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From: Joe Gwinn <joegwinn@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Mon, 02 Sep 2024 10:02:34 -0400
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On Sun, 01 Sep 2024 19:49:39 -0700, john larkin
<jlarkin_highland_tech> wrote:

>On Sun, 01 Sep 2024 17:43:32 -0400, Joe Gwinn <joegwinn@comcast.net>
>wrote:
>
>>On Sun, 01 Sep 2024 13:17:03 -0700, john larkin
>><jlarkin_highland_tech> wrote:
>>
>>>On Sun, 01 Sep 2024 15:53:46 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>wrote:
>>>
>>>>On Sun, 1 Sep 2024 17:55:58 -0000 (UTC), Phil Hobbs
>>>><pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>
>>>>>john larkin <jlarkin_highland_tech> wrote:
>>>>>> On Sun, 1 Sep 2024 17:45:46 +1000, Bill Sloman <bill.sloman@ieee.org>
>>>>>> wrote:
>>>>>> 
>>>>>>> On 30/08/2024 2:21 am, Jan Panteltje wrote:
>>>>>>>> On a sunny day (Fri, 30 Aug 2024 00:43:39 +1000) it happened Bill Sloman
>>>>>>>> <bill.sloman@ieee.org> wrote in <vaq1f2$jdj$1@dont-email.me>:
>>>>>>>> 
>>>>>>>>> It's lot easier and quicker to bread-board a circuit in LTSpice than it
>>>>>>>>> is to wire up a test circuit, but what that means is that you need to
>>>>>>>>> make fewer real circuits and they are a lot more likely to work when tested.
>>>>>>>>> 
>>>>>>>>> That, on it's own, is enough to explain why labs look different today
>>>>>>>>> than they did in the dark ages.
>>>>>>>> 
>>>>>>>> All it explains is boeings falling apart and astronuts ending up stuck at the ISS
>>>>>>>> and no moonlanding from the US, not even a probe.
>>>>>>>> Slimulations are _not_ realty and never will be.
>>>>>>> 
>>>>>>> But they can capture useful parts of reality, if you know what you are 
>>>>>>> doing.
>>>>>>> 
>>>>>>> John Larkin's simulated inductors tend not to have any parallel capacitance.
>>>>>> 
>>>>>> The trick is to know when it matters. ESR and core loss are usually
>>>>>> more important.
>>>>>> 
>>>>>> I designed this surface-mount inductor for my Pockels Cell driver,
>>>>>> after several tries using commercial parts. They all smoked.
>>>>>> 
>>>>>> It's wound on a specially marked Sharpie pen that we have carefully
>>>>>> reserved.
>>>>>
>>>>>It better have a regular calibration schedule, or your semiconductor
>>>>>customers may give you the raised eyebrow. 
>>>>
>>>>Hmm.  To be overly serious:  With traceability to NIST (US) or NPL
>>>>(UK) or the like.
>>>>
>>>>The trend in standards is to eliminate standards tied to a physical
>>>>object.
>>>>
>>>>I have a Sharpie in hand.  The barrel that is not covered by the cap
>>>>is a truncated cone, being 11.0 mm at the blunt end and 12.32 mm near
>>>>the cap, 73 mm away.
>>>
>>>Mine is pretty cylindrical for the length of the coil. I expect that
>>>the operator's (ie, my)  applied tension affects the radius too.
>>
>>Most likely.
>>
>>
>>>That inductor sees 25 amps p-p, roughly a sawtooth, at 4 MHz. The
>>>Coilcraft parts that I tried all smoked, I guess from skin effect and
>>>proximity effect.
>>>
>>>>
>>>>Actually, all that's needed is to specify an ideal geometric shape,
>>>>with tolerances, in the formal documentation.  
>>>>
>>>>Joe Gwinn
>>>
>>>I'll have someone start on a SolidWorks model.
>>
>>I bet you need the standoff, so the lossy FR4 material isn't too
>>close.  That should be in the requirements as well.
>
>The turns squish down into the gap-pad gunk, which is an OK heat
>conductor. The PCB under the pad is a big copper pour, top and bottom,
>with a zillion thermal vias.  There's more gap-pad on the underside of
>the board to dump heat into the baseplate.
>
>At 4 MHz, skin depth is 32 microns, so most of the copper is wasted.
>That's why it gets so hot.
>
>I tried three of the Coilcraft 1010VS parts in series, but they
>smoked, probably skin+proximity effect.  Maybe parallel would have
>been better.
>
>>
>>I'd specify the coil dimensions, not the mandrel dimensions, which may
>>be provided as a helpful suggestion only.
>>
>>Joe Gwinn
>
>I could have a mandrel machined or 3D printed, to more accurately wind
>the inductor. The improvement would be mostly cosmetic.

Or choose a 12mm OD mandrel, and adjust elsewhere.  The advantage of
12mm is that it's a common size. so just buy the rod and use it.

..<https://www.mcmaster.com/products/shafts/shafts-2~/rotary-shafts-5/diameter~12-mm/>

Actually, the requirement is a certain inductance while handling a
4-MHz sawtooth at 25 Amps (p-p), so the frequency band is roughly 4 to
20 MHz, to cover the first five harmonics  Which harmonic causes the
most heating?

The dimensions et al are the construction details needed for Highland
to be able to replicate the part without your help.


>Inductors are a pain.

But useful. Or essential in some cases.

Joe Gwinn