Fusor Voltages are Dangerous

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
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Frank Sanns
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Fusor Voltages are Dangerous

Post by Frank Sanns » Mon Aug 27, 2012 3:05 pm

The voltages used by a fusor in its simplest incarnations are dangerous. Even neon sign transformers can kill.

Here is a very graphic video that demonstrates what 10 KV will do to the human body. Microamps will do it to the body but much more current is present to the peripheral structures in this video. I encourage you to watch this video even though it is extremely graphic but it should serve as a warning to all of those that venture into the HV realm.


WARNING GRAPHIC VIDEO: http://youtu.be/BiHyohqxRRo

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Chris Bradley
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Re: Fusor Voltages are Dangerous

Post by Chris Bradley » Mon Aug 27, 2012 4:06 pm

Frank,

HV can kill. I trust we know that. The video proves the point, but I don't think this is a good video to link to for people to watch here, for a variety of reasons.

This is just a very disturbing video that shows what happens when the amps keep on pumping, doing little to warn folks of how to manage HV hazards.

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Doug Coulter
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Re: Fusor Voltages are Dangerous

Post by Doug Coulter » Mon Aug 27, 2012 4:14 pm

All too true, and I've been quite lucky. I have to say though, that the odd arc to me from the main HV, while scary and very annoying, hasn't done much more than find me jumping across the room involuntarily, and getting hurt mostly when I landed.

It's the volts that jolt, but it's the mills that kill. Although there is some research that a tiny shock at just the right instant can so confuse the several mechanisms that regulate heartbeat it'll just stop. That only took a few volts and a few micro-amps in the case where the investigator killed himself -and was later found with all the chart recorders still going. Graphic text in an old Scientific American about that one.

I have to say the very worst injury I've gotten in this game was from lower voltage higher current DC, in this case a filtered 4kv supply that had perhaps half an amp available. And yup, worst case, hand to hand was the path. Took me a couple seconds to get thrown free, and during that time I created burn channels from hand to hand, through the torso - that one hurt for MONTHS afterwards. But evidently, I'm hard to kill - and no one should disregard the very real dangers of any voltage high enough to make you draw mills of current. Which can be as low as 24v if you have a wound, or 48v if you're sweaty. I've gotten some serious tingles off those in those cases...just to alert people who didn't know this already.

For entirely other reasons, all fusor HV should be in coax (factory or home-made faraday outer shields). Assume you've got a 50kv supply, like mine. And you have a 50k ballast resistor. That's one amp of peak current during an arc, or about 50kw of potential EMI, which is enough to fry any PC in the room - the mouse, power, keyboard wires alone are enough antenna for that to bring in the energy required to fry the mobo - even if the PC is off and otherwise not connected to the fusor.

So, the best place to fix that one is at the source, which has the nice byproduct of being a heck of a lot safer for you too.

Another reason to have all your HV inside a grounded shield is that it becomes one pole of a capacitor to everything in the room, and stuff that is floating picks up a charge via a capacity voltage divider. You might not think of that as much of a threat, but if that object is you - and you move, you can easily create a wimshurst or van de graff effect and get a couple hundred KV on yourself. Next time you near a ground - wham; it's probably not going to kill anyone, but it's nasty...and it is enough to fry any semiconductors you might zap that charge into.
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Re: Fusor Voltages are Dangerous

Post by Tyler Christensen » Mon Aug 27, 2012 4:35 pm

Adding to the HV being one pole of a capacitor, the worst case here is if the other pole is an actual capacitor. This is the only time I've been shocked by my fusor. I did a long run while leaving a high voltage capacitor attached to an exposed wire but not actually connected to anything (and earthed on the other end of the cap). The capacitor was initially discharged, but after having a 50kV wire about 3 feet away, it sure wasn't discharged! I shut everything down, followed standard procedure of grounding the HV supply and all, then reached in to do some service on the vacuum system and got hit right in the face as I brushed by the wire to that initially uncharged capacitor. Sure took me by surprise, and took a few minutes to figure out what had happened.

Bottom line, short out all high voltage capacitors. Even fairly small non-lethal ones can give quite the surprise and could lead to property damage resulting from your surprise reaction.

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Re: Fusor Voltages are Dangerous

Post by Rich Feldman » Mon Aug 27, 2012 7:43 pm

Tyler Christensen wrote:
> ...The capacitor was initially discharged, but after having a 50kV wire about 3 feet away, it sure wasn't discharged! I shut everything down, followed standard procedure of grounding the HV supply and all, then reached in to do some service on the vacuum system and got hit right in the face as I brushed by the wire to that initially uncharged capacitor. Sure took me by surprise, and took a few minutes to figure out what had happened.
> ...Bottom line, short out all high voltage capacitors. Even fairly small non-lethal ones can give quite the surprise and could lead to property damage resulting from your surprise reaction.
I wonder if that event was a manifestation of dielectric absorption? Suppose a capacitor holding HV is discharged, through a wire or resistor, until its terminal voltage and current are zero.

After the short is removed, and with NO TERMINAL CURRENT, the voltage will creep back to some fraction of the previous "soak" voltage.

It's a dielectric material property. Can be enough to deliver an electric shock. At the instrument level, it can mess up sample-and-hold circuits with poorly chosen capacitor dielectrics.

Bottom line: keep all high voltage capacitors shorted or with bleeder resistors connected.

one ref:
http://electronicdesign.com/article/ana ... nyhow-6096
All models are wrong; some models are useful. -- George Box

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Doug Coulter
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Re: Fusor Voltages are Dangerous

Post by Doug Coulter » Mon Aug 27, 2012 7:48 pm

Dielectric absorption is a fact, but there are other issues that may be more important. It's a rare case indeed where you get even 5% chargeback. (Mylar is about the worst, which is one reason they don't use it in HV caps usually).

The example I gave of becoming a human wimshurst machine happened to BillF in my lab, and we even have a movie of him throwing the camera when he got hammered. We were running 40kv though about 5 feet of sparkplug wire (bad for this, high dielectric constant so the outside charges to the inside voltage if you don't wrap it with ground).

After a bit of walking around, he drew a ~5" spark to a nearby ground. That's a lot longer spark than you can normally get off your butt at 40kv.

And yes, the damage you get from suddenly having most of your muscles contract hard all at once is largely to yourself...but includes whatever you might land on.
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Chris Bradley
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Re: Fusor Voltages are Dangerous

Post by Chris Bradley » Mon Aug 27, 2012 8:44 pm

There are certain publications which suggest where the 'danger lines' are drawn.

In the UK HSE 'Electrical Safety at Work' documents it explains to ensure that the stored charge in any capacitors that have any chance of discharging into a human subject (viz., without appropriate safety guards and interlocks) should not exceed 0.35J. Capacitors storing more than this are not necessarily lethal - the norm for cattle lines, etc., is 1 to a few Joules. If you've ever been hit by the shock from a cattle line, that's what a few joules at a few kV feels like.... Ouch!!

In "Health and Safety Executive OC 501/11; "ELECTRICAL SAFETY AT LASERS, MAGNETRONS, ACCELERATORS, RADIO FREQUENCY EQUIPMENT AND THE LIKE..." [yes, that's the actual title!] it says "Discharge energies in excess of 50 ľC (micro-coulombs) are regarded as hazardous to life
(IEC Publications 479 and 536)."

The document which is often cited in such discussions is one from 1961, Dalziel's "Deleterious Effects of Electric Shock". I have an original electronic copy, below is the key table from it.

The thing to note is that volts and current only signify likely outcomes if they are continuous applications. If your source is a very stiff supply and will continue to pump high currents at high volts into a low impedance load (like, you!) then the rest of the table applies, but the short shock discharges are also significant danger issues, especially for the typical circuits in amateur builds.

In particular, energy discharges in the 1 to 10J are shocking but usually have no consequences - notwithstanding the sharpened tool you've just jumped on to as you get the shock! (per Doug's point).

In the range 10J to 50J you are treading on thin ice, for around 50J to 100J there is enough energy to interfere with your heart, but not stop it. Oddly enough, a single discharge above around 150J [that is, energy dissipated across your thorax] is *less* fatal because it will stop all heart activity, from which it will restart, hopefully without fibrillation. This is the principle of the defibrillator. Above around 400J this will then begin to damage the heart. (I have only built one 'big-current' mains rectified circuit, and I've put in 6600uF to keep the energy content above that 150J level.)

In the 30kV supply I have constructed in viewtopic.php?f=11&t=4887#p31976 , the total stored charge at 30kV is 50uC, and sub 0.5J at 'typical-upper' operating voltages. This was intentional. This is a very soft supply when used with low impedance loads and just goes 'flat' if there is a low impedance across it. In theory, a discharge from this at 30kV should be non-fatal ... but don't *begin* to think I am going to test that theory just to see if it is true or not!!!

It's too many joules that'll kill you in a flash, it's too much current that'll kill you in a time interval.

In the last few weeks, I received a shock from a low voltage circuit that should not have been carrying anything more than 20V. I pressed a sweaty thumb on the top of a TO-3 package can [a usual way to check operating temp!!] and got a big, pulsing, shock down my arm. The 20V circuit was attached to two 16V 15000uF caps (in a doubler rectifier). I was stunned, both from the Joule or two that pulsed down my arm, and from the fact that such a low voltage could cause me an unexpected electric shock! It was pretty strange, like a slow pulsing, surging discharge I could feel as the capacitors drained their load into my arm. Hurt for some time afterwards. Very surprising. Apparently, the lowest voltage causing death was that of a Naval serviceman with a hand-wound from a 9V battery. I once got a shock off a 2.2nF cap fully charged to 20kV, 't'was but a tingle in comparison (made me jump and yelp though!!).

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Dennis P Brown
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Re: Fusor Voltages are Dangerous

Post by Dennis P Brown » Mon Aug 27, 2012 8:54 pm

A critical lesion from all of these posts is that all high voltage systems need good shielding and all caps have bleed resistors. I would add that a insulated pole with a grounded wire is a critical piece of safety equipment to prove any system is safe.

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Re: Fusor Voltages are Dangerous

Post by Steven Sesselmann » Mon Aug 27, 2012 9:27 pm

Frank,

A very graphic point...

I would like to point out that it is a mistake to focus on one danger. In the fusion lab, there are several hazards that need an equal amount of attention, otherwise you might focus on one safety aspect and get yourself killed or injured by another.

Most of us are so busy looking for Neutrons that we forget some of the other dangers..

Especially one that can kill you without you even noticing it, at least not until a few days later...

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

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Frank Sanns
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Re: Fusor Voltages are Dangerous

Post by Frank Sanns » Tue Aug 28, 2012 3:02 am

Yes of course Steven. There are many places for problems. A bell jar or sight window imploding is a constant risk. But the silent killer is unchecked radiation.

I have recently found out that one of the experimenters on this site was exposed to a large dose of radiation accidentally. He has had radiation sickness and parts of his body have apparently been exposed up to multiple Grays of x-rays. This was an unfortunate situation where the proper detector and placement of detectors was not followed during some very high voltage and current runs. The person is tracking his blood work to better quantify the total dose that he received.

It is imperative that anybody running a fusor or even an air plasma, understand the risks of x-rays that can come from a variety of sources. Not all radiation detecting equipment will even sense these x-rays making it dangerous. I have a low energy dosimeter that I ALWAYS wear in addition to other low energy detectors around any time I operate my fusor.

Frank Sanns

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