This post from 2007 was about a highly entertaining YouTube clip of some people pulling arcs from a long string of nine-volt batteries. With those neat little clip connectors, 9V batteries are just begging to be clipped together into very long, very dangerous daisy-chains. And, in that particular case, they had 125 batteries in series, by my count. That adds up to a nominal 1125 volts DC.
(The 9V terminals are also, of course, clearly intended to make them easy to lick.)
But now, unfortunately, that video's been removed.
So I went hunting for more experiments of this type.
Here's a string of 19 (for 171 volts DC, nominal) running a compact fluorescent lamp:
The experimenter boldly holds the thin-insulation alligator-clip leads in his bare hands, but that's as exciting as this video gets. Interesting to see that these lamps run from DC as happily as from AC, though.
Here's some fun with 52 batteries:
That'd give 468V if the batteries were all at their nominal 9V, and could easily make it to 500V with fresh batteries. But apparently these were discarded "8.4... ish" cells of unknown provenance (my money would be on a company replacing the batteries in all of its smoke detectors). 52 times 8.4 gives a mere 437 volts, open-circuit.
(All of these voltages will plummet when you close the circuit, to start striking arcs, because the more current you ask for the further the terminal voltage will sag, and alkaline nine-volters aren't meant to deliver more than a very little current. Energizer, for instance, don't provide a maximum-current rating on the datasheet [PDF] for their standard alkaline nine-volters, but the maximum current on the load-versus-capacity graph is half an amp, at which discharge rate the capacity drops from a 25mA-load maximum of more than 600 milliamp-hours, to a little more than 300mAh. If you buy a Big Bag of Innocent Unsuspecting 9V Batteries the cheap way, by getting carbon-zinc "super heavy duty" batteries instead of alkalines, the rated current [PDF datasheet] is now only about 5mA, and the highest current on the performance graph is only 25 milliamps. You're not going to be able to pull a multi-amp arc out of a string of those poor little things for long. Ex-smoke-detector alkaline batteries will probably work a lot better for this sort of Unwise Experiment than will brand new carbon-zincs.)
Here we have 48 batteries in series - so, maybe more than 460 volts open circuit - molesting a coin:
(With, again, not as much attention paid to safety as might have been.)
Here, though, is what we've been looking for!
Four hundred and ninety 9V batteries, baby!
They're good for quite a lot of arcing before the chain's weaker links started breaking, too. I hope somebody was at least wearing a couple of pairs of sunglasses simultaneously.
490 times nine volts gives 4410V; fresh batteries would add up to more than 4700V. These are more ex-smoke-detector batteries, though; the video description says they only added up to "almost 4000V".
Even four thousand volts can't strike a very long arc by itself. The dielectric breakdown strength of dry air is about 33 kilovolts per centimetre (around 84 kilovots per inch). So four kilovolts, even with humid air helping it (and hindering electrostatic experiments...), can only strike an arc a few millimetres in length, at the very most.
Once you've struck a spark with the terminals close together, though, you can draw it out into a much longer arc, because the ionised air between the terminals - which may include vaporised matter from the terminals - is much more conductive than un-ionised air. That's how arc welding works (and Jacob's Ladders too, for that matter), and that's what's happening in the video clip.
If I ever do something like this, I think I'll leave the striking of arcs and burning of batteries for the grand finale, and do some low-current high-voltage stuff first.
5 May 2010 at 2:34 pm
I should think one ought to be able to do something interesting with electron beams - a few kV is not enough to get them moving relativistically, but you might be able to do something like measure the charge-to-mass ratio of the electron (put an electron beam in a constant magnetic field and measure the radius of the circle). Of course you need a vacuum, and your nearest CRT is a ready-made electron-beam gadget plus vacuum envelope and phosphor visualizer. In fact, surely an old TV makes a better (safer! or rather, less dangerous) high-voltage DC supply? Probably cheaper too, at least until flatscreens have completely replaced them...
5 May 2010 at 5:05 pm
Heh, this is one of those less wise demos I've long resisted putting on my science projects site. Fifteen new batteries can briefly light a 100W table lamp quite brightly. Old batteries usually still have over a half-ampere short circuit current, so each batt contributes a few watts. 490 batts = a few kilowatts at a few kilovolts.
One of the few times I've ever actually zapped myself was while working with an 1800VDC chain of old 9V batteries removed from theatrical FM microphones. (Odd, it felt just like a 60Hz shock.) A 4KV battery chain should just be able to run an electrostatic motor, but at 1800V you can use the ends of the chain to slightly deflect a tiny piece of aluminum foil, demonstrating that "static electricity" is really just high voltage. I also used its arc to perform Electric Discharge Machining on soap suds, and carved initials as flaming charcoal tracks on a dampened 2X4 board. Good times.
5 May 2010 at 7:00 pm
in the video with 490 batteries, how is the man able to hold the thinly insulated wire in his bare hand. according to what i understand, conductors get hot in proportion to the square of the current through them. the part of the wire just centimeters away from the battery terminal glows white hot. the same amount of current must be flowing through the rest of the wire. so why doesn't all the wire glow, and burn the person holding it?
5 May 2010 at 8:07 pm
@justin - the current is VERY low. The voltage drop across the conductor is where the heat is generated - heat is power, in this case amps squared times resistance. The resistance of the wire is minuscule so the heating energy can't be more than a small fraction of a watt there. The TIP of the wire is being heated by the relatively large voltage drop (and therefore resistance) at the spark gap (the rest of the air part of the conductive circuit). The temperature is high there but total heat transfer to the wire is low, so it can heat the end of the wire it is in contact with. However the heat cannot spread far down the wire before being dissipated to the air. Effectively he is holding a torch to the tip of the wire.
7 May 2010 at 8:18 am
I too recall many good times had with a roughly meter long stack of discarded wireless microphone batteries held together with packing tape. When we returned to play with it again the next day the shock stick as we dubbed it seemed to be dead until I in my infinite wisdom flicked the seemingly damaged battery from the end and brushed my fingers across opposite terminals. The resulting near 600v across my arms and chest sent the batteries flying and put me in a state of mild shock for the next few hours. The feeling of electric grip upon the inside of my chest and the craters on my index fingers were enough of a warning to my fellow stagehands not to repeat this trick again.
8 May 2010 at 4:30 pm
While working on the pilot for a UPS battery replacement project (12 12-volt lead-acid batteries in series, 144 volts and about 90 amp-hours) a cow-orker and I had a bit of a mishap. He was connecting the just-opened fresh batteries in the fiddly finicky fashion that was called for, I was writing the process documentation, and at some point in the process he managed to short the entire chain together to one of the PCBs serving as an electrical outlet. The arc blew a hole through the PCB about an inch in diameter and sprayed enough molten metal and plastic in the air to create a (fortunately) brief cross between welding spark explosions and a fair-sized sparkler. The best part is that there really wasn't another good way to get the entire assemblies back in that wouldn't have involved the exact same thing. The voltage wasn't too terrible but the amount of amps involved...I'm pretty sure we could have welded the entire case to the rolling grill it was perched on had said coworker not jumped about six feet straight backwards swearing like a stevedore.
The call we made back to our project manager involved a decent bit of profanity, the documentation acquired an interesting set of warnings about firey/shocky death and doom, and we never did wind up taking the contract.
Still, it was AWESOME.
10 May 2010 at 12:21 pm
I spent some time in Africa a few years back, working for an oil company. The old-timers had a lot of terrific war stories. The locals are all quite poor, and theft is a big problem. That includes copper power lines, whether energized(!) or not.
Of course, if you cut a 3-phase 480V power cable with a machete, it tends to short out the three phases. The short must have been spectacular--when the maintenance personnel got out to the site in the morning, the machete had a 3" hole blown clean through it, but there were no human bodies. At least this time (yes, there were such incidents...).
Funny thing, though--the power generators didn't even notice it, since they are producing a rather larger amount of power than the 3-phase-short represented. The maintenance people went out only because the breaker at the site had eventually tripped and the well went off-line.
11 May 2010 at 12:12 pm
I worked in the battery locker (lead acid) when I was in the Navy. I don't remember much about those anymore, other than I did a lot of 24 Ah batteries (and, after 8 months in there, I could pour 75% sulfuric acid on my palms and not feel it. Anywhere else, it burned... I could only BARELY feel anything when I put my hands in the baking soda catches... I was pretty stupid back then heh). In the Ni-Cad locker, we had either a 72 or 92 Ah battery (actually 2 in series to reach that). We'd have to take in the battery off the plane, charge it, discharge it for an hour, and then recharge it again. I know that sometimes I'd go in the ni-cad side and see one of those batteries completely taken apart, with big-honkin (technical term) resisters glowing an evil red draining the cells completely (one per cell). It got quite hot in there.
Still, that doesn't compare to the genny's from a P-3. 90 kVa, approximately 90 pounds, making the 2.5 ton test bench jump, and blowing 2 (of 3) 400 amp fuses. It got to the point where we were using soldier instead of the fuses while troubleshooting. Then there were the 200 amp inverters. We didn't have any double aught cable for that, so we used aught cable. You could feel the heat from about 6 inches away. Oh yeah, and the 1 million candle power landing lights... I forgot to wipe off the bulb once when I changed it out... that explosion was a WEE bit scary.
Good times :P
15 May 2010 at 5:40 pm
nice blog