3 to 1 ratio coil

[Carl-NC]

My only experience with an oblong PI coil is the 5x10 I got for my Sandshark. Honestly, it performs worse than the stock 8", and certainly worse than the 10" round. Maybe it's the printed spiral method that makes it worse.

When Bill H. has some shells available, I'll give one a try.

- Carl

[nncunew]

Reg, more information

You used 26 awg wire, but how many turns you probe for the 3.5 X 12 inchs coil ???

You said me that the signal (out 709) must be rise as fast as posible ? that does means that exponencial curve must be faster crecient ( max df/dt). You said that don't oscilate, my PI is no exactly a Sandbank, in the power part i used a IRF 640 and 50us the excitation, you recomend used more smalls times.

You have some method for calculate the inductance of 3:1 coils ??

The frecuency of my PI is about 100 Hz, i can use more fast frecuency for example, 1 khz ???

Ii some body wants answer, i hope for the help.

Thank, for every body

[email protected]

[Reg]

Hi nncunew,

When making a rectangular coil you can make a round coil and form it into a rectangle. The inductance doesn't change that much. So, lets say you use a form that will allow a 3 1/2" by 12" rectangular winding. Then the outer edge (circumference or periphery) would be 2 time 3 1/2 plus 2 time 12, or 7" plus 24, or a total of 31". This will be the circumference of the circular coil

Now, divide this number by pi to get the diameter of the coil. The diameter is needed for the formula. The diameter comes out to be about 9.87". Now use the link here to figure out the turns

http://my.athenet.net/~multiplx/cgi-bin/airind.main.cgi

The diameter is 9.87". just select .22" for the length of the coil. I use the inch, rather than the mm. The formula is for a single layer coil, but works very well for a multi wound coil where the wires are bunched on each other. The .22" is about the diameter of the bunch. Anyway, the number works fine.

Ok, now you determine what you want for an ideal inducatance. in my case, I wanted a coil that was about 300 uh. So, I guessed how many turns I needed and then filled in the blanks. Ok, lets guess 21 turns.

So we use the formula and fill in 21 turns, 9.87 inches, and .22 inches.

This coil calculates out to be about 325.65... uh which is close enough for me. (Use the .1% accuracy answer).

So, the answer is simple, figure out the size of a round coil that will fit the housing and then use the formula on the website to get the approximate inductance.

Note, this inductance that is calculated will be higher than that actual measured inductance if thicker insulation is used. So, if the equation says the coil is 300 uh, then the coil could be between 250uh and 300uh depending upon the type of wire you used for the coil.

Reg

[Reg]

Hi Carl,

I have tried a couple of different size rectangular coils and I am impressed with the results. One coil I made I used a 5" by 18" housing and that coil is very impressive for depth.

Overall, I will use a couple different rectangular sizes for nugget hunting. The smaller 3 1/2" by 12" is great for tight places and doesn't give up much depth. The larger one mentioned has very impressive depth. In fact, it matches anything else I have used.

Reg

[nncunew]

Reg ?

But, in the 5 X 18 what gauge do you used (26 awg ?) and how many turns ??

You consider that the shield (Faraday) is very important ???

Thank,

nncunew

[Carl-NC]

Reg, as I mentioned in another thread, I just got one of Charles' 5x18 shells, and will make a coil for for my Hammerhead.

nncunew, # of turns for the 5x18 can be calculated the same way Reg explained for the 3x12... circumference is 46 inches, so figure up the equivalent round coil of the same circumference, and go with that. 26awg is a good all-around size for small-medium coils. Faraday shielding is recommended.

- Carl

[Largesarge]

I prefer Gary's revised Aug. o3 ( http://www3.telus.net/chemelec/Calcu...nductance2.htm ) It gives much more info.