Hacker News Reader

Comment by talldatethrow | Hacker News Reader

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.

View on HN

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.

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.

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.

Reply on news.ycombinator.com