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Registered Member #575
Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263
Back in my "explode stuff up with capacitors" days I charged a 600J 3kV bank into a cup filled with saltwater.. The purpose was to safely discharge the bank, that's not what happened.
The saltwater instantly "boiled" popped the ground base of the cup while the rest was intact, I got the taste of a few kV running through my body and afterwards had a hard time explain why my whole workbench was wet and there was a nice round stain on the sealing. There was also question asked why my father sat in the living room with annoying peeping sound in his hears due to a large bang.
The moral of this story is; there is a clear parallel between too much salt in saltwater and too much voltage.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
101111 wrote ... Back in my "explode stuff up with capacitors" days I charged a 600J 3kV bank into a cup filled with saltwater.. The purpose was to safely discharge the bank, that's not what happened.
The saltwater instantly "boiled" popped the ground base of the cup while the rest was intact, I got the taste of a few kV running through my body and afterwards had a hard time explain why my whole workbench was wet and there was a nice round stain on the sealing. There was also question asked why my father sat in the living room with annoying peeping sound in his hears due to a large bang.
The moral of this story is; there is a clear parallel between too much salt in saltwater and too much voltage.
Very interesting. I'm sure you had figured, correctly, that 600 J would not heat water very much. For example, 60 grams of water (if uniformly heated) would get warmer by only 2.4 degrees C. Did you figure out what happened? Perhaps current and power concentration near the surface of an electrode with very small contact area. (did you close the circuit by dipping one wire into the saltwater?) Or high voltage might punch through the bottom of the cup, with the salt water as one electrode and a metal table top as the other?
Good point about surprises (and many accidents) caused by un-expected behavior in systems we think we understand.
In the early 1970's, "large" coke bottles (32 oz?) were made of thick glass, with thin aluminum screw caps, and were returned to the store for refilling. I made a self-powered squirt gun by putting water and dry ice into such a bottle, with a small hole in the cap. When the bottle was turned sideways (aimed into a sink), the jet of vapor was replaced by a jet of water. It got stronger by the second, as pressure built up. Suddenly there was a loud bang and water everywhere. For a moment I thought the bottle had exploded, and I wondered how many stitches I would need. Then I found myself intact, the bottle across the room, and a big dent in the ceiling. The cap had stripped its threads and blown off, discharging the remaining water in an instant and turning the bottle into a rocket which struck nothing vital.
Note: modern PET soda bottles, when overpressured (such as by storage in a hot car), fail by bursting before the cap threads strip. I bet this is also by design, because now a flying cap would be the greater safety hazard.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
First of all, see the existing "Deceitful Electronics" thread.
These kinds of water explosions happen often on 4hv, they're the basis for the so-called "Electrothermal gun".
What happens, as far as I know, is that the discharge vaporises a small part of the water, and the resulting pocket of mega-superheated steam/plasma expands violently and blows the rest of the experiment to smithereens. Probably some of the water gets dissociated, and the resulting hydrogen and oxygen mixture explodes too.
I had a similar incident to Klugesmith with a CO2 powered squirt gun. Mine was operated by a CO2 canister, and the expanding gas caused the water to freeze and block the outlet. The PET bottle reservoir blew its cap and launched itself about 50ft in the air.
Registered Member #575
Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263
Klugesmith wrote ...
101111 wrote ... Back in my "explode stuff up with capacitors" days I charged a 600J 3kV bank into a cup filled with saltwater.. The purpose was to safely discharge the bank, that's not what happened.
The saltwater instantly "boiled" popped the ground base of the cup while the rest was intact, I got the taste of a few kV running through my body and afterwards had a hard time explain why my whole workbench was wet and there was a nice round stain on the sealing. There was also question asked why my father sat in the living room with annoying peeping sound in his hears due to a large bang.
The moral of this story is; there is a clear parallel between too much salt in saltwater and too much voltage.
Very interesting. I'm sure you had figured, correctly, that 600 J would not heat water very much. For example, 60 grams of water (if uniformly heated) would get warmer by only 2.4 degrees C. Did you figure out what happened? Perhaps current and power concentration near the surface of an electrode with very small contact area. (did you close the circuit by dipping one wire into the saltwater?) Or high voltage might punch through the bottom of the cup, with the salt water as one electrode and a metal table top as the other?
Good point about surprises (and many accidents) caused by un-expected behavior in systems we think we understand.
In the early 1970's, "large" coke bottles (32 oz?) were made of thick glass, with thin aluminum screw caps, and were returned to the store for refilling. I made a self-powered squirt gun by putting water and dry ice into such a bottle, with a small hole in the cap. When the bottle was turned sideways (aimed into a sink), the jet of vapor was replaced by a jet of water. It got stronger by the second, as pressure built up. Suddenly there was a loud bang and water everywhere. For a moment I thought the bottle had exploded, and I wondered how many stitches I would need. Then I found myself intact, the bottle across the room, and a big dent in the ceiling. The cap had stripped its threads and blown off, discharging the remaining water in an instant and turning the bottle into a rocket which struck nothing vital.
Note: modern PET soda bottles, when overpressured (such as by storage in a hot car), fail by bursting before the cap threads strip. I bet this is also by design, because now a flying cap would be the greater safety hazard.
A bit wrong formulated by me, you are right, portions of the water spontaneously heated up causing a high rise in pressure. If all the water instantaneously boiled there wouldn't be a nice round stain in the sealing and I could probably also peel of my skin fairly easily not to mention 3 degreed burns on half of my body.
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