QS motor magnet max temp before demag ?

[flathill]

Max allow temp also depends on your controller

Power advance (flux weakening)

It must be tested with the stator in place

Baseline test is unpowered with motor naturally aligned (lowest resistance flux return path). Put motor in oven until entire motor at same temp. Remove motor from oven and allow to return to room temp (overnight or use water bath to speed process) remeasure mags with hole in side cover to make it easy. Bump oven temp 5c and retest. Repeat until mags do not recover at room temp. This is the best case max temp.

More testing is needed for real world max temp but it gives you a good baseline if you just want to guess and give urself leeway based on how aggressive the motor is being used (and also account for skimpy dysprosium mag batches)

 

[Doctorbass]

Max allow temp also depends on your controller

Power advance (flux weakening)

It must be tested with the stator in place

Baseline test is unpowered with motor naturally aligned (lowest resistance flux return path). Put motor in oven until entire motor at same temp. Remove motor from oven and allow to return to room temp (overnight or use water bath to speed process) remeasure mags with hole in side cover to make it easy. Bump oven temp 5c and retest. Repeat until mags do not recover at room temp. This is the best case max temp.

More testing is needed for real world max temp but it gives you a good baseline if you just want to guess and give urself leeway based on how aggressive the motor is being used (and also account for skimpy dysprosium mag batches)

Yes, that's a good method. witch would give best result as well. It require also you to accept that your motor get permanent mag field loss :lol: But if someone want to be the guinea pig, i'm open! to teh result... i dont have enough motor for sacrifice 8)

doc

 

[Doctorbass]

Motor magnetic field comparison ( loss or not! ): THE RESULTS!!:

-conditions: motor under test was in a oven at 78.1 celsius stable for 12hours
-the reason of high temp: to bake the paint that protect magnets
-emotional effect: DAMN IT !!.. i was shocked wheni have read the published temp specs about that motor relative to the temp i used in the oven


RESULTS:

The baseline motor:
QS205 50H V3 5T (not the best but the only one i have that i'm not 100% sure if it got overheated.. that motor had also suffer from severe rust and was cleaned but have some sequel)
-test on the center of the magnet plate stator removed: bwrteen 3300 and 3400Gauss
-test with the probe perpendicular on the top of junction of two magnets intersection: 5000Gauss


The two other motors under test:
-QS205 50H V3 4T ( the only motor that was never installed or ran.. however it got 12hours of 78degree C to bake protective coating on the magnets...)
-test on the center of the magnet plate stator removed: bwrteen 3400Gauss
-test with the probe perpendicular on the top of junction of two magnets intersection: 5100Gauss

QS205 50H V3 5T ( My very first QS205 and installed oh my NYX at 16kW but never seen stator temp higher than 120C)
-test on the center of the magnet plate stator removed: bwrteen 3450Gauss
-test with the probe perpendicular on the top of junction of two magnets intersection: 5450Gauss
( please note that this rotor have no paint yet and the accumulation of paint that other motor have at the top junction of two magnets create enough thickness to letthe probe to catch less magnetic field as it is less closer)

In fact the closer the probe is to the magnet the higher the reading is... as well! so even only the paint itseld is enough to make the probe to catch from 100 top 300 gauss less!

Conclusion: It is difficult to make a straight conclusion with the data i have from now.
The reasons are that the added thickness of the paint itself make the probe to catch less mag field lines because it is less close to the magnet and that the baseline motor have unknown background except that it got florida water and was driven bt a 14kW Max-E

But out of 3 motor i can conclude at least that the average magnetic filed is:
3425Gauss on the center of the magnet plate stator removed and 5300 with the probe perpendicular on the top of junction of two magnets intersection

The motor rotor that went to the oven at 78 celsius for 12h does not seem to have loss of magnetic filed

Doc

 

[xenodius]

Hey, sorry to necro this thread but like so many hotrodders here I have been looking to find a definitive answer about precisely where the threshold of reversible temperature-dependent magnetic losses becomes irreversible for years, I have never found any sort of hard data supporting max temperature recommendations, even here on ES, just... common wisdom. So I've erred on the side of caution limiting to only 110C. Recently I read the QS205 has a max rated magnet temperature of 150C which I didn't really believe is truly safe, so I tried to find the answer again... and this time I did, in no small part thanks to information in this thread and esp. Doctorbass's gauss measurements in this thread! =)

There's some very in-depth explanations and experimental data here; https://www.kjmagnetics.com/bhcurves.asp

Essentially, for a given magnet type and shape, there's a permeance coefficient. This value defines the slope of a line across a temperature-specific line of experimentally derived gauss (Y) vs. gauss-oersted (X). The gauss/gauss-oersted line is perfectly linear until irreversible demagnetization occurs, then it has a knee. The QS205 magnets are 50 x 4 x 12.5mm, 35SH-type, with the attached demagnetization curves as a single magnet in free space. An intersect line for the permeance coefficient of this size and type magnet at 120C is marked with a red square where it intersects the gauss/gauss-oersted line; as you can see, this point is right at the threshold where this line becomes nonlinear, and so right at the threshold at which any irreversible demagnitization occurs.

Being in a stator and not a single magnet in free space, as I understand it would increase the irreversible demagnetization threshold. So in free space each magnet is only 2.17 kilogauss, but Doctorbass measured ~5 kilogauss in the stator. Assuming exactly 5 kilogauss yields a permeance coefficient of exactly 1-- so the permeance line goes from origin to 1, instead of origin to ~0.33 which puts ~140C slightly below the threshold of irreversible demagnetization, and the 150C manufacturer limit right at the threshold if you interpolate the 140C and 160C curves. But picking a lower safe value as calculated above would provide margins for slow or imperfectly accurate thermal foldbacks to ensure we can push our motors hard, without ever irreversibly demagnetizing them. And this calculator can be used for any motor of known magnet type and dimensions. Personally I found this very reassuring and with Doctorbass's gauss measurements I believe the QSMotor max temperature is indeed reasonable, but should not to be exceeded-- it's a hard limit.