it’s a beautiful sunny day here in Rome (caput mundi), Italy, as I get back to you after almost three months of absence.
What happened in the meantime? Let me summarize it in a few concise statements:
1) I’ve been mostly busy doing something else. This is an unresolved issue of mine, I don’t spend enough time after these projects. I hope to change that for the future.
2) Remember the soldered breadboard? Well, I learned the hard way that simply using a digital multimeter to verify that there are no short circuits on the soldered tracks is not safe: despite having passed this test, our breadboard (shown below at an early stage of soldering) had some tracks that were not properly isolated from each other and didn’t work.
3) Remember the two transformers (shown below)? Each of them had a 12 V primary winding and two secondary windings: the main 48 V secondary winding, and a demagnetizing 40 V secondary winding. The fact that the 40 V demagnetizing winding had fewer wire turns than the 48 V main secondary winding would have allowed each of the transformers to have a duty cycle greater than 0,5 , so that the ON states of the two transformers could have overlapped for a certain time interval. However, this required a complicated control circuit, and since we had to assemble the breadboard all over again, we chose to… GOTO point4
4) We used Ockham’s razor (a fancy way to say that we simplified the system as much as possible): we ordered two slightly different transformers: each with a 12 v primary winding and two 48 V secondary windings: one to be used as main secondary winding and the other as demagnetizing secondary winding. This way, the control circuit to be assembled on the breadboard is greatly simplified: it uses just 2 Arduino digital pins (we chose pin 3 and pin 5), 2 transistors and 6 resistors. The updated DC transformer schematic is shown below, with the control and power circuits shown in different colors. Please note that both the control and the power circuit refer to a single transformer: since the system contains two transformers working in parallel, both the control circuit and the power circuit must be duplicated, and that’s why some circuit elements have two labels, one highlighted in orange for the first transformer assembly, and the second highlighted in yellow, referring to the second transformer assembly. Don’t worry, everything will be explained better as we build it…
5) Last but not least, our interest is shifting from this to the HomeMadeWatts project: we will try to finish the DC transformer project rapidly, so that we can work on HomeMadeWatts, in view of the Maker Faire Rome that will take place in October.
Have a nice day and see you soon!