Testing the TK Tar Baby

[picowatt]

TK,

Have you scoped across the battery during the osc?  Just wondering if you are seeing the osc there.  You may have to remove your chokes/LED's to check for it.  If the osc is at Vbatt, does its amplitude look symmetrical about Vbatt or does the amplitude appear to peak a bit more above or below Vbatt?

PW

[MileHigh]

TK:

I would want to burn off 50% of the energy in the three batteries before I did the light bulb test.  I know that you are ostensibly testing if the batteries are being recharged by the circuit but still.  If you know the power dissipation then run as long as needed to burn off half of the energy and then do the test.

I think that it would be very prudent to cut off the load when the voltage drops below your threshold voltage.  I can still step into the Way-Back machine and design a breadboard circuit in my head to do that easily.  Do you have your own method?  I can't envision Zener diodes helping you here unless you use a very low ohm resistor in series with the Zener diode and the battery source.  I would find that really inelegant though.  Do you want some ideas?  Do you have opamps and flip-flops?

PW:

I stumbled upon that guy tonight and he is great and the big hair and beard is great!

MileHigh

[picowatt]

TK,

I wonder if a good viscous damped compass over the wire from Vbatt would be sensitive enough to act as an inductive ammeter for current in/out measurements.  I do believe I have seen you using some nice compasses in your vids.  You could try charging the batts from a bench supply to get an idea of the sensitivity and polarity versus current fed from the supply, and then do load tests at various R values to check its discharge polarity and sensitivity.  The damping might act like an integrator and give you some idea as to current flow direction.  You might have to mount the compass level and to solid block/board with the wire running under it...

Just a thought..

PW

[MileHigh]

PW:

That's a really innovative thought.  But if I may tweak your thought since the oscillations are so high in frequency then just an ordinary compass should do the trick.  I am assuming a "DC" output from the function generator where the output is low for 10 or 20 seconds so the needle stabilizes.

Assuming that the current flow is in the tens of mA I assume that you will see the needle deflect.  You could then just run pure DC through the same wire and match the deflection angle and get your approximate current consumption and direction.

The beauty of your test is that it's a 'pure' test that does not modify the battery supply to the circuit in any way.  So if that old RAT magic needs to have undisturbed batteries the test will do that.  Very cool.

The bottom line is that it will establish which way the RAT current flows definitively, an issue that has been a bone of contention for years.

MileHigh

[picowatt]

MH,

To damp or not to damp, either would probably work.  Damped would be less prone to "moving about".  I think I recall TK using a compass in a video some time ago.  He might have been doing ths exact same thing.  TK, correct me if it wasn't you.

I can't remember all that well, I had to forget a bunch of stuff to make room for more.

PW