surfmaster PI

[solmer2]

Hi, I'm finishing my surfmaster PI and wonder if I can use another coil apart of the standar one. Using a coil calculator program I've checked the suggested coil (0.5mm thick. 23cm diameter 20 turns) and it gives me an inductance of 0.282 mH. I need to know if I can use another coil (bigger) if it gives me the same inductance.

Thanks in advance for the info.

good Luck and happy finds !!!!

[Majarit]

Hi Solmer

I think you need to do some other modifications if you want to use big coils.
Maybe you can find more information here. http://www.geotech1.com/forums/showthread.php?t=17115

I made several coils to test with the surf master and did not find much difference in performance with coils from 19 to 26 cm
also made a 40 cm coil but bad results on the standard surf master

saludos.

[Michel22]

Hello everyone,
I'll start soon wiring my Master Surfing with the pcb from Silverdog. About making the self, I wonder if it is really imperative to the shield or not.
Thank you for your answers

[WM6]

also made a 40 cm coil but bad results on the standard surf master

.

Probably you mean bad results in coin detecting? For coin detecting, coils of about 11" are optimal. 40cm and bigger coils are for bigger objects.

[Majarit]

Probably you mean bad results in coin detecting? For coin detecting, coils of about 11" are optimal. 40cm and bigger coils are for bigger objects.

Yes !! your right, bad results on coin detecting, but that is normal on such big coils.

but removing the "original" coil and just connect a big one didn`t give me good results on big objects. i know it depends on many things. i will keep testing

ciao

[bernte_one]

capacitators parallel to coil

Does it make sens to put some capacitator parallel to coil.
What is an good frequenzy for a surfmaster pi coil.

Example
Dia 300mm
Truns 30
wire 0.5mm
turn spacing 0
inductance 531 uH
capacitance 38pF (0.000038pF)
1120.421 kHz

if i change the capacitance to 0.1 uF i got 21 kHz and with 0.9uF i got 7 kHz on coil (gold spectrum)

or is this als false?

and the frequenzy is only made by the pi board?

http://deepfriedneon.com/tesla_frame6.html

[Qiaozhi]

Does it make sens to put some capacitator parallel to coil.
What is an good frequenzy for a surfmaster pi coil.

Example
Dia 300mm
Truns 30
wire 0.5mm
turn spacing 0
inductance 531 uH
capacitance 38pF (0.000038pF)
1120.421 kHz

if i change the capacitance to 0.1 uF i got 21 kHz and with 0.9uF i got 7 kHz on coil (gold spectrum)

or is this als false?

and the frequenzy is only made by the pi board?

http://deepfriedneon.com/tesla_frame6.html

No, it doesn't make sense.

You need the current in the coil at switch-off to be critically damped. If it is overdamped (damping resistor too low) the detector will lose sensitivity. If it is underdamped (damping resistor too high) the signal will oscillate, which will prevent you from sampling early enough. This will again reduce sensitivity. By adding a capacitor across the coil you will have the same effect as underdamping.

You seem to be getting confused between VLF and PI detectors. I suggest that you read up on PI theory to understand how this type of detector works. The Hammerhead article would be a good place to start.

[solmer2]

Thanks to everybody

I'll test some diferent coils before building the final one.

Thanks for the help