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Ferrite rings

Hi all

While the topics on Ferrites i thought i'd post some info i found whilst
trying to offer my neons all the protection they can have.

Torroid type           LuH
                     100 Turns

T106-2                  135
T106-6                  116
T130-2                  110
T130-6                  96
T157-2                  140
T157-6                  115
T200-2                  120
T200-6                  100
T225-2                  215
T300-2                  114
T300-2A                 228
T400-2                  180
T400-2A                 360
T520-2                  200

              Numbering system 
               e.g for T106-2 
T=Torroid   106=Size in hundredths of an inch
          2=Material mix as below

The micrometals colour coding system identifies the core material.

                        Material        Resonant
                        Pereme-         Circuit
        Basic           billity         Freq. range     Colour
Mix     Iron powder      (uO)             (MHz)          Code

 0      Phenolic           1             50-250         Tan
 1      Carbonyl C        20            0.15-2.0        Blue
 2      Carbonyl E        10            0.25-10.0       Red 
 3      Carbonyl HP       35            0.02-1.0        Grey
 6      Carbonyl SF       8.5           2.0-30.0        Yellow
 7      Carbonyl TH       9.0           1.0-20          White
 8      Carbonyl GQ4      35            0.02-1.0        Orange
15      Carbonyl GS6      25            0.1-3.0         Red/White 


Now quoting Richard Quick from 28/01/96:-

>The answers to this question may be found in Volume 15, #1 of the
>TCBA publication NEWS. The article by Herman W. Flynn gives hard
>data on the effectiveness of various chokes in Tesla coil
>applications.
>
>Basically he is showing that 30 and 44 turns of wire on a ferrite
>core (Radio Shack #273-104) has an inductive reactance of 15,500
>ohms and 24,200 ohms (respectively) at 700 kHz. The measured
>inductance of these chokes are 3.52 mh and 5.50 mh.

And more recently Ed Sonderman from 29/2/96 :- 

>You used the same wire that I did with my toroids although I measured mine at
>650 and 700 microheneries.  We need to wind these with many more turns of
>smaller wire - like 16 or 18 gauge.  The goal is to get up to 4 to 6 mh.  The
>voltage rating of the wire should not be a problem since the delta voltage
>between adjacent turns is very small.  You should wrap the toroid core with
>some insulating tape before winding the wire on however.
>

Indeed to get sufficiant R.F. current attenuation, the value of the inductors
need to be around 4-6mH. but according to my own experiments using a Marconi
L-C-R bridge and a T200-2 torroid with the often suggested twenty turns of
wire only gives me 14uH or, by calculation, nearly 100uH per 100 turns. This 
closley agrees with the table above. Winding twenty turns around Two T200-2
torroids gives very nearly double the inductance -at- 24uH. Now twenty turns
around a T130-8 torroid gives 43uH, despite the smaller diameter, so the effect 
of the peremebility of the material used in the core is important.

This would suggest that around 4150 turns would be needed on the T200-2 core.

Now, obviously, the 20-50 turn torroids work for most people. So are we looking
at kickbacks of r.f. current at the primary frequency, or very fast rise time
voltage pulses which would equate to much higher frequencys at which the value
of inductive reactance would be much greater. 

The fast rise time pulses are more likly to be the cause of transformer
secondary
failiure and hence the effectiveness of these chokes.

In summary, when winding these chokes, use the larger size diameters available,
the materials with the highest peremebility and get as many turns on as
possible,
but dont expect them to be effective at the fundamental primary frequency.

The above statements are based on my own experimentation and conclusions. If 
anybody has differing opinions or further information, Please let me know.

     
*******************************************
Ian Hopley ---->  i_hopley-at-wintermute.co.uk
Aberdeen
Scotland
*******************************************