Litz wire OK for 390V 4kW 100kHz LLC transformer?

[cupoftea]

Hi,
Doing hobby 4kW LLC converter off 390Vdc.
Will the following Litz break down if used in the LLC transformer...?

LITZ WIRE

www.wires.co.uk

LZ00400175-500
("175 strands of 0.04mm silk covered Litz")

(I am not currently interested in whether this is standards conformant, just doing as hobby)

 

[Easy peasy]

you have not stated the working volts per turn - or any other things you are doing to preserve insulation - e.g. Kapton over each layer - sleeved in and out wires - margin winding ...

 

[cupoftea]

Thanks, Its<50V/turn, and there will be tape between layers...i was hoping i could get away without tubing the in/outs and margin tape.....as a hobbyist ive always found margin tape unobtainable.

I have made offline Flybacks for 240VAC using this enamelled wire (below) with no tubing in/outs and no margin tape, just tape between layers, and to be honest, even that wasnt done terribly neatly, and got away with it....

https://www.farnell.com/datasheets/3170015.pdf

...so i was wondering if we could "get away with it" with the shown Litz aswell?....its just for a few hobby supplies.

In the event i need to wrap the Litz in tape, then i wondered what tape is cheapest to get the insulation requiremet for mains work?......i see theres polyimide, PTFE and Kapton.

We actually have some 7/0.3mm TEX-ELZ, but it just has that "i'm going to melt" look about it, ..the insulation seems quite thick....and thermally i can see bad news.

As a hobbyist, i dont get responses from Litz vendors.....well they respond, and just say "it does get used in SMPS"...without actually stating whether it needed additional serving etc for the high voltage, mains SMPS's

 

[cupoftea]

The below power integrations App Note shows that in fact, simple enamelled copper wire has superb electrical strength.....
Its concerning a 100-265VAC 60W flyback SMPS

App note DER535
https://www.power.com/sites/default/files/documents/der535.pdf

See page 20 if you wish to... (its also attached).....here you see the switching node wire, which goes up to in excess of 500V, layed right over the wire that connects to primary ground. There is no tubing. Its just bare enamelled copper wire. It shows that enamelled wire has superb strength?
If you look at other pictures there...you see other cases of High voltage being layed (touching) over low voltage wires.

The switching node wire is 0.32mm diam, and the pin 3 (gnd) wire is 0.2mm diam....and yet their enamelled insulation is good enough to handle the 500V thats between these wires.

On the same page, if you look at pins 5 and 6, there you see the mid-primary point wire, lying right over the bias coil voltage wire....again...no problem.

I think from this, it shows that if your just doing test jigs or hobby work.....its a waste of time using tubing.....and margin tape would also be a waste of time?

I bet if that secondary had been wound with plain Enamelled wire, the transformer would work fine.
(would not pass regs, but wouldnt be going in for compliance anyway)

 

[Easy peasy]

" I have made offline Flybacks for 240VAC using this enamelled wire (below) with no tubing in/outs and no margin tape, just tape between layers, and to be honest, even that wasnt done terribly neatly, and got away with it.... "

This might be OK for one offs that don't run 24/7, but,

In production the windings would be vacuum varnished to ensure lack of movement and to further improve insulation life for the intended life of the unit.

--- Updated Apr 16, 2022 ---

the nylon or silk or other servings on litz wire are there to provide a porous separation between the turns - to allow vacuum potted varnish to get in there and provide long life insulation ( as well as preventing thermal and other movement ) - they have no insulation properties ( in a safety sense ) at all.