by Motor Trend, which declared it the “best car of the year” in the publication’s entire existence. The power circuitry and battery systems in the Tesla Model S are responsible for the vehicle’s legendary range, acceleration, and breathtaking top speed.
This essay will focus on the Tesla Model-battery S’s system. The battery pack will be the primary subject of discussion, though we will touch on mechanical and thermal requirements briefly. We’ll take a closer look at the electrical components, characteristics, and features of the cell module, as well as its effectiveness and safety measures.
What is an Electric Vehicle’s Battery System?
The cells that make up an EV’s battery system are its main source of energy storage. Expertise in material science, chemistry, physics, and the associated engineering disciplines of electrical, mechanical, and thermal is required to build the battery system for an electric vehicle. The following is a diagram showing how the batteries in an EV are set up:
Battery Pack of Tesla Model S
The battery pack that Tesla manufactures excels in the areas of modularity, efficiency, dependability, and safety. Previously, we established that the battery pack can have up to 16 connected components. However, different battery packs may be used in different models of the same vehicle, altering both the vehicle’s total weight and its energy storage capacity. The battery pack in a Tesla has a voltage of about 400 Volts and is the heaviest component of the vehicle.
Example: the Model S P85’s battery pack can hold 90 kWh of electricity and tips the scales at over 530 pounds. All told, there are 7104 18650 batteries across the 16 sections. Each battery module is linked to the contactor, which provides power to the front and rear electric motors, via a central bus bar in the battery pack. The 16 components that make up a 90 KWh Tesla battery each have a 5.5 kWh capacity. The equivalence of the module’s electricity output is 84 kilowatt hours.
Battery Specification of Tesla Model-S
A battery pack consists of several individual batteries wired together in succession. Yes, cells come in all shapes and sizes, and their interior chemistry can be quite distinct. If you want to learn more about Li-ion cells, check out our previous posts on the Comparison of EV batteries.
Multiple battery components made from a series and parallel arrangement of Li-Ion cells make up the Tesla battery pack. This schematic will show you the inner workings of the Battery Module.
Tesla Model-S: 18650 Cell
Panasonic 18650 Li-ion batteries can be found powering both the Model S and the Model X. The image below depicts a single Model-S 18650 battery.
Dimension of 18650 Cell
18650 batteries are used in the Tesla Model S. There is a cylindrical shape to the cells, measuring 18 mm in width and 65 mm in height. The cellular nomenclature can be rapidly learned by breaking down the numbers into their individual parts. The first two numbers tell us the diameter of the cell in millimeters, the third and fourth tell us how tall it is, and the fifth character tells us what shape the cell is.
Types of cells used in different Tesla cars are given in the table below:
Technical Characteristics of Model-S Cell
Electric vehicle requirements inspired Panasonic to develop the Model S cell in collaboration with Tesla. This table lists some of the key characteristics of a Tesla Model-S battery.
Tesla Model-S Battery Modules
The battery module for a Tesla Model S is made up of several 18650 cells. Tesla, on the other hand, doesn’t use a single massive battery, but rather a collection of lesser ones, referred to as the battery module.
Each module employs a 6S 74P layout, which consists of 6 sets of cells linked in series, followed by 74 sets of cells connected in parallel. Tesla’s components have a continuous current rating of 500A and a peak current rating of 750A. A built-in liquid cooling mechanism regulates the battery pack’s temperature to maintain consistent performance. Each Tesla battery cell is described in detail below.
The left image is a representation of the Tesla Model S battery module, and the right image is a representation of the link between the battery cells in a 6S 74P configuration. There are 444 individual cells in a 6S 74P configuration. Check out our previous article on designing a 12V battery pack for more information on how the series and parallel connection of cells impacts their capacity and voltage. Tesla uses wire soldering to make the connection between the individual cells and the battery pack. Since the wire serves as both a fuse and a safeguard, the system is more reliable in the case of a cell failure. The red circle in the following picture identifies a spot where wire bonding was used to connect two cells.
Advantages of Wire Bond Technique
- No heat is introduced to the cell during cell connection
- Wire act as a fuse
- If join fails, it doesn’t impact cells
- Improves manufacturability
Disadvantages of Wire Bond Technique
- Increases resistance due to additional wire
- It increases heat generation in the system
- Reducing operating efficiency
Below is a chart containing the battery module’s technical details:
Module’s Thermal Management
Li-ion batteries get hot easily when under stress, and if they get too hot, they can experience something called thermal runaway. Li-ion battery packs and EVs are inherently unsafe due to the risk of thermal runaway, which can raise fire hazards in a single cell and set off a chain reaction. The Thermal Management System is an extremely well-known safety feature that removes excess heat from the battery pack to maintain a secure internal temperature. In the picture below, you can see the heat exchanger pipe that supplies the module with its cooling liquid. The following and a few other pictures here are courtesy of a YouTube account called EV Tech Explanted.
To control the temperature within the module and separate the cells from one another, the cooling tubing is coated in thermally conductive and electrically insulative material. Kapton tape, an orange insulating tape used to enhance insulation, is applied at the bends. A mixture of water and glycol is used as a coolant in a Tesla’s battery cell. The diagram below illustrates how the solution’s temperature rises as it travels through the battery.
After a lengthy and rigorous test, AVL released a picture showing how hot various parts of a battery module got. The blue lines show where the refrigerant is going in, while the red show where it is going out. Cell module high and low temperatures are also displayed for your perusal. An starting temperature of 20 degrees Celsius was used in the test, and 250 Amp charge and discharge cycles were carried out.
The above illustration shows that a minor temperature discrepancy was discovered between individual components. The internal resistance of individual cells, and thus the battery system as a whole, is affected by temperature fluctuations. The water-glycol solution is transported through pipes with a patented wavy design that maximizes both surface area and packaging effectiveness. An illustration of Tesla’s patent for the curvy coolant conduit is shown below.
Mechanical Structure of Tesla’s Battery Pack
The Tesla model S’s battery cell doubles as a structural component and is located beneath the vehicle’s floor pans. It acts as a base for the car, giving it rigidity and strength, and the placement of such a heavy object so low on the car lowers the vehicle’s center of gravity, improving its equilibrium and balance. The empty battery cell is depicted in this photo from EV Tech Explanted.
The bottom compartment can hold up to sixteen cells. Each nook can house a separate power pack. The chassis is reinforced by longitudinal members, which also provide resistance to contact from the side and side bending, and the chassis’s thick side members, which also offer protection from side impact. Modules can be placed on a grid created by the interior members, which not only increases the base’s physical strength and rigidity but also keeps them from catching fire from one another. Location of all 16 modules is depicted in the following picture. The right-hand diagram depicts the interconnections between the components.
This orientation is used to attach the HV bus bar. The positive link is shown by the red dots, while the negative connection is shown by the black dots in a battery pack. The battery pack’s busbars are substantial copper-plated tin slabs.
BMS used in Tesla Model-S
The Battery Management System (BMS) is the single most critical part of any battery cell to ensure its security. The heart of the BMS is a Chip manufactured by Texas Instruments that can track a variety of battery-related metrics, including state-of-charge, state-of-discharge, temperature, and more. The significance of BMS has already been discussed. You can see a photo of the BMS for the Tesla Model S down below.
Based on Texas Instrument’s bq76PL536A-Q1 3-to-6 Series -Cell Lithium-Ion Battery Monitor and Secondary Safety, Tesla’s Model-S BMS is a key component of the electric vehicle. Each module features a built-in BMS that tracks vital statistics like battery age, temperature, and charge/discharge cycles. It is a high-speed serial peripheral interface (SPI) for data communications and can monitor multiple batteries at once. View a simplified system connection of the BMS in the picture below.
With SPI, the BMS can talk to one another. Each module’s BMS functions as a slave BMS that relays information to the master BMS across an isolation barrier; the master BMS is responsible for communicating with the ECU and charger and for operating the primary contactors. Each battery cell has the BMS attached to one side. Wires welded to the plates of the parallel connections are used to detect the voltage across the cells. Due to a lack of information, only a small number of educated guesses have been made about the BMS module used in the Tesla Model S.
The red outlined region in the above BMS image demonstrates that there are 6 monitoring ICs present in the BMS for each series connection in the module. The yellow outlined region denotes the terminals that will receive the link from the six cells. The TI ICs used in the BMS can be daisy-chained, reducing the number of required network connections. The system uses CAN bus connectivity to talk to the car’s main computer, and its master BMS is likely made by BOSCH. Feel free to add any missing details you may have so that we can edit the article.
The efforts and engineering that went into creating the battery cell for the Tesla Model-S are simply astounding, and it’s clear that this is one of the car’s greatest strengths. Module and battery pack construction, as well as cell selection, are given careful consideration. Using the battery pack as a structural material was a technical nightmare, but thanks to some brilliant mechanical design, it’s actually quite secure and helps lower the vehicle’s center of gravity, improving its stability and maneuverability. Because of the high quality of the cells used in the battery pack, Tesla’s battery modules and cells are in high demand for reuse. As a result of Tesla’s public disclosures and internet-accessible details, it was challenging to independently verify the claims being made. To that end, please share any additional information or corrections you may have discovered in the comments section below.