which transformer winding is better?

[yoosefheidari]

i want to make a 12v to 220vac inverter and for transformer winding i need help.
which winding is better and has lower leakage inductance?
or do you recommend better winding type?
frequency is 50KHz and power is about 350watts

 

[cupoftea]

The right hand one is best...better coupling.

 

[yoosefheidari]

i did it but i have some problem
first lets describe my work
i bought a 400watt modified sine wave inverter and by add a EGS002 module , turns it to a pure sinewave inverter.
i test it with a 250watt load and it work perfecly for 1 hours but with one problem.
problem was output voltage which was 170vac under load.
so i decided change the transformer with a new one and i wind my own transformer(first post of this topic)
by changing transformer voltage issue solved and voltage was stable under 250 watt load at 220 vac.
but now i have new problem
under 250watt load dc-dc(12VDC to 310VDC) mosfets(push-pull) and transformer become exeteremly hot after 2-3 minute work.
original transformer uses 2+2 turn foil copper(1.7mm2) for primary and 48 turns(0.5mm) for secondary(like right hand in first post) on an EI30 core
my transformer uses 3+3 turn foil copper(2.2mm2) for primary and 95 turns(0.7mm) for secondary(like right hand in first post) on an ETD29/16/10

what do you think?what is problem?

 

[cupoftea]

With foil windings you may be getting more eddy current loss...maybe you need Litz.
Also, do you have a gapped core.?.and is your foil winding near it....it may be picking up its field and getting more eddy currnt loss

 

[yoosefheidari]

With foil windings you may be getting more eddy current loss...maybe you need Litz.
Also, do you have a gapped core.?.and is your foil winding near it....it may be picking up its field and getting more eddy currnt loss

you mean i cant wind with foil as perfect as original transformer?and therefore i get eddy current?
no ,my core dosn't have gap.
so it seems i should try litz winding. i'm gonna use 9 wire in parallel(0.5mm) but there is one question.for better result and best coupling how i wind them ?
1-all 9 wires strands together?
2-each 3 wire in strands and then wind this 3 strands next to each other?
3-dosn't strands wires and wind them next to each other(flat)
4-your idea!

 

[Easy peasy]

If you add another set of primaries to the outer on the sketch on the left - you will have better performance again. ( lower leakage by almost a factor of 2 ).

signed - an engineer who designs these transformers all the time ...

--- Updated May 3, 2022 ---

also each primary should be both wdgs wound bifilar and brought out to their respective terminals - this will reduce the pri to pri wdg leakage and give you much better results when you turn a mosfet off - esp at 50kHz, and 30 amps.

( you will see this later on when you power it up )

 

[yoosefheidari]

If you add another set of primaries to the outer on the sketch on the left - you will have better performance again. ( lower leakage by almost a factor of 2 ).

signed - an engineer who designs these transformers all the time ...

--- Updated May 3, 2022 ---

also each primary should be both wdgs wound bifilar and brought out to their respective terminals - this will reduce the pri to pri wdg leakage and give you much better results when you turn a mosfet off - esp at 50kHz, and 30 amps.

( you will see this later on when you power it up )

you mean using wire instead of foil is not nessecory?which you recommend at this current rating?
i didn'exactly get your points.can you explain visually?or give me pdf that explain these points?