dangers of high voltage and measurement

[waspinator]

Hi,

I recently saw Julian's Postbag which featured a high voltage (400kV) step up converter and was wondering the effects it would have if you passed that voltage through yourself, and how you would go about measuring it. Would it be painful and/or damaging? It couldn't be fatal could it? I'd imagine that the current would be very very low, and from what I understand current is the bit that's dangerous, not voltage.

Thanks

[Brumby]

In short, yes this thing could kill.

While the average current at 400KV would be less than 30uA, it could potentially deliver 10mA at 1KV if loaded appropriately.  Note - these are average currents, but the unit is described as being pulsed, so if the pulse equates to a 10% duty cycle, you could be looking at pulses of 100mA at 1KV.

The flow of electricity through the human body is not easily defined.  It is dependent on a number of variables, but make no mistake - the ability of this device to deliver a fatal shock is real.  Treat it with respect.

[alsetalokin4017]

While that output is sort of impressive for the small separation of the wire ends, I seriously doubt if the thing can actually get up to 400 kV and survive itself. At those voltages, tiny plastic insulation is essentially meaningless. Just take a look at how voltages of a tenth of that or even less are handled inside a CRT monitor or television set (remember those?).

I'd like to see a demonstration of that unit with the output wire ends connected to metal balls separated by 10 cm. 

[Brumby]

If you read the descriptions on some of those units, they say not to have a gap of more than 10-20mm and "Do not exceed the maximum arc distance electricity, energy can not be released due to high pressure, can easily damage the module."

They are well aware of the potential for this thing to self destruct.

[alsetalokin4017]

If you read the descriptions on some of those units, they say not to have a gap of more than 10-20mm and "Do not exceed the maximum arc distance electricity, energy can not be released due to high pressure, can easily damage the module."

They are well aware of the potential for this thing to self destruct.

Exactly. So how can the claim be legitimate that it produces "400kV" if it self-destructs at 60 kV?  Under what circumstances can it reach 400 kV without self-destructing?

[Brumby]

You have made a couple of assumptions there - but you may be right.

Anyone here who plays with this stuff?

[Martini]

While the average current at 400KV would be less than 30uA, it could potentially deliver 10mA at 1KV if loaded appropriately.  Note - these are average currents, but the unit is described as being pulsed, so if the pulse equates to a 10% duty cycle, you could be looking at pulses of 100mA at 1KV.

What if you run it on a coin cell, then? 

[langwadt]

What if you run it on a coin cell, then? 

The principle of this thing is, there is a flyback HV converter generates ~5kV, the 5kV intermediate voltage has a large capacitor on it to store pulse power.
Then, this 5kV passes through an air gap to a pulse transformer, which generates hundreds of kV. The pulse frequency is determined how fast can the flyback converter charge the cap to air gap breakdown voltage.
If in the first place the flyback converter can not even deliver ~5kV due to limited input power or voltage, then ti will never breakdown.
Also, the duty cycle can not be 10%. The spark interval is somewhere around 1/4s to 1s, while the discharge happens less than 50us. The duty cycle is extremely low.
However, the discharge power is tremendous. In the range of hundreds of kV, tens of amps.

there is no way that that thing has anyway near enough isolation distance inside, outside or anywhere else to handle
"hundreds of kV"

[Martini]

Does that make it somehow more dangerous?

[Augustus]

Should be sufficient for a diy mosquito zapper project   

Julian is a wimp, Big Clive would use his tongue to measure the output voltage of this device 

[waspinator]

It's amazing how a 18650 cell can become so dangerous. and that the device only costs ~$2. What's the best way to measure the waveform? I assume you need some expensive probes. I wonder if Dave would be willing to do an experiment with this. Does writing @EEVblog ping him?

[joeqsmith]

What's the best way to measure the waveform? I assume you need some expensive probes.

You could look at what North Star has to offer.  Your converter is running outside anything I have tried to measure and I am sure brings a whole bunch of problems.   I have made some capacitive divider probes that I used in the 40KVish range.  No reason this would not work.    For wide band down to DC, the best probe I made will work to around 60KV.    Maybe have a look at Pearson as well.   

Imagine a $7000 probe to look at a $2 device.  Maybe throw an extra scope in there in case something goes wrong....   

Good luck.  Post what you come up with.

[waspinator]

Just saw a video of someone touching an arc from a lighter. not sure how much voltage runs through the arc lighters, or how comparable they are to the module, but they don't seem to have real effect.