Comment by userbinator | Hacker News Reader

Comment by userbinator | Hacker News Reader

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There are probably some rare cases of this happening on gas vehicles over the years

Unfortunately, the majority of cases I remember were due to flaws in the electrical system:

https://www.autosafety.org/ford-ignition-switch-fires/

https://www.autosafety.org/category/vehicle_fires/ford_cruis...

https://www.autonews.com/regulation-safety/ford-recalls-f-15...

https://www.usatoday.com/story/money/cars/2014/08/07/gm-reca...

In other words, the (relatively small) battery in ICE vehicles provided the initial energy to start those fires, and not the fuel itself. I suppose one could say that a safety advantage of ICE vehicles when parked and off is that even a fuel leak requires a source of ignition to cause a fire (also, diesel is very difficult to actually ignite), whereas with an EV there is always a huge source of electrical energy available and a lot more components which are always supplied with power.

My guess is that once they become as common as ICE, EVs will continue to catch fire at roughly the same rate if not more.

The propulsion battery in most electric cars (certainly Teslas) is disconnected by a relay when the car is off. So the amount of powered stuff isn't any higher than gas cars. Teslas also have a 12V battery to bootstrap the system and run accessories when the main power is off, though it's smaller than a typical ICE battery because it doesn't have to crank an engine.

I don't think you can predict from theory which will have higher fire rates. All the fires are due to small flaws in the details, so it's a question of design and manufacturing carefulness.

>when the car is off

Does it count as "off" when the car periodically wakes up when parked to do everything from check for updates to warming/cooling the batteries or cabin?

(Not trolling, I can't find the actual answer.)

Nope. My car can drain the HV battery via recording video etc.

It's certainly not solely powered by the 12V as it'd be flat within the day.

Also, if the little 12-volt runs down, will it recharge itself from the main one?

Yes.

I can only speak for the Leaf, but much like a petrol/gasoline car, the 12V battery is only charged when the car is on (and when the car is actively being charged). It is entirely possible to run down the 12V battery if you leave the car parked long enough without it being turned on. Once the 12V runs down far enough, you are no longer able to turn the car on (or charge it) as the 12V powers the contactors for the main battery. I have had to jump start my Leaf due to a bad 12V battery.

In the case of Teslas, yes. The power drain on the 12V system when parked from all the computers etc is apparently so high that they have to recharge it periodically from the main battery. The service life of the 12V battery is pretty terrible because of this. They also have battery heaters that switch on periodically to keep the main battery warm, which I think are powered by the main battery. Basically, if you leave your Tesla sitting in a garage for a few days you can expect the main battery to be connected and used at least some of that time (maybe all of it) even though it has a contactor to disconnect it entirely.

You're wrong. Consider the literally billions of batteries out there every day not catching fire.

EV fires will be fewer.

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