Re: Ferrite Beads - Bad idea?

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

Original poster: "robert & june heidlebaugh by way of Terry Fritz <teslalist-at-qwest-dot-net>" <rheidlebaugh-at-desertgate-dot-com>

Terry: I seriously question the placement of your ferrite beads. Beads on
the input to the coil circuit between the NST and the spark gap are a good
idea, but you have the beads placed inside the resonant primary circuit.
This part of the circuit you want fast rise time. the faster the better.
Your beads slow down the rise time giving you less amp turns per second or
lessssss output. Put your beads on your input power lead and your NST leads.
    Robert   H
-- 


 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > Date: Sat, 03 May 2003 15:46:11 -0600
 > To: tesla-at-pupman-dot-com
 > Subject: Ferrite Beads - Bad idea?
 > Resent-From: tesla-at-pupman-dot-com
 > Resent-Date: Sat, 3 May 2003 15:48:16 -0600
 >
 > 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
 >
 >