John Warren Posted May 31, 2003 Share Posted May 31, 2003 Al- Proximity effects are dominating at 6kHz and looking at the graph I posted a foil will buy you little at 6kHz. I'd like to see how Q changes as a function of frequency from 6kHz to say 20kHz. An interesting chart would be Q vs. frequency for a fixed AWG. Have you taken measurements at higher frequencies? Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted May 31, 2003 Share Posted May 31, 2003 John, A curve of Q versus frequency is a good idea. Here's what I measure on a Solen L14.18 which is .18 mHy of #14 Litz wire: Freq, Q 1000, 9.4 2000, 18.2 3000, 26.7 4000, 32.5 5000, 38 6000, 41.7 10KHz, 46 15KHz, 46 20KHz, 37 25KHz, 36 The readings above 10KHz are not very accurate, but it does look like the Q peaks out at around 15 KHz. Al K. Quote Link to comment Share on other sites More sharing options...
John Warren Posted May 31, 2003 Share Posted May 31, 2003 Al- Good! The peak is a resonance mode set up in the inductor (you likely know more about it than I do) associated with skin effect. It looks like it is between 10-15kHz. Note that signals in this range passing thru the inductor will be distorted. The distortion harmonic distortion. This peak is absent in foils until much higher frequencies. We now want the same set of data points for the 14AWG foils. At what frequency the foil crosses the Litz response can only be determined by experiment. John Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted May 31, 2003 Share Posted May 31, 2003 JOHN, NO! The self resonance of an inductor is the resonance of its inductance with it's distributed capapcity. Skin effect is not a factor! It will be lower with a litz inductor than with foil inductor but will sill be well above 20 KHz. I started to measure distributed capacity when I did the "great inductor face-off" but didn't include it becasue it was irrelavant. Al K. Adendum: I just tried to measure the self resonance of the .18 mHy coil. It is well ABOVE 600 Khz. It resonates with a 3000 pF cap at about 220 KHz indicating it has to self-resonate higher than that. My signal generator goes up to 600 Khz and no resonance was found there or below. Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 1, 2003 Share Posted June 1, 2003 Let me clarify. I plotted the response and saw what I thought was a slope change at about 6kHz. It looks like it then continues along a new slope to about 10kHz and then peaked after. I attributted that to skin effect. I'm extracting too much from the data. I agree with you the peak occurs for stray capacitance reasons, not skin effect. I want to see the same plot for the 14AWG foil superimposed. The reason why I'm asking is that I've seen a plot with Litz, standard and foil and foil had higher Q above ~10kHz. It was published on a a KEF *white* paper which I know I still have here. Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted June 1, 2003 Share Posted June 1, 2003 John, If you made your plot using the data I posted yesterday, DON'T! The accuracy of the data above 10 KHz is only approximate. The D-Q scale on my impedance bridge is very crude between 500 and 1000. In fact there is no graduations at all between them! I have to divide the reading by (1000 / Khz) to get the Q when I am above 1000 Hz. The higher the frequency gets the lower the accuracy, so you can't trust the slope of the curve versus frequency AT ALL! To make matters eve worse, the pot is a bit dirty up that high making the readings tricky. Al K. Quote Link to comment Share on other sites More sharing options...
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