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For a start, there will be a temperature at which the dielectric fails - at this temperature, the energy is released instantly.
Plasma has a lot higher resistance than electrolyte and it will be plasma long before even a fraction of the energy is turned to heat. Nevermind the fact that the electrolyte will probably boil first any way before the dielectric fails.QuoteAt the failure point, it could be nanoseconds.
Seems fantasy to me.QuoteSecondly, when you have very high energy stored in capacitors (I am talking at least 10x the current best), there is enough energy when released to vapourise the capacitors materials.
The electrolyte first, which will push charges apart rather than into recombination. The plasma will have far higher resistance than the original internal resistance of the capacitor. The whole thing will just get hot, relatively slowly. -
The electrolyte first, which will push charges apart rather than into recombination. The plasma will have far higher resistance than the original internal resistance of the capacitor. The whole thing will just get hot, relatively slowly.
This doesn't sound like you are talking about the potential supercaps at all. The theoretical capacitance of graphene is 550F/gram of graphene. An extraordinary number. This is based on sheets of graphene an atom thick. They are still trying to work out what kind of structure can work with this since graphene sheets want to stick together. They are looking at ides like structures with curved sheets. The dielectric gap is about 1 nanometer in this theoretical capacitor. Graphene is extraordinarily strong and so the physical stress is extreme.
Do you believe that if the structure holding two opposing charges 1 nanometer apart breaks down, the charges will take their time travelling the diameter of a handful of atoms? I suggested the charge could cross in nanoseconds which is very slow for that gap.
Ok, lets say I am wrong.
Lets say things like the Graphene supercaps are intrinsically safe.
"You can hold 10 times the energy density of TNT in your pocket held apart by a 1 nanometer dielectric and it is incredibly safe!. If this capacitor fails, an App will message you to give you warning. "
"You can drive you kids in a car with a battery holding the equivalent of 500 kG of TNT and it is totally safe!".
"Firefighters can walk up to a burning capacitor powered car battery when the battery is at 250 degrees C with no fear of that the 2000 MegaJoules of energy about to be released is dangerous".
(Just using 250 deg C because some of the current graphene caps in development use plastics in the construction.)
That is incredible news. It is truly amazing! There must be capacitor developers who cannot stop talking about this.
But no-one is talking about it. No flashy website mentions failure modes. If I am wrong, can you find me a single capacitor developer who explains why these future supercapacitors are safe? How it is impossible to make a bomb out of a supercapacitor?
I would absolutely love to be proven totally wrong.
I would love it if a failing future supercap can just calmly vent a bit of electrolyte and suddenly all the energy is ....where?
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I don't think that Dave would volunteer to perform destructive tests on these units.
But there is this crazy Youtube guy who likes to experiment and destroy all things electrical..... I forget his name....he may want to do it and post a video. -
This doesn't sound like you are talking about the potential supercaps at all. The theoretical capacitance of graphene is 550F/gram of graphene.
Anything build and buildable uses graphene as a jumbled bunch of planes, they are not trying to wind billions of flawless layers of nanometer thin electrodes and insulators.
My point isn't that the energy disappears, my point is the enemy gets converted to heat slowly. A fire and an explosion can have the same energy converted to heat, with radically different results.
hayatepilot, nice catch on that Maxwell relabeling scam. Here's another one of their sites. -
My point isn't that the energy disappears, my point is the enemy gets converted to heat slowly. A fire and an explosion can have the same energy converted to heat, with radically different results.
Based on what? Is there anything any researcher has reported to confirm that this remarkable technology that can store orders of magnitude more energy then any chemical reaction will release heat slowly. It sounds like an opinion.
As I said, I would love to see proof that this technology is so intrinsically safe that safety does not need to be discussed, and no website promoting its use has to have a page on safety issues and research.
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On their website they claim 115 Wh/kg
The first google result for "energy density graphene super capacitor" is a paper claiming 148.75 Wh kg?1
"Using a scalable nanoporous graphene synthesis method involving an annealing process in hydrogen, here we show supercapacitors with highly porous graphene electrodes capable of achieving not only a high power density of 41 kW kg?1 and a Coulombic efficiency of 97.5%, but also a high energy density of 148.75 Wh kg?1."
It doesn't seem far fetched based on that. -
hayatepilot, nice catch on that Maxwell relabeling scam. Here's another one of their sites.
"Bus energy storage solutions that can charge in less than 3 minutes"
How do they charge these things so quickly, or have they just not worked out the currents and Watts needed.
I think the fork lift video shows 40A running, and 80A charging. -
They claim there is no regulation inside but a capacitor would normally have a linear discharge profile so I can't see how this can maintain approx 48VDC through 100% depth of discharge.
They are careful with their wording, making statements such as "the supercapacitor itself requires no regulation".
However, there is a constant mention of a "small discharge stabilising lithium battery" in some of the videos & the technical literature.
The following would make sense:
1/ The output of the supercapacitor is connected to a charge regulator;
2/ The output of the charge regulator is connected to the "small" 48V lithium battery;
3/ The output of the 48V lithium battery powers the forklift motor.
The supercapacitors voltage falls as it discharges. As this occurs, the lithium battery's charge regulator compensates for this falling voltage by increasing the charge current.
This process continues until the supercapacitors voltage has fallen to the point that the charge controller can no longer provide charge to the "small" lithium battery.
This charge controller could well also include some voltage step up circuitry to continue to provide energy to the "small" lithium battery when the supercapacitors voltage has fallen well below the 48V+ required to charge the "small" lithium battery. A well designed step up voltage controller could probably run until the supercapacitors voltage has fallen to just a couple of volts. -
Quote
You can drive you kids in a car with a battery holding the equivalent of 500 kG of TNT and it is totally safe!
Hmm, not very convincing
I already drive daily with a vehicle tank holding the energy equivalent of 500kg of TNT and it's more or less safe.
But I walk my kid to school, that's much better than taking the car ! -
Neither petrol or batteries have the physical possibility to release their energy quickly. Petrol has to be dispersed in a massive volume of air to fully explode. In batteries, the reagents are physically separated. In TNT and supercapacitors, the energy has the capability to be release instantly.
With petrol and batteries, firefighters can have strategies to control the danger. There is nothing that can be done to make safe a battery that could be undergoing thermal runaway. In a supercapacitor, the only thing preventing an explosion is a super stressed dielectric that may be as thin as 1 nanometre thick.
Why do you think supercapacitor safety should be a taboo subject of concern? No developer wants to mention it. -
With petrol and batteries, firefighters can have strategies to control the danger. There is nothing that can be done to make safe a battery that could be undergoing thermal runaway. In a supercapacitor, the only thing preventing an explosion is a super stressed dielectric that may be as thin as 1 nanometre thick.
Why do you think supercapacitor safety should be a taboo subject of concern? No developer wants to mention it.
What about a divide and conquer strategy? Split it up into small enough units where the explosion can be contained well enough to prevent a chain reaction.
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That is an engineering discussion you can only have once you admit their is a danger. My problem is no one wants to admit there is a danger. If it takes great engineering to make it safe, then that implies that engineering can make it unsafe and we are talking potentially about more energy then any non-nuclear bomb.With petrol and batteries, firefighters can have strategies to control the danger. There is nothing that can be done to make safe a battery that could be undergoing thermal runaway. In a supercapacitor, the only thing preventing an explosion is a super stressed dielectric that may be as thin as 1 nanometre thick.
Why do you think supercapacitor safety should be a taboo subject of concern? No developer wants to mention it.
What about a divide and conquer strategy? Split it up into small enough units where the explosion can be contained well enough to prevent a chain reaction.
The ultimate problem is that at a certain temperature, the dielectric will break down. At that point, there is nothing left to hold the charges apart. Also there is a possibility that if the dielectric is near breaking point, a shockwave will cause breakdown. I keep mentioning the danger if a car caught up in a fire. If you break up a single capacitor equivalent to 200 kg of TNT into the equivalent of 100 x 2kg sticks of TNT, do you feel safe now? How would you like to be a firefighter knowing that at any moment one of these 2kg TNT equivalents was going to go off, and that after that, there are 99 more to follow shortly?
When you start looking at potential supercapacitors - the ones that could power a car for hundreds of kilometres, you are starting to get energy densities where even capacitor leakage is a major heating problem. Basically these capacitors not only have to be orders of magnitudes higher in their energy density then anything currently available, they basically have to be made so they never get significant leakage. Leakage is a problem that usually increases with temperature so you can get a runaway.
If a imminent capacitor failure could be detected, you could design the batteries to eject from the car in fragments, but that assumes you are surrounded by free space where these energy dense fragments can go safely. Not sure how you can eject anything from a phone in your pocket if a thermal runaway was detected. -
If you break up a single capacitor equivalent to 200 kg of TNT into the equivalent of 100 x 2kg sticks of TNT, do you feel safe now? How would you like to be a firefighter knowing that at any moment one of these 2kg TNT equivalents was going to go off, and that after that, there are 99 more to follow shortly?With petrol and batteries, firefighters can have strategies to control the danger. There is nothing that can be done to make safe a battery that could be undergoing thermal runaway. In a supercapacitor, the only thing preventing an explosion is a super stressed dielectric that may be as thin as 1 nanometre thick.
Why do you think supercapacitor safety should be a taboo subject of concern? No developer wants to mention it.
What about a divide and conquer strategy? Split it up into small enough units where the explosion can be contained well enough to prevent a chain reaction.
Well you could say the same about petrol or lithium batteries. Any pockets of petrol that didn't go up in an initial explosion could explode at a later time when/if the fuel-air mix reach the correct proportions. If the thing is burning then no firefighter is going to be happy standing next to it regardless of what the fuel is. If it is not burning then engineering needs to be done to reduce the risk of the entire pack going up at once. Damaged lithium batteries can also self ignite without warning.
The point is that with proper (rigourous of course) engineering it should be possible to lower the risk to a similar level to current technology.
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Petrol and batteries are not physically capable of being fractionally as dangerous as capacitors.
Well you could say the same about petrol or lithium batteries. Any pockets of petrol that didn't go up in an initial explosion could explode at a later time when/if the fuel-air mix reach the correct proportions.
There is no mechanism in a burning car for the petrol to suddenly be evenly mixed with 588 kg of air. That is about 490 cubic meters of air. If petrol is not evenly distributed, it is not very dangerous - as seen in all the movie car explosions. Lots of fire but not much explosion. When it is mixed evenly before ignition, you end up with one of the most horrific bombs currently available. Kills you even if you are sheltered.
The inherent safe of petrol is the reason firemen can approach a burning car and smother the flames. All they have to do is keep air from the petrol and the reaction stops completely.
There is no possible way for the reagents in a battery to suddenly become perfectly mixed together. They are physically separated.
Petrol and batteries are in one class of safety that is manageable.
TNT and Supercapacitors are in a different class. They are inherently not manageble when they become unstable. Once a dielectric is breaking down, there is no intervention that can stop it.
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Petrol and batteries are not physically capable of being fractionally as dangerous as capacitors.
Well you could say the same about petrol or lithium batteries. Any pockets of petrol that didn't go up in an initial explosion could explode at a later time when/if the fuel-air mix reach the correct proportions.
There is no mechanism in a burning car for the petrol to suddenly be evenly mixed with 588 kg of air. That is about 490 cubic meters of air. If petrol is not evenly distributed, it is not very dangerous - as seen in all the movie car explosions. Lots of fire but not much explosion. When it is mixed evenly before ignition, you end up with one of the most horrific bombs currently available. Kills you even if you are sheltered.
The inherent safe of petrol is the reason firemen can approach a burning car and smother the flames. All they have to do is keep air from the petrol and the reaction stops completely.
There is no possible way for the reagents in a battery to suddenly become perfectly mixed together. They are physically separated.
Petrol and batteries are in one class of safety that is manageable.
TNT and Supercapacitors are in a different class. They are inherently not manageble when they become unstable. Once a dielectric is breaking down, there is no intervention that can stop it.
Yes I get your point. However I think dicing the super cap up into little, well protected bits solves the problem. And in this way it _slows the reaction down_.
Engineering will figure out how big the bits can be given the various constraints.
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Dielectric break down on that scale is not fun.. i used to do work with oil cooled motors and supercaps. Seen plenty of mfg defects arc / explode either and it's not something you want to be around. If these guys had something good they would be giving musk a run for the money. More likely someones fodder project that has been ear marked with grants and it working or not isn't really the point.
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If these guys had something good they would be giving musk a run for the money.
This.
Supercaps are not really useful as longer term energy storage.
They can still store only 1/10 of the energy of modern-and-cheap lithium batteries.
They are pretty much only useful as short time buffers... -
There is no mechanism in a burning car for the petrol to suddenly be evenly mixed with 588 kg of air.
There is no mechanism for a sonic shockwave to cause charge recombination in a EDLC fast enough to amplify said shockwave (ie. detonation). -
There is a whole lot of speculation here on things that can go wrong with a new technology that is not yet proven to scale, and a whole lot of assumptions. I don't think they are going to build one giant supercap for a car since the voltage is too low. As soon as you have a lot of stuff in series/parallel combinations, there are a lot of different safety options you can add. This is already done with existing Li-based batteries.
Additionally, supercaps are not true electrostatic capacitors - they depend on the motion of ions, and and such do not have a true dielectric, nor are they especially fast compared even to conventional electrolytic caps, i.e. the ions don't move that fast. Hence, they are not recommended even for 50 or 60 Hz ripple filtering, which is on a time scale of 10-20 ms. In contrast, detonation propagation in TNT is about 6000m/s, so a gas-tank sized piece of TNT would completely detonate in 50-100 us, depending on whether it was detonated in the corner or middle. This is at least two orders of magnitude faster than a supercap. If the technology improves the time constant by a factor of 10, that's still at least one order of magnitude below TNT, and that would be for one giant supercapacitor.
How about giving them a chance to succeed? Then a lot of us will have interesting work to do to figure out how to best make use of it.
John -
That's great. Can you explain the physical reasons for that statement? I would love to know.There is no mechanism in a burning car for the petrol to suddenly be evenly mixed with 588 kg of air.
There is no mechanism for a sonic shockwave to cause charge recombination in a EDLC fast enough to amplify said shockwave (ie. detonation). -
It doesn't happen with existing EDLCs. The necessity of the electrolyte to facilitate the charge transfer, which it seems to me to be impossible to maintain stable enough for long enough to do so, instead as far as I can see in an explosion it and the rest of the capacitor simply gets blown into an inhomogeneously charged cloud (with very slow moving electrons) long before it can add any energy.
No scientist as far as I can see has ever thought detonation a failure mode worth spending any writing on ... it seems to me utterly outlandish. -
That's great. Can you explain the physical reasons for that statement? I would love to know.There is no mechanism in a burning car for the petrol to suddenly be evenly mixed with 588 kg of air.
There is no mechanism for a sonic shockwave to cause charge recombination in a EDLC fast enough to amplify said shockwave (ie. detonation).
Lookup something along the lines of detonation velocity and examine say plain ol det cord
Supercaps on the other hand are made of materials that are much more stable and as such less conducive to a physical shockwave traveling down the substance compressing the material to the point of self explosion
Similar principles to a nuke as well.. the material must first be compressed to the point of reaction and once that point is achieved the reaction is self sustaining.
That said a real foe of supercaps is overcharging them or repeated cycling that breaks down the material to the point of arcing which can cause a nasty electrical fire hazard and that can chain to other nearby capacitors and also break them down from the added heat / electrical arcing -
Supercaps of the type that are being researched do not exist in any large capacitance value yet. Some exist in labs often as a signal layer capacitor the size of a coin, but even these are way down the low end of the target capacitance densities. No-one has yet gone anywhere near the porential energy densities. I am not sure how you can claim that hard materials like ceramic and graphene are not conducive to a shockwave. These are materials that will probably be under higher stress then any existing material in use today.
That's great. Can you explain the physical reasons for that statement? I would love to know.There is no mechanism in a burning car for the petrol to suddenly be evenly mixed with 588 kg of air.
There is no mechanism for a sonic shockwave to cause charge recombination in a EDLC fast enough to amplify said shockwave (ie. detonation).
Lookup something along the lines of detonation velocity and examine say plain ol det cord
Supercaps on the other hand are made of materials that are much more stable and as such less conducive to a physical shockwave traveling down the substance compressing the material to the point of self explosion
Similar principles to a nuke as well.. the material must first be compressed to the point of reaction and once that point is achieved the reaction is self sustaining.
That said a real foe of supercaps is overcharging them or repeated cycling that breaks down the material to the point of arcing which can cause a nasty electrical fire hazard and that can chain to other nearby capacitors and also break them down from the added heat / electrical arcing
I think you want it to be no problem. I have had some really funny arguments defending supercaps. That does seem to be the approach of the whole industry. I repeat the challenge. Can you find one single research paper that demonstrates the safety of supercapacitors that would be candidates for cars, etc? You are talking about potentially orders of magnitudes more energy density then any known chemical reaction and you have convinced yourself that there is absolutely no conceivable problem. Don't have to study it or talk about it, it is just so safe I gather. -
Supercaps of the type that are being researched do not exist in any large capacitance value yet. Some exist in labs often as a signal layer capacitor the size of a coin, but even these are way down the low end of the target capacitance densities. No-one has yet gone anywhere near the porential energy densities. I am not sure how you can claim that hard materials like ceramic and graphene are not conducive to a shockwave. These are materials that will probably be under higher stress then any existing material in use today.
That's great. Can you explain the physical reasons for that statement? I would love to know.There is no mechanism in a burning car for the petrol to suddenly be evenly mixed with 588 kg of air.
There is no mechanism for a sonic shockwave to cause charge recombination in a EDLC fast enough to amplify said shockwave (ie. detonation).
Lookup something along the lines of detonation velocity and examine say plain ol det cord
Supercaps on the other hand are made of materials that are much more stable and as such less conducive to a physical shockwave traveling down the substance compressing the material to the point of self explosion
Similar principles to a nuke as well.. the material must first be compressed to the point of reaction and once that point is achieved the reaction is self sustaining.
That said a real foe of supercaps is overcharging them or repeated cycling that breaks down the material to the point of arcing which can cause a nasty electrical fire hazard and that can chain to other nearby capacitors and also break them down from the added heat / electrical arcing
I think you want it to be no problem. I have had some really funny arguments defending supercaps. That does seem to be the approach of the whole industry. I repeat the challenge. Can you find one single research paper that demonstrates the safety of supercapacitors that would be candidates for cars, etc? You are talking about potentially orders of magnitudes more energy density then any known chemical reaction and you have convinced yourself that there is absolutely no conceivable problem. Don't have to study it or talk about it, it is just so safe I gather.
You lost me... I just called them out for the fire hazard they are x_x
That said I'd be surprised at a huge explosion type release, more of a giant arc welder that melts / destroys everything in its path including a person would be my own bet if they got that dense. I dont see how this would be too different than dielectric breakdown of large motor windings really. Huge fire/smoke/shock/arc welding concern more so than physical explosion since they would rather all short out and fuse/melt together.
Im not keen on lithium either... seen plenty of failed lithium reactions. In the end though if it isnt safe it will never see light of day less fully autonoums and the reward was far greater than risk given -
You lost me... I just called them out for the fire hazard they are x_x
As I mentioned, Lithium batteries are much safer as they have the reagents physically seperated so they cannot release energy quickly. There is no physical reason to think that a supercapacitor fire would be as slow as a lithium battery fire.
That said I'd be surprised at a huge explosion type release, more of a giant arc welder that melts / destroys everything in its path including a person would be my own bet if they got that dense. I dont see how this would be too different than dielectric breakdown of large motor windings really. Huge fire/smoke/shock/arc welding concern more so than physical explosion since they would rather all short out and fuse/melt together.
Im not keen on lithium either... seen plenty of failed lithium reactions. In the end though if it isnt safe it will never see light of day less fully autonoums and the reward was far greater than risk given
You are comparing future supercapacitor breakdowns to motor winding breakdowns? There is not even the slightest comparison. Dielectrics in motors are massively thick compared to supercaps, and the energy released in a motor failure is not enough to turn the whole motor into vapourised metal. The difference between current supercapacitors as the ones that can power cars is that the current ones have enough mass to absorb the energy while still remaining a solid. If you have a 200kWh capacity (10 hours highway driving) that weights 200kg, there is not enough mass in the capacitor to absorb the energy without turning into gas.