As my father used to say...
Dec. 15th, 2004 12:03 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
gizaIt's not the volts that'll kill you, it's the amps!
During a period of frequent brownouts, this hospital in Manila uses a set of car batteries wired together for server backup power. Be careful, IT pilot fish warns a tech who comes to work on the system; they can supply 50 amps for an hour. But the tech isn't impressed -- it's just 12 volts, he laughs. "Minutes later, there was a loud noise, a big flash and a 'Yeow!' The tech emerged, open-mouthed and sweating - and holding a wrench that was virtually vaporized," fish reports. "No nurse was called, by the way, but a glass of cold water helped slow down his heartbeat."
![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png){kind=small}
(no subject)
Date: 2004-12-15 05:26 pm (UTC)(no subject)
Date: 2004-12-15 05:51 pm (UTC)This guy took two screw drivers, put one on each terminal of the battery and touched them together. After an impressive spark, he found that is screw drivers were now welded together.
(no subject)
Date: 2004-12-15 05:53 pm (UTC)>together.
I can't help but wonder if that would be covered under Craftsman's "lifetime warranty"?
(no subject)
Date: 2004-12-15 05:55 pm (UTC)Yeah, that's a familiar saying in amateur radio circles. If I recall correctly, a current as little as 100 mA can induce heart fibrillation at that voltage. Between 20-50 mA can cause contractions that will prevent the person from letting go. The necessary current is far less with typical 120 V AC house current.
This assumes the batteries were wired together in parallel such that the voltage provided was still 12 V DC. Car batteries can provide 100-200 A just to start the car. This is why we like fuses.
I remember hearing a friend talk about how car batteries will likely operate at 48 V DC in future cars, because of all the electronic gizmos finding their way into cars operating at 12 V DC. That requires such a high current to deliver the necessary power. So car batteries will be able to provide even more death in the future!
Energy is what kills, AFAICT.
Date: 2004-12-15 06:38 pm (UTC)Where the power calculation was used was in things like working out how big a storage capacitor you could safely put in an electric fence or a taser.
Re: Energy is what kills, AFAICT.
Date: 2004-12-15 06:39 pm (UTC)Re: Energy is what kills, AFAICT.
Date: 2004-12-15 09:27 pm (UTC)Re: Energy is what kills, AFAICT.
Date: 2004-12-15 09:40 pm (UTC)I went to junior high school with a guy who would toss "D" engines into campfires.
Last I heard, he got charged for disturbing the peace for one of his stunts. Figures.
(no subject)
Date: 2004-12-15 09:45 pm (UTC)One switchroom I was in this afternoon is 50 volts DC, 75 amps continuous. Our biggest switchroom is something like 250 amps.
Re: Energy is what kills, AFAICT.
Date: 2004-12-15 11:12 pm (UTC)The nichrome just has to get warm enough to ignite the crud they dip the filament in, for the old-style igniters, at least. Though I've heard stories about people making their own using fine copper wire.
Re: Energy is what kills, AFAICT.
Date: 2004-12-15 11:13 pm (UTC)You've heard the "alcohol and propane don't mix" story, right?
Probably a UL, but funny regardless.
Telephone circuits can be nasty.
Date: 2004-12-16 03:12 am (UTC)That would be -48V and +48v, for a differential of 72 volts. At the current some of the batteries/PSU can provide, that's more than enough to be lethal.
Even if it can't kill you...
Date: 2004-12-16 03:21 am (UTC)Ohm's law determines how much current you will actually take from any given voltage. 12V at high current isn't normally lethal as the potential is too low to penetrate the skin. It's like a huge body of water with no pressure behind it. Generally, even wet skin won't have a resistance low enough to pass 12V.
If you somehow inserted a live wire into your body... that would be a different story.
However, if the current is high enough to vaporize a wrench it could easily blast droplets of molten steel towards your eyes or skin. A great number of electricity-related injuries occur because the flash/explosion/shock from the current causes the person to fly into something nasty.
(no subject)
Date: 2004-12-16 05:49 am (UTC)I remember the Texas A&M University bonfires. Each dorm got axes for their residents to cut trees on the weekends before. They were chipped, they'd been spraypainted, some of the handles were carved with names, and every year the Sears in College Station would cheerfully take them back and issue new ones to be abused next year, completely free.
Re: Even if it can't kill you...
Date: 2004-12-16 05:50 am (UTC)Lead/acid batteries also have a nasty habit of spraying boiling sulphuric acid vapour everywhere if you abuse them hard enough. Dropping a big wrench across the terminals could very well qualify.
Re: Telephone circuits can be nasty.
Date: 2004-12-16 08:02 am (UTC)(no subject)
Date: 2004-12-16 08:03 am (UTC)Re: Telephone circuits can be nasty.
Date: 2004-12-16 05:51 pm (UTC)*is fairly clueless on electrical engineering and knows better that to "experiment"!*
Re: Telephone circuits can be nasty.
Date: 2004-12-16 09:27 pm (UTC)Nonetheless, I've seen terminals on a punch-down board labelled +72/-72 and stayed far away from them.
Melting stuff with a car battery is fun!
Date: 2005-01-02 11:00 pm (UTC)Anyway, I was doing this one time, and the white hot drop of steel fell onto the carpet, melted its way through, and stayed on the concrete foundation below. Of course, my immediate reaction was to stomp it to keep it from bursting into flame, but.. I was wearing very thin-soled slippers and the steel was still red hot.
Ouch ouch ouch. I think I was grounded for a while when my mother discovered the blackened hole in the carpet...