Testing the TK Tar Baby

[MileHigh]

PW:

The only alternatives I can see would be to build an equivalent FG circuit running off an isolated DC to DC converter fed from the main batteries or use two batteries in series with their center taps tied to ground.  I would probably use low power opamps (for higher than the 555 rail voltage) configured as an astable and an output buffer with NPN/PNP emitter followers in the FB loop.  As stated, the supply could be a pair of batteries or an isolated DC-DC converter fed from the main batteries.  Though minimal, the added current draw on this circuit if operated from the main batteries would likely be questioned.  Even if the separate battery or batteries are used to operate the circuit, would that/those battery(s) going flat be considered proof of lack "over unity"?

My gawd, I qualified you in perhaps less than 8 postings and you are really good.  With op-amps fed by a 555, and a separate set of batteries and the NPN/PNP emitter followers it's like you are building a whole function generator.  lol

When you think about it, if you have to rely on a separate power source to emulate the function generator, you may as well just keep the bloody function generator.

I think that there may some misconstrued attributes assigned to the function generator.  In positive 'high power' mode, as long as the square wave frequency is fairly low, then the function generator is not really adding any power to the circuit and it is not recharging the batteries.

In negative oscillation mode, and assuming that the function generator is grounded before the current sensing resistor (and I am sill not convinced any of Rosemary's data captures were done like this), and knowing the open-circuit negative output voltage of the function generator itself, you can simply factor in how much the function generator is contributing to the powering of the circuit.  In that sense the function generator is just an 'ideal battery' that never depletes.

And of course in negative oscillation mode the function generator is not recharging the batteries either.  You can actually state that it's helping the batteries to discharge.  And Rosemary is using the function generator as a de facto negative DC source in this case anyways.  The NERDs were simply not aware of how the function generator fit into the circuit.

With that ground loop issue in mind, the function generator may have to be run off of an isolation transformer so the whole thing floats.

All this to discharge a bunch of batteries or to save the world.  Such dilemmas!  lol

MileHigh

[hartiberlin]

Hi TK,
in your video
http://www.youtube.com/watch?v=fC7zJouJAoU

it is not possible that there are flowing 200 mA DC bias current,
as you have a 10 KOhm pot and you turn it up into the center and
then only the oscillations occure at around Minute 2:20 .

But then the pot has already around 2000 to 5000 Ohms in this position
so the maximal current then able to flow from the battery is only around 1.8
to maximum 4.5 mA  at 9 Volts...
Just Ohms law...

So I don´t see the 9 Volt battery go flat very fast at this current level....

So a 200 mA DC bias current seems to be not required....

Regards, Stefan.

[TinselKoala]

Okay TK,
now with your new video

http://www.youtube.com/watch?v=fC7zJouJAoU

with just the 9 Volt battery and the pot
we have the perfect oscillation, just oscillations and no more
switching ! Well done.

Thank you. Unfortunately this will only work for the negative-going gate signal mode. Simply applying a positive battery voltage to the positive FG point results in hard turn on of the Q1 mosfet and, since there is no negative component there will be no oscillations. For the oscillations to happen, regardless of pulse polarity and mosfets switching or not, there has to be a voltage at the negative FG hookup point that is at least 4 volts more negative than the negative battery terminal, or if floating, than the other FG hookup point.

So this is the most easy way to get rid of the function generator
and Rosemary and her team should be able to replicate this.

Yes, one would think so. I imagine that if there actually is a "team" somewhere they are frantically trying to figure out why their batteries are now running down when they apparently didn't before. Otherwise... why haven't they shown a test already? I mean, how hard is it to hook up a battery and a pot? Even I could manage to do it.
However, the current drain on the battery will limit its lifetime, and the power it inserts into the circuit must be accounted for.

P.S. The second oscillation you have shown were probably just
some weird 60 Hz jammed overlay of your scope not triggering
as you did float one side of the pot so it was not a real voltage divider anymore...

No, it wasn't 60 Hz. The scope has a "line" setting on its trigger so it can trigger on the powerline frequency... the second oscillations were at about 25 MHz. The scope actually did trigger on it but the trace was so dim it was hard to see on the video.

So please can you show now via a shunt resistor, where you measure the 200 mA
in the 9 Volt battery case ?

I may be able to do so. I've been using a Hickock inline moving-coil meter and it is easy to peg it against the 100 mA stop.

Is that flowing through your 50 Ohms shunt ?
Can you please show a scope shot  on this shunt resistor ?

I wouldn't call this series gate resistor a "shunt" exactly. And I've found that 50R is too much and limits the current to 45-65 mA. Using a 10R instead I am able to "just" peg the Hickock at a tiny bit over 100 mA max. With no resistor I can easily exceed 300 mA when the mosfets start turning on. So when the mosfets are on or oscillating hard, there appears to be a low impedance path around for the 9v battery's current. I don't know if this goes through the load and/or the CVR. I think it probably doesn't, and just heats the mosfets, but I'm not sure at this point. If I scope across this 10R resistor, I'll have to disconnect all the other probes because neither end is at the circuit's ground potential, I think. We shall see.
(ETA: I should mention that my 9v battery is about dead, it's only indicating 8 volts or so, so maybe with a fresh battery the 50R series resistor would work better.)

Many thanks.

Regards. Stefan.

You're welcome, I'm glad to oblige.

We still need to figure out how to make the positive gate drive, high-heat mode with the 555 or battery and still get oscillations, though. I was hoping the Voltage Inverter would work out for that, but at this point I can't even remember if I tested that mode or not.

[picowatt]

TK,

Regarding your 9V battery video:

First, when you show the 9V across the pot and adjusted for oscillation.  Do you still have your DC milliammeter in the loop, if so, at what current draw does the onset of oscillation happn?  That 10K pot would drop much more voltage for a given Ibias then your 555's 10R or the FG's 50R unless you were very close to the end of the pot's rotation.  Also, as your oscillation looks a lot cleaner than RA's, it does look like the circuit is being biased at a different operating point.

Second, as for hooking the first main battery across the pot, the best you would be able to do with that is turn on Q1.  Have you looked at .99's burst osc schematic?  I was referring to applying a positive voltage to the gates of Q2 and omitting Q1 altogether.  Look at .99's schematic and you will see what I am talking about.

Third, regarding attaching the positive of the 9V to the main battery string negative terminal, I would think placing a 10R to 50R, possibly even 100R, between the 9V negative and the Q2 source terminal should start the osc.  Possibly use the MOSFET end of the CSR instead of "real" ground for the 9V plus terminal connection.

If you think about it, the first and last part of the video are essentially the same, as in both instances the positive terminal of the 9V was tied to ground, but in the first part you used the MOSFET end of the CSR and not the battery ground.

Of most interest to me, is what amount of current are you having to pass thru the 9V to make the circuit oscillate?  If you have the pot set so that the wiper resistance is very high compared to the FG's 50R (or your 555's 10R), your Ibias will be much lower than was likely used in the RA tests with the FG or with your 555.

PW

 

[MileHigh]

TK:

Wait..... OK... so by applying a negative voltage to the _sources_ of the Q2s I am effectively applying a positive voltage to their gates. Effectively, right?

Exactly.  Good old relativity.  So as you pull the source of the Q2 array down, then current starts to flow out through the source and into the function generator.  Obviously if a lot of current flows into the function generator (let's say it looks like a 50 ohm resistance going to a negative 12-volt 'ground') then the input resistance of the function generator will cause a voltage "bump up."  If the voltage "bump up" is high enough to bring the voltage to the true ground potential, then the Q2 array shuts off.  But if the Q2 array shuts off, then there is no current flow, and hence no "bump up" and the potential at the source node gets pulled down again by the 50-ohm resistor.  Therefore the Q2 array starts to switch on, current flows, which causes a "bump up" which switches the Q2 array off and then the potential is pulled down yet again by the 50-ohm resistor and so on and so on and so on.

I am not saying that is the root cause of the oscillation but as you can see, since you are pulling the Q2 source down towards the negative potential of the function generator through a 50-ohm "damping" resistor, as the current starts to flow, it tends to make the Q2 array want to shut off - which then makes the Q2 array switch on.  So the circuit is in a crazy kind of balancing act and it screams as a result.

Just delicious!

MileHigh