with external lighting protection. Years ago one summer lighting hit the pole mounted transformer near my house. Amazing nothing nothing when bad in my house. Even the transformer survived after the protection device was reset . Two weeks later lighting hit the same transformer. The time the transformer failed and had to be replaced. (And it hasn't been hit since).
Unfortunately the transformers for the 10kv demo are not current limiting enough - somewhere in the 15mA max limited current rating or so. So I have a dead mans switch setup to make sure I cant be anywhere within reach of it when its powered up.
Live panels with almost unlimited current available - scary!
Very good!
Thanks again!
Cool!
Thanks!
Great analysis and solution(s)!
Thanks Dave!
I dunno... I think the mesh looked better.
It certainly worked the best.
What you built was a "Faraday Cage" for the meter. Great for keeping RF energy in or out of your device. Yes, I know it was just 60 Hz, but this also works for anything at very high voltages, like in this application.
Play safe.
Now, how about magnetic fields on old CRTs. LOL
I am thinking about transformers in the room below. A very old story.
Also, fluorescent lights just above the CRT. Both true examples. The first was in a large building, and the other was on a submarine.
Sometimes autocorrect does the funniest swaps - it should be "Faraday Cage" :). I didn't want to get into the details of Faraday cages in this video since the main purpose of it here was in this case to raise the electric potential immediately around the meter to the same potential as the meter to prevent corona on the the meter .
"magnetic fields on old CRTs" are you referring to how things can be shielded from magnetic fields? The equivalent of a Faraday cage made with high permeable magnetic material will do it. Many CRT color TVs had a mu-metal shield in the cabinet around the from part of the tube for that reason. If you want to see a CRT exposed to a 60Hz field, see my video on demagentizing : ruclips.net/video/mGK8oYdEqyE/видео.html
@@ElectromagneticVideos Very True, Thanks for catching that. will fix. "Faraday Cage"
There was a system that had that, it was called the "Tempest System" that costed a bit more and was used by the military.
At the time (late 80's), seen that many times.
@@wrongmouse1658 I remember the tempest computers! Never used one myself, but they were notoriously expensive if I remember right. There must be some equivalent standard today with all the potential electronic eavesdropping and disruption.
@@ElectromagneticVideos Word Processor - CPT, Model 8100, circa 1982. There was a tempest version of that one. Also, a version of CPT with a "S" suffix for submarines. You know, if it did not fit thought the hatch, you could not get inside. LOL
@@wrongmouse1658 I guess that makes size a pretty strict requirement :)
I had to google CPT Model 8100 - never heard of it - 1982 was when I started university and was the time when various home computers like Apple etc were becoming widespread. I'm guessing as dedicated word processor, if I ever did see a CPT, I never paid any attention to it.
Can you measure the voltage on a Van de Graff (?sp) apparatus using this, somehow?
Unfortunately not - this is not measuring the voltage to ground - its measuring the voltage (about 40V) across a resistor where both ends are about 10kV above ground.
The problem with measuring the voltage from a Van de Graaff generator is the max current the machine can supply is usually in the micro-amp range probably at 100kV or so depending on the machine. The low current makes it hard to use something like a voltmeter because even with sufficiently high voltage dropping resistors, the current drawn by the meter would bleed off the charge faster than the machine can replenish it.
The high voltage from a Van de Graaff makes it possible to use electrostatic repulsion in a meter to measure (high) voltage while drawing almost no current. See en.wikipedia.org/wiki/Electroscope
@@ElectromagneticVideos Thanks. I've always wondered how that might work. Now my mind is going the other way wondering if those little "leaf repulsion" instruments (the electrostatic meter, which again my mind is foggy of its name)... wondering how small a voltage they can measure - a battery? Hmmm. Wish I was in a lab right now. I've got a hankering to walk around on carpet holding one of those. I guess these days we'd just use a FET or better a BiFet opamp for sensing fields. I dunno.
@@schitlipz The electrostatic meter is a (gold leaf) electroscope. Easy to make - just cut two strips of Aluminum foil 1cm x 4cm, put a hole close to the ends of each, and hang on a hook shaped metal wire in a small jar or bottle. You should easily be able to detect the type of static charges we get on clothing etc in the winter.
As to how low a charge they can detect, I'm not sure what the practical limit is. The thinner and lighter the metal strips, the more sensitive. Gold leave is used because it can be made incredibly thin. I'm guessing 500V or 1kv is the minimal practical voltage that can be detected with an electroscope. Anyone know?
A MOSFET would be the perfect thing for measuring charges at low voltages - if you can protect the input to a max voltage less than what would damage the oxide insulation lager. Maybe a NE-2 lamp would do that without drastically lowering the input impedance. I think the issue would be having the max input V so low. Maybe a combination of a MOS device for low potentials and an electroscope for higher ones?
@schitlipz and @ElectromagneticVideos. Electrostatic voltmeters measure high dc voltage and require no current (except for teeny tiny leakage) from the item being measured and except for a bit of initial current to charge the capacitance of the meter. Unfortunately, I have never seen one that measures into the hundreds of kV range. Such a unit would be large to avoid corona discharge but could be built in principle.
The vintage electrostatic voltmeters work like an electroscope except they typically use electrostatic attraction to pull a moving vane closer to a fixed vane. They require no other source of power. A pointer is attached to the moving vane and swings over a mirrored scale to give a very accurate indication of the voltage. Sensitive Research Instrument Co. used to manufacture these. There were a number of units with various full-scale readings. I saw units from 100 V full scale up to 25 kV full scale. They had the additional advantage of working just as well on ac, being true RMS responding. The ac source that is being measured needs only to supply enough reactive current to charge the meter capacitance which is on the order of 100 picofarads or so.
Modern electrostatic voltmeters include an adjustable high voltage source and a field sensor that rides on the high voltage. Feedback from the sensor is used to control the meter's high voltage such that the field becomes zero, assuring that the meter's high voltage matches the high voltage being measured. The meter measures its own high voltage using a conventional resistive voltage divider feeding a conventional electronic voltmeter. In this way, the current to operate the voltage divider is supplied by the meter and no current is required from the item being measured. A company called Advanced Energy makes instruments of this type, reading up to 20 kV.
A company called Ross Engineering Corp. makes specialized equipment for voltages as high as over one million volts.
The voltage of a Van de Graff generator can be measured approximately by measuring the arc length between electrodes of known diameter, referring to a table or graph of arc length as a function of voltage and electrode diameter. For this information, look up Jochen Kronjager for instance.
Another way is to use a conductive sphere hanging on an insulated line to transfer charge from the generator to a charge-sensitive amplifier whose output voltage is being measured. This requires a calculation of the effective capacitance of the transfer sphere when it is in contact with the top electrode of the Van de Graff generator. (Not the same as the self-capacitance of the sphere. A bunch of math is required. See a paper by John Lekner.)
Another way is to use a capacitive voltage divider consisting of a high voltage low capacitance capacitor (such as a Leyden jar) in connected series with a low voltage high capacitance capacitor and measuring the voltage on the low voltage capacitor with a charge sensitive amplifier, such as an operational amplifier with picoampere level (or less) input current. The open end of the high voltage capacitor is connected to the top electrode of the Van de Graff generator and the open end of the low voltage capacitor is connected to the base of the Van de Graff generator. Both capacitors should have dielectrics (such as polypropylene or polystyrene or teflon) that exhibit low dielectric absorption and virtually no leakage for best accuracy of results. If both capacitors start at zero volts and there is no leakage current, the total charge will be equal on the two capacitors when they are charged by the generator. The voltage on the high voltage capacitor is equal to the voltage on the low voltage capacitor times the capacitance of the low voltage capacitor divided by the capacitance of the high voltage capacitor. The voltage of the generator is the sum of the voltages on the two capacitors.
As stated by @ElectromagneticVideos, another way is to use a resistive voltage divider, but to keep the current low such that you are measuring close to the open circuit voltage, the high voltage resistor needs to be up in the terohm range and must be capable of standing off the generator voltage without breakdown. Such items are expensive specialty items and must be kept very clean to avoid surface leakage.
@@analog_guy Thank you so much for this detailed explanation of HV measurement. It never occurred to me that an electroscope device would measure RMS - in hindsight, it obviously has to, but like so many things, its only obvious once you know the answer. Also never knew about the adjustable voltage + field sensor technique. How clever.
You did such a wonderful write-up on this subject would you mind if I copied it to the Community table of this channel so it gets preserved? I find there is no easy way to find things in the comments and it would be to bad if what you wrote got lost.
do we have ring circuits in the UK because of skin depth ?
Hopefully someone from the UK can confirm this. but from what I understand the use of ring circuits in UK wiring was to reduce the amount of copper wire needed in homes that were built around and after WWII when materials were scarce. The skin depth at 50Hz for copper is about 1cm, so for any wire of smaller radius than that, it has minimal effect, and of course wires in homes as way smaller than that.
With the ring intact you are effectively doubling the wire cross section supplying the outlets. If you ran it as a radial circuit you'd use more copper to do the same job, so it was essentially a cost and materials saving move.
Quite a few electricians in the UK state they prefer to do radial rather than rings for various reasons, not least being the risk of a fault in the ring splitting it on one or more conductors and having high load on one side exceeding the rating of the wiring.
@@retrozmachine1189 Thanks for that extra info! I wonder if rings are still installed in new places, or if for reasons like what you stated everything is done with radial wiring? I suppose one could make a double breaker much like the Canada/US 240V ones but in this case connect them to the same phase and use the double breaker to cause a trip if if more than half the total current goes though one or the other side of the ring. Might be the thing to do if copper values continue to rise!