In message <[EMAIL PROTECTED]>, Bernd Walter writes: >On Wed, Nov 28, 2007 at 07:27:26AM -0500, Bob Camp wrote:
>Well - Søren wrote that it is rated for 2,5A, which is a lot of >current and lot more than the Soekris requires. >There must be a lot more current for the bead to blow that much. Actually, it might be the flank that killed the ferrite, not the raw current. A very sharp flank in the current passing through means a rapid change in magnetic field, and that can, in extreme cases, physically disintegrate the ferrite bead, either by mechanical means or thermal means, even at relatively moderate absolute current levels. This is, btw, exactly why the ferrite beard is there in the first place: to absorb high frequency (= sharp flanks) energy. The flank can be particularly sharp when power comes from lead-acid batteries that have no relevant internal resistance and flows into a capacitor which is essentially a zero ohm resistor until charged. I measured the inrush current peak on a 4801 just some days ago and found it to exceed by a good margin the 17A shutdown limit of the SSR switch I used. All that said, I'd be surprised if the ferrite is the only causalty. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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