Brief Analysis of Tesla Semi High Voltage And Charging

Since the Tesla Semi held its delivery event two years ago, various high-definition and non-high-definition pictures have been gradually released. As a Class 8 (defined with reference to the gross vehicle weight rating (GVWR)) heavy truck, the ability to haul goods + corresponding battery life has become the obvious direction of perception for users. Current Semi: 500mi (800+km)(est.)&37000 kg MAX, with three motors on the rear axle. The Pepsi model currently delivered supports day and night driving.

Part One: High Current Part

Unlike most current heavy trucks, Semi still follows Tesla's passenger car strategy of integration + modularization, skipping the transitional design of traditional energy electrification. This is also reflected in the new generation platform pure electric heavy trucks of Volvo and Benz:

●Battery modularization, adding and reducing the number of batteries according to different configurations;

● Semi has changed from placing the battery outside the chassis of most current products to inside and outside the chassis frame to increase the charge capacity. However, when the battery weight accounts for a certain proportion of the entire vehicle, it will not have a positive impact on battery life and operating efficiency;

● Based on the above, the modular overall high-voltage circuit design eliminates the conventional positive and negative electrode design of series battery packs or the circuit design of a separate battery pack for the control unit.

In terms of details, Semi has some differences (mainly compared to Volvo VNR and Benz eActros, please check the attached pictures for yourself):

● Integrating most components, the wiring harness assembly retains three modules from the battery to the control unit, the control unit to the drive unit, the control unit to the auxiliary unit and the power unit. Compared with the traditional arrangement, the three-phase power interface wiring harness assembly and charging port wiring harness assembly are reduced. Cheng et al;

● The wiring from the battery to the control unit follows the aluminum tube design of passenger cars. You can refer to the previous patent: Tesla-charging bus patent. Compared with Volvo VNR, it uses a two-core connector + cable to access the control unit;

● The plug-in part of the electric drive unit uses the same two-core handle plastic plug-in as the previous Semi. The top plane is arranged, the tail outlet is fixed simultaneously, and the bottom pipe joint + through-hole plug-in of the Volvo VNR electric drive unit is arranged horizontally;

● In terms of covering materials, the current version of Semi mostly uses corrugated tubes (cables) + braided network tubes (aluminum tubes), while Volvo VNR mostly uses tape + corrugated tubes (cables). There are layout differences here.

In terms of the overall layout, thanks to the integrated design of passenger cars, Semi uses less high-voltage wire harness assemblies and connectors than competing products, resulting in lower costs. Among them:

● The pipe joints are replaced by aluminum pipe straight plug-ins. The overall cost is lower than that of traditional connectors and the stability is higher. The modularization of parts and vehicle assembly is more convenient;

● The electric drive unit uses a plastic handle connector, which shows the connector's better vibration resistance and better layout level.

Part 2: Charging part

Compared with the current conventional solutions, Semi has challenges due to the charging demand brought by large power and the increased continuous current:

● A large amount of heat needs to be discharged during the charging process, and effective heat dissipation must be provided in the circuit;

● The resistance caused by an overly long cable cannot be ignored, and the entire charging circuit needs to be shortened;

● Excessive current requires an increase in the cross-section of the conductor, which increases the cost and difficulty of fixation. It is necessary to integrate or reduce the length of the vehicle-end charging circuit path.

In order to reduce the uncertainty in the vehicle charging + operation process, Semi chose gun-side immersion cooling + vehicle-side charging and distribution unit integration. The status after the design idea is implemented:

● The diameter of the cable at the gun end has not been significantly increased compared to the current 500kW solution. Instead, it has a better grip and solves the bug of the previous generation that the center of gravity is slightly forward;

● The connection between the tail of the cable at the gun end and the outer sheath is designed using a new process, which reduces the risk of the outer sheath of the previous cable falling off due to repeated force;

● The charging interface and power distribution path are minimized, the shared control unit has good heat dissipation conditions and the cost of the charging assembly is optimized;

● The interface uses chip terminals. Based on the actual insertion depth, is there room for optimization of the overall length? What do you guys think?

Part Three: Thoughts

At present, Semi still has a lot of undisclosed data, which will be gradually disclosed later. I will give a comprehensive summary at that time~

Before the end of the article, let’s briefly look at a failure mode: safety risks arise when the cable sheath slips.

This mode exists in non-liquid-cooled guns + multi-core wire connectors. The cable sheath at the rear of the gun cannot be limited, causing the gun wire sheath to slip out, exposing the internal wires, and the risk factor is high.

To this end, each company has a solution in terms of vehicle layout and connector design. However, in the era of liquid-cooled guns, as the length of the gun line is gradually shortened and the working conditions of the gun body are complicated + the tail is partially bent, the gun line will fail after aging. Pattern resurgence.

At present, most solutions tend to encapsulate the tail as a whole, or choose to design a stress ring to increase the cable retention force. What do you guys think?