High voltage supply 5kV DC

[c_mitra]

Also how many pins should be used (any reference will be helpful)

The ionization is caused by field ionization. For a sharp tip (pointed), the radius of curvature is very small and the electric field (V/r) is very high. In post #32, there is a reference to a video (that I looked up; it is clear and concise) that uses a carbon fiber bundle as the electrode. Being very fine, they will be very effective at 5kV. Perhaps in a dark room you should be able to see the corona discharge (not to be confused with the recent pandemic)- but I am not very sure. Some idea may be gained from https://en.wikipedia.org/wiki/Corona_discharge

...and size of plate affect this current.

Let me try to elaborate. Once you have done some significant amount of ionization, the negatively charged gas will look for a short path towards the positive electrode. Else, this charged gas shall form a capacitor with the earth and can cause a discharge to the ground (if there are no other path).

With sufficient charge present in the air, inside of the room will appear to be a rather field free space.

So the ground electrode may be placed around 1-2 ft away and file off sharp edges (sharp edges can also act as corona points (emit positively charged molecules).

 

[BradtheRad]

How do we control the loading. Does the number of pins at the -ve electrode affect the loading or series resistor of about 1Meg or 4Meg before the -ve electrode pins.

There are FET-input VOM's with extremely high resistance. I have a broken one a buddy gave me. (Maybe he tried to measure high voltage!)

The very low current makes it a challenge. My meter never gave me a usable reading of my CW multiplier. Like yourself I tried workarounds using resistors with values like 100 Megohm. However that did not do the trick.

It would have helped if I'd soldered two or more capacitors in parallel. However instead I figured the math was correct so I decided to trust theory instead of my measurements. I only needed a few uA to verify working condition of the GM tube from my geiger counter.

What's the value of your capacitors? I believe you said 40uF. That should be ample to maintain voltage as your meter draws a tiny bit. However...

In order to preserve lives I'd rather ensure output can never go above 100 uA. Because 1 mA through the human body is all that's needed to stop our heart. I gripped wires carrying 120VAC and the current went over 100uA. (Foolish, I know.) However we are not harmed by a spark jumping from our hand to a doorknob because it's only a tiny current.
So maybe it's a good idea not to make the capacitor values too large even if our meter does drag down the voltage.

 

[Easy peasy]

5 x 20 Meg-ohm resistors, 2kV rated ( leaded ) will give you 100 Meg-ohm and 50uA on 5kVDC

you need to divide the lower 1kV down to match your meter, - you need to measure your meter to make sure it is 10 Meg ohm ( fixed range 500 or 600V )

Put the meter in series with a 10 Meg ohm 1kV resistor and then apply this across the lower 20M res, you now have 10Meg ohm in total on the lower R

making 90 Meg - ohm in total or 555.55 volt on the lower 20 Meg res ( for 5kV in ) and 277.77 volts on the meter for 5kV ( i.e. reading x 18 = real volts )

you're welcome ...

 

[betwixt]

Yes Brian. I didnt try with heating method, but used layers of insulating tape on the series resistors. I tried using 390Meg (consisting of series resistor of 39 Nos of 10 meg each) to be able to measure upto 6kV, but i didnt work. Have to check the issue. I am wondering if there is any current limit to which the multimeter can respond for voltage measurement.

Most likely you are seeing the curent drawn into the voltmeter itself causing a measurement inaccuracy.

You could try doing it the other way around, use resistors in series to develop the necessary breakdown isolation but measure current through them to ground. Use Ohms law to calculate the voltage drop across the resistors from the current flowing through them. You can assume the meter has zero resistance on the current range, it isn't quite true but the difference it would make to the voltage calculation is negligible.

Wire it up and set the meter range (for uA) before switching on so there is no risk of arcing as you make connections or change the meter setting.

Brian.

 

[sabu31]

There are FET-input VOM's with extremely high resistance. I have a broken one a buddy gave me. (Maybe he tried to measure high voltage!)

The very low current makes it a challenge. My meter never gave me a usable reading of my CW multiplier. Like yourself I tried workarounds using resistors with values like 100 Megohm. However that did not do the trick.

It would have helped if I'd soldered two or more capacitors in parallel. However instead I figured the math was correct so I decided to trust theory instead of my measurements. I only needed a few uA to verify working condition of the GM tube from my geiger counter.

What's the value of your capacitors? I believe you said 40uF. That should be ample to maintain voltage as your meter draws a tiny bit. However...

In order to preserve lives I'd rather ensure output can never go above 100 uA. Because 1 mA through the human body is all that's needed to stop our heart. I gripped wires carrying 120VAC and the current went over 100uA. (Foolish, I know.) However we are not harmed by a spark jumping from our hand to a doorknob because it's only a tiny current.
So maybe it's a good idea not to make the capacitor values too large even if our meter does drag down the voltage.

Thanks BradtheRad for the reply. I have tested upto 4.6kV. I used around 240M at the output and then connected about 10 paper pins. But, how do we observe if ionization is occuring. I couldnt feel any difference, though I ran it only for a 3-4 minutes. Also some youtube videos are using 2M at the output
https://www.youtube.com/watch?v=hc0nWqrECqQ
, which means the output current is around 2.5mA. Is my understanding wrong regarding output resistors.

 

[c_mitra]

I have tested upto 4.6kV. I used around 240M at the output and then connected about 10 paper pins. But, how do we observe if ionization is occuring.

Did you try in a darkened room? There will be a faint greenish glow near the electrode tips. A dark adjusted young eye can detect a single photon in the greening yellow colour range: These lights are coming from the ion recombinations. There may be slight noise sound too.

You can measure the current at the low end (220VAC/110VAC using the multimeter) and estimate the current by assuming 5kV (or whatsoever you have measured).

 

[sabu31]

Dear All,

To see the functionality of the system in -ve ionization. I am trying to do smoke test as shown in few youtube videos. I am thinking of placing the -ve end (pins) inside a plastic bottle containing a smoke source as shown in attached figure

<blockquote class="imgur-embed-pub" lang="en" data-id="28ya4YY"><a href="https://imgur.com/28ya4YY">View post on imgur.com</a></blockquote><script async src="//s.imgur.com/min/embed.js" charset="utf-8"></script>

However, I am concerned regarding functionality and safety of the experiment as the +ve end is outside the plastic bottle and regarding the charge accumulation as mentioned by c_mitra. Is there method mentioned in figure safe and pratical way to test ionization operation or is there any other method. Thanks.

 

[BradtheRad]

safe and pratical way to test ionization operation or is there any other method

* Certain bulbs glow when high voltage is close. Try:
neon bulb, compact fluorescent bulb, fluorescent tube.

* The video of Big Clive shows him hooking up just one lead of his voltmeter to a metal plate on the table. Then he holds the electrified multiplier close, and the meter registers a small voltage. He never touches high voltage to the meter lead in the name of caution.
He observed that the carbon filaments fan out, repulsing each other because of identical charges (just like the old-fashioned electroscope made from gold leaf handing over a wire).

* A simple static charge detector is made from a jfet (I believe a mosfet works, and sometimes a sensitive logic gate, op amp, transistor, etc.):

amasci.com/emotor/chargdet.html

 

[c_mitra]

neon bulb, compact fluorescent bulb, fluorescent tube.

You are right; a neon bulb can glow without a physical contact when close to a strong electric field.

Actually it won't work if the electric field is uniform or constant. If the electric field is highly non-uniform (like close to the point of the electrode), then the two pins within the neon bulb sees different potential and can glow.

Ordinary neon lamp based testers (often build inside a small screwdriver) will also work without actually touching the high voltage pin.

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regarding the charge accumulation as mentioned by c_mitra

Right; the plastic bottle will get electrically charged soon and will act as a screen for the electric field. The ionizer will stop working after a very short time.

 

[sabu31]

You are right; a neon bulb can glow without a physical contact when close to a strong electric field.

Actually it won't work if the electric field is uniform or constant. If the electric field is highly non-uniform (like close to the point of the electrode), then the two pins within the neon bulb sees different potential and can glow.

Ordinary neon lamp based testers (often build inside a small screwdriver) will also work without actually touching the high voltage pin.

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Right; the plastic bottle will get electrically charged soon and will act as a screen for the electric field. The ionizer will stop working after a very short time.

Thanks for the reply.
Then should i keep the negative electrode and positive electrode in side plastic bottle (with sufficient space between them say about 5-10cm.) to see if smoke settles?I am sure that the system has reached around 5.9kV, but now issue is to test if ionizing is happening.

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I tried the method with N-channel mosfet, but the led is always glowing. I am not sure if its because of ions or not.

The video of Big Clive, the multimeter registers a small voltage, then can we assume the system is ionizing is it that just voltage is high .

 

[sabu31]

Can we use copper strands of 0.2 mm thick for the purpose of ionization needles. How long does it take for the ionization to take effect and at what voltage is ozone produced.

 

[BradtheRad]

I tried the method with N-channel mosfet, but the led is always glowing. I am not sure if its because of ions or not.

Does brightness vary when it detects static charge? Approach it after you scuff your shoes across the rug, or rub a balloon, etc. It's sensitive even at a few feet distance.

Polarity of the static charge makes it brighter or dimmer. (Or the reason may be it's detecting mains hum anywhere and everywhere in the room).

It's finicky. I've touched the lead and the led lights, touch it again and the led goes off. Wait 20 seconds and it may return to midway brightness.

I've thought of making 2 static detectors, one with an Nmos, the other with a Pmos. One for positive charge, the other for negative.

The video of Big Clive, the multimeter registers a small voltage, then can we assume the system is ionizing is it that just voltage is high .

The DMM voltmeter range has internal resistance of 1M ohm or more. This could be enough load to drag the reading down to a few uV (and considering only one lead is connected). I imagine the metal plate method is just a quick and easy indicator.

 

[c_mitra]

Can we use copper strands of 0.2 mm thick for the purpose of ionization needles.

Sure. Just use the finest wire bundle available. The ionization of the surrounding gas will start without delay. How you are producing the smoke? It should precipitate as soon as you turn on the high voltage: that is the way electrostatic precipitators (usually mounted close to the top of smoke stacks) work.

Production of ozone depends on lots of factors: air pressure (more ozone at lower pressure), impurities present (trace pollutants act as catalysts that decompose ozone), and effective electric field (strong electric field cause dissociation of oxygen molecule that reacts with another oxygen molecule to form ozone).

There are very simple and very effective tests for trace amount of ozone in air.

 

[sabu31]

Sure. Just use the finest wire bundle available. The ionization of the surrounding gas will start without delay. How you are producing the smoke? It should precipitate as soon as you turn on the high voltage: that is the way electrostatic precipitators (usually mounted close to the top of smoke stacks) work.

Production of ozone depends on lots of factors: air pressure (more ozone at lower pressure), impurities present (trace pollutants act as catalysts that decompose ozone), and effective electric field (strong electric field cause dissociation of oxygen molecule that reacts with another oxygen molecule to form ozone).

There are very simple and very effective tests for trace amount of ozone in air.

Thanks c_mitra for the reply.
I am thinking of using incense stick/similar material for generating smoke. Also thinking of keeping both the +ve and -ve end inside a bottle separated around 5cm along with smoke source. Do you suggest any other solutions for testing the setup.

 

[sabu31]

Dear All,

Thanks for the suggestions. The system is working fine. Using sewing needles seemed to do the trick (0.2mm coppper strand and paper pins didnt have much effect). The system is also working at -4.5kV DC

 

[Easy peasy]

Well done - can you post a photo of it please..?

 

[sabu31]

Well done - can you post a photo of it please..?

This is figure of test setup. Its working upto 4.8kV. The multimeter has scaling of 40:1.

I am intending to put it in a metal casing which is covered on inside with rubber sheet. Also Will adding a 12 V fan increase the ionization effect on a room.

 

[c_mitra]

I am intending to put it in a metal casing which is covered on inside with rubber sheet.

This is how electron guns are made but the positive electrode must be outside this metal surface.

adding a 12 V fan increase the ionization effect on a room

The charged ions will refuse to be blown away; there will be some small effect (air current) but I expect that to be small. It is FAR more useful to blow the room air onto the electrode for effective action.

The charge distribution will be determined by the Poisson equation but I cannot just set it up and say the exact effect.

 

[Easy peasy]

the photo's are excellent - smoke chamber for observing ionisation behaviour ... ?

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I see the 20 x 10Meg + the 10Meg meter in parallel with lower R = 120V = 4800VDC ... - well done ...!

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if you put the meter on AC only - what is the ripple ... ?

 

[sabu31]

the photo's are excellent - smoke chamber for observing ionisation behaviour ... ?

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I see the 20 x 10Meg + the 10Meg meter in parallel with lower R = 120V = 4800VDC ... - well done ...!

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if you put the meter on AC only - what is the ripple ... ?

Thanks easy peasy for the comments.

The smoke chamber was for testing functionality.

I used 39 * 10Meg +10Meg of meter in series to get overall 400 Meg and 40:1 attenuation so that 120V=4800V