Any Advantage to low resistance in PI coils?

[Silver Dollar]

I have a collection of various PI coils I have built. I have a few PI detectors but none are
completed yet (soon to be rectified). I plan to limit the current in the coil with a resistor
in series so does the resistance of the coil matter that much?

Here are my coils with the data I have collected so far;

12"x9" Bigfoot W / 60/46 Litz 5.8 ohms 290 - 300 uh


10" Blue Wire Wrap Wire 30 AWG Solid Silver 2.8 Ohms 410 uh
10" Natural Degauss Coil 1.8 Ohms 300 uh
10" Red RS Wire 26 AWG Wrap Wire 5.3 ohms 330 - 340 uh
10" Centronics 25T Cable 4.2 ohms 460 uh
10" Round W/Gray 24 AWG Wire 1.58 ohms 290 - 300 uh


7 1/2" Basket Coil Red White 24 AWG Wire 1.74 ohms 300 - 310 uh


6" Top Hat W / 60/46 Litz Wire 4 ohms 440 uh

Notice my choice of Litz was poor as it has more resistance than 30 AWG wire wrap wire!

I plan to do some experiments with these to see how they perform. To check the speed of them
I can just run a PI transmitter (with coil) nearby and scope across the test coil to see the ring down?

[Silver Dollar]

Hmm I did find this quote "But since we generally try to minimize the PI coil's winding resistance, I guess that's shooting for hi-Q."

So I guess low Resistance is better for a PI coil....

[CAS]

My understanding of PI coils (limited as it is) is that coil capacitance is the important factor. I think that a little higher resistance is fine if the capacitance is lower.

[Carl-NC]

Some designs (TDI & Goldscan) add a series resistor to the coil to make it settle faster during turn-on, at the expense of peak current. Other designs (GPX series) minimize series resistance to maintain a ramp current waveform regardless of pulse width. It just depends on what youre trying to accomplish.

[baum7154]

I have a collection of various PI coils I have built. I have a few PI detectors but none are
completed yet (soon to be rectified). I plan to limit the current in the coil with a resistor
in series so does the resistance of the coil matter that much?

Here are my coils with the data I have collected so far;

12"x9" Bigfoot W / 60/46 Litz 5.8 ohms 290 - 300 uh


10" Blue Wire Wrap Wire 30 AWG Solid Silver 2.8 Ohms 410 uh
10" Natural Degauss Coil 1.8 Ohms 300 uh
10" Red RS Wire 26 AWG Wrap Wire 5.3 ohms 330 - 340 uh
10" Centronics 25T Cable 4.2 ohms 460 uh
10" Round W/Gray 24 AWG Wire 1.58 ohms 290 - 300 uh


7 1/2" Basket Coil Red White 24 AWG Wire 1.74 ohms 300 - 310 uh


6" Top Hat W / 60/46 Litz Wire 4 ohms 440 uh

Notice my choice of Litz was poor as it has more resistance than 30 AWG wire wrap wire!

I plan to do some experiments with these to see how they perform. To check the speed of them
I can just run a PI transmitter (with coil) nearby and scope across the test coil to see the ring down?

--------------------------------------------

Your 7 1/2" basket coil at 1.74 ohms, 24AWG (TEFLON??) wire and 310uh should be right in the wheelhouse for small gold on
your CHANCE PI once you get it running. CHANCE is originally designed for 400uh and 1.7 ohms but that coil would not work for me on small gold.

Regards,

Dan

[Silver Dollar]

Yes the basket is Teflon and should be fast. I was disappointed with the litz. I might
get some more with more strands and do a dual concentric coil in the bigfoot case.
The 10" gray looks like a good coil too. I know that insulation is pvc but need to check
the frequency to see how good it really is!