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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Mon, 2 Sep 2024 02:20:42 +1000
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On 2/09/2024 12:09 am, john larkin 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.

And you don't simulate them either. Simulation is - in part - about 
letting the math throw up unexpected effects that appear when you hook 
up a bunch of components. Knowing when it matter relies on the 
simulation inside your head.

> I designed this surface-mount inductor for my Pockels Cell driver,
> after several tries using commercial parts. They all smoked.

So you didn't read the data sheets carefully enough. It's not a part 
that would usually be described as "surface mount". If you'd scraped the 
enamel off the bottom of the coil and soldered each turn down onto an 
isolated copper pad on the board, it probably would qualify as surface 
mount, and would have had better thermal contact with the board.

You might have had to make it as sintered metal 3-D printed structure to 
get this to work - the wound coil looks a bit irregular.

Lost wax casting could have worked too.

> It's wound on a specially marked Sharpie pen that we have carefully
> reserved.

That defines it diameter. Measuring that with a vernier caliper would 
give you a number you could document.

> https://www.highlandtechnology.com/Product/T850

> The grey gap-pad gives it some extra cooling. The board has lots of
> thermal vias down to the water-cooled baseplate.

If you'd wound it with copper tube you could have pumped water through 
the tube, or made it a heat pipe.

A 3-D printed structure would have offered more options.

-- 
Bill Sloman, Sydney