RESONANCE EFFECTS FOR EVERYONE TO SHARE

[duff]

Yes, I see what you mean .... this is why I got this USB scope... the software does the RMS surface calculations... I don't know how you can calculate that

Luc,

I could be wrong but I'll bet your scope does not know the difference between a square wave vs sine.

I'd think that the rms value is only valid for sine waves....

You might want to check your manual or with the mfg. on that one.


Also, thanks for those precise instruction on winding the inductor. Without the dimensions I'd still be banging my head trying to get it to work!!

-Duff

[duff]

(In fact the generator should feed either a tap on L1 or another coupling coil as a matching means between 50 Ohms and the resonant impedance, this would be the first to achive for Luc also and the second goal is to match the lamp's impedance to the resonant circuit with L2 number of turns at a fixed coupling.)

@Gyula,

I am interested attempting to impedance match this circuit.

I've been a ham for 25yrs - matched lots of different type of antenna but this little inductor is small with fine wire and not easily tapped. Coupling to it with another inductor would mean more losses.

Thinking that the primary is resonant and reactances canceling, I tried incrementally inserting resistors in series with the SG.

Ohms       Volts
49         3.001
43         3.014
20         3.095
10         3.221
5.6        3.250
3.9        3.269

The output voltage (across load) did exactly opposite of what I thought would happen. This circuit is very happy with the current sensing resistor (0.84 ohms), meaning that it must already look like 50 ohms to the SG (if my reasoning is correct).

I'm wondering if the load impedance is being reflected back into the primary.

Hello Duff
This may or may not apply to your coils but a Tesla Coil (TC) is usually made up of two air coils that have the same resonant frequency. The voltage increase/decrease is not based on the turns ratio but is based on a ratio of the inductance's of the two coils.  See http://www.scribd.com/doc/3876818/Denicolai-Tesla-Transformer-for-Experimentation-and-Research-96pp2001  for more info.

@Montec

Thanks for the link though I am  familiar with that article.

If you found that interesting check out the following. I thought is was an excellent article and was posted earlier in this thread:

Tesla Coils and the Failure of Lumped-Element Circuit Theory
http://www.ttr.com/corum/index.htm


-Duff

[gyulasun]

Hi Duff,

Thanks for the reports on your findings.  I was not aware of Luc's earlier activity on picking the best diode type for such circuits, though I mentioned using Schottky as first and 1N4148 and the like as second.  I looked for the data sheet on SBL3040 and it justifies the good result: its forward voltage drop is only 0.2 - 0.24V for a current from 10mA to 100mA range,  see Fig.3 on Page 2 in data sheet: http://www.vishay.com/docs/88732/88732.pdf

I am also puzzled by the half wave rectifier's performance here,  maybe the oscilloscope waveform across your L2 would reveal something  but I would expect a normal sinusoidal 305 kHz waveform with symmetrical zero crossings...

Re on the input impedance.   Maybe you could place again resistances with the hot output of the SG in series (replacing the 0.84) but in increasing values towards several hundred Ohms maybe up to 1kOhm in 100 Ohm steps and see on the scope when the divided input voltage is halved across the series L1C1 (nodes 2 and 0)?
You surely know this method when the series inserted resistance equals the unknown input impedance (at resonance of course) then the input voltage from the SG gets halved across the unknown, (a normal voltage divison happens).

I'm wondering if the load impedance is being reflected back into the primary.

Well, energy must come from somewhere and it should be coming from L1, it must have a big electromagnetic near field around it due to its sizes.  Have you tried to short circuit L2 and see the voltage amplitude across L1?  Maybe overcoupling occurs between L1 and L2? 

Regards,  Gyula

EDIT:  Once you managed to find the input impedance, you could use a Pi filter between the SG and this circuit?

[gyulasun]

Luc,

I could be wrong but I'll bet your scope does not know the difference between a square wave vs sine.

I'd think that the rms value is only valid for sine waves....

You might want to check your manual or with the mfg. on that one.


-Duff

Hi All,

Unfortunately, a PC scope software bug has misled member nul-points on pulsed capacitor discharge measurements and this indicates we have to be cautios and triple check measurements that show unusual results.

See his findings here: http://www.overunity.com/index.php?topic=4419.msg150394#msg150394

I do not mean Luc has also got a problem in his PC scope I mean only it is advisable to check some results with another type of measurement device (normal analog scope, etc).

Regards,  Gyula

[gyulasun]

Double post