Hello, Sotiris here! 👋
🚀Today we continue the PSFB transformer design we started off last week, using our online tool. We will check out and discuss the ferrite core specs. But first I want to tell you a Litz wire story, before we go into design, just to see how desperate but stubborn an engineer can be… 😅
Story time 👪
Back in 2019, before covid-19 😈 had arrived I was heavily involved into a PSFB project, as I said in the previous newsletter. I had to build that 1kW transformer, we started simulating since the last newsletter.
So:
👉 After some temperature failures with solid wires, I decided to go for Litz wire! Well in my mentor’s lab we have all sorts of solid round wires to build any 50Hz iron transformer you like, but Litz? … Nope….
👉 So I went online starting to find some Litz wire to buy. Unfortunately, I couldn’t find small rolls of Litz, and the ones I did would take forever to come to Greece, let alone 💲... 🤔.
👉I got down trying to predict the Litz that would fit the bobbin with the number of turns I need and so on. I got a number like 135strands x 0.01mm wire. Available somewhere fast? …Nope…
👉 To make a long story short, I ended up going back and forth a distance of 6m, 135 times... Got it? 😉
I built my own litz wire with a roll of 0.118mm wire.
How did I roll all strands together? With an electric screwdriver...
After a few tries I got a very nice-looking handmade Litz and also came up with an equation to predict beforehand the diameter of the final handmade Litz. The problem with me is that I have to convince myself that something will perform before testing it.
Finally, I found a paper that did the same trick and compared the results with professional made Litz wires. The handmade wire performed better than the factory-made Litz and they attributed it to the randomness of the strand twisting. That was the hope at least, because if a strand’s location is fixed in the inner part of a Litz let’s say, proximity losses may cause it to fail…🔥
👉 That’s why the Litz wires are bundled into sections like a 5stands x 5stands x 6stands for a 150 stand finished product. There is a whole science into correct bundling and how many bundles to use but I’ll skip that.
