Re: Instead scopes

On 3/09/2024 1:31 am, john larkin wrote:

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>:

<snip>

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.

That's where your gap-ad dumps the heat. It may be a terrible conductor (if a lot better than air) but it was clearly good enough for you.

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.

So not obvious to you.

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.

Ask a guy with a pulsed laser, who can melt the top 30 microns of the part for enough milliseconds for it flow into a smooth surface. I've always been puzzled why people haven't resumed silver plating RF parts when you can now fuse the surface electro-plated crystals into a continuous film of silver

Lost wax casting could have worked too.

>
And even you must concede that that wouldn't have been lossy.

 Impractical,

Why?
and cast copper is probably a worse conductor than annealed.
So anneal it.

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.

But looks cheap. And a hand-wound coil is never easy.

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.

If you'll pay for it, and the time I'd have to spend to dig out somebody to do it. Back when I was working I had access to people who would know somebody who would do it, but I moved back to Australia, and those people are less accessible (and some of them have died).

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.

But a crucial one.

Most drivers dissipate
 F * C * V^2
 in the driver itself, but it should take zero energy to charge and
discharge a capacitor.

Sadly. capacitors can be lossy, and the current involved has flow through conductors which are resistive - more so when the skin effect kicks in.

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?

Why do you think that the Coilcraft inductors were wound with flat wire?
The skin effect means that most of your magnet wire is unused.
With flat wire, you also have more surface area to couple the wire to the air you are relying on to cool it.
 From a practical point of view, changing the layout to accomodate enough of the Coilcraft parts to dissipate the heat would give you a much tidier-looking product, if marginally bulkier.
If what you've got has 5% of the volume of its competition, you've got room to do that.
--
Bill Sloman, Sydney