Swapping transformer I/O

On Tuesday, July 4, 2023 at 1:04:08 AM UTC+10, John Larkin wrote:
> On Sun, 02 Jul 2023 11:44:20 GMT, Jan Panteltje <al...@comet.invalid>  wrote:
> >On a sunny day (Sun, 2 Jul 2023 04:19:47 -0700 (PDT)) it happened Phil Allison 
> ><palli...@gmail.com> wrote in <5f09e2f5-5376-44bd...@googlegroups.com>: 
> >>John Larkin wrote: 

> >>> That's easy to think through. Power transformer models are simple and 
> >>> easy to reverse. 
> >> 
> >> ** But real transformers are not so simple. 
> >> 
> >>> >You may have to seriously de-rate the transformer in order to use it that way, 
> >>>> mains frequency transformers under 100VA are the most affected. 
> >> 
> >>> A 100 VA transformer is happy moving 100 VA in either direction. 
> >> 
> >> ** JL has such simple faith in overly simple models. 
> >> 
> >> I wonder why ? 
> > 
> >Because it works, did something for the county here like that to replaces a very complex design.. 
> >Used existing transformer models in reverse. 
> >
> My/our job is to build things that work, and we can use any design 
> tools, or none for that matter, that work. 
> 
> Spice has removed the necessity for a heap of classic and tedious  tools and equations and papers. But any non-trivial design, no matter  how derived, will probably be simulated and often lab tested. 
> 
> It's good to get away from a screen and solder up stuff now and then,  stress some parts and see what happens. 
> 
> Last week I toasted a bunch of wirewound resistors and blew up a few  solid-state relays, and learned things not on data sheets. 
> 
> The Coilcraft PL300 planar power transformers are dynamite.

They blow up violently?

> They have  6, optionally 7 windings and they call one set "primary", which is  silly; they're just windings. Leakage inductance is so low it can be  ignored.

It's never that low, and the way they measure leakage inductance isn't all that informative. What you actually need are measures of mutual inductance.

"Leakage inductance measured at 200 kHz, 0.5 Vrms, 0 Adc between pins 2 and 5, with pins 3 and 4 connected,and with all secondary pins shorted"

This includes the resistance of the secondary windings in the measurement, which isn't exactly clever, if cheap and easy to do.

Using bad models gets you bad results.

https://www.coilcraft.com/getmedia/636aef6f-8168-4ece-bb01-e16574e130d8/pl300.pdf

-- 
Bill Sloman, Sydney