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Author Topic: Lenzless resonant transformer  (Read 185221 times)

Jack Noskills

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Re: Lenzless resonant transformer
« Reply #150 on: March 06, 2014, 08:34:20 AM »
What is the root cause?  The root cause is that silly nonsensical L3 coil that straddles the toroidal core.  I already discussed the magnetic circuit for that core when it is being driven by L3.  I said that the magnetic flux leaves the "top blue" travels through the air, and then enters the "bottom blue."

Here is what I did not say:  When L3 drives the toroidal core as a quasi-cylindrical core, the left half of the toroid has CLOCKWISE flux, and the right half of the toroid has COUNTER-CLOCKWISE flux at the same time.  It's totally nonsensical!

Therefore, when L1 and L2 are in "normal resonance" at 157 Hz, the counter flux generated by each winding is CONNECTED by the toroidal core and you get a near-perfect MAGNETIC FLUX SELF-CANCELLATION, a magnetic SHORT.  Hence, for ALL AC excitation frequencies, there is a near magnetic short-circuit and the effective inductance L is reduced to a very small value.  If L1 and L2 were a perfect match, the self-resonant frequency would be "infinity" (divide by zero.)

So this one was "revenge of the nonsensical L3 and associated magnetic circuit - explained."

MileHigh


I should have drawn a picture of how I think fluxes will go in this case in the pdf, but this is the effect nicely put in words by you: Near perfect magnetic flux self cancellation. I must add that those two L2s also feed each other and because of two opposing fluxes going on in the toroid L3 does not see if there is load or not. 


I disagree with you a bit though. The inductance that is left comes from the local inductance field which is low. Just compare same amount of turns in closed loop core and in a solenoid and effective L that they produce. In this case 4.8 kHz and 1100 nf gives 0.9 mH for L in that one LC. Did not found a calculator for rectangular 8*25 mm coil on 80000 core that would give sane results though. Maybe I did it wrong, I tried with this one: http://www.eeweb.com/toolbox/rectangle-loop-inductance/



Presence of local inductance field can possibly be proved easily. If same amount of turns is used but there is more space between turns then resonant frequency will go up as the influence of wire to a neighboring wire is reduced while 'looped inductance' stays the same. In itsu's case this could be done by moving the part of coils by hand that are visible, no need to touch anything that is under L3. When coils are parallel the spacing does not need to exact, it is the total L (and also C) that is left that counts. Maybe this can be done at a later time once we learn more about the basic setup from itsu.


verpies

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Re: Lenzless resonant transformer
« Reply #151 on: March 06, 2014, 09:28:22 AM »
Just compare same amount of turns in closed loop core and in a solenoid and effective L that they produce.
Yes, it is obvious that L1 & L2 exhibit higher free inductance than L3. 
The inductance of a winding increases with the number of its turns and decreases with the reluctance of the magnetic circuit.  It is given by the  formula;
Inductance = Turns2 / Reluctance.

The difference in inductance between L3 and L1 (or L2) is mainly caused by the difference in the reluctance of the magnetic circuit.
For L1 & L2 the magnetic circuit has low reluctance through a high permeability toroidal core and for L3 the magnetic circuit has high reluctance through mostly air.

Low inductance (e.g. L3) presents low reactance to AC signal source and that causes high current to flow in it.  Colloquially this is called a "heavy load".
To decrease that load the inductance and reactance would need to be increased. L1 & L2 are examples of such loads.

Note that in Itsu's video, the mere presence of L3 increases the inductance of L1 & L2. 

@Itsu
What's the inductance of L1 & L2 with L3 shorted and open?


Did not found a calculator for rectangular 8*25 mm coil on 80000 core that would give sane results though. Maybe I did it wrong, I tried with this one: http://www.eeweb.com/toolbox/rectangle-loop-inductance/
This calculator is for a rectangular loop of wire without any core in that loop.
You will get the most sensible results with the formula:  Inductance = AL * Turns2.
You can find the AL value in the manufacturer's datasheet for this toroidal core

This formula will not work for L3 because the magnetic circuit is not contained within the core for such winding and the reluctance of this path is affected by any permeable objects outside of that core (mostly air).

verpies

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Re: Lenzless resonant transformer
« Reply #152 on: March 06, 2014, 09:48:03 AM »
I feel like the guy in the drawing
That means it's the time to set your scope to XY mode and do frequency sweeps.
The exponential sweeps produce the least artifacts because they present constant number of cycles for each frequency (Rigol calls them "logarithmic" for some reason)

Those sweeps will make you like an octopus instead of a guy with only four limbs in that funny drawing.

verpies

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Re: Lenzless resonant transformer
« Reply #153 on: March 06, 2014, 01:37:02 PM »
If you had a true closed-loop toroidal core for L3 then it would look like much more of an AC short-circuit.  (In the past few minutes I am very confident I figured it out, and that last sentence is the big clue, but moving on....)
No because "AC short-circuit" means low inductive reactance, XL = 2πfL.

This means, that the inductance of L3 must be low in order to present low reactance for the same frequency.
Since L = N2/R that means that either turn count (N) has to be small or reluctance (R) has to be large in order to minimize inductance and reactance XL = 2πfN2/R.

A "true closed-loop toroidal core" has less reluctance than air, thus a winding over a closed permeable toroidal magnetic circuit will have higher inductance than the same winding over a less permeable magnetic circuit (e.g. one containing air gaps). 

In other words, a "true closed-loop toroidal core" offers less reluctance than air and causes more inductance, which means more reactance and less current, thus less of an "AC short-circuit"

itsu

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Re: Lenzless resonant transformer
« Reply #154 on: March 06, 2014, 02:27:50 PM »
Thanks all for you comments, it will take some time to digest.

Mags, i will keep those suggestions in mind as they involve some addons and/or modifications, nice info in that pdf.

MileHigh,  thanks for your reasoning, i need to get over them again when on the bench to check out some things if possible.

Jack, i am glad you can see something positive in all of this, i will check out what you said.

verpies, i will get back on your question about L1/L2 inductances while L3 is open/shortend.

I did notice that my LCR meter showed a correct value when the caps where removed (eg 710mH), but it went into a negative sign value (like -600) when i hooked up the cap on the other coil.
Normally a negative sign on this LCR meter means a too low value, a short or measuring a capacitor in the L position or vv.
 
Regards Itsu

verpies

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Re: Lenzless resonant transformer
« Reply #155 on: March 06, 2014, 04:34:04 PM »
...your Tek scope can also display the sweep marker frequency in the gated XY mode with a mere capacitor and resistor at the Z input !
How many BNC cables do you have?

itsu

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Re: Lenzless resonant transformer
« Reply #156 on: March 06, 2014, 04:39:42 PM »
...your Tek scope can also display the sweep marker frequency in the gated XY mode with a mere capacitor and resistor at the Z input !
How many BNC cables do you have?

At least 3, maybe more.

Regards Itsu

itsu

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Re: Lenzless resonant transformer
« Reply #157 on: March 06, 2014, 07:02:25 PM »
@Itsu
What's the inductance of L1 & L2 with L3 shorted and open?

No change in inductances of L1 or L2 whether or not L3 is shorted or open, it stays 710mH  (no capacitors in use).

Regards itsu

verpies

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Re: Lenzless resonant transformer
« Reply #158 on: March 06, 2014, 09:57:53 PM »
No change in inductances of L1 or L2 whether or not L3 is shorted or open, it stays 710mH  (no capacitors in use).
But with the L3 absent, the L1 & L2 had lower inductance, didn't they?

P.S.
Do you want to do the exp. frequency sweeps in XY mode with a marker display?

itsu

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Re: Lenzless resonant transformer
« Reply #159 on: March 06, 2014, 10:29:30 PM »
But with the L3 absent, the L1 & L2 had lower inductance, didn't they?

P.S.
Do you want to do the exp. frequency sweeps in XY mode with a marker display?

Correct, both 680mH compared to the 710mH now with the L3

Yes, i am glad to do any exp. frequency sweeps in XY mode, i think it will be very enlightening.

regards Itsu

itsu

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Re: Lenzless resonant transformer
« Reply #160 on: March 06, 2014, 11:10:21 PM »


11 kHz, now you have working replication :-) I was unable to see what was going on in the isolated LC in my setup, I could only see output light which maximized somewhere between 10 and 11 kHz.


Lets simplify the circuit so there can be only one resonant frequency. Connect those secondaries in parallel (as Mags already noticed) using just one capacitor (this was my first setup). You have CW-CCW coils so start of CW must be connected to end of CCW. C is reduced so resonance frequency will increase a bit. This is good in terms of L3, higher frequency means more blocking there.


The one time I used capacitor in L3 I tuned it like this:
1. I used L2s in parallel with just one 1000 nf capacitor in series with the load so no isolated LC here.
2. Connected load in the output and looked for the frequency that gave highest amount of light without a capacitor in L3.
3. Disconnected load so L2 side was open and placed a cap so that L3 resonated at the same frequency as the secondaries. I think cap was 73 nf (three 220 nf in series) and I got close enough.


When I tested this, I connected the L3 cap while the system was running and it gave bit more output light (10 watt and 8 watt halogens in the output). Enough to notice it. Did not notice anything in the input side as the 5 watt halogen there was not lit at all. Sweet spot did not change if I dropped the 10 watt halogen off which is good.


Secondaries should not affect primary so this tuning method worked. But there is also some capacitance between L3 and L2 that goes right under it, and also local inductance field is present from the secondaries so there can be some influence. This should be small enough to be ignored though.


With 11 kHz and higher tuning capacitor can possibly be dropped from L3 as it can block better, but I am not sure about this when using signal generator as source.


Ok i followed Jack's directions and paralleled the both secondaries with only one (double) cap (1100nF).
Without bulb it resonates at 10.5KHz (signal injected through L3)

After hooking up the bulb in the secondaries LC, its resonance frequency raised to 18KHz.

Then searching the L3 for resonance (injecting a signal through the both paralleled secondaries without cap/bulb) which was 1MHz.
Bringing down this frequency to 18KHz by using 70nF capacitance (where have i seen that value before).

Now both L3 and the paralleled secondaries with cap (1100nF) and bulb resonate at 18KHz.

In this situation,

Input voltage and current (from FG) are in phase
Minimum input current (is this what you mean by blocking the current?)
maximum input voltage
Maximum input power  (144mW) from FG
maximum output power (122mW bulb max. lit   see picture*)

* as i forgot to measure in the video the voltage/current (power) across/through the output bulb, the picture shows the
blue trace the voltage across the bulb and the green trace the current through the bulb with the red math function blue * green = avg power
(times 2 for the currentprobe terminator)
 
Video here:  https://www.youtube.com/watch?v=BE7tAbYRg7w&feature=youtu.be

Regards Itsu

verpies

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Re: Lenzless resonant transformer
« Reply #161 on: March 06, 2014, 11:36:34 PM »
Yes, i am glad to do any exp. frequency sweeps in XY mode. I think it will be very enlightening.
Well then, find/make a short BNC-BNC cable to connect the CH1: Mod/FSK/Trig connector with the CH2: Mod/FSK/Trig connector - both located on the back panel of the DG4102.
The remaining connections are shown below.

Principle of operation:
SG-CH2 generates an horizontal exponential time-base for the scope using a Burst mode and applies it to the X channel (Scope-CH1).  The looped Triggers on the back of the SG are for synchronizing the start of the exponential time-base (SG-CH2) with the start of the FM Sweep on SG-CH1.
SG-CH1 generates an exponentially FM modulated sine wave for exciting the DUT and the DUT's response is sensed by the Y channel (Scope-CH2) for vertical display of the amplitude response.

The capacitor and resistor, that connects the front SG-CH1.Sync output to the Z input (Scope-CH3), will have to be chosen experimentally (they determine the marker gap through the "Z gate" input ).   To estimate their values I'd need to know if CH3 of the Tek scope can be set to 50Ω impedance.

Programming of the SG and Scope later...
« Last Edit: March 07, 2014, 02:46:02 AM by verpies »

Magluvin

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Re: Lenzless resonant transformer
« Reply #162 on: March 07, 2014, 02:28:26 AM »
Ooops, sorry.  My last post with the pdf attached, I forgot to post the other pdf on the multi cores that I was talking about. I usually post them together as they complement each other. ;)

Ive read it several times, and in it all, the one thing that is probably key to the whole article(below) is the fact that loading the secondary wont kill resonance of the primary.  But it doesnt illustrate the use of a bifi coil, or an LC, which could be run at resonance, it just states it.

Mags
« Last Edit: March 07, 2014, 05:59:52 AM by Magluvin »

Magluvin

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Re: Lenzless resonant transformer
« Reply #163 on: March 07, 2014, 03:01:04 AM »
No change in inductances of L1 or L2 whether or not L3 is shorted or open, it stays 710mH  (no capacitors in use).

Regards itsu

 ;)   L3 is well isolated from the affects for the secondaries.  So we can assume there is very little if any flux leakage to the outer sides of the core, unless at or around saturation.

What I cant get around with the orientation of L3 vs either L1 or L2, is the fact that L3 would want to initially magnetize the core through its diameter, but loading a secondary would want to magnetize the core through its loop shape. Im wondering about all the interactions of the primaries affects on the core mixed with the sec affect on the core. Does that mix have an advantage or disadvantage of in vs out.  Where with the separate cores, the cores will not have that mix of the primary trying to magnetize the core as if it were a bar or rod, and the sec trying to be in the circle, all at the same time.  And if the primary is trying to treat the toroid core as a bar/rod, then there should be flux leakage, N out one side of the diameter, and S out the other. But, possibly the 'mix' sucks, or say guides magnetically, the primary field all into the loop of the core.

Mags

MileHigh

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Re: Lenzless resonant transformer
« Reply #164 on: March 07, 2014, 05:11:21 AM »
Itsu:

In your latest clip where you have L1 and L2 in parallel and a single capacitor, you still have a very high resonant frequency, implying that L1 and L2 are in a "flux fight" and canceling each other out.  So if you cross one set of wires then L1 and L2 should add together and you should go back to a low resonant frequency.

Verpies:

Quote
A "true closed-loop toroidal core" has less reluctance than air, thus a winding over a closed permeable toroidal magnetic circuit will have higher inductance than the same winding over a less permeable magnetic circuit (e.g. one containing air gaps). 

In other words, a "true closed-loop toroidal core" offers less reluctance than air and causes more inductance, which means more reactance and less current, thus less of an "AC short-circuit"

What I was trying to compare was the "L3 straddling" configuration with having L3 wrapped around the toroid in the normal fashion, just like L1 and L2.  So then the coupling factor between the primary and the two secondaries (I think it is called 'k') would be much better (low reluctance path) and much more energy will flow through the magnetic circuit and hence you will get a "stronger AC short."  The larger inductance of L3 works "against" you and you get more of a nasty power burn in the windings.

Jack:

Quote
Presence of local inductance field can possibly be proved easily. If same amount of turns is used but there is more space between turns then resonant frequency will go up as the influence of wire to a neighboring wire is reduced while 'looped inductance' stays the same.

I don't know what you mean by "local inductance field."  More importantly, there is essentially no "influence of a wire to a neighboring wire."  That sounds like an old wives' tale.  In the context of winding wires around a toroid to make an inductor, it's the permeability of the core, and the number of turns that really count.  Also, the core can only store so much magnetic energy before it saturates.  There is a culture of experimenters neglecting or being afraid to correct each other on the forums.  That leads to stagnation, people don't learn because nobody corrects them and it becomes a vicious circle.

MileHigh