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.

So, not diminishing them, just stating reality.

[0] http://www.google.com/search?q=serious+car+crash&safe=off&cl...

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...)

> What do you expect to happen?

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.