Instruction monocoil for minelab GP series

[bigrex]

Coil completed

Well, I thought I would post the results of attempting to fabricate a coil for my Minelab gp3000. The first coil I made was a 12" coil and does not seem to work properly. But my second coil does which measures 42" x 15". It is next to an 18” coil and a car tire for comparison. You can barely swing it on the end of a long shaft without bumping your feet. I’m pleased to announce that it did not fry my detector and it does give a response to metal, although I don’t think it will be giving Nuggetfinder a run for their money any time soon. It probably won’t work that great but at least it was sort of fun to make. I haven’t yet tested it in the field where there is no interference, so I don’t fully know how poorly or well it will actually function.

[bugwhiskers]

Shielding connection

Hi bigrex,

Some time back I shielded a coil by using sisalation tape. It's an al foil tape that builders use to join sheets of sisalation on houses. Obviously it doesn't solder too well so I wrapped a few turns of copper wire around it and then use gold inpregnated glue to complete the connection. The gold glue sold as an adhesive to join wires to car rear window demisters. The joints are good as would be expected as in the car situation the connection has to be low resistance.

regards
bugwhiskers

[AzNuggetBob]

Hi All I have a question concerning using the Chemelec calculator. I'm building a 18"x3.5" rectangle shape coil. Do I enter 43" as the outside diameter or the average coil diameter by dividing 18x3.5 ? Also anyone have any thoughts on rectangle PI coils in general,verses round or oval? Am I wasting my time with this shape for a PI coil? Thanks Bob

[bbsailor]

Hi All I have a question concerning using the Chemelec calculator. I'm building a 18"x3.5" rectangle shape coil. Do I enter 43" as the outside diameter or the average coil diameter by dividing 18x3.5 ? Also anyone have any thoughts on rectangle PI coils in general,verses round or oval? Am I wasting my time with this shape for a PI coil? Thanks Bob

AZNuggetBob

This rectangular coil with a perimeter of 43" will be equivalent to a 13.687" diameter round coil. As the coil is squeezed into a tight oval or narrow rectangle, the inductance will be reduced between 5 and 10 percent. So plan on making the coil inductance slightly higher.

A coil of 18 turns of AWG 24 will produce a coil of 346uH as a round coil and about 325uh when placed into the narrow rectangle form and use about 64.5 ft. of wire. It will have about 1.6 ohms or resistance. If you use AWG22 the resistance will be 1.04 ohms.

This narrow coil will not have the depth of an equivalent round coil of 13.687" but will be closer in detection depth to a round coil of about 5" to 6" in diameter. The 18" X 3.5" coil will cover more ground than a smaller coil.

Work backwards from the DC resistance you need to match the commercial coil resistance and inductance.

bbsailor

[IBGold]

Bigrex I found it hard when I started winding my own coils for SD and GP detectors but I recieved a lot of support from members of this forum I have now completed 11 mono's and finalising 2 DD's all with great end results. If you are in OZ you can contact me direct I will be in hospital for 4 days from tomorrow but then would be pleased to pass on info that I have to you. Regards Ian, [ IBGold ]

[Unregistered]

Hi bbsailor, Thanks for your reply. That answers several questions I had. Here is another maybe you could answer for us. Ive been thinking about using silver plated stranded copper wire coated in teflon but the more I thought about it, if silver is so conductive would it not be pointless to use stranded wire? would the wire act as a solid wire because of the silver plating? It seemed to me that if you were going to use stranded that a litz type wire would be a better choice. I have also heard that a solid wire is better for large coils and stranded is better for smaller coils. Im new to coil building and just trying to get all the basics down. Take Care and thanks again AzNuggetBob

[bbsailor]

Hi bbsailor, Thanks for your reply. That answers several questions I had. Here is another maybe you could answer for us. Ive been thinking about using silver plated stranded copper wire coated in teflon but the more I thought about it, if silver is so conductive would it not be pointless to use stranded wire? would the wire act as a solid wire because of the silver plating? It seemed to me that if you were going to use stranded that a litz type wire would be a better choice. I have also heard that a solid wire is better for large coils and stranded is better for smaller coils. Im new to coil building and just trying to get all the basics down. Take Care and thanks again AzNuggetBob

AZNuggetBob

Use tin plated stranded Teflon insulated wire. Look on ebay for some good deals. Stay away from silver plated stranded wire as it defeats the whole purpose of using stranded wire...to break up eddy currents being generated in the coil wire itself. You would also needing to wait for the eddy currents to die down before sampling.

Litz wire will work but the 600V Teflon insulated stranded wire has a thicker insulation and will make a faster coil with less capacitance between the windings.

If you can accept using a 5 ohm coil, use solid AWG30 Teflon insulated wire. This makes a nice tight coil that has a low coil-to-shield capacitance because the shield area is low compared to the shield area from having a wire bundle with thicker wire. Make sure you use a polyethylene spiralwrap spacer or two to reduce the shield-to-coil capacitance on any coil you make. Make sure that the shield material is not detected as a target at your sampling delay.

What is your planned coil resistance, diameter and inductance?

Large coils are typically used for larger, deeper targets and coil speed is not the most important characteristic so any kind of wire will work. Stranded wire is good for coils in the 10" to 12" and maybe up to 14" diameter range.

I hope this helps.

bbsailor

[AzNuggetBob]

Im building a mono coil for my minelab SD 2100 I believe I need an inductance of around 0.300 at 4 Ohms. Diameter is a 18"x 3.5" pre-made housing or 43" AzNuggetBob

[rajesh]

hammerhead c 19

hi all anyone use c19 other cape i mean .1 uf ?

[Stefan]

Im building a mono coil for my minelab SD 2100 I believe I need an inductance of around 0.300 at 4 Ohms. Diameter is a 18"x 3.5" pre-made housing or 43" AzNuggetBob

The SD2000/2100 minelab coils have the following characteristics:
Coil inductance: 300 microhenries
coil resistance: 0.3 to 0.4 ohms
Coil Q: 4.5

If you are using tined stranded wire for a low capacitance coil (bbsailor) then I would recommend that the Q of the coil be around 4.3. In highly mineralized ground if the Q is >4.3 the ground balance response will be very noisy.

Stefan

[rajesh]

hammerhead

hi Stefan im wrote about hammerhead c19 capecitor no about any coil for fast retune ...... thanks for reply i built a hammerhead that nicely work but im not satisfied from c19. many thanks for a coil information ......rajesh.

[rajesh]

h h coil

characteristics:
Coil inductance: 300 microhenries
coil resistance: 0.3 to 0.4 ohms
Coil Q: 4.5
my dear friend stefan i all ready built many more coil i built a 13 inch in to 13 inch square 26 awg 20 turn for hammerhead.because my curentlly is12 inch diameter stain steel plat detect to five feet.
im not understand about >Q is >4.3

[rajesh]

The SD2000/2100 minelab coils have the following characteristics:
Coil inductance: 300 microhenries
coil resistance: 0.3 to 0.4 ohms
Coil Q: 4.5

If you are using tined stranded wire for a low capacitance coil (bbsailor) then I would recommend that the Q of the coil be around 4.3. In highly mineralized ground if the Q is >4.3 the ground balance response will be very noisy.

Stefan

hi stefan can you sent me ddcoil cofiguration for hammerhead?

[Stefan]

hi stefan can you sent me ddcoil cofiguration for hammerhead?

Hi Rajesh,

I'm sorry but I have only built coils for the Minelab series of PI detectors so can offer no help for the hammerhead coils. If you know the Q of the large coils you have made then use this value for the Tx of the DD. You will have to play around with the Rx coil a bit.

Q 4.3. This is the Q that I have found works well for a Minelab SD2000/2100/2200 series of detectors.

If you construct a low capacitance PI coil and build using the original Minelab Q of 4.5, the ground balance response on highly mineralized
ground is very noisy. I found this out the hard way whilst building low capacitance coils. So that is why I ensure that the
Q is about 4.3 and no greater.


Regards,

Stefan

[rajesh]

DEAR STEFAN VERY VERY THANKS .........................RAJESH