On 30/8/2012 18:47, Andreas Hahn wrote:
How do you accurately measure the current in the secondary's ground wire? My current method suggests my secondary is putting 2800 amps into my RF ground, which seems a tad high for a coil powered by a two amp transformer.A current transformer connected in this way produces an output mostly porportional to the derivative of the current, not proportional to the current, and with so many turns the transformer is probably full of parasitic elements. Correct measurement can be obtained by using as load to the transformer a series RC circuit, and measuring the voltage over the capacitor, that adds an integration to compensate the derivative. The connection has a band-pass characteristic that is flat over a large range of frequencies, and can easily be calibrated as you did. Typical values are at most tens of turns in the toroid, capacitor in the nF range, resistor in the hundreds of ohms. The values given seem strange. Too many turns in the toroid, too small sensitivity, too high resonance frequency.Here's what I'm doing right now.I wound ~110 turns on an FT 50-77 ferrite toroid (rated to a few megahertz) and calibrated it at 2mV/mA with 14.7k ohms of resistance between the output leads, using my signal generator to put some current into a 1 ohm resistor via a wire through the center of the toroid.Feeding the ground wire from my secondary through the center of the newly-minted CT and turning on the coil, I put my oscilloscope probe across the 14.7k ohm resistor (actually a 10k and 4.7k in series) and fired up the coil.The result is a nice 5.6V peak-to-peak sine wave at the ~500kHz resonant frequency of my secondary...(I just calibrated my 'scope this morning, too...)
Antonio Carlos M. de Queiroz _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla