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Comment by thaddeusmt | Hacker News Reader

Figured this was related to hybrid RAV4s or EVs but no - the regular old "car battery" is the issue!

My neighbor breathlessly informed me a couple months ago that I should be worried about my EVs burning down our house. She seemed a little surprised when I mentioned that my Ford (not an EV) is actually the bigger risk for spontaneously burning down my house.

Politics were involved, yes.

Unless you have a weirdly fire prone Ford, I think this is another example of people often really confusing the fire stats for ICE vs EV.

Yes, mile for mile gas cars catch fire more often.

The problem is, gas cars catch fire usually when they are older and neglected. Oil leaks and fuel leaks being 95% of the culprits. And when they do catch fire, they do so while on, not in your garage. And if they DO catch fire in your garage, they do it within minutes of you returning home... When you're still awake and alert.

Compare that to EVs, that catch fire a little less often... Except they do so when almost NEW with zero visible faults that you could catch (like an oil leak onto your exhaust). This is way more problematic.

And no, im not an EV hater. I have a Chevy volt.

I'm not talking about ongoing statistics about fires in older cars, or singling out gasoline as the problem. Just look at recalls in the last few years alone for spontaneous fires in unattended vehicles. The 12V battery and associated electronics are more than capable of starting a fire, and once a car gets going, they all burn really hot and fast whether fueled by electrons or gasoline.

Do we have good numbers on EV fires now? Aside from what, 19 fires due to the faulty LG batteries in the Bolt, I don't hear a lot about spontaneous combustion being a thing. It's really hard to get anything like current numbers, but from the few places I've looked which try to collect such data, it seems that nearly all fires are secondary to impact damage.

Once Lithium Phosphate (LiPO4) or Sodium-ion batteries become more common, this whole "burning Tesla" will become moot.

48V electrical system should help a lot too, due to lower currents, and therefore less resistive heating.

Lots of fires (in all types of car) are due to bad connections in the low voltage system.

That's an interesting point, but how would a higher voltage not cause the same problems with bad connections?

It's related to Ohm's law, but if you have a specific load you need to power (say 8 watts) a 12 volt system can run that using 0.6 amps (at 18 Ohm) while a 48 volt system can run that same 8 watt load at 0.16 amps (at 288 Ohm).

Another way to look at it is a little easier with something like a 24 volt PoE injector vs a 48 volt PoE injector. The 24 volt supplies the needed energy at 1 amp, but the 48 volt supplies the same energy at 0.5 amps. Both work out to 24 watts (volts*amps=watts) but a wire carrying 48 volts doesn't generate as much resistance, which would be lost as heat into the wire carrying the load. If it loses too much heat because the resistance is too high, well, that's how you make a heating element -- cram amperage into a wire until the resistance makes it hot.

For example a 960 watt fan - fairly typical of the cabin air fan, at 12 volts would need 80 amps, whereas at 48 volts would need only 20 amps. (Power in watts = Current in Amps * Voltage)

If you have a bad connection in that cable of 0.01 ohms, then that bad connection would generate 64 watts of heat on the 12v/80a system (enough to melt the plastic on the cable and start a fire), whereas on the 48v/20a system it would only make 4 watts of heat (probably safe). (Power in Watts = Current in Amps Squared * Resistance in Ohms).

Bad connections are far more prone to get worse, rapidly (and arc themselves bigger...) When larger amounts of current need to go through them.

All connections need to be nicely done -- the ones on your range plug, they should be very snugged, and double checked.

Etc. lugs on a 200 amp home service panel are ON there.

I've had multiple different vehicles have recalls for fire situations with them without the requirement of them being recently driven. One vehicle even had multiple recalls for fires like this.

That's great. I'm talking about vehicles that catch fire not recalls for possibilities. Beyond that, the only way a vehicle that hasn't been on to catch fire is from a really faulty 12v system. EVs have those too.

I don't, and the insurers don't, care about the car catching fire. It's the putting it out bit.

All cars, regardless of fuel, are extremely flammable. Once they get going they burn quick & hot. The fire department usually doesn't spend much time trying to put out a car fire inside a garage, they knock it down enough to throw a chain on it and drag it out onto the driveway.

> the insurers don't, care about the car catching fire

Of course they do. You think an insurance company would cover a vehicle using an open flame for power at the same rate and an ICE? And how often do charges actually catch fire where it’s not a total loss? For the insurance companies, the result is the same - a replacement.

I can tell you that insurance companies charge more (though low double digits on the year) when your house is heated with e.g. a pellet stove vs a typical oil furnace.

>using an open flame for power

is this why i can't get coverage for my steam engine with a wood burning furnace?

I had a recall on my Ford Van. The hydraulically actuated brake switch used by the cruise control could crack and leak brake fluid into the electrical contacts. That would then start an electrical fire. That could happen when it was parked. The notice from Ford said not to park it in a garage until the issue was fixed.

Brake fluid isn't conductive... There must be more to the story...

It is corrosive though, so perhaps it ate through something like a ground wire?

Ah yes - it dissolves paint and many plastics, so I could imagine some insulation was dissolved away... Although the most common wire insulations, PVC or XLPE, aren't impacted by it.

You are correct. Brake fluid gets water and other stuff in it over time. That makes it conductive. The problem was the hot side of the switch was always live because it uses the same 12V source as the brake light switch. Which has to work when the car is off.

https://www.zehllaw.com/ford-cruise-control-recalls/

My experience with electrolytic corrosion is a track develops and it gets more and more conductive over time.

When discussing fire risk, I remind people that ICE cars have "combustion" in the name for a reason - its propulsion literally comes from controlled explosions using flammable liquids.

If your gasoline is exploding in the cylinders instead of combusting, you should use higher octane or adjust your engine. When gasoline explodes in an internal combustion engine, it’s called “detonation” and if it persists, it can increase the number of parts in your car rather suddenly.

It always disappointed me that humans haven't really managed to make the rotating detonation engine work. Its theoretical efficiency and power density is really high.

Now I'm imagining something like a fidget spinner combined with a Nuclear Pulse Engine[1] and it's awesome because I'm imagining that it can provide both propulsion and rotation...but I bet we need some great advances in material science before anything like it could exist.

1.https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion

I think it would be more like an enormous Wankel engine.

A Wankel was what I thought of first, since it's the closest we've come to a rotational explosion engine, but I'm a space nerd so the combination of rotation and propulsion could make for some interesting applications related to space travel.

Technically a deflagration is also an explosion, it's just subsonic, whereas detonation is supersonic. Plenty of explosives don't detonate: they're called "low explosives" and gunpowder is an example, as well as normal petrol-air mixtures.

I stand corrected! I’ll file this one away.

To parent who I erroneously told to tune his engine: my mistake!

Fires from gasoline cars are at least extinguishable. Lithium fires aren't really.

And, credit where credit is due: remarkably uncommon in a dormant vehicle.

Does your neighbor share a structure with you?

Your neighbor was likely reacting to valid EV recalls.

"Chevrolet Bolt EVs Should Be Parked Outdoors Due to Fire Risk, Government Agency Warns"

https://www.consumerreports.org/car-recalls-defects/chevrole...

IMO it's notable that since then literally millions of ICE cars from companies like Ford and Hyundai have also had "keep outside" warnings due to recalls. For some reason that doesn't seem to discourage buyers.

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