Abruptly detaching a power source from a coil produces a back-emf: this is a well known fact.
What I would like to achieve, in my experimentation, is to convey ALL the collapsing magnetic field to the secondary side of a transformer, shorting the primary side immediately before the magnetic flux starts to collapse.
This requires a very fast switching system, probably through mosfets.
As a power source, I have a 12V/10A battery and the transformer is a big MOT (Microwave Oven Transformer): at the moment the power reaches the primary coil passing through a SPDT relay and, when it switches, the power is disconnected and the primary coil shorted.
Unfortunately the relay is not so fast to achieve the desired result so a small arc can be observed at the internal relay contacts, showing that the magnetic field has collapsed on both ends of the transformer.
Is there a way to overcome the problem?
A circuit diagram will be appreciated a lot!
Edited on 25/03/2015
The primary feeding/detaching source/shorting the primary/re-attaching source/feeding sequence (in a countinuous loop) of the primary side has to be accomplished thousand time per second...
I have to collect the spikes of the back-emf (due to the collapsing magnetic field) ONLY on the secondary side!
Like in a water pump, the water (electric field) must flow in one direction only; when the magnetic field collapses (using the above analogy) acts like a water flow under pressure which tries to exits from any hole in the piping system: I want to seal the entrance (primay side of the transformer) when the pressure is at its maximum level and convey all the flux to the exit (secondary side of the transformer); no way for the water (electric flux) to flow back to the entrance.
So, in essence, I need an electronic "valve" rapid enough to avoid the back-emf on the primary side.