Dr Ronald Stiffler SEC technology

[Lidmotor]

Itsu---That is an excellent replication and video showing what is happening in the 'Loop'.  Everyone working on this project should watch it.  You have all the proper equipment to test what we are looking at.  I really liked seeing the current in the Loop.  At 13mA it confirms what I saw yesterday that it isn't huge but it is there.  Many thanks for taking the time to do these experiments.  For those of us without proper measurement equipment you fill in many blanks with an honest evaluation of a true replication.

--Lidmotor

[gyulasun]

Hi Itsu,

Yes, it makes sense that the length of the cliplead has a role how much power is coupled capacitively into the diode loop. Your 6.5 MHz test frequency needs longer length for it (and maybe your L3 coil also has longer wire in it than the ones the Doc or Lidmotor used at 11-13 MHz).  At least your coil size judged by the look of (with my eyes) suggests this to me, I may be wrong. 
It is also possible that the longer cliplead (needed for coupling higher energy towards the diode loop) simply reduces the quarter wave resonant frequency of the coil from the 11-12 Mhz range to 6.5 MHz,  acting like a 'capacitive hat' load, just like for a Tesla coil.
The 15 diodes in the loop eat up about 15 x 0.6V= 9V and this loss could be reduced by better diodes. Say a low barrier Schottky type has only 0.25 V drop in the 10-20 mA forward current range, then the voltage loss would be only around 3.7 V. This would mean that for the diode loop inside, an 'extra' voltage of 9V-3.7V=5.3V would be available for driving higher loop current for the LEDs, this would surely increase brightness,  (hopefully not at the expense of an increased load on the L3 coil).
Thanks for the excellent and informative video !

Gyula

[itsu]

Thanks Lidmotor and Gyula,


the coil i was using was one of the 3 L3 coils i made last week for the 3 coil setup, so they should be exactly the same as the ones Dr. Stiffler is using (same inductance).

They resonate around 13.6Mhz using the earlier circuits loaded with a led strip.

Now with the long antenna-like top load it dropped to about 6.5MHz (using a shorter cliplead its about 9MHz)

I have enough BAT42, 46 or 48 diodes i could use, but the forward voltage drop is around 400mV for them in the 10-20mA range, so i don't think it will improve much (3V total).


Anyway, looking at Dr Stifflers latest video (thanks Nick) of today he was not using any antenna, just the L3 coil laying next to the diode ring.

I did not expect it would work in my situation, but it did!
Raising the frequency to 20Mhz there was the new resonance point (my FG drops its amplitude to 10Vpp above 20Mhz, so i stayed at 20MHz).

Current in the ring dropped to about 2.5mA rms, voltage across the cap still 31V.

Video here:   https://www.youtube.com/watch?v=GmikYG3j0FA


By the way, i also used the shorted turn with 1 diode around the diode loop, and indeed the leds go out, but after some retuning (to 18.4Mhz) the leds
came on again, no matter what direction i put the loop.
So this shorted turn with 1 diode does not kill the resonance, it just loads the L3 coil more i guess.

Itsu

[TinselKoala]

Perhaps even more important than Vf is the switching time or reverse recovery time of the diode. The faster the diode the higher the operating frequency it can sustain, this is obvious, but what may be less obvious is that faster diodes will "capture" more of the peak of a waveform of even a lower frequency, thus resulting in a higher capacitor charge voltage. This is because the diode shuts off faster so doesn't allow as much reverse leakage out of the capacitor.

Another thing to try is to use a few LEDs in the loop instead of diodes all around. Use, say, three LEDs in series (to approximate the same total Vf of the full diode ring) and complete the ring with a simple wire, the same total length as the 1-LED, diodes all around, loop. A tiny little trimmer cap across the LEDs may help.

[gyulasun]

Hi Itsu,

Okay, and thanks for the comments. Regarding the diodes you have, you do not need to rebuild the diode loop with the Schottky types,  you could fasten them in parallel with each 1N4148 by using say plastic paper clips. If there is no plastic clip then a small sized steel paper clip may also be used to fasten the diode legs together. The BAT42 type has a forward voltage range between 260 mV and 330 mV at 2 mA current as per its data sheet and your loop current is around 2.5 mA now.  This is just a suggestion for a later time, to see the effects of lower losses in the loop diodes on the LED current hence brightness.

In the meantime the Doc has produced yet another video... :
https://www.youtube.com/watch?v=QvuYtpMBywE

PS: TinselKoala posted an interesting and good suggestion on the switching time of the diodes while I was typing this post, so consider that too of course.  The Doc mentioned time delay caused by the diodes in the loop.

Gyula