Quote from: TinselKoala on April 15, 2017, 07:24:04 PM
But you will get very very small interturn capacitance that way because the conductors are too far apart, even in the finest plastic insulated speaker wire. As you have pointed out, the interturn capacitance is small anyway, even with close-wound enamel insulated magnet wire.

ETA: I just saw Mags's result so maybe. That's a lot of capacitance he reports with his plastic-insulated wire with relatively large interconductor spacing. I get 2.19 nF with the bifilar pancake coil I showed in the first DC resistance test video (between disconnected files) which has 58+58 turns of #27 magnet wire and 661 microHenry when files are serially connected in the TBF manner.  My calculator predicts a resonant frequency of 132 kHz for those values. We shall see, got to take dog to dogpark now.

I picked the wire for this some time ago when a RS store was going down for the count. was 29 bux and got 60%off so it was a no brainer. The flatness of the copper should give more surface area proximity than round wire per turn, that was my inspiration for going flat, to increase the capacitance.  Like imagine say 1in wide copper tape or even wider. A nice increase in both capacitance and induction in a similar sized dia with a thin insulation layer between turns.

I feel good with the outcome of the capacitance and the inductance. I was also happy with the 85khz as it clearly shows a decent amount of inductance and capacitance to not only go lower than the mhz range, but i wasnt expecting below 100khz. How many ohms is the series total on your coil?

Mags

Quote from: Magluvin on April 15, 2017, 12:33:32 PM
Nice. Can you show a closeup of the wire? I was just talking about square wire. Also could you measure the capacitance between the windings? Separated of course not in series connection. Just interested to see what you get.with that wire with more close proximity surface area.  Its gota be more than conrad had with the insulation and round wire. Not putting his effort down, just to see if you get better capacitance with what you got.

Mags

The wire used is from the primary of an old arc welder.
The wire is Ali-not copper.

So,wire size is 2mm x 3.5mm
I have the flat sides(3.5mm) wound against each other-->wire wound vertical you could say.

Values measured for bifilar coil

Capacitance value between the two windings is 1.22nF

Inductance value=EDIT=.06nH

Resistance(with series connection back in place)=.1 ohms

Picture of wire/remains of primary coil below.


Brad

So,when we say!self resonant frequency!,do we simply keep raising the frequency until maximum voltage amplitude is reached across the coil?

If so,who can calculate what mine should be,using the values given in my last post?.


Brad

Quote from: tinman on April 15, 2017, 08:52:09 PM
The wire used is from the primary of an old arc welder.
The wire is Ali-not copper.

So,wire size is 2mm x 3.5mm
I have the flat sides(3.5mm) wound against each other-->wire wound vertical you could say.

Values measured for bifilar coil

Capacitance value between the two windings is 1.22nF

Inductance value=.02nH

Resistance(with series connection back in place)=.1 ohms

Picture of wire/remains of primary coil below.


Brad

I get 1.02ghz.

Are you sure on that resistance of .1ohm? Just that I have 100ft of 14ga and it is .25ohm.  Just really looks like some stout wire there and fewer turns than 55 or so i have.

Mags

Quote from: tinman on April 15, 2017, 08:57:21 PM
So,when we say!self resonant frequency!,do we simply keep raising the frequency until maximum voltage amplitude is reached across the coil?

If so,who can calculate what mine should be,using the values given in my last post?.


Brad

yeah you can do a freq sweep to find it. I use circuit sim to do simple tests like these to help find the freq with very good results. Thats how i found the 1.02ghz for u. it should be right on or close enough to find the area, just incase there is a slight discrepancy in a component value reading that could throw of the sim a bit if the values are not dead on. I like that sim. Simple stuff can be checked quick and reliably. The default circuit is an rlc so i just plug the values and apply power then disconnect and it rings and the res freq result is at the bottom right of the screen.

Mags