Testing the TK Tar Baby

[TinselKoala]

Sorry t I thought you were using the bulb as the r in a tuned tank and changing the parameters of the r in the secondary to match the primary tanks input.

Well, you could think of the bulb-mosfet-thermistor loop as a tuned circuit of a kind, even though it doesn't slosh the same energy back and forth like a real tank circuit does.
Really, though, in this circuit the thermistor is just acting as a variable gate pulldown or gate voltage regulator in concert with the potentiometer setting, and the gate voltage-bulb current-air temperature-thermistor temperature feedback loop isn't really sloshing its energy back and forth, just moving its concentrations around from one dissipative area to another. A very lossy tank !

[TinselKoala]

Ahhh..... I am greatly amused by the thought of a NERD taking a fully charged 12 volt high capacity lead acid battery and hooking a 100 uF electrolytic capacitor directly across the terminals. Let's hope that the polarity is right, at least.

Considering the various competencies already exhibited by the principal NERD, there is no telling what could happen. Perhaps experts should be consulted.

Still, I wonder what such a test could prove that is not already evident by other means. Presumably the intent is to convince the NERD that the battery is not discharging and recharging completely a million and a half times per second, as she is apparently mistakenly concluding from her scopeshots. But this is already evident by the fact that the batteries have not BLOWN UP, and are sitting there at a perfectly normal operating temperature.

Or perhaps it's an attempt to get her to understand that the battery voltage measurements she has been using in her calculations are invalid.

That will only result in the goalposts moving. So it's not the batteries that are making the huge extra energy; they do discharge, after all. But the measurements ! The oscilloscope does not lie ! (it only answers the questions asked of it) This must mean that the magic is happening in the inductances! And the filtering on any battery just prevents that battery from participating... but the magic is still happening, because you can still see it on the "battery voltage" measurements obtained at the board, or "directly across" the battery pack itself at the end of long probeleads and interbattery wiring.

[TinselKoala]

A small quiz. (Sorry, no extra credit, just a gold star next to your name in the Great Engineer's roll book.)


Question 1: Given a capacitor of 10 nF (10000 pF) and an inductance of 100 microHenry, what is the resonant frequency of the LC tank?

If the capacitor is initially charged to 100 volts and then "suddenly" connected to the inductor by a nice fast switch, we know the form the ringdown will take. Right? Assume a high Q so the ringdown continues for some few cycles before dampening out.

The ringdown of course represents the capacitor's total charge leaving, building the magnetic field of the inductor, then leaving that to recharge the capacitor at (nearly) the same voltage BUT OPPOSITE POLARITY, back and forth again and again .... with each and every cycle of that ringdown waveform. The Q describes the value of "nearly" in that last sentence. The oscilloscope shows that the polarity of the voltage on the capacitor reverses totally, and back again, with every cycle.

RIGHT?

Question 2: What is the value of the peak current during the first few cycles of the capacitative-inductive ringdown, when a 10 nF cap charged to 100 V is connected to an inductor of 100 microHenry, assuming low circuit resistance?

[MileHigh]

TK:

It feels like we are in the winding down stage of the Ainslie drama.  She will be frustrated in trying to understand what Poynt is teaching her, and then she will do some testing and it will become a mess before too long.

I think that she is quite taken aback that the mystery American lab told her that the batteries are discharging.

Hey, she can console herself by getting in the queue to buy an Ismael Aviso 11-kilowatt dune buggy special.

MileHigh

[polln8r]

4.967 MHz--if I used the right number of zeros and the right equation from Wikipedia.

353 mA--if the 'equivalent' circuit and 'scope' readings in the simulator from http://www.falstad.com/circuit/  are being read correctly.

Probably way off, but nobody else was giving any answers, so why not give it the old 'college' try?

polln8r