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Author Topic: Dally, Shark & Ruslan workbench  (Read 53554 times)

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Quote
In that graph the S21 gain decreases monotonically with frequency and that means that the impedance of the choke made with this ferrite increases monotonically. I do not see any increase of the S21 gain anywhere which would mean that this ferrite is giving up at these high frequencies. Thus it looks like a HF ferrite in this graph.

If it was a LF ferrite, the gain would start increasing at some frequency (impedance would decrease) like here, and beside that doubtful small kink in the kHz range and slight flattening of the gain in the first 2MHz, I just do not see anything indicating that in this graph.

P.S.
Since adding more turns does not change the shape of the curve in the horizontal scale (it only scales it vertically), you are free to add more turns until it does ...or until the inductance of these empty turns cannot be calibrated out anymore.
You may also want to plot the Z21 (S21 impedance) if it is in the menu of your vna.

Thanks, so this ferrite rod (small) is not the one we are looking for.

I have two others (big and bigger) which i will test the same way.

The nanoVNA itself nor the Saver display program has the S21 impedance graph on board.
At the markers data listing there is an impedance value, but no graph.

Itsu
   

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Here a 10KHz to 100MHz sweep of the "big" (screenshot 1) and "bigger" (screenshot 2) ferrite rods.

Seems to me the "bigger" rod is the best one when hunting for a "low-frequency" requirement, but not ideal.


Itsu

   

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Here an experiment with Tesla coil.
It is a second step to success.

Have fun,
Vasik


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I had to rewind some of the coils to comply with the CW v CCW rules, but most of it is OK now.

Itsu
   

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Inspiration for you Itsu, some independent replications, self running

https://www.youtube.com/watch?v=aiFIqhneZKo

https://www.youtube.com/watch?v=jlU9UVn7qRo

 :)

PS Slightly offtopic, but anyway have you guys noticed new video from Ed Lee

https://www.youtube.com/watch?v=qTp_nYQ0CRs
« Last Edit: 2021-05-22, 08:52:18 by Vasik041 »


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Thanks Vasik,  inspiring indeed.


Ed Lee  we also know as "Dally"?

Itsu
   

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Thanks Vasik,  inspiring indeed.

Ed Lee  we also know as "Dally"?

Itsu

Yes, he posted new video few days ago

https://www.liveinternet.ru/users/edward_lee/

Quote
Well, the matter got off the ground. Today I managed to achieve self-running and power a lamp.



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The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
   

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Inspiration for you Itsu, some independent replications, self running
https://youtu.be/jlU9UVn7qRo?t=121
This device is not grounded.
Thus its operation is inconsistent with the principle given in this message.
   

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This device is not grounded.
Thus its operation is inconsistent with the principle given in this message.

Yes, true.
Author says that it is a modified version and it works without ground.
Which is even better, isn't it ?

Vasik


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Which is even better, isn't it ?
Yes, it is better for the practicality of the device
...but it is worse for understanding the principle of its operation.
   

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    Guys:
   As some of us know, some years ago Akula also showed that he could run his second self runner without an earth ground line connection.
The device did get hot, and could NOT be run like that for more than a minute. But, it proves the point, which no one else has been able to achieve, in even a small way, until now.
  I'm sure that also itsu is glad to see a self runner able to run without a earth ground line. Which will be great for mobil type of devices, like cars, bikes, boats, etc...  As the ground line is the next thing we have to toss out the window, along with the batteries.
    I'm also glad to see a non earth ground device, very glad, as now I don't have my 37.5 meter ground line going into my water well in my back yard, as I had before.
    Itsu: your new rig looks absolutely great. So, clean and simple looking without all the wires and the clutter, and stuff. I hope to see just what it can do, next. Got my fingers crossed.

   Vasik:  You are an amazing guy. Your input is much appreciated. 
   Best of luck to you, as well.
   

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Vasik, 

any details on the output toroid?

Its 10 turns each, bifilar wound, covering half the toroid, toroid being LF ferrite again.

Something like this?

Itsu
   

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Vasik, 
any details on the output toroid?
Its 10 turns each, bifilar wound, covering half the toroid, toroid being LF ferrite again.
Something like this?
Itsu

Itsu,

It is low pass filter, should block HF from gradient coil.
Presented here https://youtu.be/YkyeKCnzU3Y?t=1139 (see rk_rev2.pdf page 28 starting around 17:30 in the video)
Can be ring core or yoke, similar to push pull.

I can't see the size of your coil, point here is that it should withstand 200-300W (300v 1a) or something like this.

Vasik



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 O0


will be using this yoke then.

itsu
   

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Did i first short test without kacher, but with below (red) circuit.
Input was 24V @ 6A, but MOSFETs got hot fast and DC output (unloaded) went up to 200V quickly.

Tried with MOSFETs on 12V, but they went to 70°C within a few minutes, duty cycle TL494 signals at 30%.

Itsu
   

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Input was 24V @ 6A, but MOSFETs got hot fast and DC output (unloaded) went up to 200V quickly.
What currents flowed in the push-pull circuit?  Did the primary current ramp up linearly or did it become more curved up at the ends of the ON periods?

Could you have had some shoot-through current because both transistors conducted simultaneously for a short time ?
« Last Edit: 2021-05-23, 09:09:42 by verpies »
   
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Did i first short test without kacher, but with below (red) circuit.
Input was 24V @ 6A, but MOSFETs got hot fast and DC output (unloaded) went up to 200V quickly.

Tried with MOSFETs on 12V, but they went to 70°C within a few minutes, duty cycle TL494 signals at 30%.

Itsu

Are the MOSFET gate waveforms sufficiently fast (both rise and fall) and of sufficient voltage to ensure rapid and complete turn on/off of the MOSFETS?  Is there any ringing/oscillation observed at the gates?

In the schematic, the gate clamp diodes are specified as 1N47xx, which diodes did you use?

And, as Verpies suggested, what do the drain waveforms and their relative timing look like?

It is difficult to imagine the MOSFETS getting hot unless they are spending too much time not fully on or off.   

PW
   

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Did i first short test without kacher, but with below (red) circuit.
Input was 24V @ 6A, but MOSFETs got hot fast and DC output (unloaded) went up to 200V quickly.
Tried with MOSFETs on 12V, but they went to 70°C within a few minutes, duty cycle TL494 signals at 30%.
Itsu

Itsu,

It could be that you need swap 25 turns coil ends.
If that doesn't help, reduce duty cycle to 5% and check yoke saturation current.
What is inductance of push pull primary coils ?

Vasik


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If that doesn't help, reduce duty cycle to 5% and check yoke saturation current.
What is inductance of push pull primary coils ?
Do you know what inductance Stalker was working with?
Approaching ferrite saturation will be manifested as increasing di/dt at the end of the ON period;

@Itsu
While you are measuring the primary inductance, also please measure it with all secondary winding shorted. This will give us the leakage inductance, which usually is the primary culprit of primary spiking and ringing.
   

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Are the MOSFET gate waveforms sufficiently fast (both rise and fall) and of sufficient voltage to ensure rapid and complete turn on/off of the MOSFETS? 
A good elementary question.
   

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Good questions, i will try to collect the answers.


Some easy to answer ones are:

used gate clamp diodes ar 1N4746A (18V 1W zener)
Yoke primary inductances 34.7uH / 6.4uH    and    32.5uH / 5 uH    all at 100KHz  (the 2nd values are with both sec's shorted).


The used PCB looks nice, but the compactness makes it hard to make measurements

Itsu
   

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Good questions, i will try to collect the answers.
Some easy to answer ones are:
used gate clamp diodes ar 1N4746A (18V 1W zener)
Yoke primary inductances 34.7uH / 6.4uH    and    32.5uH / 5 uH    all at 100KHz  (the 2nd values are with both sec's shorted).
The used PCB looks nice, but the compactness makes it hard to make measurements
Itsu
Itsu,

Assuming frequency 24KHz 30% duty cycle maximum current through primary is 9.6amp.
That is probably too high.
I can't find Stalker mention about inductance but at 25-30% duty cycle his push pull without load consumes 0.4amp
(see rk_rev2.pdf page 41) That probably means max current about 1 amp, so 10x bigger inductance.
It could be that you ferrite has significantly smaller permeability, so more turns and smaller gap needed.

Vasik


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Vasik,

yes, i was running at 24.4Khz @ 30% duty cycle.

I will set up the same conditions as mentioned in the PDF ( rk_rev2.pdf page 41), and see what signals/current i have then.

Itsu
   

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Found in comments to this video https://www.youtube.com/watch?v=XDXTxPRPxSU

Quote
Inductance of one primary 110uH





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Thats a lot, i have another (slightly smaller) wound yoke with 11 turns each which measures 62uH / primary, so it must be the ferrite then.

Itsu
   
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