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As the team at Munro & Associates dives into the Skywell EV motor teardown, we’re not just dissecting components—we’re opening a time capsule. The motor at the heart of this teardown is a BYD unit, but not one that reflects the company’s latest engineering prowess. Instead, it’s a design that dates back nearly a decade. This makes it a perfect case study in how automotive suppliers evolve through iteration, refinement, and hard-earned lessons learned.
In this blog, we examine the motor architecture Skywell chose to license from BYD, contrast it with more modern systems like those in the Chevy Bolt and Tesla, and offer key engineering insights into cost, design choices, and failure mitigation strategies.
A Glimpse Under the Hood: High-Voltage Architecture Overview
When Munro popped the hood of the Skywell EV, several features stood out. The high-voltage architecture was spacious and well laid out—uncommon in today’s EVs, where space-saving measures often dominate.
Central to the system is a three-in-one box—a compact unit about the size of a shoebox that integrates the DC-DC converter, power distribution, and onboard charging controller. High-voltage cables split off to the inverter and battery, while others feed the AC compressor and a resistance heater that doubles as a battery thermal management unit.
This setup also includes a traditional 12V battery, charged by the DC-DC converter, and a legacy-style vehicle fuse box. In contrast with many newer EVs where electronics are tightly packed atop the battery pack, Skywell’s design is open and serviceable—possibly reflecting BYD’s older architecture and design ethos.
The BYD Motor: Outdated Yet Telling
The centerpiece of this teardown is the 150 kW motor supplied by BYD. What’s fascinating is that although BYD now leads in electric motor technology, Skywell opted for a previous-generation design—likely due to commercial availability and licensing convenience during development in 2019.
Size and Torque Comparison
Comparing the Skywell-BYD motor to the Chevy Bolt motor—both rated at 150 kW—shows stark differences. The Bolt motor is significantly smaller and lighter (by about 5 kg) yet delivers higher torque: 320 Nm. This highlights a key shortfall in the Skywell motor—power and torque density.
The design, reminiscent of early 2010s tech, is closer in performance to the original Nissan Leaf motor or the early Toyota Prius design. While it’s not unfit for purpose, it’s nowhere near competitive with the current state-of-the-art.
Winding Technology: Stranded vs Bar Wound
The BYD motor employs stranded wire winding, a method in use for nearly a century. It’s cost-effective, especially for low-volume applications, because the required machinery is simpler and cheaper. However, stranded windings can’t pack as much copper into the stator slots as bar-wound motors, leading to reduced efficiency and torque density.
Tesla used stranded winding until recently, but has since shifted to bar winding to push the boundaries of power efficiency. The Chevy Bolt, for instance, already benefits from bar-wound architecture—highlighting a design tradeoff in the BYD motor between manufacturing cost and performance.
Cooling and Thermal Management
The stator in the BYD motor is cooled by a water jacket, a machined aluminum extrusion with internal caps and a leak-tested layout. This cooling design was clearly refined after some initial challenges—RTV sealing led to leaks, prompting a switch to welded and machined end caps.
This evolution shows how failure modes, like coolant leaks into electrically conductive windings, shape future iterations. BYD clearly learned from these early missteps—this revised water jacket is a hallmark of iterative engineering that reduces warranty risks and builds reliability.
Bearings, Gears, and Friction
The teardown revealed that BYD’s gearbox uses ball bearings on motor and input shafts, and tapered roller bearings for the differential. This is standard for moderate-torque applications. The gear ratio sits at 11.2:1, and the assembly has a normal friction profile.
However, Munro flagged an issue with the bearing retainer plate design. It’s a blind assembly process—difficult to verify alignment and prone to cross-threading during insertion. If not installed properly, the retainer can loosen and interfere with spinning components, potentially causing a catastrophic front-wheel lockup.
Tesla, by contrast, uses a spring-loaded pin that automatically engages with a notch on the bearing—an elegant, self-aligning design that reduces assembly risk. This difference underscores the importance of design-for-manufacturability (DFM) in EV component assembly.
Inverter Insights: Modular Yet Costly
The Skywell inverter is housed in a standalone cast aluminum box, separate from the motor. While understandable for older systems, this approach increases both weight and cost. Modern designs—like those used by Tesla and GM—integrate the inverter into the motor housing, reducing complexity and material usage.
Internally, the inverter is structured into:
- A control board (microprocessor, memory, logic)
- A gate driver board (to control six IGBT switches)
- An Infineon hybrid pack (IGBTs with integrated cooling)
- A large capacitor (to smooth current ripple)
- A ferrite filter (to reduce high-frequency noise)
This configuration reflects solid engineering practice for its time, but newer systems are more integrated, compact, and cost-optimized.
Interestingly, the inverter uses only two current sensors instead of three—another indication of cost-saving measures. While adequate, this choice reduces current measurement accuracy, especially during transient operation.
Takeaways: What the Skywell EV Motor Teardown Teaches Us
Despite its dated design, the BYD motor used in the Skywell EV offers invaluable lessons in lean manufacturing, thermal management, and failure resolution. These include:
- Iterative Cooling Design
Water jacket evolution from RTV to welded solutions shows real-world feedback loops at play. - Assembly Risk Mitigation
Tesla’s approach to bearing retention is a benchmark in manufacturability and safety. - Design for Low Volume
Stranded winding, separated inverter housing, and simpler gear structures make sense in early EV launches or niche production runs. - Benchmarking as a Strategy
BYD’s early use of Prius-style magnet patterns and conventional windings reflect strategic benchmarking—a tried-and-true path to competence. - The Importance of In-House Innovation
BYD has since developed cutting-edge motors and inverters. But as this teardown shows, even top-tier companies start with foundational blocks and gradually innovate through feedback and failure.
Final Thoughts: Where BYD and Skywell Go from Here
This teardown of the Skywell EV motor gives us a behind-the-scenes look at BYD’s first-generation motor designs. It’s a masterclass in engineering progression. While this unit is no longer competitive in 2025, it played a key role in BYD’s climb to the top of the EV game.
Skywell’s use of this motor suggests a budget-conscious approach—leveraging reliable if outdated technology to get to market. As global EV demand increases, we expect Skywell (and others like it) to adopt more modern integrated drive units, perhaps even developing proprietary motors to enhance cost-efficiency and performance.
Team Up With Munro!
Curious how legacy EV designs stack up to today’s cutting-edge tech? Dive deeper into Munro’s teardown reports or explore our latest benchmarking of motors from Tesla, GM, Hyundai, and more. Stay ahead of the electric evolution—check out Munro & Associates or request a teardown consultation today.