Building a NEO Magnet Magnetizer

[EddieO]

I am looking to build a NEO magnet magnetizer for RC motors. Currently we are having issues with the motors losing magnet strength after they are run. The rotors to replace are $30+. In the Old days, we ran brushed ceramic magnet motors. With these, we had a magnetizer to simply zap the motors back to strength. Now, the entire hobby has switched over to Brushless motors, which all use a sintered NEO magnet on the rotor.

The rotors look like this. Half is magnetized to the south, the other to the north.

http://i617.photobucket.com/albums/tt258/eddiejulie/novakrotor.jpg

Now a few specifics....

I am electrically inclined. I've assembled numerous projects from the ground up, including a ceramic mangetizer, LipO battery chargers, and more. I am an extremely good at soldering and I very safe in all my projects.

I know that I will be playing with large amounts of voltage and amperage.....

The rotors can be removed from the motors very easily. The magnet cannot be removed from the shaft.

I am in need of help designing the magnetizer along with the fixture to hold the arm. If the unit can be even somewhat portable, that would be a big plus.

Any help would be great.

Later EddieO

[vk6kro]

Great photo, but where is the magnet? Is it the larger metallic cylinder on the lower image?

Have a look at this thread which is from last year and which went on for about 4 months.
It may give you some idea of what is involved.

http://www.physicsforums.com/showthread.php?p=2286084#post2286084


Neodymium magnets are very difficult to magnetise and should not demagnetise as easily as yours seem to be. Are they getting very hot?

[EddieO]

Yeah, that would be the magnet.....they are impossible to remove without destroying them.

The motors get pretty hot, which along with the rotational speed (up to 70k rpm), is more than likely causing the loss in magnetic strength.

There are multiple commercial systems out there that can do it, I am just not going to pay $20,000+ for something that has less than $2000 in parts...most of the units also have a ton of features, which I don't need.

Later EddieO

[MagnetDave]

The system has a lot more than $2000 in parts, and I honestly recommend you don't try it. Just buy a new rotor, and start cooling it, or buy one that uses SmCo magnets.

With that said, a magnetizer normally consists of a bank of quick-discharge capacitors, roughly the size of 1-gallon cans. A typical magnetizer in industry has a bank that is about 10x3x3, or 90 such capacitors, to get to a final capacitance on the order of 10-40 mF. You then have a set of transformers to convert incoming voltage up to the limit of the caps, (2-5kV), and a set of thyristors to dump the juice into a coil. (or, more likely for your rotor, an array of coils). There is also an attendant set of controls. The coils are typically heavy gauge wire wrapped around a laminate core, and potted with water jackets.

I have cleared $2000 RE-building just a coil, when I already have heavy gauge wire, laminates and plates on hand. This is ignoring that I already had the magnetizer and chilled water system.

Again, I'm not saying it can't be done - I'm saying it's unlikely to make economic sense, it costs more than you think, and even you are safe around electricity, you are running the risk of an "instantly fatal" accident, not a "unpleasantly shocking" accident. NdFeB magnets have drastically higher coercivity than the ceramic magnets you remember - you are truly in a different zone here.