(Motorsport-Total.com/Motor1) – The clear boss Peter Rawlinson, as the former lead developer of the Tesla Model S, is not only a veteran of electric car development, he is also more than just a little competent when it comes to the battery. technology. His 36-minute video on the Lucid Air battery shows that he also has a talent for imparting knowledge.
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Pure air battery pack
The video is in English, but Rawlinson speaks so slowly and explains so well that we recommend the video to anyone who is interested in building an electric car battery. Anyone with little knowledge of physics can skip the start (until around 5:30 am): It is the difference between performance (power) and energy (energy), measured in kW or kWh.
How cells connect to form a battery
But then it gets interesting: Rawlinson explains how to reach from a single cell 2170 with a voltage of 4.2 volts to 924 volts of Lucid Air Gand Touring. And from almost 18 watts (Wh) that stores a cell phone up to 112 kWh of Grand Touring.
The cells are divided into 22 modules with 300 cells each. Each module is 42 volts, and 22 times 42 volts equals 924 volts of the entire battery. At the cell level, you need to connect 220 4.2 volt cells in series to reach 924 volts.
But 220 cells store only about 220 * 18 = 396 Wh and not the 112 kWh we need. To increase the energy, a parallel connection is needed. Parallel connection increases power in kWh, serial connection increases voltage in volts.
Each module has 300 cells. Some of them are connected in series and some in parallel. 30 cells each combined in 10 groups. Each group increases the voltage by 4.2 volts. So get 42 volts of a module.
A total of 30 cells are connected in parallel and 10 in series. The 22 modules are in turn connected in series, resulting in 220 cells in series. As an engineer, such a battery pack is briefly described as 220s 30p.
Introduction of the module in the car (with foot garages)
In the middle (from around 8:30) Rawlinson also explains how the modules are placed in the car. He chose a central tunnel at the front and a completely flat floor at the back. At the front it uses the space for an additional module in the direction of travel, at the rear there is only a dual module under the rear seat. There is a module along the travel direction on the rest of the battery plate.
With the smallest battery of the base Pure version, the foot garages are set up – as with the Porsche Taycan. Here you have more space for your legs because four modules are left out. Even with 18 modules, the Lucid Air Pure still has an EPA range of over 400 miles.
“There is no substitute for voltage in terms of efficiency.” (Rawlinson)
Why Lucid works at 924 volts
Explaining why Lucid works with 924 volts is also very interesting (from 16:00). From the formula for the power P = U * I, replacing I * R with the voltage U, results the relation P = I2 * R. Current strength causes heat loss. Now back to the equation P = U * I. If you want a certain power P and double the voltage U, then you can halve the current and thus quadruple the heat losses.
Why high voltage does not mean fast charging
Rawlinson refutes the myth that more voltage can be charged faster with the simple fact that a single cell can only be charged at 4.2 volts. Regardless of whether the battery system operates at 400 or 800 volts. The individual cell does not feel the benefits, but the system as a whole.
Due to the low amperage, you can choose aluminum contacts for the cells, for example – aluminum is a much weaker conductor than copper, but apparently it is sufficient for low amperes.
Final cooling versus lateral cooling
Rawlinson also has interesting things to say about the cold. Cylindrical cells can be cooled at the top and bottom (cooling through a plate, cooling at the bottom) or on the side with a serpentine cooling layer (side cooling).
A cell transmits heat better axially than radially, which speaks to the final cooling. One disadvantage is that the heat has to travel farther. With lateral cooling space is lost in width due to the cooling carpet, with bottom cooling at height.
But the fact that Lucid chose end cooling is due to something else: the surface contact between the cell and the cooling channel is easier to guarantee in the industrial production of modules.
More information on the battery:
Tesla Model Y with “structural batteries”: new knowledge
E-GMP batteries: Thus come the 58, 73 and 77 kWh sizes
By the way, the video is just the first part of a whole series that Lucid plans to publish on his YouTube page. We will keep our eyes open for sequels.