Norvic Posted March 2 Share Posted March 2 OK coil winders ??? Does the proximity/size of the shield influence the induction of the windings? and to what extent adds or takes away from value?... shield passive and active extent same or different? Link to comment Share on other sites More sharing options...
Chet Posted March 2 Author Share Posted March 2 1 hour ago, Norvic said: OK coil winders ??? Does the proximity/size of the shield influence the induction of the windings? and to what extent adds or takes away from value?... shield passive and active extent same or different? It does not change the inductance. It acts as an active fixed circuit capacitance that reduces outside variable capacitances caused by changes in height and conductivity of the soil as the coil moves over it. If the shield is too close to the windings it can add considerable capacitance to the circuit which lowers the frequency response and response to smaller nuggets. I try to space it around 0.25 inches with a graphite resistance of around 100 ohms per inch. I have seen some Minelab coils be as low as 50 ohms per inch. If you go that low I recommend a long thin unpainted gap to prevent a circular short circuit. The gap should start top center, across, down, back across the bottom to center. On size; I shield the entire coil. Large coils could be shielded around the winding areas with satisfactory results. Metallic conductive spray paints can be a problem and should not be used for metal detector shields. 1 1 Link to comment Share on other sites More sharing options...
Norvic Posted March 3 Share Posted March 3 OK if I go with 2x0.25" Divinycel, form the coil (spiral/flat) and fix and position on one half of the divinycel, adhere the 2 divinycel half's together then paint the shield top and bottom giving that 0.25" gap from windings. Recommended litz wire and shield paint too please Chet? 2 Link to comment Share on other sites More sharing options...
Chet Posted March 3 Author Share Posted March 3 1 hour ago, Norvic said: OK if I go with 2x0.25" Divinycel, form the coil (spiral/flat) and fix and position on one half of the divinycel, adhere the 2 divinycel half's together then paint the shield top and bottom giving that 0.25" gap from windings. Recommended litz wire and shield paint too please Chet? I have sent you a PM. 1 Link to comment Share on other sites More sharing options...
Aureous Posted March 3 Share Posted March 3 Flat wound coils benefit from a vacuum compression after winding....keeps the wire in place (look at the 6000 coils from beneath after removing the coil cover). This is a lot more effort and will require a vacuum forming machine to get it perfect. A minimum gap of 5mm from shield to wire is necessary. As Chet says, 100ohm per sq inch is a great ballpark figure, but can often be higher. Use graphite paint, not nickel spray....although it works, it can get bump sensitive. Litz can be problematic due to the enamel coating...its a bast*rd to remove efficiently to enable soldering. I use a Litz type wire that is not enameled but needs loom compression to lower resistance due to its different insulation thickness. Couple extra minutes of work but reduces the endless swearing & start-overs from a failed enamel removal. If you want the wire specs and where to buy, PM me @Norvic 1 1 Link to comment Share on other sites More sharing options...
Norvic Posted March 3 Share Posted March 3 Thank You Au, Chet will be PMing you so as we can share info 3 way. 1 Link to comment Share on other sites More sharing options...
Norvic Posted March 3 Share Posted March 3 Done PM sent AU. 1 Link to comment Share on other sites More sharing options...
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