BTW, David Roberson and I have corresponded with Barry Kort about the claim that McKubre's measurements were as much as 3% in error due to presumption of constant current and average voltage between samples for calculation of average power. The claimed mis-measurement is attributed to the changing voltage due to the bubbles in the cell rapidly changing the cell resistance and hence cell voltage. Complicit in the argument is the inability of the power supply in constant current mode to adequately slew to keep up with the changes in resistance. Barry claims that reflections setup in the the connecting wires as transmission lines causes dissipation of the time varying component.
David and I both did simulations of this setup using SPICE analysis in transient simulation mode, which analyzes the circuit from first principles. In my simulation I used a model for a voltage source in a feedback configuration with a sense resistor to comprise a current source similar to how real power supply current sources are made. Finite slew rate of the voltage was introduced. A lossy transmission line was used between the source and a load resistor, that was modeled as having a sinusoidally varying resistance (+ a constant). The simulated results were compared to that of an ideal current source driving the same load. The instantaneous power waveform was computed in the simulation and its average was taken to get average power delivered by the source to the load. The simulation results confirmed that the use of the constant current value times the average voltage between samples accurately computes the average delivered power. The differences between the feedback power supply model and the ideal constant current source (the presumption) was on the order of ppm, possibly due to the slew effects of the source or just imperfect value for the constant current the power supply sets (due to offset). This ppm difference was far below other errors in any real measurement by McKubre. The "3%" figure for the error in the McKubre's measurements being attributed to use of constant current and average voltage to compute average power in the face of variations in cell resistance appears to be completely unfounded. Barry calculated his solution mathematically including the delta functions that arise from step changes in resistance. He did not go on to simulate his circuit as a check of his math; and I suspect there is an error in his math or in how he has setup his model. Bob Higgins
