Run a thousand-watt electric heater for 11 seconds, or a 100HP motor for 0.15 seconds. It’s the energy released by 2.5 grams of TNT, so it’s like a big firecracker, or maybe a couple of shotgun shells. For fast discharge cap (high voltage energy storage,) ten kilojoule discharges can deafen you temporarily, or blow a fist-sized hole in a fist-sized potato.
There is more to life than energy density. For high power / high current loads, a high energy density is meaningless if the capacitor or battery has a very limited power rating during discharge due to a high internal (Thévenin equivalent) impedance. For high power / high current loads, a 24 V, 100 Ah battery with an internal impedance of 0.01 ohms is a lot more useful than a 24 V, 1000 Ah battery with an internal impedance of 5 ohms.
Something else to consider: we may get more bang for the buck by concentrating on improving the *voltage *rating of high-density capacitors rather than the capacity (in farads). And then building efficient circuits to convert the high voltage on the caps to a lower (but more useful) voltage for the load.
If you have a 500amp supply handy, which I don’t.
Certainly plausible, given that the energy storage scales with the square of the voltage. And the voltage-converting circuits would probably be necessary anyway, for evening out the voltage output as the cap discharges.
500 amps at 2.7V is only 1.375 Kwatts. My wife’s hair dryer is more than that. But your point is a good one. 500 amps needs more than 1/2 inch diameter copper wire to be code. I actually could not quickly find the size of wire needed for 500 amps.
American Wire Gauge Chart and AWG Electrical Current Load Limits table with ampacities, wire sizes, skin depth frequencies and wire breaking strength only goes up to 380 amps. 380 amps is .46 inches in diameter.
You don’t?
“Igor!? Throw. The. Switch!!!”
I absolutely love the SDMB. I didn’t know capacitors of the size under discussion even existed; it used to drive me insane trying to come up with the physical size of a 1.0 farad capacitor and making those calculations was entirely just for fun.
Catching on fire or bursting is one thing, releasing all of the stored energy in an instant is a lot more dangerous. Especially if we’re looking at improvements in the technology that allow it to store a lot more energy. Right now this capacitor holds the energy equivalent of a big firecracker, improve capacity 100 fold and it’s practically a bomb.
Thats what fuses are for…
Actually, that’s a valid question. What sorts of failure modes would cause a capacitor to dump its energy quickly, and what would be the effect of that sort of dump? There’s more than one way to dump energy: Would it explode, or would it melt the metal in its vicinity, or would it release a broad-spectrum EMP? A fuse would help protect against shorts, as long as the short wasn’t to somewhere on the wrong side of the fuse, but what if, say, the capacitor gets impaled on a sharp bit of wreckage, or the casing is melted? If the storage in a car is designed as a bunch of capacitors all bundled together, would a failure of one of the individual units cascade to the others?
batteries can release enough energy in a fraction of a second to weld a large piece of metal shorting it, if that metal has low current capacity it will incandesce and melt.
make and model please.
If I were designing such a system, I would put fuses between each capacitor, so an individual short would not discharge the entire bank. A single capacitor shorting would probably make quite a bang, but would not result in a catastrophic explosion.
Fuses are a reasonable precaution, but with enough stored energy, does an exploding capacitor damage nearby capacitors enough for them to explode? The issue I’m having is that the physical integrity of the capacitor is the only thing that contains the energy, once that is breached, all of the energy can be released immediately. Not necessarily a huge issue in a flashlight, but you need a lot of energy to move a car any significant distance.
With a battery, even if you have a short, there’s a limitation to how quickly the chemical reaction can happen, and very high current will melt whatever is causing the short. It may cause a fire, but a significant amount of the stored energy stays stored in the chemicals.