Teflon Wire

[chemelec]

As a Favor for some stuff I did for them, A company in the USA sent me 2000 feet of 20 AWG, PTFE Coated wire.
(About 10 pounds of this wire)

The Surface has been Acid etched, So I can use Epoxy or whatever to glue it in place as is needed.

When I get back from my holiday, I will wind sme flat coils with it and see how they compare with the regular Enamel wire that I presently use.

Gary

[bbsailor]

Gary

What is the Outside Diameter of this AWG 20 Teflon wire?

Thanks

bbsailor

[KingJL]

Gary

What is the Outside Diameter of this AWG 20 Teflon wire?

Thanks

bbsailor

bbsailor
When you get the answer to the above, would you kindly let me know if this could make a good coil for a HH? Your recommendation for coil size would be well recieved!!

Thanks,
J. L. King

[chemelec]

Gary

What is the Outside Diameter of this AWG 20 Teflon wire?

Thanks

bbsailor

OD = .058 of an inch
Its a stranded wire inside
(18 strands of either a 32 or 33 AWG bare wire.)

[bbsailor]

Radial Teflon Coils

bbsailor
When you get the answer to the above, would you kindly let me know if this could make a good coil for a HH? Your recommendation for coil size would be well recieved!!

Thanks,
J. L. King

J. L. King

You can use this AWG 20 stranded, Teflon insulated wire to make a coil for the Hammerhead, but you could get by with using a much thinner Teflon insulated wire such as AWG 26 or 28 stranded or even AWG30 solid normally available on ebay.

The AWG20 will work, but it is heavier than thinner wire. You would need to add a series resistor to help increase the TX on current time constant. The optimum coil time constant (L/R) would be about 1/3 the maximum pulse width (PW) of the Hammerhead.

This type of wire is good for very large coils 3 to 6 ft in diameter with low pulse frequencies in the 100HZ range with pulse widths approaching 1000us.

If the Hammerhead has a maximum PW of 70us then you want the total coil resistance plus MOSFET on-resistance and any other series resistance (cable resistance, etc) to divide into a coil inductance of about 300uH to produce the result of 23us as a coil TC. This requires about a 13 ohm total resistance. That works out to about 5.1 ohms for an AWG 30 wire coil, plus 3 ohms for the MOSFET on-resistance, plus .2 ohms for the lead wire resistance, plus a 4.7 ohm series resistor to extend the coil TC. For some targets, however, you may not notice any change in sensitivity between a TX PW of 50us and 70us.

With this coil TC the current would raise to about 95% of maximum current (3 coil time constants) at the 70us PW setting.

The nice thing about PI mono coils is that almost any coil will work somewhat but matching the coil to the sampling time delay and other pulse parameters depends on what metal types and sizes of targets you are seeking.

Coils in the 10" to 12" range are good for coin sized objects and small gold jewlery. It is best to select the coil housing first and then build the coil to fit it. Hays Electonics has a good selection at a resonable price.

Another concern is shielding the coil to prevent it from being affected by the ground when lowered. Large coils with long delays can get away with no shield as the ground signal has decayed before the RX sample (main delay) is taken. As you reduce the main delay to respond to low conductivity objects like small gold, the having a shield becomes more important, and even the type of shield becomes important as the shield itself can become a target at low delays.

Gary likes to wind pancake/radial type PI coils because he can get more sensitivity out of them for one simple reason. This type of coil produces less induction and has less capacitance for an equal amount of wire compared to a bundle wound coil. A radial coil can use 20 to 25% more turns and be the same inductance as a similar size bundle wound coil. These few extra turns make the coil a little more sensitive.

The drawback to a radial wound coil is that shielding it becomes more difficult and the capacitance added by the large area of shielding tends to offset any sensitivity advantage for this type of coil arrangement. Without a shield, these coils have the least amount of capacitance and thus have the highest self resonance, potentially making them very fast coils. In some ground, these coils may even work without a shield.

So, this long winded answer gets down to: what do you want to optimize the coil design (meaning size, weight, and speed) to look for?

bbsailor

[KingJL]

J. L. King

You can use this AWG 20 stranded, Teflon insulated wire to make a coil for the Hammerhead, but you could get by with using a much thinner Teflon insulated wire such as AWG 26 or 28 stranded or even AWG30 solid normally available on ebay.

The AWG20 will work, but it is heavier than thinner wire. You would need to add a series resistor to help increase the TX on current time constant. The optimum coil time constant (L/R) would be about 1/3 the maximum pulse width (PW) of the Hammerhead.

This type of wire is good for very large coils 3 to 6 ft in diameter with low pulse frequencies in the 100HZ range with pulse widths approaching 1000us.

If the Hammerhead has a maximum PW of 70us then you want the total coil resistance plus MOSFET on-resistance and any other series resistance (cable resistance, etc) to divide into a coil inductance of about 300uH to produce the result of 23us as a coil TC. This requires about a 13 ohm total resistance. That works out to about 5.1 ohms for an AWG 30 wire coil, plus 3 ohms for the MOSFET on-resistance, plus .2 ohms for the lead wire resistance, plus a 4.7 ohm series resistor to extend the coil TC. For some targets, however, you may not notice any change in sensitivity between a TX PW of 50us and 70us.

With this coil TC the current would raise to about 95% of maximum current (3 coil time constants) at the 70us PW setting.

The nice thing about PI mono coils is that almost any coil will work somewhat but matching the coil to the sampling time delay and other pulse parameters depends on what metal types and sizes of targets you are seeking.

Coils in the 10" to 12" range are good for coin sized objects and small gold jewlery. It is best to select the coil housing first and then build the coil to fit it. Hays Electonics has a good selection at a resonable price.

Another concern is shielding the coil to prevent it from being affected by the ground when lowered. Large coils with long delays can get away with no shield as the ground signal has decayed before the RX sample (main delay) is taken. As you reduce the main delay to respond to low conductivity objects like small gold, the having a shield becomes more important, and even the type of shield becomes important as the shield itself can become a target at low delays.

Gary likes to wind pancake/radial type PI coils because he can get more sensitivity out of them for one simple reason. This type of coil produces less induction and has less capacitance for an equal amount of wire compared to a bundle wound coil. A radial coil can use 20 to 25% more turns and be the same inductance as a similar size bundle wound coil. These few extra turns make the coil a little more sensitive.

The drawback to a radial wound coil is that shielding it becomes more difficult and the capacitance added by the large area of shielding tends to offset any sensitivity advantage for this type of coil arrangement. Without a shield, these coils have the least amount of capacitance and thus have the highest self resonance, potentially making them very fast coils. In some ground, these coils may even work without a shield.

So, this long winded answer gets down to: what do you want to optimize the coil design (meaning size, weight, and speed) to look for?

bbsailor

I figured that I would be better off using the thiner wire, if only for the sake of weight. Just thought I would ask about this wire. I plan on using a little magic and pulse the HH with a series of 4 different pulses (only need three but the logic works better for 4) 30us, 60, 60, 200us (I may back down to 30,45,45,200). Does any of this change what you would suggest?

[Wirechief]

Good deal Gary and I will be watching for your results. I wonder if anyone thinks that a coil could be made for the Garrett Infinium? I don't think the 10x14 DD elliptical is very good. It doesn't seem to be very sensitive to small gold.

Hi BB how are you doing? I bet your staying busy. It has been awhile since I posted here. Ok happy coil building everyone!

John Tomlinson,CET

[chemelec]

Good deal Gary and I will be watching for your results. I wonder if anyone thinks that a coil could be made for the Garrett Infinium? I don't think the 10x14 DD elliptical is very good. It doesn't seem to be very sensitive to small gold.

Hi BB how are you doing? I bet your staying busy. It has been awhile since I posted here. Ok happy coil building everyone!

John Tomlinson,CET

Yes this wire is definately Heavier.

I wound a 400uH Radial coil with it today.
41 Turns of this 20 AWG Teflon wire
ID = 5 Inches OD = 9.75 Inches
"Q" Measured at 1khz on my "BK Precision 878" = 3.31
Free Air Resonance = 2.05 Mhz.
Weight after finishing with Epoxy = 220 Grams.

This weighs about Double my Normal 8 inch 400uh coil.

Compared to a 400uH coil with 20 AWG and a 5 inch ID, the OD would be about 8 inches.
And there is no significant inprovement in either the Q or the Interwire capacitance on the teflon coil.

But Compared to a 9.75 OD coil, there probably would be some improvement.
Sorry, Don't have one of that size to test now.

To bbSailor: As To Ground effects, I have never had any problems with my detector and coils.
So I never needed any shielding.

AnywayI will do some actual comparison testing When I get some time.

And after makin this coil, I agree that a smaller wire size would be more suitable, Especially for Weight.
But It was a one shot to get it and it was FREE including shipping to me.

Win Some, Lose Some, But its Fun Playing.
Take care.....Gary

[J_Player]

Which teflon wire?

I have a question about teflon wire for bbsailor or anyone else who knows the answer:
I can buy #30 teflon silver plated single strand wire-wrap wire, or a heavier stranded teflon wire. I am wondering if there is any advantage to using #28 stranded or larger to make a fast responding coil. The reason I ask is because I think the larger stranded wires may have thicker teflon insulation than wire-wrap wire, which would mean less capacitance in the coil because of better conductor separation. My objective is a fast coil, and the price of the wire-wrap wire is good.

Which should I buy? The thicker stranded wire or the wire wrap wire?

Best wishes,
J_P

[Carl-NC]

I just bought 500ft of #30 teflon hookup, but it's mostly for a specialty low-power PI I'm working on. For a GP PI, I would probably go with #26-28 stranded. However, I intend to try my #30 on an IB-PI coil, it might be a whole lot better than the #26 magnet wire I usually use.

- Carl

[bbsailor]

J Player,

If you use stranded Teflon insulated wire, do not use silver plated stranded wire as it is too conductive and does not break up the eddy currents generated in the wire like tin plated stranded wire does. Silver plated single conductor AWG30 is OK and will make a coil around 5 ohms resistance.

If you plan on making any DD coils with the Teflon wire, make sure that the wire bundle will fit into the coil housing at the crossover points. Example: AWG24 stranded Teflon has 19 Strands of AWG36 wire and is .053" OD. This would make a 19 or 20 turn coil bundle of .265" and with the shield spacer would make the wire bundle about .33" and with the shield about .37". This wire might not fit as a DD coil in a DD coil housing. As a mono coil, it is OK.

Using Teflon AWG 28 tin plated stranded will make a fast mono or DD coil. The slight benefits of using Teflon AWG28 stranded over Teflon AWG30 single strand will not show up until you get below about 7uS.

bbsailor

[J_Player]

Thank you for the replies, Carl and bbsailor.
I think I will get a small assortment of teflon wire for experimenting. The AWG 30 wire could be good for winding probes and other medium/low power applications. I doubt magnet wire could work as well no matter how thin the teflon insulation is.

More questions for bbsailor:
1. What kind of coil wire gave you the fastest response? How many uS were you able to shorten the delay to with your fastest wire?
2. How are eddy currents broken up in tin plated stranded wire? Are these eddy currents traveling from strand to strand, and require a less conductive surface coating to limit their strength? Does this mean a single strand wire cannot have these same eddy currents?
3. What disadvantage will I see with single strand AWG30 teflon wire when I try to set the delay under 7 uS? Capacitance or eddy current limitations maybe?

Best wishes,
J_P

[J_Player]

Hi bbsailor,
I just read your treatise on coil winding in the metal detector section of Geotech. It pretty much answers my questions unless you have something more to add.

Thanks for the help
Best wishes,
J_P

[baum7154]

Cheap Teflon solid copper wire source

I have not seen this source for untinned solid copper Teflon wire listed anywhere on this forum. After seeing all kinds of silver plated stranded teflon wire on EBAY I recently stumbled upon CAT5 and CAT6 PLENUM RATED cable. This cable is typically composed of several twisted pairs of 23 or 24 awg plain copper wire and is usually Teflon insulated. The Superior Essex brand of 77-240-2B cable lists it's wire insulation as FEP, a Dupont designator for one of it's teflon products.

The downside of using this wire is that you have to strip the outer sheath and untwist the inner pairs from each other. The the cable does come with a nylon sheath stripper thread with the wires so stripping the sheath is not difficult. The inner core can be unwound with a cordless drill by clamping one end of the wire bundle to a table or vise and the other end pinched in the drill chuck. Gently pull the bundle taut and set the chuck to unwind the bundle and you will eventually have 4 sets of twisted pairs colored Blue, Orange, Green, and Brown.

Once again you can unwind each of these twisted pairs using the cordless drill. In the end you will have 8 each 23awg teflon insulated solid copper wires. If you want to straighten the slight twisting ripple from the wires you can weave and pull them through a set of 4 to 6 nails clamped in a vise jaw and set about a 1/2 inch apart. They are woven through the nails much the same as a skier goes through slalom gates.

A 75' piece of this cable will yield about 600' of this wire.

Have fun!

Dan