COIL ADVICE ?????

[daverave]

ive just started to use teflon multi strand wire 28 awg 19 strand and ive wound my coil and added several layers of teflon tape around the coil bundle very tightly then added one layer of spiral wrap...i have an inductance of around 350 uH........when i added the scotch 24 shield i did a capacitance test and it seemed on the high side of around 170 pf without any cable added.
Was i correct to wrap the coil bundle tightly with the teflon tape and is a reading of 170 pf capacitance too high ????? im trying to make a faster coil !!!!!!

[bbsailor]

ive just started to use teflon multi strand wire 28 awg 19 strand and ive wound my coil and added several layers of teflon tape around the coil bundle very tightly then added one layer of spiral wrap...i have an inductance of around 350 uH........when i added the scotch 24 shield i did a capacitance test and it seemed on the high side of around 170 pf without any cable added.
Was i correct to wrap the coil bundle tightly with the teflon tape and is a reading of 170 pf capacitance too high ????? im trying to make a faster coil !!!!!!

Dave,

What is the coil self resonance of the coil only with just Teflon tape on it? The spiral wrap should be PE not PVC to have the lowest dielectric. When you wrap the Scotch 24 only use a single layer with no electrical contact on the overlap around the cross section of the coil bundle. Use electrical tape to insulate any overlap to prevent currents being generated in the shield around the coil cross section. Scotch 24 as a mesh, has less surface area than a solid shield material. Try to use the self resonance test method as outlined in my Fast Coil article to calculate the capacitance from known inductance and known resonance. The scope probe should be on the lowest capacitance setting, usually the 10 setting. Adding a second layer of a PE, low dielectric material, will space the shield a little farther from the coil and help lower the coil to shield capacitance.

Post a photo of you coil and some physical measurements so I can better help you.

Joseph J. Rogowski

[daverave]

Hi Joseph...with my past coils ive always over lapped the scotch 24 mesh and i can see now that ive made an error doing this !!!! my coil loosly wound is lower inductance but when tightly wound is around 350 uH.......ive never done a coil self resonance test so i will have to try this.

[chemelec]

I tried this fast coil link, doesn't work.

http://geotech.thunting.com/cgi-bin/...oils/index.dat

[Altra]

Try this
http://www.geotech1.com/cgi-bin/page...e=projects.dat