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From: john larkin <jlarkin_highland_tech>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Mon, 02 Sep 2024 08:31:42 -0700
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On Mon, 2 Sep 2024 17:13:59 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>On 2/09/2024 6:32 am, john larkin wrote:
>> On Mon, 2 Sep 2024 02:20:42 +1000, Bill Sloman <bill.sloman@ieee.org>
>> wrote:
>> 
>>> 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.
>> 
>> Only when they matter.
>> 
>>   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.
>> 
>> Sure I did. They should have worked, based on the data sheets.
>
>Based on your understanding of the data sheet, which was obviously 
>inadequate. It's revealing that you don't post links to the data sheets 
>or specify the number that you relied on when you assumed that they 
>ought to have worked.
>
>> 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.
>> 
>> I did that on the ends. I think the gap-pad works better thermally
>> than soldering every turn to the board.
>
>Solder is metal, and has a higher conductivity than your gap-pad 
>material. You can over-fill the joint, which would help.

It wouldn't help much to conduct heat into a PCB pad. FR4 is a
terrible heat conductor. 



>> 
>> Have you ever used a surface-mount coil that soldered every turn to
>> the board? Got a link?
>
>No. It's merely an obvious possibility.

Ha.

>
>>> You might have had to make it as a sintered metal 3-D printed structure to
>>> get this to work - the wound coil looks a bit irregular.
>> 
>> Losses would be crazy.
>
>What makes you think that? The fact that the part is sintered doesn't 
>mean that you won't get close to solid metal electrical conductivity.

Skin depth is about 30 microns here, and we need a smooth, homogenous,
annealed surface. Ask a chemist.

>>> Lost wax casting could have worked too.
>
>And even you must concede that that wouldn't have been lossy.

Impractical, and cast copper is probably a worse conductor than
annealed.

>
>>>> 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.
>> 
>> And supply a water tank and a pump and water connectors?
>
>Heat pipes don't need that. A closed system doesn't need a water-tank, 
>and lots of top-end computer coolers do rely on circulating water.

My gadget is cheap and easy and works.

>
>>> A 3-D printed structure would have offered more options.
>> 
>> Again, massive losses.
>
>Imagined massive losses.

Certainly imagined. Please make a 3D fabbed inductor and measure its Q
and report back to us.

>
>> My inductor is cheap and simple and works.
>
>It's hand-wound, so it looks cheaper than it is.

This Pockels Cell driver is maybe 1/20 the volume of competitors' and
uses a few per cent of the power. The inductor is a detail.

Most drivers dissipate 

F * C * V^2 

in the driver itself, but it should take zero energy to charge and
discharge a capacitor.

>> If I get a gigantic order, I'll have a coil winding company make them
>> and retire the Sharpie.
>
>Or come up with a more sensible solution?

More sensible than winding an inductor from magnet wire?