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The wire to wire capacitance for your Teflon coated wire is about 35pf/meter. Now, your windings are not perfectly parallel so you have also some air between the windings. This reduces the capacitance because air is a better dielectric.
If you were to suspend the wires in the air, so as to have air instead of Teflon as insulation, the capacitance would only be 16pf/meter.
Another dielectric that is nearly as good as Teflon, is PP or Polypropylene. Now, if you were to take air and PP and make a foam with it that is 50% air, the dielectric would be somewhere between air and PP and even better than Teflon. They used to make Coax cable with such kind of foam.
So how can you use this information for coil making?
I have some 0.95mm diameter magnet wire and want to wind a new coil.
To get 35pf/m inter-winding capacitance, I would need to have about 2.5mm TFE (Teflon) insulation. That must be difficult to find.
So my solution is going to be PP+air, about 2mm, I think I will manage to get the capacitance down to about 25pf/m.
The coil diameter will be 280mm
Coil inductance about 300uH
Coil DC resistance about 0.4 Ohm
Then I hope to be able to sample at 3uS, with a coil current of about 1.2A.
Lets see if I can accomplish that.
Then I would like to have somebody to come up with signal amplitude measurements for 1" square alu foil to compare with.
All the best
Tinkerer
********************************************
I copied this thread over since it really belongs into the coil forum.
So now the coil is done, it did not quite come out as planned but I think the experiment was worth doing and the results do show some possibilities.
Below is a picture of the TX coil.
280mm outer diameter
0.8 Ohm DC resistance
23 turns #20 magnet wire with Polypropylene spacer
325uH inductance
Tinkerer
If you were to suspend the wires in the air, so as to have air instead of Teflon as insulation, the capacitance would only be 16pf/meter.
Another dielectric that is nearly as good as Teflon, is PP or Polypropylene. Now, if you were to take air and PP and make a foam with it that is 50% air, the dielectric would be somewhere between air and PP and even better than Teflon. They used to make Coax cable with such kind of foam.
So how can you use this information for coil making?
I have some 0.95mm diameter magnet wire and want to wind a new coil.
To get 35pf/m inter-winding capacitance, I would need to have about 2.5mm TFE (Teflon) insulation. That must be difficult to find.
So my solution is going to be PP+air, about 2mm, I think I will manage to get the capacitance down to about 25pf/m.
The coil diameter will be 280mm
Coil inductance about 300uH
Coil DC resistance about 0.4 Ohm
Then I hope to be able to sample at 3uS, with a coil current of about 1.2A.
Lets see if I can accomplish that.
Then I would like to have somebody to come up with signal amplitude measurements for 1" square alu foil to compare with.
All the best
Tinkerer
********************************************
I copied this thread over since it really belongs into the coil forum.
So now the coil is done, it did not quite come out as planned but I think the experiment was worth doing and the results do show some possibilities.
Below is a picture of the TX coil.
280mm outer diameter
0.8 Ohm DC resistance
23 turns #20 magnet wire with Polypropylene spacer
325uH inductance
Tinkerer
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