De magnitization current for Crystalyte 408

Does anyone know the current that would demagnetize a 408, or any 400 series Crystalyte? I am asking this because my new controller monitors everything I can think of, this is the last protection feature required.

I don't think you need to worry about that since it uses rare-earth magnets. The windings would burn up way before it demagnetized.

Ceramic magnets are prone to demagnetization due to high currents.

You do need to worry about the maximum magnet temperature, since this will demagnetize them. I don't know what grade of magnets they use, but the most sensitive ones are good to 80C. High temperature versions might be good to 100 or 130C.

I suppose you could measure motor current and limit it in addition to the battery current to prevent winding failure during high load. I don't think this would be necessary if you had a thermistor in the windings to watch the temp.

Thanks Fecher,

I do have a motor thermistor (and one on the FET heatsink), the max I have had is 50C after a long hill climb without human input. The heatsink was only 23C after that, those schottkeys do help.

fechter (spelt correctly this time), I measure the battery current, know the PWM and hence can calculate the motor current.

One thing I am going to implement is battery current limiting using the speed of the motor to calculate the max PWM to give a maximum battery current for each battery, being a twin battery controller.

This is secondary to the hardware current limit (20A per battery) already there, a more elegant solution than just cutting off the PWM to reduce the amps. I can hear the motor 'fizz' when the limit comes in probably due to the somewhat random nature of the hardware limit.

But first, after the garden party for my wifes birthday on Saturday, try some phase advance. As my magneticaly sprung 'throttle' swings both ways (!) I think I will have one side normal PWM up and side two full PWM with increasing advance

I've demagnetized R/C brushless motors while leaving the windings intact.

It depends on what the magnets are made from. Neodymium magnets break down around 80 Celsius. Typical magnet wire breaks down around 150-200C. Cobalt samarium magnets are good to over 250C. I presume that most motors use cobalt magnets, but if they are ultra efficient and use neodymium magnets (like some R/C motors) then it's possible to destroy the motor at the fairly "low" temperature of ~80C and leave all the wiring intact.

http://en.wikipedia.org/wiki/Neodymium_magnet

I ran a 36v brushed motor ( not crystalyte brand but would be very similar structure to their brushed motor) on 72volt controller. Standard controller was 15amp for that motor, I used a 100amp controller but it wouldn't draw over about 40amps (not sure what limited the amps? saturation of magnetic field ?? winding resistance?? have been told for brushed motor than winding resistance doen't limit amps but dont understand why that would be if its true).
Under load for a time motor would get way to hot to touch ( certainly couldn't leave a finger on the motor ), if ran at higher rpm on flat ( not much load) motor was warm but ok ( running efficiently at higher rpm I guess).
It uses neomags, motor never burned out magnet strength seems ok, I would be guessing going to be pretty hard to demag a 408, is likely you could run it too hot to touch without damage is my guess.
Top speed in a 26" rim with standard controller was about 28km/hr, on 72volt controller got up to just over 40km/hr ( was expecting much higher increase in speed)