[OT] WWV Time Transmissions

[Vic Rosenthal]

Ferrite is a bunch of tiny ferrous particles glued together by a nonconducting substance. It has magnetic properties but currents can’t flow in it (at least not very far). I haven’t tried, but I bet an ohmmeter would say it’s an insulator.

Victor 4X6GP

> On 3 Sep 2020, at 7:48, Adrian <[hidden email]> wrote:
>
> Please quote your online reference please regarding ferrite cores being a dielectric
>
> If so then my not just use un-enammeled wire on a course wound core ? A dielectric is an insulator ;
>
>
> Dielectric
>
> From Wikipedia, the free encyclopedia
> Jump to navigation <https://en.wikipedia.org/wiki/Dielectric#mw-head>Jump to search <https://en.wikipedia.org/wiki/Dielectric#searchInput>
> Not to be confused withDielectric constant <https://en.wikipedia.org/wiki/Dielectric_constant>orDialectic <https://en.wikipedia.org/wiki/Dialectic>.
>
>
> A*dielectric*(or*dielectric material*) is anelectrical insulator <https://en.wikipedia.org/wiki/Insulator_(electricity)>
>
> I don't see any reference to ferrite cores being a dielectric online.
>
> The molecular alignment heating method regarding dielectric loss, is not mentioned on any ferrite core RF heating science, that I can find.
>
> Please read ;
>
> Predicting Temperature Rise of Ferrite Cored Transformers George Orenchak TSC Ferrite International 39105 North Magnetics Boulevard Wadsworth, IL 60083
>
>
> "Core Losses Core losses are a significant contributor to the temperature rise of a transformer. Hysteresis loss, eddy *current* loss and residual loss all contribute to the total core loss. At high flux densities and relatively low frequencies, hysteresis losses are usually dominant. Hysteresis loss is the amount the magnetization of the ferrite material lags the magnetizing force because of molecular friction. The loss of energy due to hysteresis loss is proportional to the area of the static or low frequency B-H loop. At high frequencies, eddy current losses usually dominate. Eddy *current* loss is from a varying induction that produces electromotive forces, which cause a current to circulate within a magnetic material. These eddy *currents* result in energy loss. Understanding the behaviour of the combined total core loss as functions of flux density and of frequency is most important. "
>
>
> Dielectric is not mentioned.
>
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>> On 3/9/20 2:15 pm, David Gilbert wrote:
>>
>> If you weren't too stubborn you could find many, many online references to the dielectric characteristics of ferrites.  A ferite core absolutely IS a dielectric.  There is nothing false about what I've been telling you.
>>
>> Dave  AB7E
>>
>>
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[Adrian-3]

Thinks, Jim, no the debate is purely about the cause of heat in a
ferrite core balun, not the other things you mention. I use common mode
chokes, and they work well.


 From your link ;

"Power Loss Density - P (mW/cm3 ) The power absorbed by a body of
ferrimagnetic material and dissipated as heat, when the body is subject
to an alternating field which results in a measurable temperature rise.
The total loss is divided by the volume of the body. "

Eddy currents induced from that AC field as documented on numerous
previous links , reveal themselves as heatloss and temperature rise,

in differrent amounts depending on the material properties.

Two primary things can cause the core to heat.

 1. Resistive losses in the transformer winding wire due to the primary
    and secondary currents.
 2. Ferrite core loss to to such factors as eddy currents, and magnetic
    hysteresis.

I found Barry's link interesting but no mention of heat on the various
sections.


Adrian Fewster

'




On 3/9/20 4:53 pm, Jim Brown wrote:

> On 9/2/2020 9:02 PM, Adrian wrote:
>> A dielectric is defined as an insulator . A ferrite core is not a
>> dielectric (insulator),  This is the false fact in your theory.
> You have massive gaps in your understanding of how common mode chokes
> work and the properties of ferrite materials. The best technical data
> refererence I know of Fair-Rite's catalog, which is online and can be
> downloaded as a pdf.
>
> https://ebiz.fair-rite.com/newfair/pdf/Fair-Rite_Catalog_17th_Edition.pdf
>
> The fundamental properties of ferrite materials vary widely depending
> on their chemical composition, commonly called "the mix," and each mix
> is tailored to a specific range of applications. A table summarizing
> those properties begins on page 4 in the print version, page 6 of the
> pdf. The resistivity of the materials listed varies over 7 orders of
> magnitude, from 50 ohm-cm to 10 exp9 ohm-cm.
>
> My tutorial on how common mode chokes work is here.
> k9yc.com/RFI-Ham.pdf
> The concepts were added to the ARRL Handbook around 2011. Designs for
> practical transmitting chokes are here.
> http://k9yc.com/2018Cookbook.pdf
>
> Note that these are not "baluns," a word that describes at least ten
> very different physical things, but rather common mode chokes. Their
> sole function is to minimize common mode current. They do not do
> impedance matching. That function is provided by very different things
> best called tranformer baluns, and they come in multiple forms.
>
> Extensive research I published in a peer reviewed AES paper in 2003
> found manufacturer's literature from the '50s/'60s indicating that
> they understood how common mode chokes work, and after I published my
> work to the ham community, an engineering manager from the CIA passed
> along to me an unclassified engineering report from the US Army in the
> '70s that was in agreement with all of the fundamental concepts I had
> published and had developed a family of designs for field use. The
> only thing they missed was the property of dimensional resonance,
> which I learned about in classic reference a colleague found in the U
> of Chicago engineering library. That reference, by E. C. Snelling, is
> cited in several of my publications.
>
> 73, Jim K9YC
>

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[Josh Fiden]

No.  At low frequencies hysteresis loss dominates. Soft ferrites have high resistivity. Eddy currents increase with frequency but 160m is still fairly low.

In SMPS transformer design we look at applied volt*seconds. When the applied v*s goes up, as would be the case with high SWR, you push further out the BH curve increasing hysteresis loss. With each cycle, the area inside the BH curve determines the loss (heating). As you approach the horizontal part of the curve (saturation), inductance collapses and the winding looks like a short. Same if core hits Curie temp then mag domains can no longer be aligned.

Soft ferrites are not permanent magnets, they are NOT in fixed alignment. Magnetic domains are flopping around with the applied field.

Hope this clarifies something. Hihi

73
Josh W6XU

Sent from my iPad

> On Sep 2, 2020, at 10:58 PM, Adrian <[hidden email]> wrote:
>
> core heating is affected only by the AC (induced eddy *currents*) content of the signal.

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[Josh Fiden]

For safety compliance (UL, IEC, etc.) soft ferrites are considered a conductor. All insulation requirements apply for clearance & creepage.

73,
Josh W6XU

Sent from my iPad

> On Sep 2, 2020, at 11:18 PM, Adrian <[hidden email]> wrote:
>
> They usually stick to using a thin non metallic insulator with good insulation properties, otherwise known as a true dielectric.

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