Testing the TK Tar Baby

[polln8r]

TK,

Glad your'e still making videos! Anything going on these days with your wireless power devices? How scaled down do you think they could go (i.e. a 9v Altoids box Tx unit)? Could regular transistors be used instead of the FETs?
I also wonder what two transmitters facing each other with a receiver in middle would behave like. Would there be cancellations or amplifications (or both) as the distances between them changed? Would there be a 'super-duper-nova' mode?

I've got so many questions I should just build some myself, but I'm just too ill-equipped right now (I own a soldering iron--that's about it). Someday, though... and soon!

Anyway, Cheers!
That's all I'll throw at you for now,

polln8r

[TinselKoala]

@polln8r
I think the thing is as small as is practical already. It might be possible to make a really low power one, smaller.
The mosfets are carrying a lot of current. If you look up the IRFZ44N you will see that it has a tiny Rdss and can handle nearly 50 amps if properly heatsunk. Yet I managed to blow up a couple of them, literally. There is a lot of power circulating in the drain-source-cap-loop circuit, like a flywheel, and even though the input power is steady 2-5 amps there may be instantaneous currents much higher than that in the mosfets themselves during the 500 kHz oscillations of +/- 60 V or so. I think these mosfets are operating within, but close to the edge of, their operating envelope. I suppose you might be able to get it working with a similar circuit using UJTs or IGBTs or Darlingtons, but I doubt that simple bipolars would work, they have too much resistance to use when the other types are so readily available and cheap.
The capacitors are also a big factor. You just cannot get the required characteristics in a tiny capacitor, so the transmitting caps that I am using are probably about the smallest that will actually stand up to the stresses.
I think the issue of the interaction of several transmitters is fascinating. I don't want to risk the transmitters I have operating right now, though. I need to build a proper test bed with sockets for the transistors and capacitors, and building two won't be much more of a task. So the multiple transmitter experiments will come, but not for some days yet.

Thanks for watching ! And stay tuned....
--TK

[TinselKoala]

Here's another "little" video in the Mosfets: How do they work? series.

I use a NTC thermistor to provide a variable resistance path to ground for the IRFPG50's gate charge. Then I allow the heat from the mosfet's load bulb to heat up the NTC. The resistance drops, the gate charge bleeds away and the bulb dims and cools. The NTC cools, its resistance rises, and the gate charge is replenished by the control potentiometer's wiper voltage setting. The bulb brightens as the gate charge builds and the mosfet travels through its linear conductance region. As the bulb brightens it warms the NTC which decreases its resistance... and the system immediately settles into a regulated brightness/temperature, depending on the distance of the NTC to the warm bulb.

This illustrates a basic feedback loop. With the addition of a phase delay of 180 degrees between input and output, it is easy to understand how this system would oscillate. At least I hope it is understandable, by now.

http://www.youtube.com/watch?v=t3u801ZUtXk

[TinselKoala]

Using the linear conductance behaviour of the IRFPG50 six dollar high voltage mosfet to perform a task more appropriate to a ten cent bipolar transistor, illustrating the use of a feedback loop to monitor airflow.

http://www.youtube.com/watch?v=tUJ9PIlAOAs

I wish I had a bit of Nitinol wire.... heh.

[PhiChaser]

Hey 'Guys',
Sorry  I haven't been participating in the discussion, RL has been extra busy for me and I have been exhausted after long days and more long days. Throw in some happy circumstance and my time is spent (kinda like me at the end of those long days...)! You 'Guys' know brain sweat is still sweat... College seems so far away sometimes...
I DO plan on ordering parts and building a TK headlight, and generally boning up on resonant circuits. You will be hearing from me about that (eventually, time/money permitting...)! You guys are awesome and I wish I had more free time to devote to learning new stuff (and participating in the discussion of course!). I won't fade away into obscurity, I just try and think of it as more of a 'vacation' from the internet for a bit. Suffice it to say that my choice of 'lifestyle' is either 'feast or famine' and feast means I don't have much free time (famine means I have too much free time heh heh...). Sad to hear RA isn't joining in the discussion any longer, I had a feeling she would eventually wear out her welcome with her hyperlinks without any additional correspondance.
Good luck and happy experimenting everyone, I hope to have more free time in the future where I can play 'catch up' with your experiments. I will also try to 'catch' the new tube vids when I get a chance...
And WHY can I never have time AND money both at the same time?!?
Thanks again 'Guys',
PC