Water? On an electrical fire? Caused by Lithium-based chemistry? Not smart?
Tesla's make up less than 0.008% of the US passenger car fleet. Perhaps emergency workers are simply not aware of how to properly deal with electric vehicle accidents? Formula 1 had to deal with this as KERS starter to be introduced. I would be nowhere near a 375 Volt DC battery pack playing with water.
Well, good for him. I'd like to see him stand in a pool of dirty water in contact with a 400V DC power system trying to remove someone who might be hurt from the car. If you've ever seen what things look like around a serious car crash you know what I am talking about.
Here, pick one and let's "use large amounts of water" as the emergency response manual recommends.
If the water is flooding the battery compartment and basically shorting between every positive and negative terminal of every cell simultaneously inside the armored battery compartment, I very much doubt this puts someone walking near the car at risk of themselves becoming a short circuit.
Please think a little about the geometry of the situation.
EDIT: Okay, physics challenged people out there: electricity tries to take the shortest route of least resistance. Please use reasoning more sophisticated than: "Water! Electricity! Oh Noes!"
Please think a little bit about (a) not being condescending and (b) that the scenario you painted is ONE in a range of scenarios for a 400 VDC system with enough energy to propel a 4,000 pound vehicle a few hundred miles. I am not going to get into hypotheticals. All I am saying is that elecric cars have inherent dangers not found in gasoline cars. You can stand in a puddle of gasoline and you'll be OK.
Please think a little bit about (a) not being condescending
Please think about physics and use specifics in your reasoning. If you have better logic in your head, please relate it. What you have posted is indistinguishable from spin doctoring and therefore receives appropriate treatment.
I am not going to get into hypotheticals.
Because they'd sound pretty stupid if you came out with specifics. Remember, the context here is dealing with batteries encased in 1/4" thick aluminum armor. Scenarios that can expose dangers in the wreckage for one type of vehicle would also be dangerous for the other type.
All I am saying is that elecric cars have inherent dangers not found in gasoline cars.
Gasoline cars have inherent dangers not found in electric vehicles. See how hazy statements like that are?
You can stand in a puddle of gasoline and you'll be OK.
And you'd be much more foolish for doing that than standing in a puddle of water near a Tesla S whose battery compartments have been breached, but are mostly intact and are being inundated by fire fighters.
EDIT: "Water, electricity! Oh noes!" was directed at my downvoters, not you.
> Please think about physics and use specifics in your reasoning.
What do you imagine I was thinking about? Underwater basket-weaving? Please look at my profile on HN. I think I get it, and not just from a college course on physics theory.
Specifics? You are asking for hypothetical scenarios. Severe crash damage is random. It cannot be predicted. Not to a deterministic degree at least. We recently had a horrific crash in our neighborhood. An 18 year old decided it would be OK to drive his car at 100 miles per hour down an avenue.
He lost control at a turn and plowed into a bunch of cars on the side of the road. We heard the impact from over two blocks away and went to investigate. He destroyed FIVE cars. His car and an SUV were mangled into a ball of twisted metal to such an extent that it was hard to tell the two cars apart. He was severely injured. Nearly died. It took them OVER TWO HOURS to get him out. They had to cut the two cars apart from each other and used a crane to separate them. They they had to cut his car to pieces just to get him out. When his car crashed into the SUV the resulting ball of metal demolished another four cars. They were all mangled to an unbelievable degree, a couple of them on top of each other.
There was lots of gasoline everywhere. His tank and the SUV's ruptured. No fire. The firemen sprayed a foam and water over areas and just kept everyone away. There were probably a dozen rescue workers and two ambulances working on this ball of metal to get this kid out.
Now. Stop for a moment. Don't be defensive about Tesla. Think about that wreck. Try to picture what I described in your mind. Picture at least two cars mangled into a ball to such an extent that you have trouble telling them apart. Picture one or more people in there who are in desperate need for help. Now replace the gas-powered cars with electrics with fully charged 85 kW battery packs. Think about powerful super-hot fires. Think about a variety of conduction paths. Think about more than the battery packs but also about the high voltage cables going from the battery packs under the car to the motor controller and motor. Think about any number of potential random arrangements and damage scenarios for these components. Think about a hefty high voltage and high current cable from the battery pack to the motor controller becoming severed and making contact with the body metal. I ask you to think in terms of a severely damaged system, not a battery pack full of water. Now think about the people in there and the rescue workers trying to get to them.
Surely somewhere in there there has to be something that might cause you to take pause and realize there are issues with electrics that we have not yet experienced because electrics are truly rare in a population of over 250 million gasoline vehicles.
This idea that gasoline powered cars are more dangerous is a huge fallacy that is being used to try and protect the reputation of electrics. I get it. I get what they are trying to --and have to- do. That's far from the truth though. If you really want to compare electrics to gasoline vehicles look at the entire history of gas powered vehicles from the 1800's until today. You have over 200 years of history on various designs. The number of gasoline powered cars in the world today easily exceeds a BILLION units. Sorry partner, I have to say that gasoline, as much as you and I hate it --and I do-- is pretty damn safe stuff. The data on Tesla's causing fires due to collisions isn't statistically significant yet. If you were to do the math with this imperfect data today you'd find that Tesla's are six times more likely to catch fire in a collision when compared to gasoline cars. Again, this is based on insufficient data, so it's nonsense. Don't waste any time on it at this point.
I am rooting for Tesla. I truly am. My comments about electric car safety are more about the general issues with electrics rather than Tesla specifically. For all I know Tesla's designs are the safest around. Without detailed engineering data this is pretty difficult to evaluate. I'll take their word. I think it is a cool company.
My concern is that the entire electric "dream" could easily be damaged if we have one or two horrific electrocution or high energy fire incidents. I've purposely blown up LiPo batteries in order to learn more about their failure modes (we use them for our RC planes and helicopters). They produce explosive high energy fires. I don't even want to imagine what a large pack could do.
This, to me, is THE area that requires the most intense work in electrics. Forget range. Forget increased capacity. Safety is the number one consideration. Imagine, if you will, if we had the technology to make electric cars with packs that could take you a thousand miles. Maybe that's a couple of hundred thousand kW. How do you deal with these things in serious accidents? You can't discharge them quickly enough. The fires could be unimaginably hot and violent with electrical systems capable of delivering hundreds of volts and probably thousands of amps in an instant. This is dangerous stuff. Combine such a vehicle colliding with a gasoline powered vehicle and, well, now things are even scarier.
All that is needed for the electric car industry to suffer a serious setback is for an event to occur that would plant fear in the minds of buyers. I don't care how much of a proponent of electrics anyone might be. If a mother is in fear of her kids being electrocuted or burned to death in a horrible way you lost that buyer forever. No amount of reason or statistics is going to fix that problem. That's the scenario I am concerned about. Tesla and the entire electrics industry could be destroyed overnight if something horrible happened. Panic is a powerful force. That's the plain truth.
No disrespect. I am not trying to diminish you. I am simply not sure you've thought this through. If you are coming to this conversation from a perspective of having taken a usual dose of physics courses in high-school and college and without a reasonably amount of experience with high-power/high-voltage systems I will respectfully suggest you might not be equipped to fully grasp the gravity of the situation. Again, this is not a personal attack. I am just stating facts. I am not a doctor and would not be equipped to fully grasp a range of medical issues. That's just a fact.
Yes, understanding the theory is important. However, as the saying goes, in theory, theory and practice are the same, in practice, they are not. I've dealt with a wide range of high voltage and high power systems throughout my engineering career. High voltage is dangerous. Very dangerous. Period. I could not imagine any reasonably experienced electrical engineer not agreeing with me on this one. You don't want to be anywhere near an uncontrolled system with several hundred volts and lots of available energy, much less be in it, wet and injured. Not fear-mongering. This is as real as it gets.
Try to picture what I described in your mind. Picture at least two cars mangled into a ball to such an extent that you have trouble telling them apart. Picture one or more people in there who are in desperate need for help.
This situation is going to suck, no matter what. It's also a sure bet that this sort of situation sucked worse while it was still relatively new and experience was being gained by emergency responders and procedures were being worked out.
This, to me, is THE area that requires the most intense work in electrics. Forget range. Forget increased capacity. Safety is the number one consideration.
You make a lot of good points, and you do seem to have the background to know what you are talking about. It would seem that what's needed is a way to reliably disconnect every cell from every other cell, lowering the voltage to around 4 volts. If one can do this in response to the high g from a collision, this would go a long way towards making these things safer.
> It would seem that what's needed is a way to reliably disconnect every cell from every other cell, lowering the voltage to around 4 volts.
Yes, absolutely. Something along those lines will probably be essential as we move forward. Maybe not to 4 Volts. That's probably not necessary. Somewhere in the range of 20 to 50 V there's a good safe spot. I am not up to speed on where safety levels lie for different circumstances. I's more about current through your body than absolute voltages. Of course, a higher voltage makes producing high currents that much easier.
High voltage and current circuits are not the easiest to interrupt mechanically. They tend to make such things as mechanical contacts explode with molten metal flying all over the place. The arcs produced when trying to mechanically interrupt high current circuits can be massively destructive. That's why most high power mechanical contactors are very large, loud and fast. More here:
See my other response. Great, until you have a crash that looks like these [0] and you have a bunch of people trying to help victims while walking around in a wet 400 Volt DC environment.
Now add more electric cars into the mix for a fun multi-electric car accident. Would YOU walk into that on Elon's recommendation? I'll tell you, I've been around high DC voltages, from a few hundred volts to tens of thousands. Water while handling components? No fucking way.
Don't get me wrong. I love electric cars and would have been in line to buy a Tesla SUV had they not pulled that bone-headed design stunt with the falcon wings. At the same time I am a realist in that I understand that there's much to be learned about having thousands of cars with fully charged multi-hundred-volt power systems sharing the road at the same time. The emergency manual says that the pack can easily re-ignite and that it should be under observation for at least 24 hours. That's one of the issues with electrics. You can secure a gasoline powered car by simply draining all of the gasoline and dealing with it chemically. Imagine an electric car catching fire again as it is being towed away on top of a flatbed truck. We are going to have to develop new approaches to all of this. Tesla, I would think, will be at the forefront.
What do you expect to happen? To the extent that the battery is compromised, the water is mostly going to make it short to itself, and it isn't as if a raging battery fire is going to be a better situation for the apparently trapped occupant (the only time the immediate car environment is particularly troublesome).
(The linked manual specifies using water to cool the battery and discusses observation procedures to limit the risk of re-ignition...)
At one extreme, nothing. At the other, a potentially horrible electrocution. Run a google image search for something like "serious car accident" and insert an equally mangled battery pack in there. I very much doubt Tesla or any other electric car manufacturer would even remotely consider issuing a blanket guarantee stating that their design is electrocution-proof under all conditions.
Not trying to be a troll. Simply saying that high voltage systems are extremely dangerous. That's it. No need to agree with me. Just remember I said it.
It would be nuts if the interconnects have higher survivability than the firewalls. Mangling the battery will almost certainly significantly reduce the voltage (I didn't quickly find anything on the Model S, but for the Roadster, the output voltage is achieved with a final series arrangement of sub-assemblies, breaking that should directly reduce voltage).
Of course it will still create dangerous situations and experience will be valuable in judging just how dangerous.
How about some emergency equipment electric power dischargers? You could discharge huge amounts of energy in the form of steam. Just include a collapsible nozzle to direct the steam into the sky. Maybe this could be built into fire trucks?
When a battery might have been damaged, it's dangerous to discharge it, so I never see this becoming a standard procedure for handling EV crashes.
A solution that might be more practical: individual Li-Ion cells are only 3.7-4.2V, so it might be possible to split the battery in smaller low-tens-of-volts sections which disconnect from each other in case of a crash.
But now I'm wondering if it's feasible to quickly discharge such a large battery pack so let's assume for a moment that the battery pack is undamaged.
Batteries have a limited discharge rate, imposed mostly by their internal resistance and thermal limits. There seems to be some tradeoff between energy density and power density, so I expect the batteries in electric vehicles to only be designed and rated for discharging at peak motor power. Looking at the Model S, motor power seems to be 310 kW and the smallest battery pack stores 60 kWh, so it might be possible to discharge this pack in around 12 minutes. In fact, I suspect this battery is only rated for discharging at the peak rate for a limited amount of time (maybe just for a few seconds), but let's ignore this for a moment.
Add the time required to set up, and even with this naive estimation it seems impractical.
If this energy is used to boil water, a back of the envelope calculation shows that you'd need to completely boil off at least around 80 litres in order to discharge a fully charged 60 kWh battery. Now, I have no idea how a device capable of boiling off 80 litres of water in 12 minutes would look like, but it might be a bit challenging to fit on a fire truck.
80 liters is only around 20 gallons. A fire truck would certainly have that amount on hand. If you heat an element enough, water that hits it will flash to steam. I think you could make a heating element robust enough to accomplish this but still light enough to fit on a truck. Now, the wisdom of suddenly producing 2700 cubic feet of superheated steam in a residential area -- maybe it's a bit too cumbersome and potentially dangerous to be worth it.
A number of years ago I had to fix a fairly sophisticated 5 VDC 200 W switch mode power supply. Due to the design the only way to work on it was to have the supply fully loaded. We had to make a rig with a bunch of large wound power resistors in parallel submerged in a bucket of ice water. It was really surprising to see how quickly the ice melted and the water warmed up.
Large quantities of water are the recommended way to mitigate battery fires in EVs. The primary reasoning that you want to cool the cells to stop the thermal runaway process.
The worst case scenario is that the flood of water directly shorts the battery (which has likely already happened, if it's on fire).
Tesla's make up less than 0.008% of the US passenger car fleet. Perhaps emergency workers are simply not aware of how to properly deal with electric vehicle accidents? Formula 1 had to deal with this as KERS starter to be introduced. I would be nowhere near a 375 Volt DC battery pack playing with water.