3 ms·

This is true of all energy storage. Your laptop lithium-ion batteries are pretty decent fire starters when shorted correctly (incorrectly?). This is why there

by mey 11y ago

This is true of all energy storage. Your laptop lithium-ion batteries are pretty decent fire starters when shorted correctly (incorrectly?). This is why there is so much safety circuitry in batteries. https://www.youtube.com/watch?v=HCGtRgBUHX8 https://www.youtube.com/watch?v=HCGtRgBUHX8 Another way to think about it is to compare Energy Density to larger scale things we have closer experiences with, such as Gasoline https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density The difference between a fire and explosion is really how quickly you can release the energy potential, so capacitors should be rather interesting in that case.

jws 11y ago
The trick with capacitors such as these is that you are talking 1nm spacing between the layers. It doesn't take much to punch through a layer, and if that releases enough energy to get through the next, then you might have an exciting day. The thinnest metalized, plastic film capacitors have a plastic film 600nm thick.¹ ␄ ¹ https://en.wikipedia.org/wiki/Film_capacitor https://en.wikipedia.org/wiki/Film_capacitor wherein you will also learn that the process of making the ends of the metalized plastic conductive by a "schoopage" process, named after Max Schoop who invented combustion spray method for the application of tin and lead. And now I am lost down the internet wormhole, "Detonation thermal spraying" is a thing! Explode your contacts into place!
mitchty 11y ago
Yep, all batteries and capacitors amount to is electron storage devices. Capacitors are much more prone to becoming coulomb bombs than batteries mostly because they are designed to discharge quickly, which is what makes them implicitly good bombs. It doesn't take much electron movement to make an explosion. In fact, this is how alkali metals react with water. We learnt that only in the past few years. http://www.nature.com/nchem/journal/v7/n3/full/nchem.2161.html http://www.nature.com/nchem/journal/v7/n3/full/nchem.2161.ht... https://www.youtube.com/watch?v=LmlAYnFF_s8 https://www.youtube.com/watch?v=LmlAYnFF_s8
ridgeguy 11y ago
Agree - rate of energy release is everything. A pound of hamburger releases about 1152 kcal, or about 4.8 megaJoules of energy when metabolized over a day or so after it's eaten. One pound of TNT releases about 2 megaJoules of energy in a few microseconds when it's detonated. Big difference in the results. One makes me fat. The other makes me dead. I'd be worried about a super capacitor that contained a week's worth of my laptop energy, and that might release it in a second.
- pavs 11y ago
  > Big difference in the results. One makes me fat. The other makes me dead. Well both makes you dead, but at different rate...
- jmichelz 11y ago
  Actually the bun (and ketchup) makes you fat. The meat (and fat in it) makes you thin. https://en.wikipedia.org/wiki/Why_We_Get_Fat https://en.wikipedia.org/wiki/Why_We_Get_Fat
ChuckMcM 11y ago
Not exactly. Batteries store energy in a reversible chemical process. In so doing their ability to discharge that energy is limited by the rate at which that reaction can occur internally. The reaction is exothermic so the batteries get hot and sometimes catch on fire. Lithium ones are particularly nasty as the materials are reactive with oxygen in the air so once the battery begins to disassemble itself the additional reactions are started. Capacitors on the other hand simply store charge. There is no chemical process involved and so their internal resistance is much much lower (it is basically the metal conductivity of the plates and the wires to the plates). So a capacitor with with the equivalent of 2mJ of charge, can release it all in picoseconds. [1] Such an energy release would be indistinguishable by people observing it from any other high explosive detonation. Further is would have no warning, batteries at least get hot, then start smoking, and then catch on fire. This would simply consume what ever conductor had shorted it and immediately turn it into a raging ball of plasma. [1] I once considered a supercap as a "fun" battlebots weapon with the 'fork of dooooom' which when it hit your bot would vaporize that section.

by mey 11y ago

jws 11y ago

The trick with capacitors such as these is that you are talking 1nm spacing between the layers. It doesn't take much to punch through a layer, and if that releases enough energy to get through the next, then you might have an exciting day. The thinnest metalized, plastic film capacitors have a plastic film 600nm thick.¹ ␄ ¹ https://en.wikipedia.org/wiki/Film_capacitor https://en.wikipedia.org/wiki/Film_capacitor wherein you will also learn that the process of making the ends of the metalized plastic conductive by a "schoopage" process, named after Max Schoop who invented combustion spray method for the application of tin and lead. And now I am lost down the internet wormhole, "Detonation thermal spraying" is a thing! Explode your contacts into place!

mitchty 11y ago

Yep, all batteries and capacitors amount to is electron storage devices. Capacitors are much more prone to becoming coulomb bombs than batteries mostly because they are designed to discharge quickly, which is what makes them implicitly good bombs. It doesn't take much electron movement to make an explosion. In fact, this is how alkali metals react with water. We learnt that only in the past few years. http://www.nature.com/nchem/journal/v7/n3/full/nchem.2161.html http://www.nature.com/nchem/journal/v7/n3/full/nchem.2161.ht... https://www.youtube.com/watch?v=LmlAYnFF_s8 https://www.youtube.com/watch?v=LmlAYnFF_s8

ridgeguy 11y ago

Agree - rate of energy release is everything. A pound of hamburger releases about 1152 kcal, or about 4.8 megaJoules of energy when metabolized over a day or so after it's eaten. One pound of TNT releases about 2 megaJoules of energy in a few microseconds when it's detonated. Big difference in the results. One makes me fat. The other makes me dead. I'd be worried about a super capacitor that contained a week's worth of my laptop energy, and that might release it in a second.

pavs 11y ago
> Big difference in the results. One makes me fat. The other makes me dead. Well both makes you dead, but at different rate...
jmichelz 11y ago
Actually the bun (and ketchup) makes you fat. The meat (and fat in it) makes you thin. https://en.wikipedia.org/wiki/Why_We_Get_Fat https://en.wikipedia.org/wiki/Why_We_Get_Fat

ChuckMcM 11y ago

Not exactly. Batteries store energy in a reversible chemical process. In so doing their ability to discharge that energy is limited by the rate at which that reaction can occur internally. The reaction is exothermic so the batteries get hot and sometimes catch on fire. Lithium ones are particularly nasty as the materials are reactive with oxygen in the air so once the battery begins to disassemble itself the additional reactions are started. Capacitors on the other hand simply store charge. There is no chemical process involved and so their internal resistance is much much lower (it is basically the metal conductivity of the plates and the wires to the plates). So a capacitor with with the equivalent of 2mJ of charge, can release it all in picoseconds. [1] Such an energy release would be indistinguishable by people observing it from any other high explosive detonation. Further is would have no warning, batteries at least get hot, then start smoking, and then catch on fire. This would simply consume what ever conductor had shorted it and immediately turn it into a raging ball of plasma. [1] I once considered a supercap as a "fun" battlebots weapon with the 'fork of dooooom' which when it hit your bot would vaporize that section.