Maybe OT electrical

[The Other Mike]

Fortunately skin effect exists at 50Hz, but I think we've been here before and you possibly claimed a contrary view.

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[Tim Streater]

Presumably the issue is that the current carrying depth decreases as the frequency goes up, so that there is actually no lower bound to frequency WRT to skin effect. But the issue is really how "useful depth" is defined in terms of the decrease of capacity with depth. F'rinstance, do we say we define that as the depth where the current carried is only 10% of that at the surface? Or some other %-age?

Doubtless there's a formula that returns a depth given frequency and percentage. Anyone have any representative figures for say 50Hz, 50kHz, and 50MHz?

[Clive Arthur]

<snip>

Plenty of on-line calculators and formulae. For copper...

50Hz 9.2mm 50kHz 290um 50MHz 9.2um

It's the depth where the current density is to 37% of that at the surface, 37% being 1/e.

Cheers

[Tim Streater]

Thanks for that. So 0.3mm at 50kHz if I read that right? Surprising, that.

[bilou]

Andrew Gabriel a pensé très fort :

Very clever ,cost effective,trick. May be coiling the wire around the tube could avoid having to tape it.

[FMurtz]

This was not said by F Murtz (me ) it was Paul Saccani

[Harry Bloomfield]

FMurtz was thinking very hard :

There was no post I was able to find, from a Paul Saccani and you didn't directly quote one.

[Andy Burns]

IME you didn't make it very clear you were quoting someone else

[The Natural Philosopher]

Skin effect exists at 0.000000001Hz, biut its not a matgter of its existence, its a matter of how significant a loss it is, and frankly having engineered all the way from DC to gigahertz, it's really not very important below tens of MHz at most.

[The Natural Philosopher]

at 50Khz 0.6mm dia copper cable is fully utilised.

And 'elecronic transformers' are in any case rectified and smoothed.. ...the interference of 50watts of 50KHz RF would be massive.

[The Natural Philosopher]

Nopt accoprding to te article I linked to - wiki. Its way more than that

[Clive Arthur]

<snipped>

No, it isn't. You really have no idea of when to stop digging, do you?

[Roger Hayter]

That's simply not true. Every transistor radio had a long wave coil on it's ferrite rod wound in Litz wire to mitigate skin effect at 200kc/s. (Before the evil EU made us change to 198kHz.)

[The Natural Philosopher]

Odd that they didnt have litz wire on the much higher frequency MW isn't it?

[The Other Mike]

Start messing with a few thousand amps at 50Hz and it becomes somewhat important. Like I said I think we've been here before.

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[Tim Streater]

its

Nothing to do with the EU, of course, else the Yanks would still be using c/s.

[Clive Arthur]

They often do use Litz for both, but for the same tuning capacitor, you need many fewer turns at medium wave frequencies and so can use thicker

- and cheaper - wire.

Cheers

[The Natural Philosopher]

Oh dear. You said that skin effect meant that thicker wire didnt make any difference anyway...

[Roger Hayter]

Not really. Firstly because you need less wire so the copper losses are less anyway, compared with poor magnetic coupling. And second because of increasing capacitative losses. I suspect that Litz wire would have been ok but not bery valuable at MW, but higher than that thick copper with a large surface area is higher Q.

[Roger Hayter]

Improves conductance proportional to the radius rather then the square of the radius And inversely with the length both of which explain why other losses become relatively more important.