magnetics question

You can see if there is any transformer you are looking for https://www.easybom.com/c/transformers

Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

[...]

> Can't it be more or less simplified to: 
> if you take a suitable transformer and run it at 8 times the frequency
> you can also increase the voltage 8 times, and thus get 8 times the
> power 

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



-- 
MRM

On a sunny day (Wed, 6 Apr 2022 11:17:32 -0700) it happened
dplatt@coop.radagast.org (Dave Platt) wrote in
<s221ii-pqmv2.ln1@coop.radagast.org>:

>In article <t2ki95$afi$1@dont-email.me>,
>Jan Panteltje  <pNaonStpealmtje@yahoo.com> wrote:
>
>>Yes, that is how I make 60 Hz here in 50 Hz land,
>>100 W audio amp  60 Hz from PC signal generator
>>in 50 Hz mains transformer connected the other way around.
>>Not very efficient, but nice sinewave and no harmonics.
>>A simple raspberry followed by a low pass could drive that
>>(raspi audio out is some PWM I think, sure has RF on it).
>
>It's pretty easy to connect a $10-or-so I2S audio DAC board to a Pi,
>rather than using the on-board audio DAC.  The ones I've been using
>(based on Ti/Burr-Brown PCM-series DAC chips) put out a pretty clean
>waveform - one can add a very simple low-pass to block noise up
>above a few hundred kHz if necessary.

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 
 http://panteltje.com/pub/alsamixer_c_1.gif
  show just an other USB device

Those sticks are about 3 USD on ebay with free shipping, something like this:
 https://www.ebay.com/itm/144291219756
Sounds 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
<bombald@protonmail.com> wrote in <t2kv1u$2c98k$1@portraits.wsisiz.edu.pl>:

>Arie de Muijnck wrote:
>
>> Yes, which is exactly why switching PSU's are now the standard. The cost 
>> saving in iron (ferrite) and copper and capacitors, and all transport 
>> costs, far outweighs (pun intended) the cost of the semiconductors.
>
>Their regulation capability is far better than that of the more 
>conventional PSUs.
>
>> And why airplanes use 400 Hz - the tiny transformers I had designed in 
>> in the product were amusing, 8 times smaller than the usual 50 hz versions.
>
>But why 400 then? A typical scaling factor would be 10, so 500Hz should 
>be expected. Instead, they have selected the odd value of 8. Backward 
>compatibility with an arbitrarily selected frequency back in the 
>medieval times?

Railroad here also uses 400 Hz.

 Mike Monett wrote:
================
> 
> > Can't it be more or less simplified to:
> > if you take a suitable transformer and run it at 8 times the frequency 
> > you can also increase the voltage 8 times, and thus get 8 times the 
> > power

**  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 

Lasse Langwadt Christensen wrote:

> can't it be more or less simplified to:
> if you take a suitable transformer and run it at 8 times the frequency you can also
> increase the voltage 8 times, and thus get 8 times the power

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

whit3rd wrote:

> Yes, that's correct.   I was thinking, though, of resizing the core which would shorten
> the wire length required, thus allow thinner wire with similar resistance; a redesign of
> the transformer for the higher frequency is different from using the same transformer.
> So, my scaling assumes a transformer reconfiguration in shape.  It doesn't get into
> the correct way to do that wire re-dimensioning, because that includes dissipation of heat
> changing with size... and heat can be shed by conduction, or convection, with different
> power laws.

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

On 2022-04-07 08:25, Phil Allison wrote:

> At 8 times the frequency, core losses go up by the same ratio dramatically increasing the heat that must be dissipated.

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

https://www.tme.eu/Document/a26e91abd72e59c56f207dc94b9eb235/ARNOLD-MS-184026-2.pdf

	Best regards, Piotr

On 06/04/2022 4:53 pm, jlarkin@highlandsniptechnology.com wrote:
> https://www.dropbox.com/s/jnb3jmw8rcmdeir/XfmrScatter.JPG?raw=1
> 
> How does the mass of a transformer scale with frequency?
> 
> I want to make a 120v 400 Hz power supply. I might boost my 48v up to
> 200DC and use an isolated h-bridge out to the load, or we could put
> the bridge down at 48v and boost with a biggish transformer.
> 
> I'll have lots of air flow, so maybe I can push things some too.
> 
> 
> 

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:
> Lasse Langwadt Christensen <lang...@fonz.dk> wrote: 
> 
> [...] 
> 
> > Can't it be more or less simplified to:
> > if you take a suitable transformer and run it at 8 times the frequency 
> > you can also increase the voltage 8 times, and thus get 8 times the 
> > power
> P = E^2 / R 
> 8^2 = 64 
> 

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