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Rare earth N42 magnets and temperature

Rare earth N42 magnets and temperature

Rare earth N42 magnets and temperature

(OP)
I'm having inconsistent results using magnets and hall effect switches and it seems to be temperature related. The temperature can vary between -5°C and +40°C. The manufacturer states there should be no change in the strength of the magnets in that temperature range. I have eliminated all other variables that I can see with temperature change and still seem to have the issue.

If the magnetic effect is triggering the switches, but only just and if there is a reduction in "pull" from the magnets at the higher temperature this would fit with what I am experiencing.

Is there a non permanent reduction in pull force at 40°C when compared to -5°C?

TIA

RE: Rare earth N42 magnets and temperature

Small changes in the gap due to thermal expansion/contraction might be playing a role as well.

Try making a test using a ceramic spacer and running it over the range.

Also, you mention that the magnet strength is of concern - what about changes in the hall effect sensor?

edit:

per https://www.first4magnets.com/us/tech-centre-i1093... they lose 0.1% per degree C and there are special classes of material with higher temp resistance.

Are you using them with a ferrous magnetic field concentrator?

edit 2:

More detailed info https://e-magnetsuk.com/introduction-to-neodymium-...

RE: Rare earth N42 magnets and temperature

Neo has a huge tempCo.
And it depends greatly on the operating slope.
Br only changes (alpha ~ 0.12%/C) about 5% over your range, but the Hc changes (beta ~ 0.7%/C) more like 30%.
If this is operating a low slope (as is common with RE materials) you could even be dropping below a knee at you high temp.
Check to assure that you are at a high slope.
This is one reason that Alnico is still used for high temp application, higher service temp and lower tempCo.
There are doped RE grades that give up Energy Product in exchange for better stability, but they get expensive.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Rare earth N42 magnets and temperature

(OP)
Thanks 3DDave and EdStainless. Some pretty interesting reading.

That should be enough to run some tests.

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