Hello Silvio! How are you? I am making a DC-DC converter from 12Vdc to +-35Vdc for car audio.

It turns out that I have tried to use the ATX EE33 transformer without rewinding, they give me 90Vdc at no load and then with a load of 36 to 40 ohms the voltage drops to 46Vdc consuming 1.3A so I want to try rewinding the transformer.

I have 18, 21 and 25AWG enameled wire. I was thinking of using the 21AWG (0.7mm) one since I don't often use it and working at 30khz it will be fine.

I attach a screenshot of the calculation that the software produced.

View attachment 7417
I want to understand how I should do my calculations to know how to accommodate the sets of wires and that they fit well.

According to the soft for the primary I require 11 wires of 0.71mm, I was thinking of braiding 2 groups of 6 wires leading them in parallel. As the internal height of my reel is 17mm, I think that half of the primary would fit in the first layer.

Is there any calculation to know what diameter a group of "x" number of 0.7mm cables will end up with? I had to do a bit and as a result it gives approx 2mm, that's why I know that only half of the primary would enter in 1 layer.

For the secondary it tells me 21+21 turns with double wire.

Thank you! I hope you can help me!