2013 Tesla Model S Long-Term Road Test

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2013 Tesla Model S: Looking at the Battery Pack From Below

November 7, 2013

 2013 Tesla Model S

Reports of a third Tesla Model S fire are just filtering in, and the Tesla forums are bogged down with extra traffic, presumably from news media trying to figure out what's going on.

I'm curious, too, so I put our 2013 Model S long-term test car up on our Rotary lift for a look around.

The first fire was reported to be the result of an impact with a "large curved piece of metal" that fell off or was kicked up by a semi. Tesla described a "pole vault effect" that pierced the battery pack from below, creating a three-inch hole. The fire didn't spread throughout the battery pack, and in fact most of what we saw burning in the photos and videos was in front of the battery, involving other components. Still, we understand the initial spark may have come from the battery in that case.

The second fire occurred in Mexico, after the driver ran through a roundabout and struck a tree and pole. So much was going on there it's hard to tell what the cause was, but most certainly the crash came first.

The latest fire is also reported to be a debris strike, but I'm not yet sure if the main traction battery is involved. Photos show a fireman dousing the nose of the car, well ahead of the battery. The main traction battery box begins behind the front axle centerline and extends back under the passenger compartment. It remains to be seen whether or not the battery pack sparked off the blaze.

 2013 Tesla Model S

Here I've pulled off the cover to reveal some of what's up front. I can't ID all of the components without a shop manual in hand, but you can see how the battery pack (that big gray box spanning the underside of the car) starts behind the rear axle centerline. Its unseen vertical front edge is protected by the front subframe, which carries the electronic power steering system and other components. Farther forward, those pipes appear to be part of a refrigeration system, most likely the air conditioning. I can also see electronics (and the compressor, I think) related to the air suspension. The 12-volt "normal" battery is in there somewhere, too. Numerous other systems are nearby, out of sight.

Here are a few observations:

The plastic cover I removed to get this view is quite thin. It's just an aerodynamic cover. This design is similar to other cars, but they don't necessarily have electronic components hanging this low under the nose. Most cars have the oil pan of their engine filling this area. Trucks and SUVs will have a metal skidplate because of possible rock impacts that may occur off-road, but few, if any, sedans have one because they don't venture off road.

That said, the Model S does run quite low to the ground, especially at freeway speeds where the air suspension drops the car even more. Check out the ride height of the next Model S you see. They look slammed, but that's how they come from the factory. It's done in the name of improving aerodynamics to reduce drag and improve efficiency.

Finally, the battery box curves in around the back side of the front tires. It's essentially a part of the inner fender liner in places. Direct debris contact is theoretically possible here if a front tire kicks up something. They say the battery box is one-quarter inch thick. Still, I've hit debris in my own cars plenty of times and have never had anything pierce the thin sheet of plastic that made up their fender liners. But that doesn't mean it couldn't happen.

Is there a problem with the battery pack, the thing everyone is concerned about? We don't have enough information to tell. We're not yet certain if the pack was involved in the ignition of the third fire at all. But the confined nature of each fire is actually heartening. It tells me that the compartmentalization of the battery pack is preventing the spread of flames back under the cockpit, as designed.

The proliferation of flames up front seems to indicate that something else is contributing to the visible flames. It's impossible to know how to think about this until we see and analyze pictures of what the drivers struck and where it impacted the underside of the cars in question.

Whatever the case, it's very likely that the impact zone resides within the area depicted in the above photograph.

Dan Edmunds, Director of Vehicle Testing @ 11,321 miles

Most Recommended Comments

By applecar22
on 11/07/13
1:55 PM PST

I understand the interest in these incidents given the newness of the technology involved and the high public profile of the product and the manufacturer. This article is also to be commended for its objectivity. However, it would interesting to know about the frequency of fires in cars with conventional powerplants, particularly luxury cars in accident situations. Such information would allow the public to put the Tesla incidents in the proper perspective. Most of us don't seem to have much concern driving around with thin plastic tanks full of gasoline hanging unprotected under our vehicles which would seem to be at least as vulnerable as batteries behind quarter inch thick metal.

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By actualsize
on 11/07/13
2:23 PM PST

Agreed, but the number of Tesla incidents is still low enough (3) that a good comparison can't yet be made, even though data on gas-powered cars is quite mature. Certainly gas powered cars have a number of potential fire sources: gas tank, gas lines, refuelling piping, underhood fuel system leak, oil cooler lines, transmission cooler lines, exhaust system (including catalyst), power steering lines, wiring harness and underhood electricals, 12V battery. An EV seems to have fewer sources: battery pack, power cabling, 12V battery, wiring harness and underhood electricals. That may or may not mean a fire is less likely, but there seem to be fewer "pain points" for the engineers to deal with. And based on what we've seen so far a ruptured gasoline tank, if it ignites, is a far more unpredictable and violent event than a smoldering battery that, in these incidents, at least, doesn't appear to spread rapidly outward from the affected cell and consume the entire battery pack. But, again, three is still a small sample size, and millions of road miles of data is not nearly as much as trillions of road miles of data.

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By quadricycle
on 11/07/13
3:07 PM PST

I'd hate to join the speculation frenzy, because if there's one thing economics tells you, its that people's reaction to an event can easily become more harmful than the event itself. Besides the actual fire risk itself, I don't see too much of a problem here. The battery probably isn't the initial problem, and a somewhat-light aluminum skid plate could easily protect the problematic components. I look forward to hearing a hype-less description of the problem once it is found.

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