How to make the best coil.

[detectormods]

There are a few things that by design and testing stand out in making a very efficient pulse induction detector coil, litze wire where each strand is insulated by a low dielectric varnish or resin type material, this reduces strand to strand capacitance, the same goes for wire bundle insulation, air spacing with polypropylene micro sleeving insulators spaced out reduces the wind to wind capacitance and the critical separation of each wind for optimum magnetic coupling is 0.3 the wire bundle diameter, but the most critical of all is the shielding, just about every manufacturer mucks up the shielding, for the last 20 years the shielding has not really changed and is the absolute downfall of current coil designs.

[Carl-NC]

What is your suggestion for shielding?

[detectormods]

What is your suggestion for shielding?

You know that is if i spell it out every manufacturer will have that light bulb moment, but why not, anyone that has the most basic understanding of transformer theory would know that a complete encapsulation of a coil by way of carbon paint or other conductive medium would create a shorted turn, i wonder what happens when fringe return energy is reduced by a resistive shorted turn. Most of these coatings are 80 ohms per inch, causing a resistive shorted turn.

[David_1]

I dont know what it is, can you share ?

[detectormods]

I dont know what it is, can you share ?

I can, but this will be used by every coil manufacturer, I will make a video and stick it up on YouTube.

[Gwil]

It seems to me that as you intend to put your scheme into the public domain via Youtube, there is nothing to stop you revealing it here. Or am I wrong?

[Carl-NC]

I suspect the coil companies know the secrets to making better coils but there are other considerations like cost and whether a better coil makes a better detector. If the detector is designed for a minimum delay of 10us then making the extra effort to get the coil to perform down to 5us doesn't make sense. Detector companies also have to weigh the trade-offs. Ferinstance, the TDI was always designed to run a minimum of 10us and so they applied a spray-on carbon paint to the inside of the coil housing, and with no gap to prevent eddies. It worked well enough and fit into the manufacturing flow already established. But the intent with the Impulse AQ & Gold was to have a minimum delay as low as 3-4us, so the coils are hand-wrapped with conductive tape on top of a spacer, much slower and expensive than the carbon paint but necessary to achieve the delay.

BTW, put an Impulse coil on a TDI and the TDI can instantly run down to 6us. And at White's we knew how to make a faster coil, I was building lab coils with wrapped shielding and had intended to use that in production on the next model that never got finished. We also knew about Litz and wire spacing and crossover angles and solder joints and the like. But if you have some tricks to share, I'm eager to learn.

[detectormods]

I suspect the coil companies know the secrets to making better coils but there are other considerations like cost and whether a better coil makes a better detector. If the detector is designed for a minimum delay of 10us then making the extra effort to get the coil to perform down to 5us doesn't make sense. Detector companies also have to weigh the trade-offs. Ferinstance, the TDI was always designed to run a minimum of 10us and so they applied a spray-on carbon paint to the inside of the coil housing, and with no gap to prevent eddies. It worked well enough and fit into the manufacturing flow already established. But the intent with the Impulse AQ & Gold was to have a minimum delay as low as 3-4us, so the coils are hand-wrapped with conductive tape on top of a spacer, much slower and expensive than the carbon paint but necessary to achieve the delay.

BTW, put an Impulse coil on a TDI and the TDI can instantly run down to 6us. And at White's we knew how to make a faster coil, I was building lab coils with wrapped shielding and had intended to use that in production on the next model that never got finished. We also knew about Litz and wire spacing and crossover angles and solder joints and the like. But if you have some tricks to share, I'm eager to learn.

I remember a conversation that i had with Minelab’s international sales manager going back some years, i asked why their coils seemed to lack innovation in regards to some technical aspects that i had pointed out, his reply was this “ we are a detector company, not a coil company” anyway, i am going out to make some videos today on the newest upgrades on the GPX series of detectors, when i get back i will set up a lab experiment and video it, then i can show the before and after effects on changes to the carbon based shielding.

[David_1]

I do not want to dilute the conversation away from better coils, but can I ask for direction on what to read to learn about faster coils please

[detectormods]

I do not want to dilute the conversation away from better coils, but can I ask for direction on what to read to learn about faster coils please

Read this for starters, https://docshare.tips/fast-coil_5750...61d8b4aa7.html

[RH-Lightning]

But the intent with the Impulse AQ & Gold was to have a minimum delay as low as 3-4us, so the coils are hand-wrapped with conductive tape on top of a spacer, much slower and expensive than the carbon paint but necessary to achieve the delay.

Hello Carl,

Do you by chance recall the type of conductive tape? Was it a fabric or copper type?

[Stevedbk]

I am still very much in the experimental stages of PI detectors, but my pulse times appear to be short.
At this time I am using a parallel wire twin similar to 300 ohm tv ribbon wrapped around the shaft. If this is balanced ie equal turns around the shaft is it a viable option or will earth field, radio etc interfere with it?
I am using a 280mm 300uH coil made from recycled cat5 wire with a 3mm spaced foam shield and wrapped with a strip of emi interference cloth.
Steve

[Carl-NC]

Do you by chance recall the type of conductive tape? Was it a fabric or copper type?

It's the same stuff mentioned on a lot of threads here, 3M 2191FR or equivalent. Off-brand is cheaper and easily found on Amazon, eBay, and AliExpress. Search for "Faraday tape" with maybe 'fabric' and 'nickel'.

[Carl-NC]

At this time I am using a parallel wire twin similar to 300 ohm tv ribbon wrapped around the shaft. If this is balanced ie equal turns around the shaft is it a viable option or will earth field, radio etc interfere with it?

300 ohms will have low capacitance (good) but without any shielding may be more susceptible to EMI.

[RH-Lightning]

Search for "Faraday tape" with maybe 'fabric' and 'nickel'.

thanks, that's what I thought.