recharge or renew magnetic strength of magneto rotor 1

[markweitkamp]

I am trying to recharge or renew the magnetic strength of a magneto rotor. The magnet is made up a stack of thin metal plates laminated together and then riveted into the middle of a shaft which allows it to rotate. The usual way to do this seems to be to expose it to very strong magnetism from a big electromagnet for a short time. I don't have a big electromagnet. I'm wondering if it would work to use smaller magnets for a longer time to accomplish the same thing. I have a couple of welding magnets (magnets to hold parts in position for welding) and I'm wondering if I just stick them on the magneto rotor and leave them there for a week, will they increase the strength of the magneto rotor?

Thanks for any help.

 

[ishkabidle2]

I'm not uber-experienced, so take this with a grain of salt.

According to the hysteresis curves (the full curve, not just the demagnetization quadrant), remagnetization is caused through the exposure to a large magnetic field, which gets the domains in the magnet material to line up and produce a magnetic field of their own. Time is only a secondary factor, only necessary to allow the domains time to rotate to the amount the strength of the applied field dictates.

Depending on the materials of the various magnets, the welding magnets could increase the rotor strength, but I doubt it will fully restore the possible strength of the rotor material.

 

[MagMike]

Are you sure the laminated structure is the permanent magnet portion of your magneto? Laminates are usually used for the soft magnetic portion of a magnetic device, to reduce eddy currents generated by magging/remagging.

Assuming the laminated portion is the permanent magnet:
1) Time is not a factor. Magnetization occurs very quickly, within seconds. Leaving magnets sitting for a week makes no difference.
2) The best way to remagnetize is with a fixture that'll make contact with and charge all the poles on the rotor simultaneously.
3) Since it sounds like you won't be able to obtain a magnetizing fixture, there is a small chance that you can restore some of the magnetism by using permanent magnets, one on each pole, with alternating polarity. Try to match the size of the magnets with the pole face and try to go with rare-earth permanent magnets (no assemblies, such as welding magnets).

 

[IRstuff]

One potential flaw in that line of reasoning is the assumption that the "good" magnet will "overcome" the "poor" magnet. The supposition is that the "poor" magnet won't weaken the "good" magnet, leaving you with weak magnets all around.

If you want it done right and done well, then send it out to someone who does it for a living. You'll save time and money in the long run.

TTFN

FAQ731-376

 

[markweitkamp]

Thanks to all who answered. And MagMike is probably right, the laminated structure I can see is probably packaging around the actual magnet. I couldn't tell for sure without destroying it, but I think the recharging will work right through the laminations if I can make the right fixture. I got a pile of big old coils from a junkyard, and thought I was on my way. The coil had a central hole big enough to put a 2" steel bar through it, and I ran enough current through the coil to light up a 12-volt DC light bulb, but the magnetism induced was so faint I could barely tell it was there. My coils are wound on a spool made of some metal like brass, bronze or copper. Would this prevent magnetism from being induced in the steel bar? On that theory I started unwinding one of the coils and rewinding the wire directly on the steel bar. The wire is fairly heavy, I would estimate it about 12 gauge by comparison to household wiring. One of the things I'm noticing as I do this rewinding is that the covering on the wire is flaking off as I unwind it from its original coil, leaving bare copper showing and making me worry about shorts from one loop to the next. Is this a real concern? On the original coil, all the loops are touching each other, very densely wound, and the only insulation seems to be some kind of varnish on the wire. Since I'm losing that in the rewind, I have been spacing the loops about a quarter-inch apart and wrapping each layer in elecrical tape, so mine is much, much less dense than the original. Am I wasting my time? My arms are getting tired.

Thanks again for any help.
Mark

 

[MJR2]

You are wasting your time. And you may hurt yourself. You will need many thousands of amp-turns to recharge your permanant magnet. Count your turns when you are finished and you can estimate your required DC amperage. That should discourage you. Your spool should be steel to direct the flux lines into the circuit you are charging. If when turned on you can pull a ferrous object off your charger it is probably not strong enough. You must have the ends of your spool complete the circuit (N-S) for the PM you are charging.

Mike

 

[IRstuff]

Are you sure you don't have an squirrel-cage motor? There is no magnet in such a motor, and the rotor would look like:

http://en.wikipedia.org/wiki/Squirrel-cage_rotor

TTFN

FAQ731-376

 

[IRstuff]

If you actually do have a magneto, then it's really unlikely that you can magnetize the magnet without dismantling the rotor:

http://patimg2.uspto.gov/.piw?docid...1=6873073.PN.%26OS=pn/6873073%26RS=PN/6873073

The magnet in this patent is a very small portion of the rotor.

TTFN

FAQ731-376