Testing the TK Tar Baby

[Magluvin]

Hey TK

When you show that trace A, the lower one, is a reading of the battery, is the ground of the probe on the neg of the batt and the probe on the pos side of the battery?

Mags

[MileHigh]

TK:

A real quickie:  The LEDs of Doom test on the Altoids box.  It works fine with a single forward-biased LED so...

If you had a CVR waveform that showed significant negative current but only the forward-biased LED lit up that would at least be indicative of impending doom...

MileHigh

[TinselKoala]

Hey TK

When you show that trace A, the lower one, is a reading of the battery, is the ground of the probe on the neg of the batt and the probe on the pos side of the battery?

Mags

The schematic and the measuring points are as .99 posted. Yes, the grounds of both probes are at the same point. The positive lead of the battery channel is not directly at the positive battery terminal but is separated from it by 4.4 uH of inductance, to simulate the long leads and interbattery jumpers of the NERD device. (In every position on the schematic where 3.3 uH is specified I used 4.4 uH because of the availability of components.) The negative probe leads are similarly separated from the neg batt terminal. You can think of it as if the battery is separated by the inductors on both sides, simulating the long leads.

Remember, the Altoid demonstrator was designed to model the extra "stray" inductances of the NERD device in a smaller package. The same measurement "error"... that is, taking a contaminated measurement as the battery voltage .... is used in Altoid to make the same result as it does in NERD and Tar Baby: a major contribution to the negative mean power product.

[Magluvin]

Hey Tk

Im just wondering about the A trace of the batt.

Lets say you have your base line set. Is that 0v or is that set to show the 9v as a base line?

If 0v, then the 9v line is just above that? Or is the 9v up near the peak of the waveform?
Doest the battery trace A show any voltages above 9v? And is all the rest of the trace showing below 9v, as though the battery is being drained most of the time?

Because if you think about it, if the base line is 0v, or 9v, anything above the 9v level would be a higher voltage. And those higher voltages would mean that the battery is getting some charge at those times that the voltage is above 9v.

Im just not getting the idea of the negative part as being anything but a showing of the battery being drained hard, possibly through inductive forces.

If you can clear that up for me I would appreciate it. ;]

Mags

[TinselKoala]

Hey Tk

Im just wondering about the A trace of the batt.

Lets say you have your base line set. Is that 0v or is that set to show the 9v as a base line?

If 0v, then the 9v line is just above that? Or is the 9v up near the peak of the waveform?
Doest the battery trace A show any voltages above 9v? And is all the rest of the trace showing below 9v, as though the battery is being drained most of the time?

Because if you think about it, if the base line is 0v, or 9v, anything above the 9v level would be a higher voltage. And those higher voltages would mean that the battery is getting some charge at those times that the voltage is above 9v.

Im just not getting the idea of the negative part as being anything but a showing of the battery being drained hard, possibly through inductive forces.

If you can clear that up for me I would appreciate it. ;]

Mags

I generally give the baseline positions and values in the video or along with the screenshots. In the latter series which we have been discussing, the battery trace is shown at 20 volts per division, and when I ground the channel to show the baseline, that of course makes the scope show its "zero" volts position since the channel is shorted to ground.

The whole point of these exercises is to indicate that the "battery" trace as viewed on the scope using these probe positions and lack of filtering.... does _not_ actually indicate what is happening at the battery! The "battery" trace is telling you more about the inductances in the circuit than anything else. And this is true of the NERD measurements as well. I don't think the battery is being "drained hard" at any time by this circuit: the most real current I've seen is under 100 mA with the mosfet fully on.

Perhaps the scope shot below, which I posted earlier in the thread I thought, will help. I have indicated, as usual, the zero baseline level and the channel settings. This shot was taken with a weak battery, though; it only indicated about 7.9 volts no-load, IIRC. A fresh battery would make the frequency go up a little and raise the "average" of the battery trace wiggles up to near the nine-volt level, just below one half major division above the zero volt baseline.
The CVR in Altoid is one ohm, uncorrected for inductive reactance. So you can just read the current directly off the trace or multiply by whatever correction for the CVR inductance at around 2.5 MHz.