Stronger Motor Magnets

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ekline309   10 W

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Re: Stronger Motor Magnets

Post by ekline309 » Dec 23 2020 9:10pm

neptronix wrote:
Dec 20 2020 9:13pm
Better cruise efficiency does not make sense because the same forces that cause cogging during freewheeling are acting on the motor when under power too.
I don't think this is correct, you actually want a design that has high cogging torque when the motor is running, this is what makes an easy path for the flux to complete its loop. Like others have said typically I^2R losses are the largest proportion, so anything you can do to lower current (i.e. by using stronger magnets) will be good. Also for direct drive hub motors (very low frequency compared to high-speed machines) I would not expect hysteresis to be a large portion of losses, but this depends on the steel and I don't have numbers on this.

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neptronix   100 GW

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Re: Stronger Motor Magnets

Post by neptronix » Dec 26 2020 4:16pm

ekline, your theory makes a lot of sense.
The increased efficiency from increased electromagnetic conductance under load may far outweigh the additional drag at all times.

Chinese manufacturers likely use weaker magnets because they are cheaper. In the same way they dragged their feet on going to 0.35mm lams that cost perhaps $30 per 9C DD clone while increasing efficiency 8% and improving power by 50%. Which is well worth an additional $50.

It would be relatively easy to unglue magnets in a DD hub using high heat.
Getting your hands on stronger magnets of the appropriate size/shape may be difficult. But worthwhile as an experiment.

Convincing a DD hub manufacturer to perform this modification for you would be very hard.
The owner of leafmotor knows who i am and how i accidentally made his brand famous but will not take a $1000 payment to make me a DD hub with 0.27mm lams with the promise of me testing this modification for them and reporting back. That's how hard this is.
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hias9   100 W

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Re: Stronger Motor Magnets

Post by hias9 » Dec 26 2020 4:51pm

Yes, the Chinese motor manufacturers would only do it if ordering a high quantity.

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ekline309   10 W

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Re: Stronger Motor Magnets

Post by ekline309 » Jan 05 2021 10:15pm

Also I forgot the original post was about upgrading the existing magnets in the motor. Ideally the system (motor core + magnets) would be designed to operate at some optimal point on the hysteresis curve of the steel. Essentially it should be operating right at the top end of the linear region. If you throw in stronger magnets the steel will probably saturate and hysteresis losses would be quite high, maybe this was the original concern in the post :?:

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Re: Stronger Motor Magnets

Post by hias9 » Jan 07 2021 1:16am

Is there a way to calculate the optimal point of the hysteresis curve if you know the amount of back iron (it‘s about 7-8mm thick for these motors) ?
If I would replace the magnets with ones that are 10% stronger, but Kv would only decrease by 5%, that would probably mean that the back iron is saturated, correct?
And if it decreases linear (10% stronger magnets result in 10% less Kv) mean that is has not saturated yet?

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Re: Stronger Motor Magnets

Post by hias9 » Mar 15 2021 3:48pm

I am wondering if the motor would saturate at less phase amps after upgrading to stronger magnets. If it just depends on the amp-turns, it would still start to saturate at the same phase amps (so at a higher torque).

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