I'm specifically talking about the windings in the motors themselves. There's only so much current they had take before they start heating up, and that's when they can start to fail - just as melting or burning the insulation, creating a short across some of the winding, making them even less effective and even more prone to short circuiting which can cause even higher currents.
In normal use, only one phase is active an a time, so the duty cycle is 1/3. When the motor slows almost to a stop, the duty cycle on that winding is 100% meaning that the effect of that current on heating the wire is much worse than normal.
The catastrophic failure is when the MOSFET fails in a way that it doesn't protect the winding or battery from a short circuit which could lead to runaway heating in the battery as well as the motor. But even before then, unless the controller is actively limiting current to safe levels, the motor will get destroyed.
The only happy day scenario is if the motor control is actively limiting the current to safe levels well below the expected failure point, and then the EV will just fail to move at all under that load, other than rolling backwards.
As I said, the limit for this will be based on what the manufacturer expects the maximum load will be, but people have a knack for trying to carry more weight than their vehicle was designed for, or taking it places that are unsuitable. That's just humans being humans.
It's possible to design an EV that could withstand significantly steep hills with heavy loads, e.g. by putting many more sets of individually wired windings in parallel, but it'd be expensive and unnecessary for the typical situations that they'd be used in, and so unlikely to be commercially viable.
In normal use, only one phase is active an a time, so the duty cycle is 1/3. When the motor slows almost to a stop, the duty cycle on that winding is 100% meaning that the effect of that current on heating the wire is much worse than normal.
The catastrophic failure is when the MOSFET fails in a way that it doesn't protect the winding or battery from a short circuit which could lead to runaway heating in the battery as well as the motor. But even before then, unless the controller is actively limiting current to safe levels, the motor will get destroyed.
The only happy day scenario is if the motor control is actively limiting the current to safe levels well below the expected failure point, and then the EV will just fail to move at all under that load, other than rolling backwards.
As I said, the limit for this will be based on what the manufacturer expects the maximum load will be, but people have a knack for trying to carry more weight than their vehicle was designed for, or taking it places that are unsuitable. That's just humans being humans.
It's possible to design an EV that could withstand significantly steep hills with heavy loads, e.g. by putting many more sets of individually wired windings in parallel, but it'd be expensive and unnecessary for the typical situations that they'd be used in, and so unlikely to be commercially viable.