What I learnt this year.

On a sunny day (Thu, 09 Jan 2014 11:05:07 +0000) it happened Syd Rumpo wrote in :

Intrsestng. I have a small one that measures 60 k, and a same one that was broken and I glued back together with superglue measures 78 k (while pressed against a non-broken half). Maybe one can find cracked cores that way.

ed 10k or so over a cm or so.

past half century I've believed/assumed ferrite to be an insulator.

lf of the core only, so mixing up types could happen if you were careless. I have been. But it seems that the two types I'm using have quite differ ent resistivities, so I can match up the two halves again.

I've been aware that ferrites were conductive since I first played with the m in the late 1960's, and furthermore I knew - from the start - that mangan ese-zinc ferrites were a lot more conductive - but had higher permeability

- than nickel-zinc ferrites.

The old Mullard ferrite data books were horrible in many respects, but they did spell this out.

--
Bill Sloman, Sydney

I've never seen it spelled out, but I knew it was true (didn't know it varied that much). Perhaps that's at least partly why some are coated with epoxy.

Best regards, Spehro Pefhany

--
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I knew it, but got reminded recently when I got a 32kV tingle from touching a supposedly insulated core!

Cheers,

James arthur

How did you contact the cores? The size of the contact area can make a lot of difference.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
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So you actually learned that _some_ ferrite cores conduct electricity.

Bulk resistivity of ferrite cores is on the data sheets, and is one of the things you take into account if you get really detailed about choosing a material.

Or, you choose a material by recommended frequency range, which essentially means that someone else has taken the core resistivity into account for you.

The higher the frequency the material, the less it conducts.

And no, I'm not an expert in this -- I just have a magpie mind.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

Oh, just meter probes, good enough for a comparison. These are RM12 cores, so a better way might be to clip them together and use the spring clips as terminals. . . . No, not really better - I get about 2k between clips on the RM12 N41

1000nH cores I'm using, and about 7k on an N87 160nH set, but all rather sensitive to pressure. Still, a clear difference.

I guess conductive epoxy would make a good contact, but I'm not *that* interested.

Cheers

--
Syd

A four-terminal measurement would eliminate contat resistance from the measurement - if you ever wanted to go to that much trouble to get a definitive answer.

--
~ Adrian Tuddenham ~ 
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www.poppyrecords.co.uk