Gnorts, Vorts, Some of us are confusing the issues above. Energy cannot be stored in an inductor because there are no magnetic charge carriers. Hence, when trying to open the circuit on an inductor, the magnetic field WILL COLLAPSE. This forces the potential of the two port device to approach infinity until the field collapses. This means arcing fer sure because the current must leave the inductor.
Back EMF, while related, is not exactly the same. Take a NdFeB magnet in your hand and rapidly move it across a sheet of copper. You will feel Lorentz reach up and grab your wrist clutching tighter the faster you try to move. This is an example of Lenz Law, a changing magnetic field in a conductor generates a force in opposition to the change. There is a great demonstration of the Lenz law on the web: http://www.youtube.com/watch?v=fxC-AEC0ROk When Steorn claims no BEMF, they are not saying there is no arcing when switching the inductor. Indeed, this is why their reed switches were failing. What they are claiming is that there is no drag when the magnet moves near the conductor. And they are right due to the asymmetry of the toroid. In an external changing field, half the toroid is creating a current in one direction and the other half creates a current in opposition. Finally note that they are applying voltage to the toroid continuously except when the magnet approaches. They then briefly turn the voltage off and the magnet is attracted to the core. When they re-energize the toroid, they force realignment of the domains of the core and the rotor with the magnet doesn't stick because it's attraction to the core is diminished. There is nothing here which is not known. They are actually showing an INVERSE pulse motor which must be remarkably inefficient since the pulse motors I have tested are only about 20% efficient. They energize the coil through most of the cycle whereas a pulse motor only energizes the coil during the approach of the magnet. I think. Terry
