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Author Topic: Effects of perm. magnets on bifilar toroid transformer output  (Read 16628 times)

void109

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Hi all.  I've been doing a lot of experiments in The Lab(tm).  I haven't posted any videos, as after making my inductance video showing increased inductance with presence of permanent magnet, my video camera failed.  Unfortunately I haven't learned enough about electronics to troubleshoot and repair it ;)

I've stumbled on too many things that are interesting to not start posting them - so here's a series of pictures I took showing an effect I dont understand.  It looks brilliantly positive, however I'm old enough to know I likely just dont understand something obvious. 

It appears that simply adding the presence of a few neo magnets to this transformer DOUBLES its output without changing the input.  Hopefully some of you here can either tell me what I've done wrong, or suggest further details or experiments to validate/invalidate these findings.  I initially saw these results in a much more complicated setup I was doing while inspecting a previous idea for a magnetic flux gate generator, I did this to trim it down to the core of the matter.  Thanks in advance!

(btw much respect to JLN, just adding annotations and preparing images for upload is a big pain, much thanks for all of his hard work)


void109

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #1 on: May 31, 2010, 08:57:33 PM »
The frequency isn't important to the effect, I can see it over a very large range of frequencies, I was just using trial and error to find the most voltage gain for the effect to make it as pronounced as possible.  If its important I can get scope shots of the freq gen output - its just a square wave output with a very small pulse width.

gyulasun

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #2 on: May 31, 2010, 11:26:23 PM »
Hi,

For me it is not a 100% sure what is your exact circuit?

I mean:
1) you drive the primary coil directly by the generator output, via a series 1 Ohm resistor, right?
2) You load the secondary coil with a 1 Ohm resistor, this is ok.
3) what does the "input measured over the 1 Ohm resistor after 12V" mean? You measure the voltage drop across the 1 Ohm by the scope and the generator gives out 12V peak pulse voltage at 7.18kHz? Please clarify.
Or you mean on 12V a battery as seen in the photo, perhaps a binding point?

Yes, it would be good to see the input pulse, please make sure the scope zero line be clearly indicated, where it is with respect to the pulse waveform.

From what I can see so far, your core is saturated by the input pulse and when you add the magnets, then saturation changes to a "better" position on the core B-H magnetization curve (this is seen by the "nicer" output pulses versus the output "spikes-like waveforms" when no magnets added.

rgds,  Gyula

void109

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #3 on: June 01, 2010, 03:11:12 AM »
1) 12V Pos Battery Terminal ==> 1 Ohm Resistor ==> Primary Coil ==> n-mos drain (Hope that makes sense)
2) Yes, the output from the secondary is just going to a 1 Ohm resistor, measuring across that with the probe
3) I mean that I'm measuring across the resistor identified in #1 above

I'll draw up the circuit tomorrow to post, as well as take better scope shots when I have time.

MrMag

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #4 on: June 01, 2010, 06:11:51 AM »
You answered your own question in the first post. By adding the magnet you are changing the inductance. (Inductive Reactance)

Pirate88179

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #5 on: June 01, 2010, 06:45:04 AM »
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

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #6 on: June 01, 2010, 08:04:04 AM »
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

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #7 on: June 01, 2010, 09:07:49 AM »

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

gyulasun

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #8 on: June 01, 2010, 11:38:53 AM »
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, XL,  (neglecting MOSFET rDS 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

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #9 on: June 01, 2010, 12:17:48 PM »
@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

exnihiloest

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #10 on: June 01, 2010, 02:05:14 PM »
...
It appears that simply adding the presence of a few neo magnets to this transformer DOUBLES its output without changing the input. 
...

Magnets change the permeability of the coil core therefore the inductance is also changed.
A coil has internal resonance frequencies due to LC effects, C being the resultant of the capacities between turns.
It follows that at some position of the magnet, the coil becomes resonant at the working frequency, increasing the voltage.



gyulasun

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #11 on: June 01, 2010, 03:42:44 PM »
Hi exnihiloest,

What you propose could be possible but in this particular case we should see some sinusoid voltage waveform at the output instead of the still uggly pulse shape.  LC resonance always involves forming sinusoid or distorted sinusoid waves but not such straight lined pulse shapes.
I think void109 mentioned he swept the frequencies and it is like that everywhere as he showed in ScopeB.jpg if I recall correctly.

I agree that magnets change the core permeability, hence they can tune the coils just like a variable capacitor.

void109

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #12 on: June 01, 2010, 04:50:24 PM »
I have a lot of work to do today (the kind that pays for my hobbies like this), but later today I'll do as you request Gyulasun.  I really appreciate the attention and insight.  After I posted those pictures I stripped down that setup (its easy to set up again and reproduce, I've done it a few times) for another test for which I'll start a separate thread - another interesting effect.

Thanks again!

mscoffman

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #13 on: June 01, 2010, 08:14:55 PM »
@void109

I see from another thread you have seen the self-running coil thread.
Basically as you add neo's the coils inductance become much smaller
this allows your coil to become resonant with parasitic capacitance
of the driver device and coil self-capacitance. The core is very near
saturation as magnets have strong magnetic fields. This saturation
is why the inductance is reduced. The first screen shot is primarily
inductive back emf kicks from high inductance and the second is
nearer resonant. Your meter is happier nearer with the inductor nearer
resonance. Which is why it claims the voltage is higher. All of this goes
to show you *must* measure power as a DC level. Rectified and filtered
so that the voltage changes very little during the meters gating time of
about one second. You can't measure AC pulses voltage accurately and
you definitely can't measure current when the voltage is changing with
a DVM. AC voltage measurements of the DVM are sinewave RMS. AC
measurements are meant for 50/60Hz line voltage of sinewave shape.
Gotoluc's power supply and power reading set up was nearly perfect.

:S:MarkSCoffman

void109

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Re: Effects of perm. magnets on bifilar toroid transformer output
« Reply #14 on: June 02, 2010, 06:52:09 PM »
Thanks for the feedback, I played with the setup further and I find I must agree, power measurements do seem like they should be made with stable, rectified DC signals - it started dawning on me how meaningless these readings must be when they are getting pounded with fast pulse streams.

Even the amperage drop I was showing - I was taking that using the 10A setting on the meter, I was just looking at the accuracy differences between the 200ma and 10A settings - I bet its just an aberration.