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post #1 of 25 (permalink) Old 05-08-2012, 09:39 AM Thread Starter
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Default Question for Harrysin..or anyone who understands elctricity

Recently saw a video where a guy used some sort of a transformer to generate 12K volts DC. He paints water on wood, in this case a bracelet, and places two contacts on the wet wood. When he applied the current, nice random burn marks appeared.

My question is, what sort of a transformer, or other device, could be used to generate 12K DC safely?

I can envision many applications for this technique.

I couldn’t get the video to embed here, so here is a link to it.

Thanks for any suggestions.

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post #2 of 25 (permalink) Old 05-08-2012, 12:54 PM
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Gene,
A HID floodlight or neon sign ballast could produce voltages in that range. I saw the Thunderwood demonstration video Steve Good posted and was quite impressed. He has contact info on his website if you would like to ask him for more details.

I'm curious to know if it is just water he's using, or if he has added any electrolytes to it to make it conduct better. I don't know how much current he is pushing through there, or if it's AC or DC. With the one clip showing the marks coming from both direction leads me to think in may be AC

The random pattern it produces are beautiful.


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post #3 of 25 (permalink) Old 05-08-2012, 03:37 PM Thread Starter
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Thanks Doug.
I assumed it was DC because he was painting the water(?) on while it was working. I wouldn't do that if it were AC.

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post #4 of 25 (permalink) Old 05-08-2012, 09:10 PM
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It's certainly possible he was using that much DC to pyro-craft. If the 'equipment' was 'home crafted', it is far more likely he was using AC. Neon sign transformers were fun to play with in school to make 'Tesla Toys'....

The fundamental distinction between AC and DC is whether the voltage measured across the same two points fluctuates (Alternates) or remains constant (direct). Voltage coming 'directly' out of a transformer is AC by it's very nature. The induction process relies on the fluctuation of pulses flowing through the input winding (usually called a primary) in order to transfer them to the output winding (usually called a secondary). The frequency or pulses per second is transparently transferred across.

That being said, in a purest sense, DC isn't really 'pure' DC unless it comes out of a battery.

The DC in your car battery is really DC. The DC coming out of the alternator that keeps it charged and powers the vehicle when it is running is more along the lines of 'close enough to true DC', or what is often called 'ripple DC'.

I was taught that anything with a measured frequency greater than 2800 cps can be regarded as DC, especially for power purposes.

When there is a need to convert it to DC, devices classified as 'rectifiers' are used to accomplish the conversion. A basic rectifier is called a diode, and only allows current to flow in one direction. 4 diodes, connected to form a circle create what is called a 'full wave bridge rectifer' and is a very common way to convert AC to DC. The modern semiconductor of choice in power conversion is what they call an SCR, or silicon control rectifier.

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post #5 of 25 (permalink) Old 05-08-2012, 10:01 PM
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Obviously not very many amps if he is using automotive wire and small alligator clips. Depending on the tapwater, there might be enough mineral in it to carry a charge at that voltage.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #6 of 25 (permalink) Old 05-09-2012, 08:09 AM
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Quote:
Originally Posted by wbh1963 View Post
It's certainly possible he was using that much DC to pyro-craft. If the 'equipment' was 'home crafted', it is far more likely he was using AC. Neon sign transformers were fun to play with in school to make 'Tesla Toys'....

The fundamental distinction between AC and DC is whether the voltage measured across the same two points fluctuates (Alternates) or remains constant (direct). Voltage coming 'directly' out of a transformer is AC by it's very nature. The induction process relies on the fluctuation of pulses flowing through the input winding (usually called a primary) in order to transfer them to the output winding (usually called a secondary). The frequency or pulses per second is transparently transferred across.

That being said, in a purest sense, DC isn't really 'pure' DC unless it comes out of a battery.

The DC in your car battery is really DC. The DC coming out of the alternator that keeps it charged and powers the vehicle when it is running is more along the lines of 'close enough to true DC', or what is often called 'ripple DC'.

I was taught that anything with a measured frequency greater than 2800 cps can be regarded as DC, especially for power purposes.

When there is a need to convert it to DC, devices classified as 'rectifiers' are used to accomplish the conversion. A basic rectifier is called a diode, and only allows current to flow in one direction. 4 diodes, connected to form a circle create what is called a 'full wave bridge rectifer' and is a very common way to convert AC to DC. The modern semiconductor of choice in power conversion is what they call an SCR, or silicon control rectifier.
Yi! where to begin? Electrical current is DC(direct current) if it always flows the same direction. AC(alternating current) reverses direction/polarity.

A properly designed DC power supply provides pure dc as long as operated within its ratings. Even the output voltage of a battery will vary as the load changes. Measure the voltage of your car battery when the starter is running for instance!

Raising the frequency of AC does NOT make it DC for ANY application.

Fluctuating or rippling dc is still dc unless the polarity reverses. It has an AC component but is still DC!

SCRs are usually used for either regulation or switching, not USUALLY for rectifying per se.

Just trying to clear a few misconceptions. Too big a subject to cover in depth in 1 post!
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post #7 of 25 (permalink) Old 05-09-2012, 08:49 AM
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The only safe way to produce 12Kv DC is with a switch mode power supply where a high frequency oscillator is stepped up to the required voltage in a Ferrite cored transformer, because of the high frequency, the transformer is a fraction of the physical size of one designed for 50 or 60Hz. The output is rectified and filtered. Whilst such power supplies can be designed for high currents, for 12Kv the current available would be milliamps, plenty for the purpose described.
Cathode Ray tube TV used a somewhat similar system by using the high voltage produced by the flyback pulse, that is at the end of each line, the spot had to "flyback"to the start of the next line and this back EMF was stepped up in the line output transformer which operated at 15,625Hz on our system and 15,750 on the American NTSC system.
These days we find small switch mode power supplies in all manner of everyday items from battery/mains shavers, to downlight and fluorescent fittings to flat screen TV's. They are far cheaper to produce than linear power supplies containing a wound transformer operating at mains frequency. Even though toroidal transformers are commonly used in linear supplies and they are wound on ingenious machines, they are far more costly than circuit boards that are produced and fully populated so fast that it makes one feel dizzy watching!

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post #8 of 25 (permalink) Old 05-09-2012, 05:41 PM
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Many thanks to Duane & Harry for helping me touch up my perceptions of the electron!

Their comments make sense to me, some of Harry's (as they typically do!) have a way of zooming over my head...

In the context of 'ocilliscope displays', AC = "Sine Wave" and DC = 'Flat Line".

Even when I was working in the field (1980-1990 or so) the equipment that I was working on and working with was designed in the mid 70's or before.

Yesterday while thinking about this, my brain ground to a screeching halt trying to remember the fundamental differences between a 'generator' and an 'alternator' within the scope of 'automotive' power systems.

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post #9 of 25 (permalink) Old 05-09-2012, 10:47 PM Thread Starter
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Thanks Harry. I knew you'd come through.
You've given me quite a lot to ponder.

Quote:
Originally Posted by harrysin View Post
The only safe way to produce 12Kv DC is with a switch mode power supply where a high frequency oscillator is stepped up to the required voltage in a Ferrite cored transformer, because of the high frequency, the transformer is a fraction of the physical size of one designed for 50 or 60Hz. The output is rectified and filtered. Whilst such power supplies can be designed for high currents, for 12Kv the current available would be milliamps, plenty for the purpose described.
Cathode Ray tube TV used a somewhat similar system by using the high voltage produced by the flyback pulse, that is at the end of each line, the spot had to "flyback"to the start of the next line and this back EMF was stepped up in the line output transformer which operated at 15,625Hz on our system and 15,750 on the American NTSC system.
These days we find small switch mode power supplies in all manner of everyday items from battery/mains shavers, to downlight and fluorescent fittings to flat screen TV's. They are far cheaper to produce than linear power supplies containing a wound transformer operating at mains frequency. Even though toroidal transformers are commonly used in linear supplies and they are wound on ingenious machines, they are far more costly than circuit boards that are produced and fully populated so fast that it makes one feel dizzy watching!

Gene Howe
Snowflake, AZ

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post #10 of 25 (permalink) Old 05-10-2012, 01:47 AM
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Quote:
Originally Posted by wbh1963 View Post
Many thanks to Duane & Harry for helping me touch up my perceptions of the electron!

Their comments make sense to me, some of Harry's (as they typically do!) have a way of zooming over my head...

In the context of 'ocilliscope displays', AC = "Sine Wave" and DC = 'Flat Line".

Even when I was working in the field (1980-1990 or so) the equipment that I was working on and working with was designed in the mid 70's or before.

Yesterday while thinking about this, my brain ground to a screeching halt trying to remember the fundamental differences between a 'generator' and an 'alternator' within the scope of 'automotive' power systems.
Just to be pedantic Bill, AC doesn't have to be a sine wave, it can be square, triangular or any other irregular shape. You mention oscilloscope, if you view your voice on one that is alternating current...AC.
DC or direct current is as you say, a straight line, the current flow is in one direction only.

Harry



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