bigmoose wrote:The magnets weaken with heat which provides unintended flux weakening which actually will increase your top speed (less back emf)
As long as they cool down when you decelerate they will recover and you'll have full torque off the line
Sorry, but I need to correct this. When you overtemperature the magnets you "knock down" their flux. It does not recover when the magnets are cooled. Their flux is permanately "knocked down".
http://www.ndfeb-info.com/temperature_ratings.aspxAn irreversible but recoverable loss occurs when the output falls but does not return when the magnet cools down (e.g. the high temperature takes the Intrinsic working point beyond the knee of the Intrinsic curve, causing demagnetisation) but this would be recovered if the Neodymium magnet is remagnetised. For all extents and purposes, this output is lost because the magnet will not be remagnetised during practical application... When cooled, such a demagnetised magnet will have the original Hci but a lower Br (the Br will have increased by the reversible temperature coefficient amount applied to the reduced high temperature Br).
auraslip wrote:I just can't think of a way to use peltiers to cool the hub that doesn't require plugging it in each time you use it. As in: glue a peltier to the side of the hub and plug it in when you stop running. Now, this might be useful for races!
GCinDC wrote:any suggestions how to prep a 9C? particularly the wiring/halls...?
andynogo wrote:Then coat everything in an engine lacquer or windings lacquer.
...Seal the wires where they pass into the axle with automotive silicone
fechter wrote:If the motor is filled with oil, rust should not be a problem, so the laminations shouldn't need any coating.
johnrobholmes wrote:Regular mineral oil is used for cooling transformers.
andynogo wrote:As I said before, I follow the KISS principle. Keep It Simple, Stoopid!
ATF is thin, easily available and good for gears in a geared hub. It's also specifically engineered to also be good for bearings, like those found in a DD hub. I don't want you DD guys feeling left out here. This simple splash system should be good for most people. If you want to really turn the power up, sure, a radiator, pump etc is better but way more complicated.
I guess the downside of simple splash oil cooling is that if you let your oil get to more than 80 celcius constantly, you risk damaging your magnets. If that's the case then you have to either try the radiator approach or air cooling and turning the power down a bit. If you have alot of spare time on your hands, you could do the liquid cooling/radiator approach with a coolant channel formed around the base of the stator laminations like have been done on this site (the carbon fibre channel- nice). This would prevent any of the hot coolant getting at the magnets but it also wouldn't take heat directly away from the windings either so they would still be susceptible to burning.
Of course we could buy motors that are rated for the power that we desire.........nah!
motomech wrote:Anyone actually seen these damaged magnets?
My gut tells me this is a theoretical problem that is not going to manifest in practice. I thinking other things[like winding insulation and wiring] will be damaged long before the magnets lose any strenght.
At least that's my experience working as a motorcycle/automotive/heavy equipment mechanic for more decades than I care to admit.
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