Ferrite Beads - Bad idea?

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi All,

My small coil has four big ferrite beads (Digikey # P11384-ND) on my 
primary cables to cut RFI.  The have a 1/2 inch hole and are 1 inch in 
diameter and 1 1/8 inches long.  They are shown here.

http://hot-streamer-dot-com/temp/P5030001.jpg

I thought they would not affect anything but maybe higher frequency RF 
noise off the gap (which they do well).  However...

Last week I noticed that they get quite warm!  Today I measured that they 
also add about 2uH each to the primary inductance for a total of ~8uH.  I 
would imagine they would saturate at say 300 amps at 200kHz...  The primary 
coil is 32uH.  But I tried my present signal generator setup with and 
without them:

http://hot-streamer-dot-com/temp/030503-01.gif

Yips!!  The white waveform is without them and the blue is with them.  They 
lower the resonant frequency some but they appear to dramatically increase 
the primary system loss!  In an actual running situation this difference 
would not be so dramatic, but it does show the beads are probably a bad 
idea...  On the shelf they go...

I did have two of these beads left on the primary in my testing of 
magnifiers too so they may have affected things some.  I will take them out 
from now on.

Cheers,

	Terry