Surf PI coil.more questions than answers.

[nickel_n]

I used Qiaozhi's coil calculator V.2 to calculate the coil for a surf pi that I try to build using the info of the forum and the board that silverdog supply.
Coil diameter 210mm,wire diameter 0.48mm 16 turns the calculator give's me 0.379mh.
its all good to now.
I made the coil 16 turns, tie and cut the wire, and then measure it with my new LCR meter,and here is my problem.
the meter reads 0.171mh.
am i missing something, is the coil calculator wrong , or I got a dad LCR meter?
i would like to know what do you think.??
Nickel_n

[WM6]

I used Qiaozhi's coil calculator V.2 to calculate the coil for a surf pi that I try to build using the info of the forum and the board that silverdog supply.
Coil diameter 210mm,wire diameter 0.48mm 16 turns the calculator give's me 0.379mh.
its all good to now.
I made the coil 16 turns, tie and cut the wire, and then measure it with my new LCR meter,and here is my problem.
the meter reads 0.171mh.
am i missing something, is the coil calculator wrong , or I got a dad LCR meter?
i would like to know what do you think.??
Nickel_n

It depend on how tight or lose your coil windings is.

It depend on measured frequency of your LCR meter too. So LCR can be OK and calculator too.

But briefly say 16 turns are someway low for 21 cm diameter - better try with 22-26 turns. In all cases you need to adapt your dumping resistor to your finalised coil.

[Qiaozhi]

I used Qiaozhi's coil calculator V.2 to calculate the coil for a surf pi that I try to build using the info of the forum and the board that silverdog supply.
Coil diameter 210mm,wire diameter 0.48mm 16 turns the calculator give's me 0.379mh.
its all good to now.
I made the coil 16 turns, tie and cut the wire, and then measure it with my new LCR meter,and here is my problem.
the meter reads 0.171mh.
am i missing something, is the coil calculator wrong , or I got a dad LCR meter?
i would like to know what do you think.??
Nickel_n

Classic mistake!
You have entered the diameter of the coil into the calculator instead of the radius. Using a 105mm inner radius, with 0.49mm diameter wire and 16 turns, gives 167uH.
Try using 24 turns to achieve 361uH.

[gautenglion]

Hi
Sorry to hijack this thread
Ive been reading all the threads regarding a basic mono coil for a PI machine. Is there a set inductance for the coils. I have seen people mention anything from 230-380 uH. What i would like to now if anything between those values would be sufficient. Is it just a question of testing and adjusting the damping resistor. Its for a Surf Pi project.
Thank you

[nickel_n]

Thank you Qiaozhi.
It was obvious to me that I was doing something wrong, I just couldn’t see what.
I will try again and pay more attention to the formula.
Thank you for the advice WM6
Nickel_n

[Qiaozhi]

Thank you Qiaozhi.
It was obvious to me that I was doing something wrong, I just couldn’t see what.
I will try again and pay more attention to the formula.
Thank you for the advice WM6
Nickel_n

No problem.
The estimated coil inductance may vary slightly from the calculated value for a number of reasons. The inductance is very sensitive to the inner radius value, so any deviation here can cause some discrepancy. Also, the formula assumes a square cross-section for the coil, whereas homemade coils tend to be jumble-wound and more circular in their cross-section. However, the discrepancy here is small. As WM6 pointed out, the tightness of the bundle can make a big difference. Often you have to add or remove a turn or two to get the exact value, depending on your construction method.

[Qiaozhi]

Hi
Sorry to hijack this thread
Ive been reading all the threads regarding a basic mono coil for a PI machine. Is there a set inductance for the coils. I have seen people mention anything from 230-380 uH. What i would like to now if anything between those values would be sufficient. Is it just a question of testing and adjusting the damping resistor. Its for a Surf Pi project.
Thank you

Lower value inductance coils tend to get used where fast decay times are required, such as for nugget hunting. But coil inductances can be higher than 380uH. The Hammerhead, for example, uses 500uH coils as standard. The important point is to use the correct value of damping resistor for the coil in question.

[gautenglion]

Thanks for the info.
I will try a couple of coils i have wound and adjust the damping resistor. I actually made the same mistake first time round with the calculator.

[Qiaozhi]

Thanks for the info.
I will try a couple of coils i have wound and adjust the damping resistor. I actually made the same mistake first time round with the calculator.

A few people have made that mistake, so you're not alone.
Perhaps I should issue a Rev2.1 version that uses the coil inner diameter instead.