magnetics question

[...]

P = E^2 / R 8^2 = 64

On a sunny day (Wed, 6 Apr 2022 11:17:32 -0700) it happened snipped-for-privacy@coop.radagast.org (Dave Platt) wrote in snipped-for-privacy@coop.radagast.org>:

I have a couple of those USB audio sticks, adds a clean output and also a mike input. Also has auto-gain for the mike alsmixer -c 1

show just an other USB device

Those sticks are about 3 USD on ebay with free shipping, something like this:

a bit like 'expanded' audio....must be the '3D' part...

For the original Pi output I made a cable with a simple RC lowpass in it, that goes to my audio amp for background music in the room.

On a sunny day (Wed, 6 Apr 2022 23:00:32 +0200) it happened Piotr Wyderski snipped-for-privacy@protonmail.com wrote in <t2kv1u$2c98k$ snipped-for-privacy@portraits.wsisiz.edu.pl>:

Railroad here also uses 400 Hz.

Mike Monett wrote: ================

** That is too simple.

At 8 times the frequency, core losses go up by the same ratio dramatically increasing the heat that must be dissipated. But more importantly, there are strict limits on the voltages that can be safely tolerated by insulation. High voltage transformers groups windings into insulated sub sections consuming much available window space. Destructive corona discharge becomes a big issue between layers and even turns.

...... Phil

Core losses in ferrite/powder materials do not obey simple rules and the exponents in the approximate equations have fancy values like f^2.8. So these are not exactly equivalent.

Best regards, Piotr

I used to have a copy of an article from the ETH I believe, where they ran global optimisation on power transformers and simulated them with FEM solvers. The conclusion was that 200kHz is the optimal switching frequency given the current state of the art. Switching faster to get smaller size makes other parameters worse, switching slower makes things unnecessarily bulky.

Best regards, Piotr

One can see here how complex the formula is e.g. here:

Best regards, Piotr

Your first option eliminates an output transformer and means you could make AC out as low a frequency as you want, even DC. Only problem could be if customer wants to see a DC winding resistance but perhaps even that could be synthesiesed?

piglet

torsdag den 7. april 2022 kl. 07.46.39 UTC+2 skrev Mike Monett:

current must stay the same it is limited by the wire sizes

Yeah, I guess we'll do a high frequency inverter to 200 volts dc or so, and then a floating h-bridge. That can output bipolar dc, ac, anything. May as well have ferrite custom magnetics, than steel.

The Coilcraft PL300 transformers are fabulous, 300 watts in a surface-mount package. Their Spice coupling coefficient is 0.9996.

I bet we could push some more watts if we blow some air through the planar kapton windings.

Transformer power is usually limited by heating from copper loss. 64x power implies 8x current, which won't work.

It might be worse than 8x power at 8x frequency, if skin and proximity effects increase copper loss.

On a sunny day (Thu, 07 Apr 2022 07:50:22 -0700) it happened snipped-for-privacy@highlandsniptechnology.com wrote in snipped-for-privacy@4ax.com:

How will a H bridge like that without transformers react to inductive peaks from loads?

In the past? Could be, I designed it more than 30 years ago.

But airplane equipment should still be as light-weight as possible. Nowadays of course even those 400 Hz transformers will have been replaced by switchers.

Arie

Inductive peaks? Like saturation? It would current limit.

Our PM alternator simulator is similar, uses a full-bridge output stage, and can drive a dead short. Regulators for PM alternators usually short the alternator to limit voltage. That blew up our first-gen design that used a TI audio output chip.

torsdag den 7. april 2022 kl. 01.22.48 UTC+2 skrev John Larkin:

?

afaiu some newer airplanes have power that varies in frequency because it is simpler and lighter to do than a fixed output frequency as engine rpm varies from idle to takeoff

Piotr Wyderski snipped-for-privacy@protonmail.com wrote in news:t2m3g2$38tt4$ snipped-for-privacy@portraits.wsisiz.edu.pl:

Ferrite core miniature transformers we used for HVPS design ran best at around 56kHz. It varies too depending on the ferrite formulation and finished product functional characteristics. But you should know that.

Essentially, you are off the mark on this too.

On a sunny day (Thu, 07 Apr 2022 09:12:47 -0700) it happened snipped-for-privacy@highlandsniptechnology.com wrote in snipped-for-privacy@4ax.com:

I actually meant flyback pulses

I have this one:

12 V DC to 230V AC 50 Hz It is heavy, 4.7 kg

Works great so far, so have not opened it yet :-) was 200 Euro No idea of the circuit.

I'm leaning towards a full h-bridge in the first stage. It uses the copper better and doesn't need snubbing.