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Author Topic: Self running coil?  (Read 302260 times)

gyulasun

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Re: Self running coil?
« Reply #405 on: March 30, 2010, 03:05:25 PM »
Hi Gyula,

The inductance of the main coil depends on the frequency specified for the resonance to happen... So at for example 8Khz, the main coil mH is much higher then when the circuit is operating at say 20Khz.  We might say it the other way around.. The inductance mainly dictates at which frequency the circuit would work [this is in combination with the given mosfet due to the mosfets Capacitance].

The pulse coils inductance is again depending on the inductance of the main coil... I *think* the resistance of the pulse coil was rather high... some 50 Ohm or so... not sure. Maybe Luc can tell.

Hi NextGen67,

I understand and agree with what you said here. The MOSFET at such low frequencies mainly have capacitances what do influence the oscillating frequency. And these capacitances change by the pulse voltage amplitudes between its electrodes, what we have to consider in this respect is the change from zero to the peak pulse voltages of cca 10-11V. The effect of these capacitance changes may cause but a few kHz change, this rate of change also depends on the frequency whether we are at 5kHz or 20kHz.

And then there remains the change of the inductances by you to tune the frequency in a much wider range if desired, and you always have to adjust both inductances (sometimes only the one in the gate-source) for the 'correct' values to insure oscillation at a new frequency, this is quite normal and accepted.  The problem of self-starting remains to be solved at certain frequency ranges, this surely depends on the amplitude and phase conditions ruling in the circuit (just like in any oscillator circuit) when you just apply the 3V supply to start.

Thanks for the possible pulse coil DC resistance estimation, it is possibly correct if Luc uses that coil taken from a shaded pole motor: my good news is that if this coil has indeed 10-20 Ohm or higher DC resistance then the reactive power circulating in it could be increased freely by using a coil with similar inductance but wound with thicker wire so that the copper loss should reduce, the peak to peak gate-source voltage could go up to 30-35V or so peak to peak, the limit is the max +/-20V from the data sheet.  (+/-20V=40Vpp)    However if you increase the Q factor of this coil by using thicker wire, you have to consider the adjustment for self oscillation becomes more cumbersome (gate-source voltage amplitude changes quicker with the higher Q if you adjust the position of the ferrite rod).

Quote
Quote
I do not agree that the IRF640 does not use external energy for its operation, sorry. The 3.8 mW or so power must be the reactive power inside the pulse coil which must be parallel resonant with the gate-source and gate-drain capacitors.


Not sure how to interpret this? I think Luc refers to the fact that the switching energy needed for the mosfet itself, *might* be greater then what the circuit as whole is consuming.... Say at 8Khz, 3Vdc the circuit takes 0.000014A, which would be 42uW of consumption. Then *if* the mosfet would use some 3+mW or so for its *own* switching, then where is that coming from, because the circuit only uses 42uW in the first place. In other words, does the [in this case] IRF640 switched at 8Khz uses more or less then this 42uW of energy normally for it's switching. I agree however that this 42uW is coming from a battery or capacitor.

I think the key point in here is determine *exactly* what the IRF640 would theoretically consume in energy when it is being switched on and off at the 8Khz rate, with the given info, as we know the circuit energy usage as a whole.

--
NextGen67


Well, first of all, I have to correct myself on the 3+mW (I wrote 3.8mW minimum) because I used data sheet numbers for the gate to sorce and gate to drain 'Miller' charge quantity but it was connected to conditions higly different from the 3V and microamper drain current range (what is given is charges needed at 160V drain voltage and 18A drain current).  Sorry for this and I would like to correct my mistake as follows:

From Luc scope shot (Reply #345, 2 pages back) we see the gate source voltage is 7.75V peak to peak.  This is its maximum value and means all the energy swinging in that LC parallel resonant circuit is stored in the input capacitance, Ciss of the FET.  From data sheet, Ciss consists of about 1600pF gate source and about 500pF gate drain capacitances at the 3V drain voltage, together it is 2.1nF. 
Now if you calculate the stored energy in this cap (.5CV2) you get .063uWs  (microWatt second) energy. If you relate this energy to 50us (one time period for 20kHz) you get 1.26mW power, this swings in the resonant circuit in every 50us. This is called reactive power, it changes at every fraction of moment, if you try to extract it, then the effect of any load manifests as a loss in the LC circuit, consuming from this swinging energy, hence you have to take it from the battery for making up for the loss.

So eventually 1.2mW peak reactive power circulates in the gate source circuit (my earlier 3.8mW came from not relevant data sheet calcs), this controls the gate and the loss in it is supplied from the 3V by the 14 - 20uA current taken from it.

rgds, Gyula

gotoluc

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Re: Self running coil?
« Reply #406 on: March 30, 2010, 05:24:55 PM »
@Luc:

Thanks for posting the data.  Isn't it based on the standard formula as shown below.  I'll work on a resonance calculator.

Here's the formula:

Fr = .159 / square root of LC

Fr = the resonant frequency in hertz
L = the inductance in henries
C = the capacitance in farads

I really do appreciate your work,  I apologize for being hard on you (it was uncalled for).

GB

That's great GB if you can figure this out and a bigger bonus if you can create the calculator program.

I must let you know that each one of those scope shots the coils are tuned to the point where the circuit uses the less amount of current. So one little change like a drop in inductance on the pulse coil and the circuit stops as at this point it is just using the tops of the resonating sine waves to switch. So if one wants to start the circuit by just taping the positive feed connection it would work if you would raise the inductance of the pulse coil by a little and then when the circuit is started it can be dropped to the most efficient point. But keep in mind that if it goes too low there is nothing that can start it as not enough energy is at the pulse coil to trigger the gate.

I think using mosfets with a smaller gate voltage would have much benefit for this and should show more energy gains since so much less energy from the mail coil will need to go to the pulse coil which will have a drop in inductance from the test data I did.

Hope this helps.

Luc

gravityblock

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Re: Self running coil?
« Reply #407 on: March 30, 2010, 07:07:50 PM »
Here's a resonance calculator I found on-line, http://www3.telus.net/chemelec/Calculators/LC-Calculator.htm

Enter the total inductance of both coils, then enter the capacitance, somewhere between 900 -1000 picofarads.  The capacitance appears to be varying slightly.  It's coming really close to the actual resonance frequency.

I'll see if I can find a better solution.

GB

gyulasun

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Re: Self running coil?
« Reply #408 on: March 30, 2010, 07:09:07 PM »
@Luc:

Thanks for posting the data.  Isn't it based on the standard formula as shown below.  I'll work on a resonance calculator.

Here's the formula:

Fr = .159 / square root of LC

Fr = the resonant frequency in hertz
L = the inductance in henries
C = the capacitance in farads

I really do appreciate your work,  I apologize for being hard on you (it was uncalled for).

GB

Hi GB,

It is the Thomson formula for LC resonance calculations, there are several online calculators for this, here is one I already included several of my answers to Luc or else:

http://www.whatcircuits.com/lc-resonance-frequency-calculator/

Sorry for not able to answer to you on this, hope it is not too late for you.

rgds, Gyula

void109

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Re: Self running coil?
« Reply #409 on: March 30, 2010, 07:32:55 PM »
I hope this doesn't seem unrelated, but I'm working with Luc's setup and trying variations to which this applies.

I worked out a circuit to get an AC square wave pulse to drive my parallel resonant circuit for the coil, however, it ends up with:

555 timer x 1
p-mos x 1
n-mos x 5

I spent quite some time foraging through google before I came up with this solution - however it seems ungainly (a lot of components!  I'm new to electronics in general) - does anyone know of an easier way to turn a 12V source into an AC square wave?

You can view the circuit at

http://www.falstad.com/circuit/

And then import the schematic I'm attaching to this post.

Also, I appreciate all of the work that's being shared here, I know I haven't posted much, but I try to refrain unless I have something new and or original to say.  Most of what I'm seeing others are seeing and posting in more than sufficient detail to warrant a post from myself :D  Thanks all

NextGen67

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Re: Self running coil?
« Reply #410 on: March 30, 2010, 07:40:42 PM »
HI Gyula, Gb,

Yes, those are the standard tools to find out either L, C or Freq...

However, to complete the picture, it would be nice to come up with a rule to determine the Capacitance of the mosfet being used (using the data from it's data sheet)...

Something Like:

Enter Ciss
Enter Coss
Enter Crss
Enter Rds(on)
Enter Vgs(th) [ or enter input voltage ]
Enter Vgs [ or enter tank voltage ]

And then the formula would spit out the C[apacitance] value that matches Luc's data (and for any given mosfet).

As for his IRF640 data, one can see that all Frequency's hang around 1533 to 1579 pF. The value of 1578.54 pF probably having the most accurate [and best/lowest 0.0000xx result ]

--
NextGen67


gotoluc

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Re: Self running coil?
« Reply #411 on: March 30, 2010, 08:06:21 PM »
Hi everyone,

I decided to make a video using the 2 identical toroid's of test 15 video to demonstrate what I had done for myself yesterday that the magnet affects a ferrite core toroid more than just dropping it's inductance.

Below are the scope shot of each at the peak efficiency tuning points.

Please note that I had a little bit of tuning problems with the magnet toroid as the efficiency tuning point is super sensitive compared to the non magnet toroid. But I got it at the end just before the 10 minute limit.

Link to video: http://www.youtube.com/watch?v=zQxL9W6gVG4

It is also clear by comparing the data of the two shots that there is a gain in the magnet toroid and this is with identical generator gain to each test as I did not touch the generator output.

Luc

forest

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Re: Self running coil?
« Reply #412 on: March 30, 2010, 08:31:36 PM »

mscoffman

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Re: Self running coil?
« Reply #413 on: March 30, 2010, 09:46:54 PM »
remember that  http://www.rexresearch.com/szili/szili.htm

The experiment shown is based on what we now know is faulty.
This circuit supposedly tuned for max overunity actually
represents the worst case of gate energy being made available
to a low voltage supply. Is some overunity energy in there?
We can not tell.

:S:MarkSCoffman

gyulasun

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Re: Self running coil?
« Reply #414 on: March 30, 2010, 10:53:44 PM »
Hi everyone,

I decided to make a video using the 2 identical toroid's of test 15 video to demonstrate what I had done for myself yesterday that the magnet affects a ferrite core toroid more than just dropping it's inductance.

Below are the scope shot of each at the peak efficiency tuning points.

Please note that I had a little bit of tuning problems with the magnet toroid as the efficiency tuning point is super sensitive compared to the non magnet toroid. But I got it at the end just before the 10 minute limit.

Link to video: http://www.youtube.com/watch?v=zQxL9W6gVG4

It is also clear by comparing the data of the two shots that there is a gain in the magnet toroid and this is with identical generator gain to each test as I did not touch the generator output.

Luc

Hi Luc,

Could you make a test for me?  It would be this:

Just connect a 533pF capacitor (ceramic or mica or any normal capacitor) in parallel with the toroidal coil that has your split wound coil and also the magnet attached and please repeat the same test you showed in your present video but this time you would find resonance also at around 6kHz like in case of the other normally wound coil that has no magnet atteched.

I would be interested to know the current value.  No need for making a video on it, just tell.   (I know 533pF cannot be had, maybe you could combine some smaller standard values in parallel to make up for it, no problem if you approach it only to +/- 10pF precision, maybe you have a variable capacitor then it would be good to use, together with the C meter first.)

Thanks,  Gyula

EDIT: one more thing: would you measure the DC resistances of the two toroidal coils you have used? thanks.

gyulasun

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Re: Self running coil?
« Reply #415 on: March 30, 2010, 11:11:32 PM »
HI Gyula, Gb,

Yes, those are the standard tools to find out either L, C or Freq...

However, to complete the picture, it would be nice to come up with a rule to determine the Capacitance of the mosfet being used (using the data from it's data sheet)...

Something Like:

Enter Ciss
Enter Coss
Enter Crss
Enter Rds(on)
Enter Vgs(th) [ or enter input voltage ]
Enter Vgs [ or enter tank voltage ]

And then the formula would spit out the C[apacitance] value that matches Luc's data (and for any given mosfet).

As for his IRF640 data, one can see that all Frequency's hang around 1533 to 1579 pF. The value of 1578.54 pF probably having the most accurate [and best/lowest 0.0000xx result ]

--
NextGen67

NextGen,

Sorry I do not fully get you, something is foggy: what kind of formula do you think of?
And for the IRF640, which capacitance is the 1578.54pF ? Ciss, Cgs, Coss? How did you get it?

By the way, would it not be better to wait for the person referred to by Luc what he comes up with first?

Gyula

skywatcher

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Re: Self running coil?
« Reply #416 on: March 31, 2010, 12:20:31 AM »
I decided to make a video using the 2 identical toroid's of test 15 video to demonstrate what I had done for myself yesterday that the magnet affects a ferrite core toroid more than just dropping it's inductance.

It's clear that it does more. Imagine that the magnet brings the core close to saturation. If you are feeding a sine wave into your coil, without the magnet it would create a magnetic flux which changes its direction as the current changes its direction. Let's say, you get a megnetic flux inside the core which changes between -100 mT to +100 mT. If the core has a saturation flux of 1 T, and with the magnet you create a flux of 950 mT inside the core, you get a bias from the magnet, and if you apply your sine wave the flux is centered at 950 mT with +/- 100 mT, but because the saturation flux is 1000 mT it will be clipped. So you have some kind of asymmetric behavior here.

This could, as i already explained some days ago, also have the effect of 'magnetic rectification' which might explain some of the strange effects.

skywatcher

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Re: Self running coil?
« Reply #417 on: March 31, 2010, 12:23:53 AM »
Yes skywatcher, you understood correctly. I can even start it just by tapping the positive connection. No signal generator even needed.

Luc

What about the battery ?  Is it connected only for startup, or all the time ?

gotoluc

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Re: Self running coil?
« Reply #418 on: March 31, 2010, 12:49:26 AM »
Hi everyone,

Since I changed my cap bank meter to a 10 Ohm instead of the 1 Ohm resistor to get more resolution on my meter I'm getting confused. In my latest video test 16 I said the normal wound coil with no magnet was using 320uA and that is not correct!... it is 3.2uA used
Same goes for the toroid with magnet I said it was returning -350uA and it is -3.5uA returning.

It will take me some time to adjust using the 10 Ohm but it's worth it as it gives me much better resolution. Maybe I should even go to 100 Ohms!... but I don't have a 1%

I also decided to retest the 20KHz self pulse test I posted on page 26 first post. The more accurate reading is 17.5uA and not 14uA

I also took a new scope shot of it once it was tuned to the most efficient and is below.

Sorry for the confusion in video test 16

@Gyula, I'll do the test you asked by adding the capacitance and post the results.

Luc

« Last Edit: March 31, 2010, 01:16:37 AM by gotoluc »

gotoluc

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Re: Self running coil?
« Reply #419 on: March 31, 2010, 01:02:57 AM »
What about the battery ?  Is it connected only for startup, or all the time ?

Hi skywatcher,

yes battery still needs to be connected as it is using 18uA but at least it is creating its own energy for the mosfet switch at 20KHz.

This is an accomplishment on its own! as I don't know of a pulse circuit that can create a 20KHz pulse of 7.19vpp with 3vdc at 18uA input. Can think of one?... or anyone else reading this topic?

Hopefully with a new main toroid coil of less DC resistance and a little more inductance we can come to unity or better.

Luc