Re: Inductance calculations

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
 >
 > Original poster: "Barton B. Anderson by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>
 >
 > Hi Antonio,
 >
 > I ran Inca v1.0e- 11/3/2003 and obtained the following primary inductance
 > in question:
 >
 > n1= 5.00; h1= 0.20; r11= 0.50; r12= 0.50; b1= 0.00 (wd doesn't print to
 > screen, but was 0.002)
 > Primary inductance L1:    0.0379600169 mH

This is Wheeler's formula. Check the boxes for "Maxwell L" and
"Elliptic fun.".
The site below has a program "coil" that the author says that is
accurate:
http://www.moshier-dot-net/coildoc.html
Its calculation for solenoids gives also the 46 uH.
Lundin's formula gives 39 uH.
Mandk also gives 39 uH.
I see that discrepation between Maxwell and the others appears when
the number of turns is small. But Maxwell's formula is based on
single turns?! The problem is not a consequence of not considering
an helix, because my numerical integration considering the helix also
gives 46 uH.

A test, to see if the results are consistent:
If I stack two identical coils, the total inductance must be 2L+2M.

With Inca:
L=45.9691043 uH
M=18.6011663 uH
2L+2M=129.1405412 uH
Calculating the inductance of a coil with 40 cm of height and 10 turns:
Ltotal=129.1411539 uH
(The "coil" program gives 130 uH)

With Fantc:
L=39.37069 uH
M=18.68313 uH
2L+2M=116.10764 uH
Ltotal=116.1666 uH

So both are consistent... Some program is doing something funny...
I will continue to check the program. Maybe I can build that 1 meter
coil to check.

The Inca program is in http://www.coe.ufrj.br/~acmq/programs

Antonio Carlos M. de Queiroz