Reply by Robert Baer ●July 21, 20152015-07-21
John S wrote:

> On 7/19/2015 8:13 PM, Robert Baer wrote:
>> Syd Rumpo wrote:
>>> Hi
>>>
>>> Another magnetics question!
>>>
>>> I have a SMPS which uses a toroidal ferrite transformer. It switches at
>>> ~100kHz, works very well, it's not my design and I can't change it.
>>>
>>> However, it introduces noise at about 50kHz onto/into my electronics
>>> which causes a problem. After much experimentation, I found that putting
>>> an earthed screen around the transformer kills the problem quite
>>> dramatically. The screen must be earthed, and doesn't need to be
>>> magnetic.
>>>
>>> This is something I can do. I don't have much room but I guess that
>>> wrapping copper tape around its exposed enamelled wire will cause
>>> problems for Edward Current. Is there a rule of thumb for what sort of
>>> gap to leave between the windings and a screen? How quickly does the
>>> field drop off?
>>>
>>> (And yes, I know not to make a shorted turn.)
>>>
>>> Cheers
>> OK, i will bite: what is Edward Current? and where do i get a
>> description?
>> The quacker DuckDuckGo fails.
>>
>
> He is using the formal name rather than the nickname (Eddie).

   Thanks. Kissing cousin of Mister Justin Case..
Reply by John S ●July 20, 20152015-07-20
On 7/20/2015 1:20 AM, Tim Watts wrote:

> On 20/07/15 03:15, John S wrote:
>> On 7/19/2015 9:14 PM, John S wrote:
>>> On 7/19/2015 8:13 PM, Robert Baer wrote:
>>>> Syd Rumpo wrote:
>
>
>>>>    OK, i will bite: what is Edward Current? and where do i get a
>>>> description?
>>>>    The quacker DuckDuckGo fails.
>>>>
>>>
>>> He is using the formal name rather than the nickname (Eddie).
>>
>> Oops! Should be Eddy.
>>
>
> I thought it was rather clever!


Me, too. I wish I had thought of it. In fact, I did and from now own 
it's mine.
Reply by Syd Rumpo ●July 20, 20152015-07-20
On 17/07/2015 15:59, John S wrote:

> On 7/17/2015 6:30 AM, Syd Rumpo wrote:
>> Hi
>>
>> Another magnetics question!
>>
>> I have a SMPS which uses a toroidal ferrite transformer.  It switches at
>> ~100kHz, works very well, it's not my design and I can't change it.
>>
>> However, it introduces noise at about 50kHz onto/into my electronics
>> which causes a problem.  After much experimentation, I found that
>> putting an earthed screen around the transformer kills the problem quite
>> dramatically.  The screen must be earthed, and doesn't need to be
>> magnetic.
>>
>> This is something I can do.  I don't have much room but I guess that
>> wrapping copper tape around its exposed enamelled wire will cause
>> problems for Edward Current.  Is there a rule of thumb for what sort of
>> gap to leave between the windings and a screen?  How quickly does the
>> field drop off?
>>
>> (And yes, I know not to make a shorted turn.)
>>
>> Cheers
>
> The toroid will see your shield only if the mu is quite low. I don't
> know how low it would need to be, but you seem to be doing some good
> experimenting, so watch your results as you apply the shield at various
> distances.
>
> Consider such things as copper-clad kapton tape, or, for test purposes,
> you can get metalized tapes from the hobby stores.


Thanks for your input, I'll try the tape.

Cheers
-- 
Syd
Reply by Syd Rumpo ●July 20, 20152015-07-20
On 20/07/2015 03:14, John S wrote:

> On 7/19/2015 8:13 PM, Robert Baer wrote:


<snip>


>>    OK, i will bite: what is Edward Current? and where do i get a
>> description?
>>    The quacker DuckDuckGo fails.
>>
>
> He is using the formal name rather than the nickname (Eddie).


Well, I haven't met the guy, so it seems a bit forward to use his 
diminutive.

Cheers
-- 
Syd
Reply by Tim Watts ●July 20, 20152015-07-20
On 20/07/15 03:15, John S wrote:

> On 7/19/2015 9:14 PM, John S wrote:
>> On 7/19/2015 8:13 PM, Robert Baer wrote:
>>> Syd Rumpo wrote:




>>>    OK, i will bite: what is Edward Current? and where do i get a
>>> description?
>>>    The quacker DuckDuckGo fails.
>>>
>>
>> He is using the formal name rather than the nickname (Eddie).
>
> Oops! Should be Eddy.
>


I thought it was rather clever!
Reply by John S ●July 19, 20152015-07-19
On 7/19/2015 9:14 PM, John S wrote:

> On 7/19/2015 8:13 PM, Robert Baer wrote:
>> Syd Rumpo wrote:
>>> Hi
>>>
>>> Another magnetics question!
>>>
>>> I have a SMPS which uses a toroidal ferrite transformer. It switches at
>>> ~100kHz, works very well, it's not my design and I can't change it.
>>>
>>> However, it introduces noise at about 50kHz onto/into my electronics
>>> which causes a problem. After much experimentation, I found that putting
>>> an earthed screen around the transformer kills the problem quite
>>> dramatically. The screen must be earthed, and doesn't need to be
>>> magnetic.
>>>
>>> This is something I can do. I don't have much room but I guess that
>>> wrapping copper tape around its exposed enamelled wire will cause
>>> problems for Edward Current. Is there a rule of thumb for what sort of
>>> gap to leave between the windings and a screen? How quickly does the
>>> field drop off?
>>>
>>> (And yes, I know not to make a shorted turn.)
>>>
>>> Cheers
>>    OK, i will bite: what is Edward Current? and where do i get a
>> description?
>>    The quacker DuckDuckGo fails.
>>
>
> He is using the formal name rather than the nickname (Eddie).


Oops! Should be Eddy.
Reply by John S ●July 19, 20152015-07-19
On 7/19/2015 8:13 PM, Robert Baer wrote:

> Syd Rumpo wrote:
>> Hi
>>
>> Another magnetics question!
>>
>> I have a SMPS which uses a toroidal ferrite transformer. It switches at
>> ~100kHz, works very well, it's not my design and I can't change it.
>>
>> However, it introduces noise at about 50kHz onto/into my electronics
>> which causes a problem. After much experimentation, I found that putting
>> an earthed screen around the transformer kills the problem quite
>> dramatically. The screen must be earthed, and doesn't need to be
>> magnetic.
>>
>> This is something I can do. I don't have much room but I guess that
>> wrapping copper tape around its exposed enamelled wire will cause
>> problems for Edward Current. Is there a rule of thumb for what sort of
>> gap to leave between the windings and a screen? How quickly does the
>> field drop off?
>>
>> (And yes, I know not to make a shorted turn.)
>>
>> Cheers
>    OK, i will bite: what is Edward Current? and where do i get a
> description?
>    The quacker DuckDuckGo fails.
>


He is using the formal name rather than the nickname (Eddie).
Reply by Robert Baer ●July 19, 20152015-07-19
Syd Rumpo wrote:

> Hi
>
> Another magnetics question!
>
> I have a SMPS which uses a toroidal ferrite transformer. It switches at
> ~100kHz, works very well, it's not my design and I can't change it.
>
> However, it introduces noise at about 50kHz onto/into my electronics
> which causes a problem. After much experimentation, I found that putting
> an earthed screen around the transformer kills the problem quite
> dramatically. The screen must be earthed, and doesn't need to be magnetic.
>
> This is something I can do. I don't have much room but I guess that
> wrapping copper tape around its exposed enamelled wire will cause
> problems for Edward Current. Is there a rule of thumb for what sort of
> gap to leave between the windings and a screen? How quickly does the
> field drop off?
>
> (And yes, I know not to make a shorted turn.)
>
> Cheers

   OK, i will bite: what is Edward Current? and where do i get a 
description?
   The quacker DuckDuckGo fails.
Reply by DecadentLinuxUserNumeroUno ●July 17, 20152015-07-17
On Fri, 17 Jul 2015 09:59:24 -0500, John S <Sophi.2@invalid.org> Gave
us:


>Consider such things as copper-clad kapton tape, or, for test purposes, 
>you can get metalized tapes from the hobby stores.


  Home depot  Copper roof flashing by the roll.

http://www.homedepot.com/p/Sandell-Flash-Guard-8-in-x-20-ft-Copper-Step-Flashing-FG030820/202090786

or amazon makes these, which are quite a bit cheaper than a 20' roll.

www.amazon.com/Sheet-Metal-Caps-Copper-Flashing/dp/B00D0U4GH0

  Or better still a variety pack from ebay:

http://www.ebay.com/itm/Copper-Strip-50mmx0-6mm-PER-METRE-C101-Roofing-Flashing-Moss-Valley-/141631726911?pt=LH_DefaultDomain_0&hash=item20f9e8a53f
Reply by John S ●July 17, 20152015-07-17
On 7/17/2015 6:30 AM, Syd Rumpo wrote:

> Hi
>
> Another magnetics question!
>
> I have a SMPS which uses a toroidal ferrite transformer.  It switches at
> ~100kHz, works very well, it's not my design and I can't change it.
>
> However, it introduces noise at about 50kHz onto/into my electronics
> which causes a problem.  After much experimentation, I found that
> putting an earthed screen around the transformer kills the problem quite
> dramatically.  The screen must be earthed, and doesn't need to be magnetic.
>
> This is something I can do.  I don't have much room but I guess that
> wrapping copper tape around its exposed enamelled wire will cause
> problems for Edward Current.  Is there a rule of thumb for what sort of
> gap to leave between the windings and a screen?  How quickly does the
> field drop off?
>
> (And yes, I know not to make a shorted turn.)
>
> Cheers


The toroid will see your shield only if the mu is quite low. I don't 
know how low it would need to be, but you seem to be doing some good 
experimenting, so watch your results as you apply the shield at various 
distances.

Consider such things as copper-clad kapton tape, or, for test purposes, 
you can get metalized tapes from the hobby stores.