The large voltage potentials exists as they are structured in series and in parallel in a connected pack. You rip into that pack and you’ve exposed the connections to a shorting situation.
The Tesla uses literally thousands of batteries; its battery pack basically looks like it is composed of AAs (though they are actually a little larger than that). What happens when you “rip into that”? It is like scattering the batteries of thousand of TV remotes all over the place.
Nevermind the fact that the battery pack is under the floor. Ripping into it in the first place is the kind of collision that even airbags would struggle to help you survive.
The battery of the Tesla Model S (and presumably the other models) consists of several independent banks of hundreds of individual cells, which have fundamental limits in how much current they can provide. The individual cells are connected in parallel to achieve the desired voltage potential, and the banks are managed by a power distribution system to provide adequate current draw for the instanteous need (high under acceleration, lower under cruise). In the case that any one of the banks is disrupted (internal shorting, thermal overload, et cetera) it is shunted to prevent overvoltage. If the bank is physically broken, the connections between individual cells would be broken and the ability to develop voltage potential is eliminated. Although there are serveral hazards with a damaged battery (intense combustion, venting of toxic gases, release of caustic electrolyte), some kind of massive electrical discharge is not among them.
Stranger
That’s a complete divorce of reality.
Well, that was a substantive response. Good one.
Stranger
You connect batteries in series to get the desires voltage potential.
Magiver, did you mistake this for a political question, or something? This is just a matter of physics, with a simple and known scientific answer, and Stranger on a Train being in fact a physicist, he correctly knows that answer.
It’s not even like he’s trying to argue that ruptured battery packs are safe: He acknowledges that, depending on the sort of damage, they can be very dangerous, for multiple reasons. They’re just not the same reasons that you in your ignorance are trying to claim.
My error; you are correct. Nonetheless, batteries cannot rapidly discharge in the way that a capacitor can.
Unlike a capacitor, where energy is stored as a developed electrical charge in the potential difference between “plates” (a historical term, most capacitors are not flat plate configuration) separated by a dielectric material and will discharge (when unregulated) in an exponential fashion when connected to a circuit. (There are certain types of capacitors that do use an electrolyte as the cathode which mediates delivery of charge, and so are more “battery-like” but the energy is stored as a developed electrical charge.). In an electrochemical battery, the energy is stored in a difference between electronegativities between the cathode and anode, and electrical (conventional) current is created when the terminals are connected togetherin a circuit by the exchange of electrons through the electrolyte.
In other words, current from a capacitor is a purely electromagnetic coupling with no chemical reactions occurring (in the primary release of stored energy); current from a battery is driven entirely by electrochemical interactions within the electrolyte. If an attempt is made to overdrive the reaction rate to get a higher voltage or current delivery (by adding too much cathode and anode material for the electrolyte to manage, or heating the cell) the electrolyte and/or liner materials start to break down and emit gas products or catch fire. This is the main hazard of electrochemical batteries, and especially when they experience structural or thermal damage.
I’m an engineer (with a physics minor), but yes, large amp-hour batteries have numerous hazards. It is possible to receive a hazardous shock from an intact and nominally operating battery (hence why the first thing done when working on high voltage electrical systems is to disconnect the battery or shunt the power supply) but with one that is damaged the far greater hazard is inhaling caustic fumes, being sprayed with electrolyte from a burst case, or in extreme cases, having a battery literally explode (I have seen it happen in testing, and it is as much of a mess as you might imagine.)
The danger of such reactions is that once they start that can’t be suppressed the way a gasoline fire can be smothered from atmospheric oxygen; they’ll keep combusting or venting until the temperature drops sufficiently that the reaction starts, which often means burning of virtually all electrolyte and any other combustable materials adjacent to the battery. High amp-hour batteries can be quite dangerous when damaged or allowed to experience thermal runaway, but spontaneous electrical discharge is not one of the significant hazards.
Stranger
Hell–lead-acid batteries emit hydrogen even during normal operation. They’re an explosion hazard even when the battery itself is completely undamaged (of course, a lead-acid battery system without proper ventilation is a design failure, but that’s nothing to do with the battery itself).
That’s not how it sounds. I cited a story where the fired department feared risk of electrical shock. the answer provided did not address that issue.
You mean the same sensationalist Daily Mirror article which incorrectly implied that the Autopilot system was operating at the time of the crash? Yeah, that’s a reliable source of technical information.
Stranger
Do you have a cite that the fire department wasn’t concerned about electrical shock?
Emergency responders never have absolute certainly of their risks. They can only make a judgment based on the available evidence. Since there was no time pressure and Tesla specialists were available, they decided to wait. That doesn’t imply that either their perceived risk or the actual risk was significant. But why take even negligible risks when there’s an alternative?
It’s ever so nice the guy killed himself and there were Tesla specialists available to consult. But that doesn’t address an issue that needs to be resolved now instead of later.
EV’s are poised to enter the mass market right as gas prices are at historical lows and car companies are quickly reaching the cap on the tax credit. We don’t need another Oldsmobile diesel debacle sinking public opinion.
you’re hand waving this away.
I’m not clear on what kind of point you are trying to make but it clearly isn’t based on any factual information or technically informed speculation about the hazards of large electric vehicle battery packs. The only “handwaving” here comes from you and is based on a poorly written tabloid article.
Stranger
Yes, it’s certainly possible the fire department was concerned about electrical shock. So let’s stipulate that the reporting was accurate, and that, in fact, the fire department really was concerned about electrical shock.
Just because they were concerned about electrical shock that doesn’t mean they were actually at risk for electrical shock. A battery isn’t like a live wire connected to a power source. It generates electricity by a chemical reaction. The chemical reaction has to occur in order for electricity to be created.
If that reaction happens all at once you don’t have a high-voltage metal part just waiting to shock someone. Instead you have a standard exothermic chemical reaction–the battery gets really hot and explodes. Just like in gasoline engines where if the gasoline combines suddenly with oxidizer you get an explosion.
Do EV accidents pose different dangers than IC accidents? Yes. Do emergency responders need to be trained on how to deal with EV accidents? Yes, that sure sounds reasonable to me. But getting shocked like touching a downed power line is not one of the hazards emergency responders need to be trained to avoid. Instead they need to be trained that shocks like that are not a real problem. Just like emergency responders are trained that gasoline powered cars don’t explode spontaneously like they do in movies, they need to be trained about the real dangers of EVs.
nm
This is simply not true.
If a battery pack is severely damaged then you have large amounts of electrical energy exposed in the form of positive and negative wiring. By themselves they are harmless. Exposed they represent enough power to weld with. Imagine trying to extricate someone from a mangled car and you move 2 live wires together in the process. I’ve seen crossed batteries vaporize most of a battery terminal in the plasma arc.
Like the others, I don’t understand what point you’re trying to make.
Tesla puts out the emergency response guide I linked to, which has clear information on how to deal with their vehicles in an accident. They also run training sessions with fire departments and others for in-person training.
Obviously they can’t personally train every fire department in the world, so they also work with groups that put out training material. Here’s one example of a training video; another for the Model X.
Firefighters are professionals and keep up to date on their own training. And if they still have questions about a particular situation, Tesla is happy to help out. I don’t know what else they could be expected to do.