A look inside the Tesla Model 3

We’ve already discussed some of the obvious differences between Model 3 and its older and larger cousins: its size, its minimalist interior, and some subtle features that optimize it for ride-sharing. Looking under the hood (so to speak), there are three important technical differences: the battery pack, the motor and the body materials.  

Above: Some of the more well-known Tesla Model 3 features (Image: The Street)

In order to deliver a vehicle at a more affordable price, Tesla had to redesign its battery pack architecture. Electrek was able to obtain a wealth of technical details, and published a detailed description of the new and improved Model 3 battery pack.

It’s been known for some time that the new Tesla uses a slightly larger battery cell, which was co-designed by Tesla and Panasonic. From the outside, there isn’t much difference to be seen between the 2170 cells (21 mm in diameter and 70 mm high) and the 18650 cells (18 mm x 65 mm) used in Models S and X. Inside, however, the new cells can store a lot more energy. According to Elon Musk, it’s “the highest energy density cell in the world, and also the cheapest.”

Above: Comparing the Model S/X 18650 battery cell with the Model 3 2170 battery cell (Image: DNK Power)

The 2170 cell is around 50% larger by volume than the 18650, but it can deliver almost double the current (up to 6,000 mA, compared to 3,000 mA). Tesla has said it hopes to produce the new, larger cells at the same cost as the old cells, which means a reduction in total battery cost. It’s also widely believed that Tesla has made some incremental improvements to the battery chemistry, and Elon Musk has confirmed that the 2170s are more energy-dense.

The larger cell size also allows the Model 3 battery pack to use fewer modules - only four, compared to 16 modules in a 100 kWh Model S pack. The Standard 50 kWh Model 3 battery pack contains 2,976 cells in groups of 31 cells per brick - there are 2 modules of 23 bricks and 2 modules of 25 bricks. The Long Range 74 kWh pack (the one now in production), consists of 4,416 cells in groups of 46 cells per brick.

Above: Diagram of the distribution of modules and cells in Tesla's Model 3 battery pack (Source: Electrek)

There are a few other slight differences from the Model S/X packs. Unlike the Model S and Model X battery packs, the Model 3 pack is not made to be easily swappable. It seems that battery-swapping has been consigned to the tech history scrap heap. Some time ago, patent applications revealed that Tesla was working on an autonomous charging gadget that would use an external high-voltage connector on the vehicle’s underside. However, Model 3 has no such connector, so it seems Tesla has abandoned that idea as well (it is surely working on some other kind of autonomous charging system, perhaps the cool-looking “snake charger“).

Model 3’s battery pack is generally more compact and streamlined. The charger, fast-charge contactors, and DC-DC converter are all integrated into the pack, saving weight and cost, and simplifying assembly. Tesla has also eliminated the external battery pack heater - the new pack can be heated using only waste heat from the powertrain, even when the car is parked.

Above: A look at Tesla's Model 3 battery pack (Source: Electrek)

Tesla has made a major change in the motor department. According to Model 3’s EPA certification papers (as reported by Edmunds), Model 3 uses a permanent magnet (PM) electric motor instead of the AC induction motors used in Tesla’s previous vehicles. The change was doubtless made for technical reasons - we know that Tesla constantly models new motor types, using sophisticated simulation software. However, it’s an ironic choice in two ways. The company was named for Nikola Tesla, who invented the AC induction motor, and the Tesla logo is said to be a cross-section of an induction motor lobe. Also, on more than one occasion, Tesla has pointed out the drawbacks of the PM motors used by pretty much every other EV-maker. PM motors tend to be less efficient at higher speeds, and they include rare earth elements, which is inconvenient for environmental and geopolitical reasons.

On the other hand, PM motors can be more efficient overall, because they don’t need to use electricity from the battery to generate the necessary magnetism within the motor. Edmunds points out that this may lead to cost and weight savings.

Above: Cutaway view of a permanent magnet electric motor (Image: Machine Design)

Cost and weight were doubtless the considerations that led Tesla to design Model 3 with a different mix of metals than it used for its earlier vehicles. The Roadster used carbon fiber, which is light but very expensive. For Models S and X, Tesla went with a mostly aluminum chassis, with some high- strength steel reinforcements.

As Electrek notes, this made sense because the main priority was to keep the weight of these larger vehicles down. However, aluminum is expensive, not only for an automaker, but for an auto owner (some Tesla owners have been shocked at the bills for bodywork after a crash). The company apparently decided that, for the mass-market Model 3, price is a more important consideration than weight, so it used steel for most of the new car’s chassis and body.

Above: The Tesla Model 3 body repair guide's exploded view of the car's alloy body mix (Source: Electrek via Reddit member User_Juan)

As Model 3’s body repair guide reveals (thanks to Reddit member User_Juan), a few bits of Model 3 are aluminum, but most is steel - some is high-strength steel, and a few critical parts of the frame are “ultra-high-strength steel.”