How would aluminum balloon develop 1MV without ground reference

[Deactivated-1]

I came across a video talking about the balloon boy incident, and was wondering, how would the balloon develop said 1MV if it didnt have a ground reference, it would just be floating (electrically) right?
or is the voltage developed across the inner and outer skin, although then it seems it would be near impossible to insulate the 2 layers so they wouldnt arc over at such voltages.

[magic]

I'm not familiar with the incident but I would guess that somebody has charged (and, perhaps, violently discharged) an air dielectric capacitor consisting of the balloon and ground

[Terry Bites]

You can only have a potential in respect of a reference- it doens't have to be ground, it could be another charged or neutral body. Conservation of energy and the like. The charge density on the ref and charged body do no need to be the same. But lines of flux have to terminate somewhere.

[David Hess]

I came across a video talking about the balloon boy incident, and was wondering, how would the balloon develop said 1MV if it didnt have a ground reference, it would just be floating (electrically) right?

It would develop a large potential compared to "ground" in the same way that a cloud or aircraft would.

[T3sl4co1l]

The better question is how one would measure such a thing.  I don't recall anyone had an electrometer handy during the incident.  Did they give a source or is this "1MV" factoid completely made up?


Normal atmospheric electric field is about 100 V/m.  If peak altitude was around 600m, that's only 60kV potential -- and that's assuming charge equilibriated during the flight and then, say, someone dropped a wire from it down to the ground, where that potential could be measured.

By electrostatic induction, simply flying from ground, up and down, the potential on the vehicle follows altitude and no charge results from the trip.  If the charge is equalized at each peak of a trip, some energy can be extracted (i.e., flying up, then discharging, then flying down and discharging again, etc. etc.).  But no charge lost means it simply follows the electric potential versus altitude, nothing interesting happening at all.


Aircraft normally pick up additional charge due to triboelectric effect, flying through particulates, dust, rain, snow, that sort of thing.  Or maybe even the air itself, I'm not sure about that.  There might not be much of these on a clear day, but there's always some, and a trip is long (say, some hours), so it doesn't take much charge per particle to add up.  The charge is in turn dissipated through corona points near the wingtips, etc.  And additionally, when fueling, by a ground strap to the fuel truck / station, also because tires and passengers can generate charge by the same effect.

Flying (passively) on the wind, probably doesn't generate much charge, at least I'd assume it's a necessary aspect that the charged particles are blown away from the vehicle by wind shear (else they'd rub against and displace some charge, but then stay stuck in place).

Tim

[TimFox]

An upper limit to the "voltage" on a flying metal object is given by the breakdown field strength of dry air under normal conditions:  30 kV/cm = 3 MV/m.
At high altitude, the pressure decreases and one needs Paschen's Law (or more accurate formulations) to predict the breakdown voltage.

[RoGeorge]

I came across a video talking about the balloon boy incident, and was wondering, how would the balloon develop said 1MV if it didnt have a ground reference, it would just be floating (electrically) right?

The context matters.  Without the video where you saw that, nobody can tell what it was about, or if it really was how you remember.  To get a relevant explanation put a link to that video and the timestamp where it was said about 1MV.



To get voltage you don't need a circuit, you only need charges.  If you charge a balloon with a very small charge then lift it up, then the "parasitic" capacitor formed between the balloon and the Earth will decrease with altitude.

Constant charge and decreasing capacitance automatically raises the voltage (because by definition C = Q/V, so V = Q/C, so if C becomes very small, V becomes very big - assuming the charge stays the same because the balloon has no contact with the Earth to discharge its initial charge Q).

C decreases with altitude, because C = k*A/d, where d is the distance between plates, here the distance between the Earth and the balloon.  So the farther the balloon, the lower the capacitance, the bigger the voltage.  1MV between Earth and a raising balloon doesn't seem much at all.

Another situation that raises the voltage can be if the baloon is kept still, and the wind is rubbing the balloon and charge it electrostatically (because of the triboelectric effect).  Since the capacitance between the Earth and the balloon is very small , huge voltage will appear.



TL;DR
- to have voltage, you don't need an electric circuit, you only need charges
- after you charge a capacitor then disconnect it, if the capacitor's plates are moved apart then the voltage will increase with the distance between plates (this trick is sometimes exploited in practice, for example in the "vibrating capacitor" from some very sensitive electrometers).

[mark03]

https://en.wikipedia.org/wiki/Balloon_boy_hoax

[Doctorandus_P]

I did not follow the balloon story, but to me it's quite logical.

Things floating in the air are electrically isolated from GND, and that means they can develop a charge.
If it flies through a positively charged cloud, there is a local lack of electrons, and some electrons will be ripped from your balloon and it takes over that same positive charge, and if it flies through a negatively charged cloud, it will gain some electrons and thus takes over a part of that negative charge (All compared to a GND reference).
The voltages associated with those charges are on the order of magnitude of lightning bolts, depending on which cloud it flew through last.

Mike Harrison (From Mike's Electric Stuff) once designed a 10+ kW led lamp (with a bunch of small generators) which was flown across London dangling below a helicopter (I would have liked to see that for real).
There is a youtube video about the contraption, and part of that video is about landing the thing (which needed a few men personnel) but before anyone could touch it, it has to be discharged through a long pole and some wires.
Helicopters generate a lot of wind, and this turns then into a quite big vandergraaf generator.
Normally all airplanes are also grounded with a clamp before and during refueling.

"Discharging" does not necessarily mean to bring the charge to zero, but to get it to an equilibrium with the local charge level on the GND where the helicopter lands.
I once heard there is a shortage of electrons in the universe, which means that on average everything will be positively charged.

Also fun to research:
Have a look at ion drives for satellites. These things work by expelling charged particles, and they have some pointy antenna's to get rid of excessive amount of electrons.