Max safe Flux Weakening

That question was 4 years ago and I neither use those motors or controllers any more.

Limiting to 80 degrees is not required at all for DD hub motors.
Even with only 120 degrees rated magnets I had no permanent demagnitisation when running a motor (with Statorade) up to 170 degrees celsius at the windings.
Kv still unchanged and I checked the magnets with a gauss meter.

But you need to rewind the motor with higher quality winding wire (I use 200-220 degrees rated). Stock is usually only 130 degrees rated wire and the insulation usually fails before the magnets will start to demagnitized permanently.
Limiting the stock motors to 120 degrees at the winding should be fine based on my experience.

However on sur ron motors I have heard about demagnitized magnets several times.

It takes high temps and 600-800Amps phase current to demag a Sur Ron motor. I've never seen it happen from any amount of field weakening, just from cooking them with extreme weakening.

@hias9:
Yes, there’s a difference between theory and reality and it’s huge. I hoped someone would bite and show the background to the difference between magnet in free space and magnet in circuit. I guess we won’t see that :wink:

@LFP but why? 600-800A plus field weakening seems like… user should get a different motor?

larsb said:

@hias9:
Yes, there’s a difference between theory and reality and it’s huge. I hoped someone would bite and show the background to the difference between magnet in free space and magnet in circuit. I guess we won’t see that :wink:

@LFP but why? 600-800A plus field weakening seems like… user should get a different motor?

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I've personally never cooked one, and just enjoyed the insane torque and HP it pukes out when you feed it everything you can. This keeps it light and agile for technical riding.
When folks demag, it's from road racing or continous MX riding, and then a bigger motor or added active cooling would be needed to maintain that output over long periods.

When somebody cooked a hubmotor, it was usually the insulation of the winding which was burned.
For the cooked sur ron motors, it was because of the magnets and the winding was still fine. They run up to 550 phase amps, but only up to around 100A field weakening. At least they claimed it was because of the magnet.

@LFP: Do you think on the sur ron motor, the magnets get hotter than the winding (with about max 550 phase amps and max 100amps field weakening) ?

I haven't Instrumented Sur Ron rotor temps. My hunch is the copper winding heats the stator up until the rotor magnets exceed 140-165degC and permanent relaxing there PM field. The winding can handle much higher temps than the magnets.