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NNTP-Posting-Date: Mon, 02 Sep 2024 15:45:10 +0000
From: john larkin <jlarkin_highland_tech>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Mon, 02 Sep 2024 08:45:10 -0700
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On Mon, 2 Sep 2024 17:52:09 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>On 2/09/2024 12:49 pm, john larkin 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>:
>
><snip>
>
>>>> 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.
>
>If the FR4 losses matter, the printed circuit board under the coil would 
>darken, which the customers wouldn't like. The Cambridge Instruments 
>0.5nsec beam blanker did that so we swapped to a different substrate 
>that didn't discolour.
>
>> 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.
>
>It's a sawtooth so it has quite a lot of higher harmonic components with 
>even thinner skin depths. Baxandall's preference for sine waves has 
>incidental advantages.
>
>The turns are wide and flat, which reduces the effect of skin dept.
>> I tried three of the Coilcraft 1010VS parts in series, but they
>> smoked, probably skin+proximity effect.  Maybe parallel would have
>> been better.
>
>https://www.coilcraft.com/getmedia/55a4b40a-2e02-4bf5-b0af-2ea5db75b6cf/1010vs.pdf
>
>There are five 1010VS parts, all rated at about 25A rms. You haven't 
>specified which one you used three of.
>
>That 25A rms isn't going to include any allowance for skin effect.
>
>They don't look as if there would be much cross-talk from one to the 
>next. Making space for more parts might have been a better approach.
>
>With +/-20% tolerance on inductance, putting them in parallel wouldn't 
>have been a good idea.

Don't they have the same tolerance in series?

In parallel, each would get 1/3 the current. But each would need to be
9x the inductance. I suspect that's a wash, something fundamental
going on.

My coil opens itself up for a lot of air cooling, and bare copper can
run pretty hot.


>
>>> I'd specify the coil dimensions, not the mandrel dimensions, which may
>>> be provided as a helpful suggestion only.
>> 
>> I could have a mandrel machined or 3D printed, to more accurately wind
>> the inductor. The improvement would be mostly cosmetic.
>> 
>> Inductors are a pain.
>
>Particularly when you don't think about what you doing.

But it works. A big laser company buys them.

Why don't you design a 1200 volt, 4 MHz pulse generator and we can
discuss it here.