Bigger coils less winds?

[punagold]

If all settings remain the same on the same detector, is it safe to say that a bigger coils requires less winds? I have 200' of litz and have discovered that I can only get 20 turns each in a DD style coil for my desired size. I'm shooting for rectangular with rounded ends, 24 inch length and 8 inch wide for each coil. The smaller DD I'm trying to copy is much smaller in size and uses 26 winds and 42 winds. (infinium DD). Am I way short of wire or do I have enough to try this? Still waiting for LCR meter to arrive. Thanks

[Davor]

Roughly speaking, for a same inductance you'd need roughly the same length of wire. It also turns into less windings for a bigger coil.

[punagold]

Thanks, that what I was hoping for. My new meter should be here if a few days. Yesterday I tried to measure resistance of the 200' with my old meter but couldn't get any readings. This litz is strange wire in that the insulation is some kind of spun material, not pvc.

[6666]

Dont forget TRUE litz wire is made from insulated wires , you will have to remove the insulation off each individual wire to measure the R

[6666]

According to Q's coil calc if you compare two ROUND coils you get this

Coil dia 400mm 15 turns .5mm wire = 314uH

then double the size

Coil dia 800mm 10turns .5mm wire = 323uH

When you start making other shapes it gets tricky.

[IBGold]

Punagold for a 24' x 8' rectangular coil with radiused ends for TX if you are winding for a 300uh coil I would have wound 18 turns then checked it before cutting the wire for the RX I would not use the same wire I use 40/44 Litz for the RX windings I have just finished a 21 x 7 coil centerline measurement 3 to 1 rectangular mono with radiused ends and that has 19 turns for an inductance of 313uh finished but this is made with home made Litz wire with 2 layers of poleofin heatshrink applied over the wire to lower the interwire capacitance but the extra insulation also lowers the inductance slightly also the larger the coil the more wire they use and the lower the turns hope this is of some help to you.

Regards, Ian.

[6666]

According to Q's coil calc if you compare two ROUND coils you get this

Coil dia 400mm 15 turns .5mm wire = 314uH

then double the size

Coil dia 800mm 10turns .5mm wire = 323uH

When you start making other shapes it gets tricky.

Left off a sentence, the larger you go, the less turns you need to maintain original inductance .

[punagold]

Thank you guys, this is all very helpful. For the life of me I cannot get the coil calculator to work on my computer.

Question for IBGold:

The litz I have now is 175/46. You are suggesting that I use this for the TX only? And the RX should be the same number of winding but use 40/44 instead? The coil that I am following also uses different wire. It has 26 turns of light duty tin plated multistrand PVC coated for the TX and 42 turns of single strand Kynar wire for the RX. Can you explain what the purpose is for the different size of wires? I am very curious.

I can purchase a 40/44 litz for a much cheaper price than the 175/46, so this is good news.

Is your 21 x 7 a true mono coil or does it have separate TX and RX coils?

666Guru:

My understanding is that uH changes with changes in the shape. That being the case, would it be wise to adjust the shape to match the inductance right before I seal it in epoxy?

[6666]

My understanding is that uH changes with changes in the shape. That being the case, would it be wise to adjust the shape to match the inductance right before I seal it in epoxy?

YES

[IBGold]

Thank you guys, this is all very helpful. For the life of me I cannot get the coil calculator to work on my computer.

Question for IBGold:

The litz I have now is 175/46. You are suggesting that I use this for the TX only? And the RX should be the same number of winding but use 40/44 instead? The coil that I am following also uses different wire. It has 26 turns of light duty tin plated multistrand PVC coated for the TX and 42 turns of single strand Kynar wire for the RX. Can you explain what the purpose is for the different size of wires? I am very curious.

I can purchase a 40/44 litz for a much cheaper price than the 175/46, so this is good news.

Is your 21 x 7 a true mono coil or does it have separate TX and RX coils?

666Guru:

My understanding is that uH changes with changes in the shape. That being the case, would it be wise to adjust the shape to match the inductance right before I seal it in epoxy?

Hi Punagold, What detector are you winding coils for you need to copy the manufacturers inductance and resistance of their coils as close as posible as this will dictate the type af wire required for a coil for a Minelab PI machine You need a wire with a minimum of 17AWG with a maximum strand size of 32AWG in either Litz or tinned wire with Poleofin insulation for the TX for coils up to 14" this would be 600/46 Litz or 30/.2 tinned marine wire for TX the RX is diferent you can use 32AWG silver Teflon wire for this or ,2mm magnet wire or as I prefer the 40/44 Litz this does not need to be as heavy as the TX as it is receiving the returned much weaker signal to put it in simple terms also with the RX coil for a Minelab we usualy wind it to around 450UH to increase the capture of the weak RX signal as for shape yes it makes a big diference if you wind a coil round then colapse it to make a eliptical or rectangular one the inductance will decrease dramaticly it is best to work out your shape and wind your coil to that shape that way you get what you want when the coil comes of the former I use a chipboard former with 4mm dowels to the shape of the ID of the coil bundle I am winding and I lace my windings tight before removing them from the former.

Regards, Ian.

[punagold]

Thank you Ian,

I am winding a coil for the Garrett ATX.

I appreciate your explanation of the different wire sizes.

How can one test inductance ( I have an LCR meter coming soon) while winding a coil before cutting the wire? Or do I do extra winds, cut and test? If too much, remove a wind, cut and test again?

I was planning on a DD, or more like an 00 style coil. but after thinking about it I may be better off with one shape using a TX and RX within that one loop. It would be much easier and less shielding material if do that. I have ordered some copper tape to use for shielding. My goal is for a long narrow search field. If I go this way, should I wrap the TX coil with electrical tape first before I wrap the RX loop to separate them a little?

Thanks again.

[6666]

Punagold, make a former in the shape you require then adjust your turns to the inductance you require, wind more turns than required and measure, its easier to remove a turn than add a turn, do not let the shields of the TX and RX touch, keep them insulated. Is the original ATX coil IB ?

[punagold]

Thanks 6666,

The original coil is a DD. It is a PI machine, not a VLF. They also offer so called mono coils, but in reality they are 2 coils in one. A TX and a RX sealed up in one coil loop. So correct me if I am mistaken, the original is not IB.

[IBGold]

Punagols a DD is an IB (induction ballanced) coil and yes you need a LCR meter to measure the inductance what I do is work out roughly how many winds I think I need then I work out the length of one turn at the centerline of the coil bundel multiply that by the number of turns add a couple of turns and cut the Litz wire at that then I wind the number of turns I worked out then measure the inductance then add or subtract a turn as need be, With the tinned wire it is easyer you just wind the coil to the number of turns you worked out then you connect the wire at the start of the wind to the LCR and the other probe I have sharpened to a sharp point which I gently push through the insulation to get the inductance measurement that way you do not have to cut the wire until you have it correct I am sorry I have no sugestions for you as I have no experiance with the Garret ATX.

Regards, Ian.

[punagold]

I thought it might be an IB coil, but then I read somewhere that only VLF were IB. Thanks for clearing that up.

I hope that I do not need a scope to get the 2 coils in balance. I was thinking I could just turn the detector on and move the coils around and test with targets until I get the best response, or I may have to buy one of those cheap $70 scopes that use a laptop to balance the coils. I saw a youtube video where a guy moved the 2 coils back and forth until the RX was a straight line on the scope.

Thanks for the tip in measuring the inductance. I think with the litz I may have to solder tinned wire to the tips in order to get good meter readings. Monday a holiday so waiting for Tuesday to order the 40/44 Litz.