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Micro SSTC for drawing arcs to skin?

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ahahn

Thu Aug 09 2012, 12:33AM

Registered Member #6075 Joined: Wed Aug 08 2012, 11:48PM
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Posts: 29

Hello all,
Ages ago I encountered a small commercially-made SSTC where the power was low enough you could draw an arc to your finger. At the time it seemed like the most wonderful of ideas, and it's stuck in my head ever since.

Now I have some time and I'd like to make one. Ideally a simple design, because I'm lazy.

The critical consideration seems to be minimizing current. Drawing arcs with your skin carries of course the risk of RF burns, and those seem to be the result of the skin performing like a 1/4W resistor where a two-watt unit is required. Unfortunately, I don't know what's a safe number to design for -- milliamps? microamps? Assuming a longer-duration discharge into skin, even 20uA @ 50kV would be a watt of power.

The most obvious design would be Steve's MicroSSTC:

Specc'ed to draw 50W of supply, that makes the arc current no more than 1mA (assuming a secondary voltage of 50kV and impossibly perfect efficiency)

There's also the Kacher Brovina Russian ultra-simple SSTC:

With such a simple design, it seems easy to modify to keep the output power down.

And lastly there are the NanoTESS series:

Sadly there's no schematic for the second and third, but the visual design and size are eternally endearing. Made safe to handle, they'd be a perfect pocket toy.

[added]
It seems there already are modified Tesla coils called Violet Wands that are meant for discharging to skin -- it looks like they put an evacuated or rare-gas filled glass chamber between the output electrode and the skin. For example:

Unfortunately, that link's instructions are pretty heavy on mechanical fabrication. I don't have the capability to do that.

Sulaiman

Thu Aug 09 2012, 01:37AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

not a subject that I'm experienced with,
but I think that there are two hazards;
1) rf burns - damage to skin tissue due to heat - easily healed
2) nerve damage due to current flowing along nerves/axons etc. - slow/no healing.
i.e. you may suffer long term nerve damage ....
I think that you should research it before significant exposure.

ahahn

Thu Aug 09 2012, 02:05AM

Registered Member #6075 Joined: Wed Aug 08 2012, 11:48PM
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Sulaiman: thanks for the advice. The Violet Wands don't seem to cause nerve damage. Those put out similar voltages and are used where there are lots of nerve endings ('adult' situations). Can you provide me any references as to what does cause the kind of nerve damage you're talking about?

Ben Solon

Thu Aug 09 2012, 02:39AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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Posts: 600

note that its not just current that burns you, plasma is *HOT*

Goodchild

Thu Aug 09 2012, 06:33AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I may just be crazy, but I think I've touched the sparks coming off of every Tesla coil I've every built excluding maybe only the 12 footers coming off my large 12Kw beast, oh wait never mind I've touched those as well.... :P

Not saying you should do the same nor am I saying it's safe in any way, I just happen to be stark raving mad.

With that being said I think it has a lot to do with the type of plasma you are dealing with. High frequency dense plasmas like what you find with CW SSTC and QCW don't seem to cause much nerve discomfort although they tend to be very hot and dish out RF burns with a nasty bite!

The nastier more pulsed plasma like you get with pulsed SSTC, SGTC, and DRSSTC can hurt a lot! But they don't as easily give you RF burns because they are usually low duty and pulsed.

Personally I would jive for Steve's mini SSTC or micro SSTC if you want to go class E and simple.

A coil don't unnecessary have to be low power to touch it hehe. Don't try this at home kids I'm what you call a lunatic.

ahahn

Thu Aug 09 2012, 09:01PM

Registered Member #6075 Joined: Wed Aug 08 2012, 11:48PM
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Steve's designs do seem to be the way to go. For what I'm looking to do, I would have to modify them to add current limiting. The obvious and simple way is an LM317 as an adjustable current limiter just before the primary's 2200uF capacitors -- thus limiting the overall power draw. Would this fail to work as I expect, or is there a better way?

Ben Solon

Thu Aug 09 2012, 09:39PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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Posts: 600

a 317 in current limit mode simply drops an adjustable voltage across itself to adjust the voltage across the load to a value that sets the desired current. in that way it dissipates power equal to I*V. if you use a 30v supply and it drops 20v to get the input limited to 1A, that's 20W of power lost as heat. why complicate things by burning unnecessary power when you can just use a smaller input voltage instead?

ahahn

Thu Aug 09 2012, 09:46PM

Registered Member #6075 Joined: Wed Aug 08 2012, 11:48PM
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Posts: 29

A current control just seems more precise. Limiting max current given a known voltage means there's a known output power (limit). Limiting only voltage means there isn't. But I see your point.

Goodchild

Thu Aug 09 2012, 10:50PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I agree with Ben using a LM317 would be a tremendous wast of power not to mention it doesn't have nearly the power handing capability for a SSTC even a small one. If I was to add limiting to something like this and make it supper simple I would probably go with one or two options: CT and a comparator looking at LC current or a SCR chopper on the input.

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