Home » Here’s How Tesla Keeps The Cybertruck’s Battery From Exploding Or Getting Wet

Here’s How Tesla Keeps The Cybertruck’s Battery From Exploding Or Getting Wet

Cyber Battery Munro Ts2
ADVERTISEMENT

The heart of any EV is the battery. In larger vehicles like the Tesla Cybertruck, the battery is not only key to the vehicle’s long range, but it’s also a key structural component. We’re now learning more about the Cybertruck’s battery thanks to another teardown from Munro & Associates.

This time around, we’re getting the low-down from Sandy Munro himself, along with Tom Prucha, director of electrification at Munro & Associates. The pair have spent their time pulling apart the Cybertruck’s battery to find out what makes it special.

Vidframe Min Top
Vidframe Min Bottom

Munro begins by explaining that there is little need for protective gloves at this stage of the teardown. While there are high voltages inside the battery, the contacts are widely separated and most of the cells are protected under foam. He explains that to get a shock, they would first have to remove a ton of insulating foam and plastic and then reach across the battery to bridge both contacts. With that out of the way, he and Prucha get into the finer points of the battery’s design.

800-Volt Architecture

Right away, Munro notes the pack uses 4680 cells, based on a simple visual inspection. He also observes the mica sheet in the pack, and the bright green foam used to hold all the cells in place. Munro notes that he’s contemplating selling the batteries from the truck, but that the company has lost money doing this before. It’s very hard to free individual cells from the pack thanks to all that sticky insulation.

ADVERTISEMENT

Foam1

Image4170

Like many new EVs, the Cybertruck has an 800-volt architecture, and Prucha steps up to explain what that means. “The entire array would give you an 800-volt pack, which, by very definition, doesn’t mean 800 volts very often,” says Prucha. It all comes down to how lithium cells work. Fully charged, they sit at around 4.2 volts, and they’re considered pretty much empty when they dip down to 3.4 volts. Nominally, they’re said to sit at 3.6 volts—which lies somewhere in the middle. Hence, depending on the state of charge, the Cybertruck’s battery could sit anywhere from perhaps 600 to 900 volts in total.

“We haven’t tried to dive in yet to figure out exactly what this electrical configuration is yet,” says Prucha. Further teardown work will reveal the number of 4680 cells in series and parallel. The configuration is then described as xSyP, where X is the number of cell groups in series, and Y the number of cells in parallel in each group. You can visualize this in a general sense with the diagram below, denoting a 4S3P pack.

Rect3907
A diagram showing a battery pack in a 4S3P configuration. Blue denotes the cells, orange denotes the busbars connecting the cells.

Fourpack

ADVERTISEMENT

“96s9p I think was the configuration for the Model Y… this is a lot more Ss, and probably quite a few fewer Ps, if you will,” says Prucha. That makes sense, given the Model Y has a nominally 400-volt battery. The Cybertruck would have around double the number of cells in series to reach its 800-volt nominal rating; how many cells are in parallel remains to be seen.

Counting the the batteries in the pack is frustrated by the thick foam covering the cells. Prucha expects the pack to be 48 cells long, perhaps 49. The pack is laid out in four blocks, each sitting seven cells wide. Back of the envelope maths would have you multiply 48 by 7 by 4 to get 1344 cells in total in the pack.

Let’s take that number—1344 cells—and do some maths of our own. We could then assume the Cybertruck has double the number of cells in series as the Model Y—or 192. Divide the total number of cells by that number, and you can calculate that the Cybertruck could be rocking a 192S7P pack. However, some have speculated that regulatory filings suggest the configuration is instead 224S6P, which adds up to the same total number of cells. Further disassembly will allow the team to count the cells and determine the electrical configuration directly.

Structure and Fluid Flows

Prucha also dives deep into the minute details of the cooling system. “Regarding the cooling ports, normally we have a single serpentine cooler that fishes its way through the cells like a snake, if you will, and would cool the edges of two rows of cells,” says Prucha. “Very oddly, we have one of those cooling channels on one edge of the cell.” He notes it could lead to one row of cells being cooler than others, if there is nothing being done to correct this. However, he notes Tesla may have equalized temperatures by flow restricting a given channel. “It is common in battery design where you have multiple coolant paths to try to equalize the flow through those paths,” says Prucha.

Image4310

ADVERTISEMENT

Image17772

Image17748

The pack is also interesting in that it’s not really modular in the slightest. While there are clearly four distinct slabs of cells, they’re not designed as individually replaceable modules. They’re very much glued in place with all the foam insulation around them. “When we think of modules of a battery, we think of something you can remove as a subset of the total number of cells, and you could even replace that and put a new section of cells back in it,” says Prucha. “This has obviously gone away from that.” He refers to this as a “cell-to-pack” configuration, rather than a “cell-to-module, module-to-pack” design. “There’s very little hope for replacing anything unless you just take this [whole pack] out and put another one in,” says Munro.Image17724

The bright green foam also comes in for assessment, with Prucha noting just how stiff it really is. He explains that the foam plays both a structural role, given the way Tesla uses the battery as part of the chassis, and it also helps mitigate thermal runaway risks. It’s also key to damping vibrations that could otherwise prove harmful to the “rather frail” welded links between individual cells.

The battery has been upturned for the video, so the shots here are actually looking at the bottom of the pack. It gives us a great look at how the battery is designed to deal with firey failures. The cells themselves are vented in the base, releasing gas downwards in an overtemperature/overpressure situation. “If a cell were to let loose in a thermal runaway situation, the bottom of the cell would push out, it would poke through this mica top,” says Prucha. “The bottom of the cell will push right through it like it’s nothing… this turns this whole area into a vent trough, if you will.”

ADVERTISEMENT

Image4286

Dealing with outgassing batteries is key to safety. A pack that doesn’t vent excess gas can explode, so designers are careful to give gases a safer path to exit the pack. “Ventilation capacity is a big thing in battery design,” explains Prucha. “When a battery starts to go into thermal runaway, it’s like hundreds of roman candles going off in a sequence.”

We’ve already seen the troughs underneath the cells in the Cybertruck pack. From here, the gases can pass through special vents designed specifically for this purpose. Tesla built a moisture-trapping vent into the pack to allow the battery to equalize its internal pressure as the local air pressure changes, or as the vehicle travels to different altitudes.

Image4334

Image4370

ADVERTISEMENT

Image4382

“That being the case, that [vent] is nowhere near enough ventilation capacity for this entire group of cells to let loose through,” says Prucha. Instead, in the event the battery needs to vent a lot of gases in a failure scenario, the plastic snap-on tangs that hold the device together are designed to snap. The orange lid blasts off, leaving the black part of the vent behind. This houses a spark arrestor that can vent far more gas while stopping hot sparks from shooting out of the battery. Many other automakers use check valves for this purpose, but Tesla went with a more single-use design.”This is a rather one-way valve that’s, you know, only one way once.” says Prucha.

The vent trough design also nets benefits for off-roading, too. “In off-roading, sooner or later you’re gonna run over a log or a big rock, and it’s gonna bang into the bottom of your floor,” explains Munro. “When that happens, you’re gonna have a dent.” It would be bad if this directly impacted the cells, but the clearance in the Cybertruck pack helps avoid that. Munro notes there is approximately 1.3 inches of clearance in the bottom of the pack beneath the cells. This means even a hard hit should leave the cells largely unscathed. “[The trough] does two functions,” says Munro. “One, it gives you a big area for the gases to vacate to, “and two, this allows me the comfort of going off-road and not having to worry about if I hit a big rock or a tree stump or something like that.”

There’s a similar gap at the side of the battery, where there are no cells installed. “This gap is to prevent intrusion from a side impact,” says Munro. On the Model Y pack, Tesla fills this area with foam, but the Cybertruck design leaves it empty.

Image4226

ADVERTISEMENT

More Vents

Prucha also walks us through the design of the flood ports. “If you look inside, there’s a stack of wafer discs that are inside there that will absorb moisture,” he says. In the event that coolant leaks inside the battery pack’s penthouse section, it’ll find its way to the flood port, which will open up to dump the fluid. You’ll then see a coolant leak on the floor of your garage, letting you know something is wrong.

There’s also a second type of flood port installed on the side of the pack, with a spring-loaded design that can help release water if it somehow enters the pack.

Floodo

Image4418

Discflod1  Image4406

ADVERTISEMENT

Image4394

Prucha notes he went down to look at a Tesla at one point that had accidentally been submerged to some degree at a boat ramp. Details of his story suggest he’s talking about a Tesla Model X we’ve covered previously. It burned for hours underwater in Florida last year.  “There’s YouTube videos of this car burning underwater where it spent four and a half hours outgassing,” he says. “If you just look at the volume of gas that’s coming out of that battery, you get an idea of the importance of the vent capacity of the battery.” He suspects the car’s 12-volt system was responsible for igniting the flammable gases that were pouring out of the battery.

The question was how the battery came to fail in the first place. In the aftermath, Prucha noted the state of the battery’s flood ports. “They were all open as you would expect them to [be], and they were dried out and they did not close,” he says. “The question is, is that a cause or an effect?”

His theory is that the flood ports may have been moistened previously, leaving them in an open state. Then, on its fateful last trip to the boat ramp, the already-open ports acted as a route for water to flood into the battery. “That could be the difference between the first time when it went in, and it got a couple tablespoons of water, and the second time, where it was completely inundated,” he explains.

We also learn about the value of the Cybertruck’s Scuba Mode, though we don’t get to see the equipment involved. It lets the Cybertruck ford water with less risk of damage to the batteries. “To facilitate that, the [air suspension] air compressor has an airline that feeds into the battery pack that pressurizes this as a cavity,” says Prucha. Thus, if the battery pack has some minor leaks, the pressurization will see air slowly pump out of the back, stopping any water from getting in. “It’s a really brilliant idea that I would argue should be on every [electric] car,” says Prucha.

ADVERTISEMENT

Even if you’re not interested in the Cybertruck specifically, this teardown teaches us a ton about how modern EV batteries are built. If you’re starting an engineering job at an EV automaker, it couldn’t hurt to watch a few videos like this to brush up on the state of play in the industry. If you’re simply an enthusiast, this could help you understand more about how EVs are built and the dos and don’ts around using them on a day-to-day basis. Knowledge is power!

Image credits: Munro Live via YouTube screenshot, diagram via Lewin Day

Share on facebook
Facebook
Share on whatsapp
WhatsApp
Share on twitter
Twitter
Share on linkedin
LinkedIn
Share on reddit
Reddit
Subscribe
Notify of
12 Comments
Inline Feedbacks
View all comments
Matt A
Matt A
2 months ago

The foamed in cells are really a drawback for repairability. I get why there are assembly and thermal reasons for it, but having to get rid of a whole pack (at least for car use) when a few cells go is not great

WaitWaitOkNow
WaitWaitOkNow
2 months ago

This is fantastic. Thank you!

Peter Andruskiewicz
Peter Andruskiewicz
2 months ago

The pack is almost certainly a 192S7P design for a few reasons.
First, in between each of those longitudinal rails there are seven staggered rows of circles which almost certainly correspond to holes in a cell tray to allow each cell’s vent plate to open into the trough.

Second, 7 rows using Tesla’s “bandolier” assembly order in which two rows of cells are assembled and glued with thermal interface material (TIM) around a single cooling ribbon would result in one extra row of cells being cooled by it’s own dedicated ribbon, as observed and noted in the video. This cooling ribbon serving only a single row of cells likely has a smaller diameter flow restrictor somewhere in the manifold as mentioned by Prucha so that this cooling ribbon would only get about half the flow as the other ones.

Third, the first cell of each of these 7 rows are almost certainly bussed in parallel, as are the second, then the third etc so that the bus bars all the way down the length are the same shape, part number, locate in the same way, and are welded in the same way. This avoids part and process proliferation, making for a pack that is simpler to manufacturer correctly.

Finally, 400V charging stations typically have a maximum voltage of 500V, they’re called 400V since that is closer to their “nominal” rating. Similarly, 800V stations will go to roughly 1000V. This is necessary so that the station can provide more voltage than the pack when fully charged so that it can “build the pressure to push the final elections into the battery to reach 100% full”, since as mentioned, the NMC cathode cells that Tesla is using here will have an open circuit voltage (so no current drawn or supplied) range of about 4.2V at 100% SOC down to 3.3V at 0%. However, the voltage required to push more current into the battery (when charging) will be higher than the open circuit voltage, so you need some extra voltage capability at the station over the max the pack can achieve to actually fully charge it, plus some more headroom to overcome losses in the wiring connections, contactors, plug, etc. Running the numbers, 192S would give a max OCV of 806.4V, while 224S would be at 960.8V, so much less overhead and thus much less ability to get to 100% charged, especially if there is some variation from charger to charger as is going to be more likely now that Tesla is opening up their standard to more equipment manufacturers.

Also quite notable is the huge amount of open space for the cell to vent into in the trough. 1.3 inches is more than double what they have on the model Y with the 4680 cells, giving a lot more room for that vent to open, a lot more volume to minimize pack pressurization during a cell thermal runway, and likely enough clearance for the cell in runaway to completely spit the burning jelly roll out into the trough, decreasing the amount of heat left in the can to conduct towards neighboring cells that could initiate a second cell’s thermal runway. This is also a lot of pack volume and height that in normal use would be considered “wasted”, but that matters a lot less in a truck (especially the Cybertruck) than in a smaller vehicle like the model Y.

Ben
Ben
2 months ago

It’s a really brilliant idea that I would argue should be on every [electric] car

Given the amount of grief air suspension seems to cause owners, I would disagree with the “every” part of that. It’s a clever way to reuse something already included in this particular maintenance nightmare, but if being unable to ford streams in my EV is the cost of not having to deal with air suspension, it’s one I’ll willingly pay.

Harmanx
Harmanx
2 months ago

Excellent recap. (Most readers on automotive news sites have long been groomed to have no interest in anything about Tesla unless it’s negative/sarcastic. Skepticism is sometimes warranted, of course, but there’s plenty of impressive tech that should be given coverage — and there are definitely readers who appreciate it.)

10001010
10001010
2 months ago

I love watching these teardowns but something deep inside me just feels it’s wrong to tear apart a perfectly working machine like that.

10001010
10001010
2 months ago
Reply to  Lewin Day

Oh I’d want to as well but I know me, it would sit there in a pile of unassembled parts for a decade before I finally sold it.

AlterId
AlterId
2 months ago

I don’t know why they went through that much trouble. Just reading the ravings of Amanita muskaria var. douchebag keeps me from exploding or getting wet for quite some time.

12
0
Would love your thoughts, please comment.x
()
x