Quote:
Originally Posted by DGthe3
A shorted out 12V system can still spark & cause fires. It happens all the time. Sure, 12 volts can't arc quite as far as 300, but the danger is still there. Each year there are something like 65,000 vehicle fires in the United States that can be attributed to failures of the electrical system (mechanical failures are responsible for about twice that number, for comparison purposes). If I had to guess, I'd say that something on the order of 99.9% of these are conventional vehicles with a 12V electrical system.
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A 12V lead acid battery in the typical normal car only has a few amps of current. The LiIon battery in a hybrid battery can supply hundreds of amps. The Fisker battery nominally has 336V and amps in the hundreds if not more.
Voltage is like electrical pressure. A large volatage is like a higher pressure. Amperage is like the size of a pipe.
So, if you have a 1/4" pipe with 12PSI in it, you could easily stop it by sticking your finger over the end of the pipe.
The same 1/4" pipe with 336PSI in it you could probably stop with your finger as well, but it would be painful.
Increase the size of the pipe to 1" diameter (more amps) and at 336PSI it would probably take your arm off.
People think these batteries are so wonderful, but they demand a lot of respect. They contain all of the potential energy needed to move a vehicle for the rated distance in a form that is very much ready to be released in an instant.
The battery wants to get rid of all that stored energy and it takes only a small problem to unleash it.
A whole tank of gasoline contains all the stored energy to drive 300-500 miles (depending on the car) and you can unleash it with a fire, but it is released in a relatively slow manner because it needs to combine with oxygen to burn and this reaction is limited by the surface area of the gas.
You would have to convert all of a tank of gas into a vapor and mix it with oxygen and contain the vapor mixture somehow and ignite it to achieve the same effect as shorting out a massive battery.
The battery discharge is really only limited by the internal resistance and so it wouldn't be able to fully discharge instantly, but a dead short would release a huge amount of it all at once. A lot more than a 12V car battery or some dino juice that leaked out.