That's to be expected.  Inductance in series decreases the average current through the bulb at high frequencies.  That's why I asked you to measure the inductance of the bulb (note that I did not ask you to add inductance to the bulb).

Hi Verpies,
  I did try to measure the inductance using a meter, but it couldn't get a reading - it came up with a negative value.

However the bulb is not a good indicator of the input power at all, because a bulb in series with the input measures current, not power and the MPTT rears its ugly head.

I don't really get that TBH - surely the bulb is showing real power - as it needs both volts & amps in phase etc...?

I do get how there's an 'optimum' load - i.e. resistance - that is apparent in the circuit. It 'feels' like the small bulb isn't too far off ideal. The 60w bulb is terrible - i.e. far too high resistance - virtually no power transfer. The LEDs are good.

If the bulb's resistance was the same as the supply - would it then show real power accurately?

Capacitances form frequency-selective LC tanks with delibrate and stray inductances.
Also, don't forget about the formation of standing waves...

It is interesting that all versions of the Vialle gen. have similar resonant frequencies. I wonder if the U-shaped bar also has a higher resonance at around 7.2 MHz like my small one does...

It's odd that mine works at 3.7MHz - despite only being 1/3 the length of the normal version. I currently have no hypothesis to account for that.

A Mazzilli circuit? If so, it might be more efficient but also less controlable.  You will not be able to tune its frequency precisely.

Yes. Agreed about the frequency being difficult to predict / set - I do have some variable caps though. To get it working at 4 MHz would need a coil with very low inductance and low self-capacitance too. Which might be difficult to acheive.

Unfortunately I have replaced the mosfets, but the driver's still not working... It'll take another leap of understanding for me to fix it.

Hi Folks,
  It's all working ok, and I have some results...

1) I'm able to light a small incandescent bulb from the 2 copper tubes in the coil. Picture attached of the setup.
 - The resonant frequency for my 2 6" copper tubes is around 3.7MHz.
 - It is a sharp resonance being much dimmer at 3.6 or 3.8MHz, an the lamp doesn't light at all past about 3.5/3.9Mhz...

2) Power into the transistor is about 60v, and 0.37a (about 22w)

3) The gate-driver setup has a sweet spot at about 5.7v.
 - It keeps the current through the gate & the mosfet reasonably low, but there's a peak of lamp brightness there too.
 - Above 5.7v the load current reduces, and the lamp dims, up to about 7v where it reaches it's former brightness again.

4) The scope shot shows:
 - Yellow - the Gate voltage
 - Blue - the Drain voltage

5) I think my gate driver needs power resistors - the 1/4w ones can't take the current with the full 15v available. They get very hot at 9v.
They're currently at 10 Ohms, I'm tempted to try 5 Ohms to see if I can improve the gate signal.
The UCC211 can handle 0.3a continuous at 18v according to the specs - so a pair of 5 watt resistors maybe?
Maybe I'll just put a load of 1/4w ones together so I don't have to worry about them burning out...

6) In order to measure the input & output HF power, I'd like to build something like Verpies HF wattmeter...
I suppose an off-the-shelf SWR meter would be good enough to make relative measurements though...


Tim

Hi tim.

Nice to see you are in progress

For reducing load for power consumption protection, I understand what you mean, but remember that more the output is (short-circuit and light bulb are powerful), more the negative power has changes to take place at the input. 

For SWR meter, do you mean like a mini NVA or a HF FWard BWard power meter & SWR Meter? If last one, Blue has registered funny behaviours in his last vid.

Cheers
K.

Further tuning.

 - The 145pF capacitance in parallel with the coil is still good.
 - I've tried adding small amounts of inductance & or capacitance in series or parallel with the bulb, and have only seen the bulb dim.
 - I've tried connecting the GND to one or other of the bars - and that gives a small increase in brightness - when connected to either bar.

What's going on...?

Capacitive vs. magnetic coupling...

There are 2 reasons why it looks like the effect is due to capacitive coupling:
 1) The addition of the ferrite cores makes no difference
 2) Placing my hand on the coil makes the bulb go out. If it was magnetic - I don't see how this could happen.

Relative Power Usage

 - The test bulb with 12v DC uses 0.4a, and makes about 40,000 Lux (as tested with a luxmeter at zero distance)
 - If powered by the circuit - the bulb needs about 45v and 0.3a to reach the same brightness. (Ignoring the gate rdriver)

Questions

 - If it is capacitive coupling, I don't understand why it has particular resonance points. I suppose caps do have their own resonances...
 - I don't really get why the 2 bars inside the coil would be oppositely polarised.

Next Steps

 - I have a ZVS driver with a bad mosfet that I need to fix. Maybe tomorrow.
 - I want to try running the coil with the ZVS driver - it's likely much more efficient.
 - In order to do that - I also have to add another layer of winding to the coil - so there will be two. I know that's not typical for the device, but hey...
 - I might actually just do a new coil, with fat wire - as the ZVS driver prefers lower inductances, and fewer turns.

Did you try to connect one extremity of one half bar to the same side extremity of the coil? Biganos did it with success and an other experimenter of Cos too. If I remember well they connected it to the "0" point of the signal; something like that. (Which looks to me avoid at least partially the possibility of capacitive coupling while both coil and bar are connected...).

@ verpies & tim

Quote

Quote from: tim123 on February 21, 2014, 07:17:36 PM
There are 2 reasons why it looks like the effect is due to capacitive coupling:
 1) The addition of the ferrite cores makes no difference
 2) Placing my hand on the coil makes the bulb go out. If it was magnetic - I don't see how this could happen.

That's logical reasoning

Wouldn't be you both forget it is supposed to be about mainly inner coupling with the energy of electrons? And that it is supposed too to be about a magnetic flux sent back in the coil by the cold current in the bars (for negative power)? That inner core doesn't matter much because current locates maily close to the outsurface the the bars? none of  what you notice looks to me to avoid these supposed and expected phenomena; or I am mistaking?

Unfortunately I have replaced the mosfets, but the driver's still not working... It'll take another leap of understanding for me to fix it.

Just to let you know that Blue, in his last vid, uses Arduino stuff and Biganos amplifier.

However, you cannot trust non-inductive bulbs to accurately indicate input power (because in that case the bulb is not the indicator and load in one - it is merely an intermediary between the power supply and a 3rd element in that circuit...

Hi Verpies,
  in this case, isn't the bulb the DUT? As we're trying to measure the power through it - and there's nothing else in the (output) circuit.

Also I have a couple of questions that perhaps you could help with:

1) The driver for the Vialle gen is clearly the most important part, and the hardest to get 'right'...

What do you think would be the 'best' way to drive the device - given the requirements of:
 - High efficiency,
 - Variable, high frequency
 - Balanced output, sine-wave oscillator

For example, I have a linear amp - with a D1020UK, MOSFET. Balanced push-pull type. I've not used it yet. I'm reluctant to hook it up to the VG in case i kill it. That MOSFET is cool - but expensive. Is there anything similar but cheaper you know of?

A multipactor might be good. Shame they're not available to buy these days...(?)

I would like to be able to explore the higher harmonics of the series that is apparent in my device: 3.7, 7.3 MHz found, - so 14.6, 29.2 may be there too etc... Although the reactance of the coil may prevent them...

2) I think it's clear that there is capacitive coupling between the coil & tubes. The fact that putting my hand near the device makes the bulb go out is compelling evidence. Also, it would be remarkable if there wasn't, so:

I'd like to cancel out the electrostatic part of the equation - so we just have the magnetic component... How could I best do that?
 - coil with 2 layers, one wound CW, the other ACW, drive one layer -ve, the other +ve...?
 - shielding?

Regards, Tim

Tim,
What is the difference between:
- Touching a device changes the tuning and so the output by changing stray capacitance
And
- The device works by and because of capacitive coupling?

Hi Khwartz,
  I don't know. It's a good question... Changing the tuning would decrease the magnetic field... It would be so useful to have my ZVS driver working - as it auto-tunes...

If it does change the resonance - and the bulb then lights up at a different frequency - what would that mean I wonder?

BTW, is that my translation so bad that the tests to check capacitive coupling looks not relevant for you? But true that verpies could suggest other relevant stests, so...

No mate, it wasn't bad. I was just wondering if there was a way to cancel it out completely in the device itself - so I didn't have to try doing those calculations...

I could do the alu-foil shield - but i believe what Pascal said - and I'm not sure if it helps...?

I was also wondering if perhaps the cap-coupling might interfere with the desired effect - i mean - it's supposed to work because of the magnetic field - but maybe the electrostatic field is interfering with it... Just a thought.

The best idea i can think of so far - but it's not perfect - is the 2-layer counterwound coil - fed with balanced + & - signals... That way the 2 counterwound coils would make the same magnetic field - but the electrostatic field would (more or less) cancel out.

Maybe it would be possible with a normal bifilar coil...?

Regards, Tim