Permanent Ring Magnet as Transfomer Core

"Ken Sutton"

With no context, your Q is just another dumb, annoying troll.

.... Phil

Depending on the direction of magnetization WRT that of the field induced by the windings, the core might saturate faster in one polarity than in the other.

As a rectifier?

Mark L. Fergerson

Hard magnets have low permeability over almost the entire B-H curve; you'll do little better than air cored, with the exception of excessive eddy current losses if a fairly conductive material is used (e.g., SmCo, NdFeB).

After a whole lot of magnetization (NdFeB requires >10^5 A/m, which is >1T in free space, to change state!), you'll change the magnet's field from axial to tangential. Also, as the magnetization slips, a large amount of flux will suddenly flow, which is to say, if a constant current is applied, the voltage will shoot up suddenly; or if a constant voltage is applied, rate of current rise dI/dt will slow down considerably as the magnetic domains flip, one by one.

The nonlinearity of the core will look like this:

- Small signals: very low permeability (around 1), little hysteresis loss. The winding *might* make a good inductor (in the sense of, the impedance is mostly inductive reactance), but it's little better than air.

- Medium signals, enough to exceed the coercive force: average permeability is greater than unity, most of which is hysteresis loss. In other words, the tan delta (loss angle) of the impedance is large, maybe, I don't know,

- Large signals, up to and past saturation: losses remain fairly constant (you can't push more hysteresis than the biggest loop on the B-H curve), inductance goes back down (because in saturation, it has about the same permeability as in any other state).

This may be somewhat familiar from plain old laminated iron cores, which exhibit low initial permeability (maybe ~800 or so), excellent operating permeability (5k, up to 20-40k for annealed, grain-oriented toroids), and less and less going into saturation. The difference is, a hard magnet's variation is severely exaggerated, making it useless for inductor or transformer duty.

Tim

If it's solid metal, it will have a lot of eddy-current losses.

Someone used to, maybe still does, make an inductor with a permanent magnet in a gap in the core. That roughly doubles the current before saturation in one direction.

For normal transformer use - forget it. You'll lose energy proportional to the area of the hysteresis loop on each cycle.

They have already been invented, and used by the millions, as ferrite-memory cores.

Also, some early computers (e.g. British Elliott series) used the cores as logic elemnts.

Late at night, by candle light, John Larkin penned this immortal opus:

Dismantling old monitors and TV's I've come across inductors with a PM stuck on one end of the core. I guess it's there to counteract the DC component of whatever passes through it.

- YD.

I think there was some saturation thing going on, sweep linearization maybe.

seen that done to curve the reluctance away from a critical near by area. Actually, we do something like that to steer the beam in a particular area just to counter act a structure to prevent a hump in the scan.

Jamie

Might be interesting to wack a couple of neo's across the E-core of an audio coupling transformer and see what it does to the sound (?)

Ken

Maybe that configuration was used in the nega-polar infinite energy source..

Hey! a Magnetic Rectifier..exactly useful for detecting high frequency magnetic fields emanating from a hypnotist with a magnetic personality..

In one direction, the amp turns and permanent magnetic field add, driving the core further into saturation, hence inductance decreases. In the other direction, amp turns and permanent field cancel, hence inductance increases. You get something like a 5:1 change in inductance.

Used to compensate for nonlinear scanning dI/dt arising from nonzero resistance of the scanning coils.

And reduces it in the other.

Used in CRT monitors and TVs to compensate for the nonzero resistance of the horizontal scanning coils, which would otherwise cause a nonlinear current ramp.