curious question on a ready made coil

[darrenk]

I have a donor machine and after 1 hour taking the casing off with a stanley knife (all other attempts failed with heat gun, hot water) damn good glue

the question is, would it be possible to use the outer coil and eliminate the inner one for the surf pi, this coil is from an md-3009 seben

[joop]

It's a different type of coil, which you can't use for the surf-pi. To make sure measure the coil's resistance. For the surf-pi it should be in the order of 1 ohm.

[kt315]

yes. your way is good. measure inductivity of the TX coil and write pls.

[Qiaozhi]

It depends on the inductance of the outer TX coil. It will need to be somewhere around 300uH to 500uH (which is unlikely) so I suspect the answer will be "no" in this case.

[kt315]

I do not know all details but last newest detectors of Eric Foster working on 10000 pps have a coil with big inductivity and big resistance. I suspect the answer will be yes very unhesitatingly.

good luck

[darrenk]

As you can tell this is my first build, I have tested the outer coil and it settled to 19.5ohms, so going off what has been said it looks like a no go for this coil

after trying some coaxil cable, the amount of cable I can wrap inside still gives me 10.5, I can get as low as 5.5 with two wraps at approx 46"

either that or my meter is playing up

anyone know what would be a good cable to use, I have checked a post by sven, and rather than using the single core coaxil, use multi strand at about 36" in length

Going off these, not sure which is the best cable for an 8" casing

Size Shape Turns Wire size Inductance Resistance
Ø 120 mm Round 36 Ø 0.40 mm / 0.14 mm2 405 µH 1.9 Ohm
Ø 150 mm Round 31 Ø 0.40 mm / 0.14 mm2 394 µH 2.0 Ohm
Ø 175 mm Round 28 Ø 0.40 mm / 0.14 mm2 387 µH 2.1 Ohm
Ø 200 mm Round 26 Ø 0.40 mm / 0.14 mm2 406 µH 2.2 Ohm
Ø 250 mm Round 22 Ø 0.40 mm / 0.14 mm2 380 µH 2.3 Ohm
Ø 300 mm Round 20 Ø 0.50 mm / 0.20 mm2 390 µH 1.6 Ohm
Ø 400 mm Round 17 Ø 0.50 mm / 0.20 mm2 396 µH 1.8 Ohm
Ø 500 mm Round 15 Ø 0.50 mm / 0.20 mm2 400 µH 2.0 Ohm

[darrenk]

damn cheap multimeters, have dug out the decent one, the readings above are wrong by a long shot

The outer coil is giving a reading of 4.7 ohm

the inner coil is giving a reading of 2.7 ohm

so it should be possible just to unwind some of the outer coil, the inner has been removed alltogether

am I on the right tracks you guru's?

not sure if sven gets on here, but have had some help regarding multistrand coaxil cable, but wondering if the above theory would work

[kt315]

you are on the right way. look my post #107 and will see a cable you need.
http://www.geotech1.com/forums/showthread.php?14973-DEEPERS&p=167795#post167795

good luck

[darrenk]

cheers kt315, I am concentrating on finishing the board off then will get around to the coil, just thought I would test the water and see what people have done, and what cable they have used, I'm a virgin at this building from scratch malarkey

[darrenk]

unwound just over half of the outer coil, with 1.2ohm and works ok, but may try audio cable or microphone cable to test different results on depth