Hi All, I made some extreme low voltage measurements: Feed Meas. Integer Vsec Vpri Ratio ----- ----- ----- 120.2 684mV 176 110.5 625mV 177 100.7 565mV 178 090.1 502mV 180 080.5 445mV 181 070.5 386mV 183 060.1 326mV 184 050.4 271mV 186 040.6 216mV 188 030.1 158mV 190 020.1 104mV 193 010.2 52.5mV 195 ** 008.15 42.1mV 194 ** 006.06 31.1mV 195 ** 004.02 20.6mV 195 ** 002.106 10.8mV 195 ** 001.069 5.5mV 194 ** This data presents some obvious questions.When I managed a low enough level (10V down to 1V), the voltage ratio showed about 195 consistently (what was affecting the voltage ratio seems to have stopped). Did I manage to get below shunt inductance influence? Is it possible the turns ratio is 200, yet the voltage ratio is entirely something different thanks to the shunts at greater voltages (and the manufacturers account for this in their Voc rating)?
My measured output at 120.2V input was 16390 which is a voltage ratio of 136 (not 125 as spec'd). Voltage ratios and assumed turn ratios are very different. There is now no doubt about that, but still, how to determine the real turns ratio is a mystery (and maybe not possible?).
Bart bartb wrote:
Hi Dave,Yes, I agree. The magnetic shunts are causing the non-linearity. As I mentioned a moment ago in my reply to Phil, the voltage ratio is non-linear because of this. Were trying to use the voltage ratio to determine turns ratio. This won't work "IF" the shunts have influence because it affects the voltage ratio. I think everyone measuring is seeing this affect.The problem I have is the inductance factor is based on the turns ratio. So, how to remove shunt influence? The only way I can think of is to use "extreme" low voltages. Maybe instead of inserting 120Vac to the secondary, we need to bring down the voltage to something between 1 and 10V input to the secondary and measure the millivolts at the primary? There must be a point at which the shunts have little affect and the voltage ratio becomes linear enough for a decent approximation.Take care, Bart sparktron01@xxxxxxxxxxx wrote:Bart Is it possible that the inductance varying is hosing the apple cart? Instanteous voltage for an inductor (complete) is: V = iR + L (di/dt) + i (dL/dt) The last term in "linear" circuits tends to zero and (usually) has no bearing on circuit. But with a magnetically shunted circuit the third term starts influencing the second, and vice versa (i.e the whole circuit becomes VERY non-linear...) Regards Dave Sharpe, TCBOR/HEAS Chesterfield, VA. US
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