Cylinder Coils?

[Tinkerer]

MiscEl.zip

this app is old and does not update anymore, but it is very useful.

[Nova]

Tinkerer, yeah that would be good for us newbies for sure.
BUT, i keep hearing about how coils can be made better than what's mass produced, all you who are experienced in making your own coils, have you done extensive testing against these mass produced coils?
Let's say you build a 14in mono coil , you have multiple companies that have/had made this version coil, so to really prove your homemade coil is superior i would say you would need to test against at least 3 other versions and if your coil beats all 3 then average out that extra depth.
In my mind to be a worthwhile pursuit, i would expect a minimum of 4-6 inches better depth on a coin sized object, have you done these tests or has anyone else?, if not, then by what reasoning are these coils "better"?

[Carl-NC]

In my mind to be a worthwhile pursuit, i would expect a minimum of 4-6 inches better depth on a coin sized object

Wow, that's rather optimistic. I'd be OK with 1 extra inch.

[Nova]

Damn Carl you are the optimum inspirationalist LOL!!! 1inch? no chunk is safe now, lookout goldfields i'm coming for you, with the extra inch i'm going to clean you out, i'm comin just you wait...................

[Eddy71]

https://coil32.net/online-calculators.html

Best selection of inductor calculators

[GeoMax]

https://coil32.net/online-calculators.html

Best selection of inductor calculators

There is also a fantastic coil calculator available for download on the same website suggested by Eddy71.

[Tinkerer]

Tinkerer, yeah that would be good for us newbies for sure.
BUT, i keep hearing about how coils can be made better than what's mass produced, all you who are experienced in making your own coils, have you done extensive testing against these mass produced coils?
Let's say you build a 14in mono coil , you have multiple companies that have/had made this version coil, so to really prove your homemade coil is superior i would say you would need to test against at least 3 other versions and if your coil beats all 3 then average out that extra depth.
In my mind to be a worthwhile pursuit, i would expect a minimum of 4-6 inches better depth on a coin sized object, have you done these tests or has anyone else?, if not, then by what reasoning are these coils "better"?

If you look at it like that, I say: Just buy a Minelab detector and use a Minelab coil.

Why?
For some of us it is different. We enjoy tinkering with electronics. Usually it starts like that:
Phase 1:
We assemble a kit or repair a simple fault on a detector. It works. That makes us feel good. After a few like this, it becomes routine, kind of boring.
Phase 2:
We try to build a whole detector from a schematic. It is a challenge. When we get it working, we feel joy and satisfaction.
Phase 3:
We design our own detector and build it. After many trials and immense difficulties, vast amount of work and tribulations, we got it working. It does what we wanted. We find the first nugget or coin or unique relic with our own creation. Now we burst of joy. We feel on top of the world. The satisfaction is profound. We feel accomplished, alive. There are no more limits. The elation is such, that we feel that life is so good that it could not get any better.

Is that the end of it? Not by a long way. It is just the beginning. The real life is only starting.

[Tinkerer]

https://coil32.net/online-calculators.html

Best selection of inductor calculators

Thank you Eddy71, excellent link.

[bbsailor]

If you look at it like that, I say: Just buy a Minelab detector and use a Minelab coil.

Why?
For some of us it is different. We enjoy tinkering with electronics. Usually it starts like that:
Phase 1:
We assemble a kit or repair a simple fault on a detector. It works. That makes us feel good. After a few like this, it becomes routine, kind of boring.
Phase 2:
We try to build a whole detector from a schematic. It is a challenge. When we get it working, we feel joy and satisfaction.
Phase 3:
We design our own detector and build it. After many trials and immense difficulties, vast amount of work and tribulations, we got it working. It does what we wanted. We find the first nugget or coin or unique relic with our own creation. Now we burst of joy. We feel on top of the world. The satisfaction is profound. We feel accomplished, alive. There are no more limits. The elation is such, that we feel that life is so good that it could not get any better.

Is that the end of it? Not by a long way. It is just the beginning. The real life is only starting.

Tinkerer,

I agree with your observation about building your own metal detector. However, I have one additional point to add to your observation. Manufactured coils need to be made quickly, consistently, and efficiently. Home made coils are not bound by these things. When I started to wind many coils for my fastcoil.pdf paper, I observed a wide range of performance differences based on these variables.
1. MOSFET coil driver capacitance.
2. Coax capacitance that connects the coil to the detector control box.
3. Coil capacitance based on coil wire insulation thickness and insulation type with Teflon being better than PVC for less capacitance.
4. Coil shielding effect on coil capacitance with solid shields adding more capacitance than a fine mesh shield such as Scotch24.
5. Shielding technique of putting the wire mesh on the coil like this:
A. The letter o is the wire bundle size that is 5x the coil wire OD for a 19 turn coil.
B. The letter U is the wire mesh shield that wraps around the cross section of the coil wire bundle.
C. The upper part of the wire mesh is cut wide enough not to make conductive contact or insulated by placing tape on the overlapping part.

I set up my O scope to measure all my coils self resonance and discovered that any coil building technique that resulted in less coil seen capacitance allowed me to use a higher damping resistor value which resulted in a faster mono coil shift from TX to RX.

I discovered that making the coils wrapped around 16 cup hooks allowed me to hand apply a spiral wrap to secure the coil wire as well as add a spacer to the shield from the coil wire bundle. This technique is labor intensive and would not be a good technique for mass producing detector coils.

Making coils for specific targets with a known time constant allows using coil making techniques to optimize the coil diameter and delay for that target. However, the treasure hunting environment may alter the design requiring making tradeoffs to maintain the best coil performance.

Building good detector coils is an educational process that folks like Tinkerer share with geotech1 members.

Thanks for your insight and shared knowledge!

Joseph J. Rogowski

[Nova]

Tinkerer, yes i understand that part, i have another hobby where that same drive has made me close to 40k over the years , it's a challenge that not many people in the world that i'm aware of would care to take up, but the joy is beating it and winning in the process.
Speaking about electronics, there are now 36v batteries available for electric chainsaws and other equipment, could these batteries be adapted to work on Minelab machines, i understand that some of the electronics would need to be redesigned or perhaps just upgraded. Current Minelab's work on around 8v, 36v is 4.5 times as much power, if it is extremely hard to get any real depth out of building your own coils, surely you could get this extra 4-6 inches by increasing the power, and screw the regulations, who is going to know that your using a much more powerful machine?, i am asking you and anyone else that would know the answer to this question, can it be done? (and i'm not asking anyone to do it for me, just a general question?).

[Tinkerer]

Tinkerer, yes i understand that part, i have another hobby where that same drive has made me close to 40k over the years , it's a challenge that not many people in the world that i'm aware of would care to take up, but the joy is beating it and winning in the process.
Speaking about electronics, there are now 36v batteries available for electric chainsaws and other equipment, could these batteries be adapted to work on Minelab machines, i understand that some of the electronics would need to be redesigned or perhaps just upgraded. Current Minelab's work on around 8v, 36v is 4.5 times as much power, if it is extremely hard to get any real depth out of building your own coils, surely you could get this extra 4-6 inches by increasing the power, and screw the regulations, who is going to know that your using a much more powerful machine?, i am asking you and anyone else that would know the answer to this question, can it be done? (and i'm not asking anyone to do it for me, just a general question?).

The limitation is not the battery voltage or the TX voltage. We can make a very powerful TX pulse with less than 4V TX voltage.
Limits exist, but there are many, many possibilities that are still unexplored, within the limits.
Limit 1: The Flyback voltage. Mosfets with 1700V rating are easy to find.
Limit 2: The stronger the TX pulse, the stronger is also the ground response.
Limit 3: Depth, how deep do you want to dig? How many holes to 1 meter depth have you dug in your life? Tough job.
Limit 4: what is the use of detecting specks of gold that are so small you can not see them?
Limit 5: Large diameter coils reach deep. Large coils are also heavy and cumbersome to carry.

You keep talking about 4 to 6 inches more depth.
For what target?
In which environment?

[Tinkerer]

Tinkerer,

I agree with your observation about building your own metal detector. However, I have one additional point to add to your observation. Manufactured coils need to be made quickly, consistently, and efficiently. Home made coils are not bound by these things. When I started to wind many coils for my fastcoil.pdf paper, I observed a wide range of performance differences based on these variables.
1. MOSFET coil driver capacitance.
2. Coax capacitance that connects the coil to the detector control box.
3. Coil capacitance based on coil wire insulation thickness and insulation type with Teflon being better than PVC for less capacitance.
4. Coil shielding effect on coil capacitance with solid shields adding more capacitance than a fine mesh shield such as Scotch24.
5. Shielding technique of putting the wire mesh on the coil like this:
A. The letter o is the wire bundle size that is 5x the coil wire OD for a 19 turn coil.
B. The letter U is the wire mesh shield that wraps around the cross section of the coil wire bundle.
C. The upper part of the wire mesh is cut wide enough not to make conductive contact or insulated by placing tape on the overlapping part.

I set up my O scope to measure all my coils self resonance and discovered that any coil building technique that resulted in less coil seen capacitance allowed me to use a higher damping resistor value which resulted in a faster mono coil shift from TX to RX.

I discovered that making the coils wrapped around 16 cup hooks allowed me to hand apply a spiral wrap to secure the coil wire as well as add a spacer to the shield from the coil wire bundle. This technique is labor intensive and would not be a good technique for mass producing detector coils.

Making coils for specific targets with a known time constant allows using coil making techniques to optimize the coil diameter and delay for that target. However, the treasure hunting environment may alter the design requiring making tradeoffs to maintain the best coil performance.

Building good detector coils is an educational process that folks like Tinkerer share with geotech1 members.

Thanks for your insight and shared knowledge!

Joseph J. Rogowski

Thank you for your feedback bbsailor.
There is always a lot to learn from your posts.
Everybody should read your article about coil building before attempting to build a coil.

[Nova]

Tinkerer, you must of missed my previous post where i said "1oz+ chunks of gold at 3-5ft deep". Yes, i have dug no less than 4 holes at 3ft deep for junk in very hard goldfields ground, if i was healthy that would be nothing for me, but i have lung disease, just one hole like this in the day and my day ends after that, i am f.....
Fly****e doesn't interest me, but sometimes when your chasing the bigger bits, it can go days to weeks without finding anything, so occasionally a smaller piece would be good to find.
And large coils, i have a 1metre coil that someone made for me, i made the housing for it, i used it in Victoria for a couple of hours, didn't find anything with it, but i know that it won't pick up 10 cents in the middle of the coil (Australian 10 cents is about the size of large marble, it is sensitive to small ****e close to the windings but won't hit this 10cents in the middle.
I am a bit lazy to test it properly, but i'm going to have to do it to see if this thing was made properly, i will have to make up a palm size lead target and bury it at the 4ft mark in the side of a creek and then compare to the smaller coils, to really find out if this thing will do what i want, maybe it's all i need to do the job?, and it weighs about 3.4kg , i use an army style harness, but it still gets heavy after a couple of hours, but its fun believing you my walk over a very deep chunk!!!!!

[Tinkerer]

Tinkerer, you must of missed my previous post where i said "1oz+ chunks of gold at 3-5ft deep". Yes, i have dug no less than 4 holes at 3ft deep for junk in very hard goldfields ground, if i was healthy that would be nothing for me, but i have lung disease, just one hole like this in the day and my day ends after that, i am f.....
Fly****e doesn't interest me, but sometimes when your chasing the bigger bits, it can go days to weeks without finding anything, so occasionally a smaller piece would be good to find.
And large coils, i have a 1metre coil that someone made for me, i made the housing for it, i used it in Victoria for a couple of hours, didn't find anything with it, but i know that it won't pick up 10 cents in the middle of the coil (Australian 10 cents is about the size of large marble, it is sensitive to small ****e close to the windings but won't hit this 10cents in the middle.
I am a bit lazy to test it properly, but i'm going to have to do it to see if this thing was made properly, i will have to make up a palm size lead target and bury it at the 4ft mark in the side of a creek and then compare to the smaller coils, to really find out if this thing will do what i want, maybe it's all i need to do the job?, and it weighs about 3.4kg , i use an army style harness, but it still gets heavy after a couple of hours, but its fun believing you my walk over a very deep chunk!!!!!

Hi Nova
what you describe, sounds like a lack of magnetic flux density at the center of the coil.
If very small gold is detected on the rim of the coil, we can assume that the RX is fine. but the TX cold be beefed up. If it is a traditional PI platform, it is probably already running at its design limit.

Every now and then, we get people asking on the forum for extra deep detectors. So maybe we should design a few extra deep coils and show the whole process of doing it here.

Is anybody interested?

There are several factors that need to be considered and compromises to be made:

• Ergonomics - weight, shape, how do you carry it, does it fit into a car
• Power, battery consumption, battery weight
• Cable
• Cost, cost of wire, overall cost
• The coil design has to fit the whole detector platform.

There are numerous third-party coils for Minelab detectors. Ample choice. I am not interested to compete there.

the AMX platform is an advanced platform that has limitations that lie far beyond the traditional PI platforms.
Just one example:
Traditional PI TX coils are limited at about 300uH inductance.
The AMX TX coil limits have not even been explored yet. However, I have made many coils for it with an inductance of around 4000uH and yet a first sample delay of under 5us.

[Nova]

Tinkerer, absolutely, i would be really interested in the whole process, of course to simplify it, a large mono coil for a Minelab would be the go, like i said i have a large coil but i have seen a vid of someone who had built a 1metre mono and that coil could easily pick up this 10c size in the middle and at about 2ft height, so i would say that my coil is not made right.
AMX?, what the hell is that if you don't mind me asking, has this design/platform got the potential for large increases in depth?