transformer thermals

On Thu, 6 Aug 2020 07:08:33 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

>Phil Allison <pallison49@gmail.com> wrote:
>>  Piotr Wyderski wrote:
>> 
>> ===============================
>>> > 
>>> > I think people design transformers for
>>> > equal copper loss in the primary and secondary
>>> 
>>> BTW, what is the source of this and similar rules of thumb (e.g. equal 
>>> copper and core losses)? Logic says that one should always design for 
>>> minimal total losses, given the economic constraints.
>>>
>> 
>> ** The source is simple calculus that finds the minimum or maximum in a curve. It's also kinda obvious that if the primary and secondary run at different temps then you have one heating the other. Same goes for core and windings. 
>> 
>> The issue with tape wound toriodals is their very sharp saturation 
>> curves - forcing the designer to keep away from that condition. Hence 
>> their low contribution to heat from the core.
>> 
>> Commercial toroidals are made using a clever machine passing wire 
>> through the centre hole - this sets a limit on the amount of copper that 
>> can be used.
>
>It looks like they could dump more copper on the typical toroidal 
>transfomer. The diameters for large ones get huge, with 
>gigantic empty holes in the middle. The stacking factor, if that's the 
>right term is terrible on most toroids. Not sure why this is though. They 
>seems to scale the wide and thin vs. taller with more copper stuffed in 
>the hole and around the rest of it.
<snip>

For windings, it's a 'fill factor'.

If you check the ratio of copper vs air in the inner 
diameter of a toroid, as the fill approaches a certain 
percentage, you'll see a diminishing return for agravated 
difficulty in fabrication.

Any time manual winding methods enter the equation, costs 
traditionally skyrocket. There may be different considerations 
in today's off-shore sourcing. 

Forty years ago, you would be considered foolish to ship 
anything with a high density - resulting in relatively local 
magnetics fab.

RL

Phil Allison wrote:

> ** The source is simple calculus that finds the minimum or maximum in a curve.

Ultimately yes, but the curve is multidimensional and non-linear, 
especially when the frequency is high. I wonder if there is some FEM 
simulation evidence actually supporting this rule.

> It's also kinda obvious that if the primary and secondary run at different temps then you have one heating the other. Same goes for core and windings.

Sure, but it is a local optimisation. Globally one may get 8W of losses 
instead of 10 by disturbing this balance.

> I know of one amplifier designer who at my suggestion had the winder use his machine for the primary and wind the secondary by hand in order to fill the hole almost completely. This almost doubled the amount of copper used.

Yes, this is a good idea in low volume.

	Best regards, Piotr

On Wed, 5 Aug 2020 18:36:12 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>whit3rd is Witless wrote:
>
>-------------------------
>> 
>> > > It is going to be hotter with AC.
>> > 
>> > Hardly any.
>> 
>> Iron lossses due to eddy currents and hysteresis aren't insignificant.  
>>
>
>** They are with GOSS tape wound into a toroid. 
>
>
>> It this for variable frequency use?
>> Those iron losses are frequency-dependent.
>> it might take a bunch of testing to characterize.
>
>** No it wont. 
>
>JL's tranny is rated for 50/60Hz and will work fine with lower losses at any higher frequency. Core magnetisation goes DOWN with rising frequency for a given primary voltage. 

We rated the tranny for 100 Hz to 4K, but the box currently works from
200 to 4K. We got a bunch more VAs by raising the low frequency limit.

On Wed, 5 Aug 2020 22:02:16 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Wednesday, August 5, 2020 at 6:36:17 PM UTC-7, Phil Allison wrote:
>> whit3rd ...
>
>> > > > It is going to be hotter with AC.
>> > > 
>> > > Hardly any.
>> > 
>> > Iron lossses due to eddy currents and hysteresis aren't insignificant.  
>> >
>> 
>> ** They are with GOSS tape wound into a toroid. 
>> 
>> 
>> > It this for variable frequency use?
>> > Those iron losses are frequency-dependent.
>> > it might take a bunch of testing to characterize.
>> 
>> ** No it wont. 
>> 
>> JL's tranny is rated for 50/60Hz and will work fine with lower losses at any higher frequency. Core magnetisation goes DOWN with rising frequency for a given primary voltage. 
>
>Iron losses are zero with DC testing, and certainly not 'lower' at all higher frequencies.
>Core magnetization goes down with frequency, but losses go UP when the secondary
>doesn't draw current.   And, the core shape determines the magnetization profile,
>at higher frequencies it's unclear whether the entire core shares the induction (so
>the behavior at 4 kHz ought to be tested... at 4 kHz.


Yes, and copper losses go up with frequency, typically, too.

On Thursday, August 6, 2020 at 3:51:07 AM UTC-7, Phil Allison wrote:
> whit3rd is a physicist wrote:

> > Core magnetization goes down with frequency, but losses go UP when the secondary doesn't draw current. 
> 
> ** Complete BOLLOCKS  !!!! 

But not untrue; secondary current lessens the core magnetization because it is in the opposite
sense as primary current.
> 
> > And, the core shape determines the magnetization profile,
> 
> ** On which planet is that faintly relevant here ? 

On any magnetization by AC, there's a skin depth that depends on the frequency, and
that determines how much of the core actually polarizes during the cycle.  That affects
the saturation and the resultant hysteresis loss in the core.

It's just physics.

whit3rd = context shitfing LUNATIC TROLL 


========================================

** FOAD  you ridiculous pile of dung 

legg wrote:

==========

 
> For windings, it's a 'fill factor'.
> 
> If you check the ratio of copper vs air in the inner 
> diameter of a toroid, as the fill approaches a certain 
> percentage, you'll see a diminishing return for agravated 
> difficulty in fabrication.

** Cost is everything in manufacture. 

But as here like to consider what physics allows, it is clearly a fact that filling a toroidal with as much copper as possible maximises the VA for a given core. 

This IS the practice for all other types of core shape. 

Most toroidals are low and flat - again not optimum but liked by many customers. Same goes for R-cores and U cores which result in low height products. 



....  Phil 

 booB the bullshitter wrote:

============================

> 
> Yes, and copper losses go up with frequency, typically, too.


** Really - in a mains or audio frequency tranny ??

  GOSS tape wound toroidal cores are not used at higher frequencies.

  But you just HAD to be a smartarse - didn't you ? 


.....  Phil 

On Thu, 6 Aug 2020 15:01:10 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Thursday, August 6, 2020 at 3:51:07 AM UTC-7, Phil Allison wrote:
>> whit3rd is a physicist wrote:
>
>> > Core magnetization goes down with frequency, but losses go UP when the secondary doesn't draw current. 
>> 
>> ** Complete BOLLOCKS  !!!! 
>
>But not untrue; secondary current lessens the core magnetization because it is in the opposite
>sense as primary current.
>> 
>> > And, the core shape determines the magnetization profile,
>> 
>> ** On which planet is that faintly relevant here ? 
>
>On any magnetization by AC, there's a skin depth that depends on the frequency, and
>that determines how much of the core actually polarizes during the cycle.  That affects
>the saturation and the resultant hysteresis loss in the core.
>
>It's just physics.


Yep.   Core flux is Volt-Seconds.   the lower the frequency, given the
same voltage, the volt-seconds go up and further towards saturation.

Worse case losses on the core is no load for a given frequency and
amplitude of H.

On Thu, 6 Aug 2020 16:41:03 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>legg wrote:
>
>==========
>
> 
>> For windings, it's a 'fill factor'.
>> 
>> If you check the ratio of copper vs air in the inner 
>> diameter of a toroid, as the fill approaches a certain 
>> percentage, you'll see a diminishing return for agravated 
>> difficulty in fabrication.
>
>** Cost is everything in manufacture. 
>
>But as here like to consider what physics allows, it is clearly a fact that filling a toroidal with as much copper as possible maximises the VA for a given core. 
>
>This IS the practice for all other types of core shape. 
>
>Most toroidals are low and flat - again not optimum but liked by many customers. Same goes for R-cores and U cores which result in low height products. 
>
>
>
>....  Phil 

Those last few turns also have the longest length 
per turn, further diminishing their 'return'.

The 'practice' is to assume a fill factor of less 
than 80%, to allow for insulation, wire shape and 
cover. For mains voltage wall thickness, creepage 
spacing, and bobbin tolerancing, it's even worse.

Toroids depend upon 3xlayer film overlapping weave for 
reinforced layering and core or outer wrap, though 
some cores use fitted caps at the expense of efficiency.

Low and flat toroids are a 'style' (at the expense of 
efficiency) - the most efficient physical ratio being 
roughly 2.2:1 / OD:H.

High frequency stuff . . . . 

RL