Creating a coil for Vallon VMH3CS, need some support

[Thomas Weissbach]

Dear all
I have recently purchased a Vallon VMH3CS PI-detector from 2010. It works pretty well with the original small coil.
I am planning to make a 40cm/15inch coil for it.
I have read quite a lot about making coils here in the Forum, including the thread of the late Eric Foster, who created several coils for this detector.
Nontheless I still have some questions/doubts about it.
Maybe someone can help me out or has some tips.

The Vallon VMH3CS has a self test function, which at least verifies the resistance and seems to check the inductivity of the coil too. This means the coil specs must be as close to the original coil as possible.
The specs of members made coils that work range from around 3.5-4 Ohm and somewhere around 1.4-1.6mH.

Members used different materials, magnet wires or thin plated stranded copper wires for the winding, Scotch 24 and lead tape for the shielding (and some even no shielding).

I have checked through existing double layer ennamelled copper wires; to get close to the spec i could use:
20AWG, 42 windings, calculated 1.47mH, calculated wire resistance 1.79R, additional R in series 2R
21AWG, 41 windings, calculated 1.45mH, calculated wire resistance 2.22R, additional R in series1.5R
23AWG, 40 windings, claculated 1.5mH, calculated wire resistance 3.42R, additional R in series 0.2R

Calculations done with the coil64 app.

I have not yet checked for tin plated stranded copper wires (teflon or PVC), any proposals?

Thinner AWG wires are not usable because of the low resistance of the coil and the Vallon selftest function.


Concerning the shielding material of the coil, it is originally shielded with Scotch 24 (thin plated copper mesh) (according to Eric Fosters analyzes).
Eric shielded his coils with 0.1mm lead tape in some cases
Boths shielding materials are potentially detectable.
What material would be suggested as shielding today? I read about graphit paints etc.


Material for the coil housing; 3D Printed coils could be a solution (but honestly I have neither the knowledge nor the material to do it), since I can not find any supplier that produces round 40cm/15inch coil housings.
I also thought about using FOREX, that can be cut easily to any shape, glued, is very light and water tight, but has potential to be charged statically.
Does anyone have a proposal for a housing or supplier?

Thanks a lot for your replies and tips
Thomas

[GeoMax]

Hi,

there is a approx 60cm search coil for this detector from the manufacturer available. Maybe this is an option for you too.

[Thomas Weissbach]

Hello GeoMax
I know that Vallon produced a large UXO coil for the VMH3Cs, but this was long ago, in the meantime, the VMH4 is produced.
On the other hand, the prices of material developped for military, gouverments and other groups are way too high, it was according to my information in the thousands.
So this is no option. They also do not appear used.
Thanks for your answer anyways.
Thomas

[Carl-NC]

Looks like 23awg is about perfect, by the time you add the cable resistance you'll be right on target. As I recall, the Vallon isn't terribly sensitive to coil capacitance so you can likely use any wire you want. Simplest is PVC-insulated stranded wire. I would wrap it with plastic spiral wrap for a spacer and then use metallized fabric tape for shielding. No idea where to get a shell.

[Thomas Weissbach]

Hi Carl
thanks a lot for that feedback.
I already thought about using plywood for the coil in the meantime.
Thomas