Smudge,
Here is the heart of our disagreement!
First, you claim that the differential voltage of 1.516v across C1 seen in ST7 SP1 is valid. I agree!
Next, you claim the voltage of 1.505v measured across Ct in ST7 SP2 is invalid if I understand you correctly. I am not saying it is an invalid measurement. What I am saying is that it is incorrect to claim that is the voltage across Ct. It is clear to me that you do not understand what effect a closed loop that encloses the flux can have on two different probe measurements as evidenced by your next remark. You also claim that the brown wire measurement is the opposite polarity shown and that voltage is the actual voltage across Ct. I wholeheartedly disagree!!! And I wholeheartily disagree with your disagree. Here's why. Look again at the ST7 P2 picture of the setup. The CH2(blu) probe is connected at the top of Ct with the ground wire connected to the bottom of Ct at 0v reference. Now please explain to me how that probe mean measurement of +1.505v could be anything else? And how could it possibly be negative? That measurement is quite correct. The top of the brown wire is also connected to the top of Ct again at a reference voltage of 1.505v mean. The bottom of the brown wire is open and measures -1.504v mean on CH3 with the ground at 0v reference. Therefore the magnitude of the voltage across the brown wire=|1.505|+|1.504|=|3.009| with the polarity at the top of Ct being more positive with the open end being more negative. And that is where we diverge in our undertanding. The voltage along the brown wire is zero because the voltage drive into the scope forms a closed circuit going from scope ground, up through Ct and down the brown wire. That does not enclose the flux, there is no induced voltage so the scope only sees whatever voltage is in Ct from some "external" current drive. (That is external to that particular scope measurement). In this case the current drive comes from the closed circuit that does enclose the flux which is Ct plus C1 in series around that loop. So CH3 is genuinely measuring the voltage across Ct. Your ground reference is of course a centre point of Ct and C1 in series then of course one scope channel reads positive and the other reads negative. These are actual measurements! I see no way of justifying your theoretical measurements! They are not theoretical, they are your measurements. We just disagree on the interpretation of those measurements. Here is another problem for your proposed values. Below is ST7 SP5 which shows the peak differential voltage measurement across C1 at 1.19us to be 2.412v and the average current of 2.41A flowing between Ct and C1 over 1.19us. We can then calculate the value of C1=di*dt/dV=2.41*1.19e-6/2.412=1.19uF which is close to the value of C1. The average 2.41A is flowing out of Ct into C1 not the reverse. And just as the current flowing out of the bottom of C1 is driving that end negative so that same current flowing out of the top end of Ct is making that end negative. Again, Ct is the 'charge separated' source supplying resonant current to C1. For that to happen (for current flowing out of the top of Ct to be a discharge) Ct would have to be already charged at the start of the current pulse. This is your supposed 'charge separated' source so how has that happened in advance of any flux appearing in the core? I honestly don't see how these measurements can be justified any other way!!! You have already agreed that you get the same measurements if you have a single turn driving Ct and C1 in series where neither are situated within the ring core hole. We would have no disagreement about interpretating those measurements, both capacitors get charged by that initial current pulse. Moving Ct within the hole does not change anything, both get charged. Take away your hypothetical 'charge separated source' and concentrate on the single turn driving two capacitors in series and there you have the justification. As you make that single turn ever smaller in length (so that one of the C's gradually gets drawn into the hole) makes no difference to the interpretation, it would only affect the self inductance of the wires and the AC ringing that occurs, but since you used whole cycle mean values that would not affect the result. Regards, Smudge
|