Figure 1. Dunning-Kruger Curve
🤓 The Learning Phase
With a good book, some decent coffee and a couple of weeks spare I began to understand and appreciate the complexity of designing a transformer, I learned:
- That the turns ratio affects the converter operation and therefore must be chosen carefully.
- How the simplified transformer model affects the simulation, and the importance of choosing the right magnetizing inductance.
- How the core size, shape, material, choice of airgap and number of turns affects the magnetizing inductance.
- Also, that I needed to find an appropriate number of turns to keep flux and current densities at reasonable levels (both of which conflict each other).
- That flux and current densities directly affect the losses in the transformer, as well as operating frequency and transformer volume. Finding the formula for Area Product early on helped to strike this balance.
- That the temperature rise of the magnetic could be estimated from a basic formula taking into account its surface area and the power throughput.
I also ventured a little further, learning about winding area geometry, leakage inductance and the importance of Litz wire to reduce AC losses in the windings. I had a brazen confidence that I had covered the many aspects of a transformer design, and it was working in my simulations so practically the job was done…
⚠️ Harsh Reality
I had waited so long for the Litz wire to arrive that it was a whole event, this magic wire that was just going to make it work… I wound the transformer myself, added the necessary isolation and taped it all together. It looked beautiful.
It didn’t work. It got far too hot. I didn’t even manage to get my converter to half of the full power (which isn’t actually half-way in terms of losses). Thermocouples embedded in the windings told me I was ridiculously far out in my calculations for copper losses. At this point I was ignoring the fact that my leakage inductance estimates were out considerably, but it was the least of my issues (for now). I had a customer waiting in the wings to see a working prototype.
💪 The hardest Yards
I had an important decision to make. My eagerness to learn and prove myself as an engineer sent me along a path of trial and error (I would tell you now that I was adopting the scientific approach, but it didn’t feel like that at the time, it was more of a controlled panic).
🔎 Every time, however, I got closer and closer to the truth. I varied turns ratios and played with different winding strategies. Then I made the call to change to a different Litz wire to try and improve my AC losses. I had tried to torture different designs out with the same wire to avoid going through the rigmarole, what with the minimum Order Quantities (MOQs) and long lead-times, but I was sure this is where I had gone wrong. I wasn’t a mathematical genius; I was a practical engineer and the papers I had read on these topics seemed far too complex and uncertain for me to confidently adopt.
Imagine my disappointment in knowing I now had a kilometre of Litz lying around that I probably wasn’t going to use again, Whilst I sat waiting for the next “better” batch to come in (I did this again actually after finding out I was still wrong). Imagine the discussions that ensued with my customers…
💡 The journey from the valley of despair to enlightenment can be a slow and painful (and an extremely costly) process, but this is where the real learning is done. I learned a lot over this course of time, but my most valuable lesson had nothing to do with magnetics.
I was an engineer; my job was to provide a solution that worked so that the company could sell a product and grow. If you are an engineer, you have a responsibility to balance priorities, not just in the design phase but in the project phase. You have a timeline, budgets, and stakeholders. If you manage these poorly, it can have a huge impact on your company. Sure, I learned a lot, but when I left the company how much of that learning do you think stayed there?
🤝 When I started on a new project, I took my learnings with me and from these I made the best decision I could for the company. That is, I chose to use Frenetic to help me design the transformer. I was worried at first that I was going to miss out on learning by outsourcing the knowledge, but instead, with their online platform I learned far more about magnetics than I ever knew existed, I learned a lot about the reasons why I failed in the past, and I was able to spend more time learning about and experimenting with the rest of my converter.
⚙️ Not only did Frenetic know what they were doing from a design point of view, but they had ample stock and different Litz wire, so that I was able to create prototypes without waiting 3 months for kilometres of wire that I might not need. In fact, I got a working prototype for the first time around and I was so happy with the service I joined the team!
Frenetic design, build and test infinitely more magnetics than any engineer could possibly cover in a lifetime, we go through these cycles of learning many times a week by applying the scientific method. We have learned from the failures, so you don’t have to.
🧗 So, when you are considering your climb up that mountain of enlightenment, remember that Frenetic has been up the mountain, put the guide ropes in place and is sitting waiting at basecamp with a nice cup of coffee for you.
