Effects of perm. magnets on bifilar toroid transformer output

[Pirate88179]

My experience with neos on transformers or JT circuits is that they raise the frequency.  In a JT circuit, the higher the freq, the lower the voltage.  I use them mostly to cut down on the noise of the transformer or windings.  It raises the freq. above hearing range.

Bill

[void109]

You answered your own question in the first post. By adding the magnet you are changing the inductance. (Inductive Reactance)

This is confusing to me.  Placing the magnet near the toroid, as has been measured, lowers the inductance.  Doesn't this also mean that the saturation point is reduced as well, meaning that it reaches saturation sooner?  Would reaching saturation sooner cause doubled output voltage while reducing input current?  Because that is how it appears.

Wouldn't reduced inductance, decrease the opposition to current flow, resulting in higher input current?  Because that is not what I am seeing, I see reduced input current.

[leo48]

Good morning
interesting effect, you could post a schematic of the whole?
leo48

[gyulasun]

This is confusing to me.  Placing the magnet near the toroid, as has been measured, lowers the inductance.  Doesn't this also mean that the saturation point is reduced as well, meaning that it reaches saturation sooner?  Would reaching saturation sooner cause doubled output voltage while reducing input current?  Because that is how it appears.

Wouldn't reduced inductance, decrease the opposition to current flow, resulting in higher input current?  Because that is not what I am seeing, I see reduced input current.

Hi,

Thanks for the infos, and sorry but I did not realize you use a MOSFET switch, I simply overlooked it from your pictures. Now your setup is clear how it is connected.
What is puzzling to realize is that your toroidal core already SATURATES without adding the magnets! It is clearly seen (as I wrote in my 1st post) from your scope shot picture 'ScopeA.jpg'  where you can see those voltage spikes going up positive or down negative: they should have been rectangular shaped pulse waveforms as they came from your generator.

How did the core get saturated?

I think when your MOSFET is ON, the main resistance to define the current taken from the 12V battery is your coil reactance, this consists of DC wire resistance and AC reactance, X_L,  (neglecting MOSFET r_DS ON resistance and battery inner resistance).
You measure 320mA current taken from the battery, this means the peak currents must be in the some Amper range. If you measure the DC resistance of (any one) coil, suppose it is 2 OHMs, then the peak current is less than 12V/2=6 Amper, because the AC reactance and the duty cycle reduces this peak value. BUT the spiky output waveform shown in ScopeA.jpg shows the remaining peak current in the primary coil saturates the core because those spikes can only occur whenever the coil's inductance gets reduced just due to saturation.

You may wish to check your core separately: just run through some hundred mA static DC current via its primary coil from a battery and via a series resistance of about 20-30 Ohm, and measure the inductance across the secondary coil with your L meter.  This is only roughly corresponds to the pulsed situation because the big peak currents will be absent but may indicate your core behavior for DC bias.

Your next dilemma is why the current reduces to 310mA from the 320mA? I think this is also explained by the magnets' effect on the core: during the pulsing your core is already biased by the pulsed current and the coils on the core already have a reduced inductance, and when you add the magnets then they must have been shifting the core's operating point towards a less saturable area on its B-H curve, i.e. the magnets strangely enough now REDUCE saturation caused by the current pulses! 'ScopeB.jpg' clearly shows this: those voltage spikes shown without the magnets case now are now not so spiky, they resemble much better to the rectangular input pulse coming from the generator (but there is still saturation involved of course).
And if there is less saturation in the core, then the coils self inductance can increase, this means two things: switching current decreases (10mA) and output voltage across the secondary increases because of the inductive reactance is higher  (voltage drop across it will be higher).

So what I think is that in your setup adding the magnets creates a higher inductive reactance for the coil by shifting the core's operating point on its B-H curve, versus the magnetless pulsed operating point.

If you could reduce your battery voltage to about 3-4V only and watch the waveforms again without and with the magnets, I believe the output pulse shapes would resemble much better to the waveform coming from the generator, and the magnets' real inductance reducing effect just due to its extra flux given to the core could be seen better, at least the original switching current's possible saturating effect could be kept at a minimum.  (You can reduce battery voltage by feeding your circuit via a series 60-80 Ohm resistor, just for a test.)

rgds,  Gyula

PS I hope I managed to express clearly what I wanted, if you do not get something please ask.

[pese]

@all

pls give attention for testing non-sinuoidiales waves (voltages/currents)

G.Pese
---------
http://www.padrak.com/ine/DANGERSPOWER.html
Messen nichtsinusfoermiger Wechselspannungen !Ein Problem!

www.alt-nrg.de/pese