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Magnetic, or Attractive, Question

01/10/2011 6:26 AM

http://www.eamagnetics.com/gen_faq.asp

"How long will a permanent magnet last?"

A permanent magnet will retain its magnetism unless it is affected by a strong outside magnetic or electrical force, or elevated temperatures. If they are not exposed to any of these conditions, permanent magnets will lose magnetism on their own, however this degradation is very slow, on the order of one percentage point every ten years or so.""

I have downloaded this from the above link, website.

Kill me if this against copyright ect, 'n do it slowly.

Q. Why in the case of a Permanent magnet motor, doesn't the rotating magnetic field induced into the Rotor, destroy the magnetism in the magnetic pole pieces.

It is most probably biting me on the arse, but I just can't see it.

Cheers.

Mark N.

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#1

Re: Magnetic, Or an attractive question

01/10/2011 8:07 AM

Correction; A permanent magnet will retain its magnetism unless it is affected by a strong (unidirectional and negating) outside magnetic or electrical force, A pulsating force does not have a net effect.

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#2

Re: Magnetic, Or an attractive question

01/10/2011 8:08 AM

Still under water ?

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Commentator

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#3
In reply to #2

Re: Magnetic, Or an attractive question

01/10/2011 10:40 AM

Yep, Sitting on a log, waiting for me dog, here in the fog.....

water is a good thing, in the right quantities.

And Yes. Of Course. Alternating....!

thanks Fellas.

cheers mark N

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#4

Re: Magnetic, or Attractive, Question

01/10/2011 10:50 AM

So, why under the law of "efficiency" ie.diminishing returns, doesn't the "additive" lose out to the "Negative". At the RPM, in general speak it should diminish 'er Rapidly

And Thanks Guest. some poor Bastards are copping it up the bum, all around Queensland at the moment. Me. "I'm all right Jack" Just waiting for it all to subside, then chip and lend a hand. Rockhampton Check out this website...http://www.boston.com/bigpicture/2011/01/australian_flooding.html

there is a picture of a boat with a load of Roos.......bloody lovely!

Mark N.

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#5

Re: Magnetic, or Attractive, Question

01/10/2011 1:14 PM

"Impermanent Magnet Motor" would not be such a sexy marketing term, but in the loooooonnng run might be more accurate....

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#7
In reply to #5

Re: Magnetic, or Attractive, Question

01/10/2011 2:13 PM

""Impermanent Magnet Motor" would not be such a sexy marketing term, but in the loooooonnng run might be more accurate.... "

According to entropy, ALL things considered permanent are not so.

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#6

Re: Magnetic, or Attractive, Question

01/10/2011 1:45 PM

For a standard permanent magnet motor, excessive armature/rotor current can demagnetize the stator magnets. The motor manufacturer will usually specify the maximum allowable peak current above which demagnetization can occur. Most DC drive controllers have a current limit setting which should always be set somewhere below the demagnetization threshold.

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#9
In reply to #6

Re: Magnetic, or Attractive, Question

01/11/2011 5:41 AM

Totally correct about demagnetizing a permanent magnet motor.

Had some problem in the past. Small Permanent magnet motor were used a truck.

They just turn on and off the motor by means of a switch, so no current limitation.

In the beginning everyting went well, but after a year, the permanent magnet field became weaker and when trying to deliver its torque, the armature took a lot more current and burnt.

Now they use 20 meters connection wire rolled up to a coil in the motor supply.

This is enough to limit the peak current at start.

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Commentator

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#8

Re: Magnetic, or Attractive, Question

01/10/2011 10:59 PM

well considering no one has actually answered the question, the answer,not including rare earth magnets (neo) is about 20 years then deterioration of about 5 percent per year.

Neos are unknown in real terms as they have not existed commercially for long enough to measure.

The reason the magnet loses no energy to the induction is simple, the magnet only provides one third of the equation and it is not the primary energy component. EG a wind turbine receives energy from the wind, in reverse an electric motor receives its energy from electricity.

The copper coil cuts through the field exciting the electrons in the copper coil, the action itself does nothing to the magnet, time and decay of the substance and heat factors are what kills it.

We say how much energy/psi is used by a hydraulic ram to hold up an object, but we do not ask it of a kitchen table, we know there is energy from the tension on a kite string but we do not ask why the kite does not wear out, because the energy is from a different source and the kite merely a facilitator passing the energy to the string.

A magnet in a motor is a facilitator.

Please note this does not mean magnets do not have energy, my belief runs against common science opinion on this, as i regard them as batteries, two magnets facing each other on a pole, one suspending the other is a performance of work, whether you like it or not that is a fact. I will not read this thread again, as i have had this argument more than 500 times genuinely and will not have it again. So in short a machine that can produce energy from a magnetic drive is not perpetual motion, simply a super efficient battery operated device.

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