[JN] magik ???

Hanski hanskinposti at gmail.com
Tue Feb 2 14:41:23 CST 2021


Hi gents, my 2cents.
magnetic energy is stored in an air gap. 
So if you need to store energy in a choke, you need an air gap.

Sendust like other powder cores have a distributed air gap (there is always some air between powder particles).
Sendust is used in SMPS because it’s cheap and has lower magnetic flux swing related losses than plain iron powder cores.
Usually they come in toroid shapes. One could also use a gapped ferrite toroid there, but it’s usually a bad idea because you would need to locate all windings on top of the air gap to cancel the external flux (less outside flux, less EMC).

Other powder core materials:
https://www.coilws.com/index.php?main_page=page&id=41 <https://www.coilws.com/index.php?main_page=page&id=41>


-Hanski

P.S. I really like homemade audio transformers. 
For small signal stuff one can use even plain SMPS ferrite. a few thousand turns primary gives 200H inductance (Al = 12u) with commonly available  ferrite toroid. (No DC bias)
Just wound a couple with 50um thick wire. (My skills don’t go below that, it’s already human hair thick) :)



> 
> ©
> 
> PS i’m not so sure Sendust would be that good for a transformer core. Sendust (aka Kool Mu) is often used in power supply chokes … because it stores energy well. is the capability to store energy better than other materials a good thing in an audio transformer? i don’t know (no irony). but i can imagine that the release of the stored energy «smears» the timing. isn’t the best core … an air core? because it does exactely the opposite — it doesn’t store any energy?  (btw. Sendust has seen wide spread use in audio when tape and cassette recorders were still mass produced. many of the better recorders used Sendust heads because it is very hard.)
> _ _ _
> aka christian rintelen
> 

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