# grams (or kg) of neodymium

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How do you calculate how many grams of kilograms of neodymium you need in order to build a permanent magnet motor with, let's say 10kw power? Thanks

wasn't sure which forum to choose to post this.

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I have no idea how one would calculate this (no experience with designing motors, just the circuits to drive them). But I can't imagine there is any direct relationship between mass and the power of the motor.

There will be many factors: the number of turns for the coils and thickness of the wire for them to generate sufficient magnetic field but with sufficiently low resistance that it doesn't get too hot; the field strength from the permanent magnet which will depend on the physical size and shape.

I expect those factors change depending on things like speed of rotation, how much torque you need to generate (I don't know how torque relates to power ...) etc. Might also change if it is an AC or DC motor.

I imagine one would have to do a rough design to find out the size of magnet needed to find out what the mass is (and then adjust the design if necessary).

Or you could look at the specs of a 10kw motor and estimate how much of the mass is the magnet. Or buy one and take it apart...

It will be interesting to see answers from people who know what they are talking about!

!

Moderator Note

I have moved this to Engineering (but left a link from the original location) as that seems more appropriate.

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2 hours ago, Fans said:

How do you calculate how many grams of kilograms of neodymium you need in order to build a permanent magnet motor with, let's say 10kw power? Thanks

wasn't sure which forum to choose to post this.

I don't think there's a direct correlation of mass and magnetic field strength.

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Just now, swansont said:

I don't think there's a direct correlation of mass and magnetic field strength. ﻿

Is it not based on length and width of the magnet?....  I guess it could be related to the volume as it is to do with the dimensions of it... and thus mass by default according to the material density. I do not know if width/bredth or length are more relevant than volume as a whole....  I would imagine (but can't remember if is correct or not) that a magnet with a high area on the face that is attracting (like a square plate) would be stronger than a long thin bar with the same volume... it would be harder to separate 2 of them for sure - but that could be due to mechanical properties and leverage of breaking apart two rods end to end compared to the plates rather than field strength.

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3 hours ago, DrP said:

Is it not based on length and width of the magnet?....  I guess it could be related to the volume as it is to do with the dimensions of it... and thus mass by default according to the material density. I do not know if width/bredth or length are more relevant than volume as a whole....  I would imagine (but can't remember if is correct or not) that a magnet with a high area on the face that is attracting (like a square plate) would be stronger than a long thin bar with the same volume... it would be harder to separate 2 of them for sure - but that could be due to mechanical properties and leverage of breaking apart two rods end to end compared to the plates rather than field strength.

If I raise the temperature above the Curie point, it loses its magnetism. The alignment of the domains depends on the field its in when it cools. Striking a magnet can make lose magnetism. Putting it in a strong field can weaken the magnet.

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I'm fairly sure that I can use an arbitrarily weak magnetic field and still make as powerful a motor as I wish by using lots of turns of thick wire.

It would be stupid, but I can do it.

And that proves that there's no single answer to the question.

If I wanted to get a sensible design for a 10KW permanent magnet motor... I'd look on the web and copy someone else's design.

I can buy one with a shipping weight of 31 KG (the first one I found on Google)
so the answer must be "Less than 31 Kg".

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10Kg of Nd with zero magnetism will not be better than 1Kg of strongly magnetized Nd to make a motor run.

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It's slightly worse than that.

Nd is not (usefully) magnetic.

An alloy of Nd, Fe and B is

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