'unitepower.com' 48V 1800W brushless motor teardown

A friend recently acquired a '1800W 48V' brushless scooter motor and I decided to have a look inside, ostensibly for the purpose of doing thermal testing.

The rotor measures 63mm (diameter) by 73mm (stack height). This gives an air-gap-area*radius metric of 289 cm^3, which is not too shabby; for comparison, the Sonata HSG, which is a 60Nm motor, is 415 cm^3. The laminations are about .56mm thick, which is not great for high speed performance and is probably a huge reason why these motors are not very efficient.

The stator is surprisingly well-made. The fill factor is OK, and the concentrated windings mean there aren't a ton of end-turn copper losses. The stator also has a pretty high iron-to-copper ratio, which is good for peak torque and not good for efficiency. The large volume of iron in the stator is probably another contributor to the high losses - at peak efficiency, copper losses are less than half of the total losses.

The motor has hall sensors, installed using the standard in-the-slots technique:

The housing is mediocre. The end caps are cast aluminum, and the stator is pressed into a piece of steel tube, which adds quite a bit of weight. The motor is also much longer than it needs to be - out of the 177mm of total length, only 72mm contribute to torque production.

Motor specifications:

Type: Surface PM machine
Pole Pairs: 3
Resistance (line-to-line): 73 mOhms
Inductance (line-to-line): .415 mH
Flux linkage [derived]: 0.036 Vs

Back EMF:

Full of harmonics, but reasonably sinusoidal.

Thermal testing:

Thermal testing was done by passing DC current through a pair of phases while watching the temperature of the end turns with a Flir A65 thermal camera. We initially set a temperature cutoff of 110C, but backed down to 95C after noticing some degradation in the either the enamel or epoxy in the stator at around 100C (this is pretty terrible; good wire can operate at 200C!).

Performance with no additional cooling proved to be rather poor; at 28A (which is the RMS current at 40 peak phase amps), the stator hit 95C and started overheating.

Performance with active cooling (a Sunon PMB1297PYBX-AY 12V blower) proved to be much better; we were able to achieve 33Arms (46 peak amps) with a stator temperature that stabilized at around 90C.

Note that this is a best-case operating scenario; at stall, there are no iron losses. Further testing at speed is planned for a later date.

Conclusion:

This is "a lot of motor" - it can produce huge amounts of peak torque. Unfortunately, terrible efficiency, non-existent high-speed performance, and a dubiously low temperature cutoff all serve to severely limit its applications. Even for its advertised application (small electric scooters) it is a poor choice, as 70% peak efficiency means around 20% of the battery pack is wasted (versus a 90% efficient machine).
These motors are very close to being good - better wire and thinner laminations, both of which wouldn't drastically increase costs, would go a long way to making them more useful. Maybe in the future, we will see an updated version with these improvements, but for now, I would steer away from these motors.