Testing the TK Tar Baby

[TinselKoala]

TK,

With your new resonance measurements, I think you are in the ball park. I used all the stated inductance values in the sim, and the results are close to Rosemary's.

Good. It's too bad that the ProsKit meter is useless... I purchased it more or less specifically for this little project. Oh well.... it was cheap, at least.

You are right about the CSR value, it is of little consequence when for starters one is obtaining a negative VV from the CSR and VBAT trace products.

Yep.... the sign of the power is determined by the sign of the current, not its magnitude, and although RA _claims_ to have seen negative voltages on a battery trace, I am not able to produce them (at least not with a mere 48 volts main battery) and none of the scope traces from Ainslie that I can find, either in the papers or the video demo, seem to show any negative component on the battery traces. The final shape of the sampled power curve that I obtained is of course virtually identical to the shape of Ainslie's VV traces, with the expected smoothing due to the lower bandwidth, and of course the lower resolution caused by my manual sample rate of 18 samples per cycle, which is a mere 36 megasamples/second at the approx 2 MHz osc frequency.

Have you measured across ONE of your battery's terminals directly with the scope, while all other scope and FG leads are removed? If so, what did you see directly across the ONE battery?

No, I have not yet shown this, although I have done the measurement of course. Which of the 4 series batteries would you like to see measured in this way?

[TinselKoala]

You know another interesting tidbit here is about when to use 10X attenuation on your scope probes.  I think that some people might always defer to 10X attenuation thinking that it's better all the time.  I believe it's preferable to use 10X attenuation if your signal is very high in voltage or you are looking at a signal that has a really high inherent impedance and you want your probes to be as high an impedance as possible to reduce the disturbance that they cause to the device under test.  The trade-off is that your signal seen by the scope is weaker and it's own impedance is higher as subject to disturbance, and I believe that you lose some bandwidth.

So I would suggest that you don't keep the probes on 10X attenuation in this case.  The signal source impedance is a very robust 50 ohms, and you won't disturb it with the normal probe setting and you will get a "clearer" signal and hence a more accurate measurement of the AC voltage across the resistor array.  In other words, you won't have to worry about any possible frequency roll-off.  I am pretty sure that there are no roll-off issues for 10X probes at 1.5 MHz but using non-attenuated setting just "feels better."  I am sure you can relate to that.

Note one more thing.  If you assume inductive wire-wound 10-watt resistors, they are wound like like little inductors.  When four of them are in close proximity the mutual inductance between resistors may come into play.   I am not really sure, but it implies that you could arrange 2 + 2 such that there is some self-cancellation, hence reducing the inductance of the array.

Again, I am not an analog guy so what I am saying may be subject to correction.

MileHigh

All of the probes I have here are old-fashioned, fixed attenuation probes, Tektronix P6047. I usually monitor the FG with no attenuation by simply plugging it directly into the scope with a BNC T-connector, but the probes are all 10x. You are right of course. Normally one wants to use the "lowest" amplification gain settings on the vertical amplifier and the least attenuation. But I'm stuck with what I've got here and I'm not going to be buying any more equipment for a while. This skipping dinners to pay for my hobbies is getting old.

And you are right about some arrangements of parts being a lot less or more inductive than others. Running wires antiparallel or putting resistors in a "hairpin" loop... even using tightly twisted pair wires for PS and load connections ... all will reduce intercomponent and wiring inductances, but might increase capacitances. It's a tradeoff. Take a look at the so-called "bifilar" coils that some people use, wound in a hairpin arrangement for very low inductances, or even Tesla's true bifilar coil primaries, which have current path always in the same direction but greatly increase inter-turn capacitance by the wiring arrangement.

[picowatt]

TK,

If you are going to do .99's scope shots at the batteries, I'd like to see, as .99 stated, with all other probes disconnected, one probe ground at the Batt- and then a shot of the scope with the 'scope probe tip placed at each battery terminal starting with the positive terminal of the first battery terminal above Batt-.

This would provide some evidence as to the battery impedance at Fosc, and the effects of the interconnect lead inductance.

You have already done so much, I am reluctant to ask more from you.

PW

[poynt99]

Good. It's too bad that the ProsKit meter is useless... I purchased it more or less specifically for this little project. Oh well.... it was cheap, at least.

I found similar problems with my cheap $30 meter from China. When I sprung for the TH2821A meter, things got a lot better.

Yep.... the sign of the power is determined by the sign of the current, not its magnitude, and although RA _claims_ to have seen negative voltages on a battery trace, I am not able to produce them (at least not with a mere 48 volts main battery) and none of the scope traces from Ainslie that I can find, either in the papers or the video demo, seem to show any negative component on the battery traces. The final shape of the sampled power curve that I obtained is of course virtually identical to the shape of Ainslie's VV traces, with the expected smoothing due to the lower bandwidth, and of course the lower resolution caused by my manual sample rate of 18 samples per cycle, which is a mere 36 megasamples/second at the approx 2 MHz osc frequency.

Actually in my sims, I found that it was indeed the battery voltage trace that caused the negative power computation. As you measure closer and closer to the battery, the product gets less negative until finally you get a positive product when looking directly across the battery(s), assuming the superimposed oscillation drops to negligible levels.

No, I have not yet shown this, although I have done the measurement of course. Which of the 4 series batteries would you like to see measured in this way?

Pick any single battery that is most convenient for you. I wish to know how much superimposed oscillation there is (if any) when looking directly across the battery terminals. Of course with all other probes and FG connections removed.

[TinselKoala]

Tar Baby circuit schematic currently in use, with revised component inductances (until further notice!)  and the DC bias supply shown.