Hacker News Reader

Comment by silasb | Hacker News Reader

I know they have Formula E, but I'd love to see a all-electric Tesla in Le Mans.

Le Mans would probably be the worst place to get an all electric car performing adequately. Energy density and refill times just aren't anywhere near up to the task compared to gasoline.

EDIT: or diesel

What if an all electric car was equipped with a complete battery swap out mechanism. Stock up a bunch of batteries. Pop out the dead one, pop in a fresh one, begin charging the dead one to reuse in a few hours (you may need quite a few spares)

This could actually REDUCE refill times (if the swap out is efficient enough). If temperatures could be controlled to allow it to run in an all out mode, this could be a competitive edge?

Or would this be somehow disallowed? I imagine this would be akin to swapping out the complete fuel tank in a car instead of refueling the tank, and I have no idea about racing rules.

> This could actually REDUCE refill times (if the swap out is efficient enough)

Have you ever watched Formula 1 or NASCAR? They can fill 20 gallons of fuel in ~10 seconds. Do you really think a battery swap system could even come close to competing with that?

Just did some googling, and _including_ exit and entry through pit lanes, fastest refuel is 51.3s. I think a battery swap would be reeeeeally tough to accomplish.

And most cars refuel every 14 laps, and races are about 384 laps. Totals over 5000km in 24hrs. That's a lot of batteries...

Just for comparison, your numbers come out to one refill every 52 minutes. If we assume that charging a battery takes about an hour and a half (pretty reasonable based on current charge times for an 85 kWh battery), you really only need 3 batteries total. The battery swap that Tesla originally demoed was done in 90 seconds, and that was obviously for a low-speed, consumer-friendly environment. I don't see why you couldn't do a battery swap in 60 seconds if that was an engineering priority.

I still think this is a pipe dream with current battery tech for other reasons (weight, power density, overheating, etc.), but from a logistics standpoint it might actually be possible.

Can an 85kWh battery do 190km at race speeds? Le Mans records are 140mph (225km/h) avg speed and 253mph (407km/h) top speed.

EDIT: thanks for noticing, added metric equivs. The difference was just in the sources I found reporting the units differently.

This is confusing: Why is the distance in km, but the speed in miles per hour?

No, hence the last part of my comment. I was referring purely to logistics, not to practicality for winning the race.

Just moving the mass in and out seems doable with proper design and gear (some kind of hydraulic lift?), but can you find a competitive car design where the battery is mounted properly (low and central) and still allows good enough access? Operator safety is of course an issue as well, you really would not want some power switch to fail.

Before they installed some additional armor to the bottom of the Model S to increase crash safety in the event the car goes over something dangerous sticking up in the road, the Model S actually possessed the ability to do a quick battery swap by dropping the battery. There's a video out there with Elon Musk demonstrating the functionality.

It never took off, I guess because the infrastructure never existed, and because of the aforementioned armor issues. It's too bad. I always thought battery swaps would be an ideal way to deal with the aging of these batteries. Depreciate the value of the battery based on some formula and allow people to get a newer one once their battery passes some usage threshold, seamlessly, and bill them for the upgrade.

Good question. I'd say it is probably possible to replace a battery pack on the gasoline-refill time scale with a well-engineered drive-over clip-in type mechanism or a side-trolley replacement mechanism.

They replace whole nose assemblies in <30sec in F1. Audi some years ago replaced the entire rear transaxle & suspension assembly at LeMans in < 5 minutes in the middle of the night, because they'd anticipated the potential need for it and done the prior engineering necessary (iirc, that car finished 2nd and their other one won).

Reliability and safety would take some real work, just like the high-speed fuel rigs previously used in F1.

With proper engineering, 10 second is enough to change the Battery. It's like VMC tool changer.

Then you probably want an aluminium battery.

Tesla did this, it was operational in california, and all cars were designed with this capability. you can find the video where they demo'd this. There was little or no customer demand, because supercharging works so well on teslas that its a fine solution for most people's long trips.

You're joking about the diesel part right? Audi was dominant in the Prototype class with diesel tech for years.

I meant that batteries couldn't compare with gasoline _or_ diesel. I decided to add it exactly because of Audi :)

Reply on news.ycombinator.com