Transformer core variable reluctance

[sondreL]

Hi , When DC is applied to a transformer there is no secondary induction because DC current creates no changing flux in the Core. If I could change the reluctance, or permeability is another word I guess, of the transformer core while still having DC applied to the primary , would that then result in a secondary induced current?

 

[rumborak]

Yeah, I think so. What matters in the end is the magnetic flux that is encompassed by the secondary coils and the change of that flux; whether you change that total flux by modulating the external magnetic field or by changing the inductance of the coil shouldn't matter.

 

[sondreL]

Ok , can anyone else please confirm, would having DC on the transformer primary and then somehow varying the reluctance of the core result in induced secondary , I myself think it should the above poster rumborak also said so. It would turn out as a reverse magnetic amplifier , since mag amps work on having AC as the load on primary and DC as the control current for more or less core saturation. Also if I could change the reluctance of the core while DC is applied to the primary inducing changing flux in the secondary how would this affect the DC in the primary from the perspective of the incoming DC ?Normally when I apply DC to a transformer nothing happens just the winding heats up slowly , what would happen here ?

 

[rumborak]

I think it's worth asking the question of how you plan to change the reluctance of the secondary coil? The only way I can imagine is a) by changing the area the magnetic circuit encompasses or b) changing the number of windings. In both cases it should result in an induced voltage.

 

[mrspeedybob]

This very principal is used in many automobiles for sensors that measure the rate of rotation of things like the crankshaft, wheels, transmission gears, etc. A coil of wire is wrapped around a permanent magnet. A gear rotates through the magnetic field. The permeability changes as the teeth of the gear move toward and away from the sensor, this induces an AC voltage in the coil. A circuit in the cars computer measures the frequency of the signal and tells the computer how fast the component is rotating.