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Re: Choke winding question

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On 3/15/2017 11:12 PM, bill.sloman@ieee.org wrote:
> On Thursday, March 16, 2017 at 12:41:17 PM UTC+11, rickman wrote:
>> On 3/15/2017 7:36 PM, Clive Arthur wrote:
>>> On 15/03/2017 22:16, Winfield Hill wrote:
>>>> Clive Arthur wrote...
>>>>>
>>>> What frequency are you choking?
>>>>
>>>>
>>> 10kHz to 100kHz.
>>>
>>> But my question is simpler, I probably haven't explained it well.
>>> When I use a manufacturers PC software to see what's the most
>>> inductance I can get from an RM12 core with 2.5A DC going through
>>> it without it saturating, accepting that I will need multiple
>>> chokes in series to attain 5mH, it seems that the /total/ number
>>> of turns required is much the same.  Is that physics or just
>>> luck?
>>>
>>> According to the Ferroxcube software, a 400nH core with 57 turns
>>> giving 1.3mH saturates at 2.5A, so to get 5mH I'd need 4 of
>>> these, giving 228 total turns for 5.2mH or 22uH/T
>>>
>>> 250nH, 89T, 2.5A, 2mH, 3 needed, 267T for 6mH or 22uH/T
>>>
>>> 1000nH core, 22T, 2.5A, 500uH, 10 needed, 220T for 5mH  or
>>> 23uH/T
>>>
>>> All the same core material, 3 different gaps for 3 different Al
>>> figures.
>>>
>>> It seems suspicious that these three configurations come up with
>>> the same total number of turns for the same inductance at the
>>> same saturation current.  Is this something simple which is well
>>> known in the choke-winding fraternity, is it coincidence, or is
>>> it an inevitable consequence of inductor physics?  It may well be
>>> an obvious thing which I simply didn't know.
>>
>> What is different about the cores that give them the different
>> ratings? Is it size, materials, what?  Are the winding dimensions
>> the same?  What is the same vs. what is different?
>
> Gap. The Ferroxcube RM12 core range offers a small series of cores
> with the same external dimensions, but with a progressively large gap
> in the centre leg.
>
> http://www.ferroxcube.com/FerroxcubeCorporateReception/datasheet/rm12i.pdf
>
>  The effective magnetic path length for all of them is 56.6mm, but
> the largest gap - 1.57mm - is equivalent to more than a metre of path
> length in ferrite and dominates the inductance of any coil wound on
> the core.
>
> Whence the 160nH per root turn for a core which offers 5.6uH when
> ungapped.
>
> The EPCOS data sheet isn't much different
>
> https://en.tdk.eu/inf/80/db/fer_13/rm_12.pdf
>
> but their application notes used to be a whole lot better.
>
> https://en.tdk.eu/blob/2078018/20e26ff3aff21de38c410d79990ddeb6/ferrites-db-17-pdf-data.pdf
>
>  is 6688 pages and 33.15 MB. It's more comprehensive than
> accessible.
>
> The late great Tony Williams circulated a bunch of  the more useful
> material to his friends some ten years ago in smaller chunks.

Thanks for the info.  As to the cores, Clive says he is using the RM12 
cores in 250, 400 and 1000 nH.  But I don't see a 1000 nH core listed.

-- 

Rick C

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Thread

Choke winding question Clive Arthur <cliveta@nowaytoday.co.uk> - 2017-03-15 15:42 +0000
  Re: Choke winding question Winfield Hill <hill@rowland.harvard.edu> - 2017-03-15 09:48 -0700
    Re: Choke winding question Clive Arthur <cliveta@nowaytoday.co.uk> - 2017-03-15 17:03 +0000
  Re: Choke winding question John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-03-15 10:29 -0700
    Re: Choke winding question Winfield Hill <hill@rowland.harvard.edu> - 2017-03-15 11:37 -0700
    Re: Choke winding question Clive Arthur <cliveta@nowaytoday.co.uk> - 2017-03-15 22:02 +0000
      Re: Choke winding question Winfield Hill <hill@rowland.harvard.edu> - 2017-03-15 15:16 -0700
        Re: Choke winding question Clive Arthur <cliveta@nowaytoday.co.uk> - 2017-03-15 23:36 +0000
          Re: Choke winding question rickman <gnuarm@gmail.com> - 2017-03-15 21:41 -0400
            Re: Choke winding question Phil Allison <pallison49@gmail.com> - 2017-03-15 19:28 -0700
            Re: Choke winding question bill.sloman@ieee.org - 2017-03-15 20:12 -0700
              Re: Choke winding question rickman <gnuarm@gmail.com> - 2017-03-16 00:00 -0400
                Re: Choke winding question Clive Arthur <cliveta@nowaytoday.co.uk> - 2017-03-16 09:03 +0000
              Re: Choke winding question Winfield Hill <hill@rowland.harvard.edu> - 2017-03-16 05:56 -0700
                Re: Choke winding question bill.sloman@ieee.org - 2017-03-16 09:42 -0700
  Re: Choke winding question legg <legg@nospam.magma.ca> - 2017-03-15 19:23 -0400
  Re: Choke winding question "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-15 22:56 -0500
    Re: Choke winding question Phil Allison <pallison49@gmail.com> - 2017-03-15 22:30 -0700
      Re: Choke winding question "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-16 15:08 -0500

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