COIL FORMULA

[strujas]

I couldn't b find wire thinner than 0.30mm how much turns of 0.30mm wire i need to wind for
L3 = 160mm
wire thickness = 0.23mm
turns = 176 / 177
inductance = 26.2mH / 26.5mH

[Qiaozhi]

I couldn't b find wire thinner than 0.30mm how much turns of 0.30mm wire i need to wind for
L3 = 160mm
wire thickness = 0.23mm
turns = 176 / 177
inductance = 26.2mH / 26.5mH

Strujas - I made a big mistake with my previous calculations. :o
In fact I'm surprised that no-one noticed.
Accidently I entered the diameter of each coil into the calculator instead of the radius. Here are the correct calculations:

L1 = 6.375" (162mm)
radius = 81mm
wire thickness = 0.36mm
turns = 85
inductance = 2.74mH

L2 = 3.937" (100mm)
radius = 50mm
wire thickness = 0.36mm
turns = 27
inductance = 0.17mH

L3 = 3.188" (81mm)
radius = 40.5mm
wire thickness = 0.23mm
turns = 275
inductance = 11.03mH

To wind a search coil with an L1 inside diameter of 320mm ->

L1 = 320mm
radius = 160mm
wire thickness = 0.36mm
turns = 54 / 55
inductance = 2.67mH / 2.76mH

L2 = 198mm
radius = 99mm
wire thickness = 0.36mm
turns = 17
inductance = 0.17mH

L3 = 160mm
radius = 80mm
wire thickness = 0.23mm
turns = 174 / 175
inductance = 10.95mH / 11.07mH

Increasing the wire thickness for L3 to 0.3mm gives:

turns = 177 / 178
inductance = 10.95mH / 11.07mH

Sorry about the original mistake.

Did the coil calculator not work ok for you?

[strujas]

I just wanted to check did I calculate right,,I had calculated with your coil c.... 179 - 180 windings and I had made a coil but she doesnt work(cant see coin more then 10cm distance,,instantaneously i cant to measure inductance of the coil,,,for few days I will be able to do that and i hope that i will find what is the problem,,,,,thanx for your time

[Qiaozhi]

I just wanted to check did I calculate right,,I had calculated with your coil c.... 179 - 180 windings and I had made a coil but she doesnt work(cant see coin more then 10cm distance,,instantaneously i cant to measure inductance of the coil,,,for few days I will be able to do that and i hope that i will find what is the problem,,,,,thanx for your time

Concentric coils can be quite tricky. The coil calculator will get you close to the values you want, but assembling the coils changes the inductance readings slightly. You have an even more difficult task here (particularly since you don't have an LCR meter) because the original dimensions have been scaled up. Even though making the coil larger does not change the ratio of the coil areas (L3/L1) you still have to do some final adjustment of the nulling coil L2 to achieve good balance. It's quite likely that this is the cause of the problem. This sort of thing is quite difficult to do without the right equipment.