Good vid Fez. Very little out there about transformers and mag fields. It's interesting that still today, the interaction of iron with the copper coil remains a complete mystery.
I guess that its not that big of a mystery, these phenomenon where studied and documented 100 years ago, but rather nowadays people interested in electronics only focus on the higher level topics to the point of completely skipping the fundamentals. The same can be said about all of the fundamental components, there are so many behaviors associated with them, other than the main function.
You have great tutorials. Thank you for that. I might suggest you write a little bit about calculating the number of windings for different types of ferrite cores. Thanks
Regarding the reduction of the capacitive coupling between the two coils, it might be interesting to do some experiments with faraday-shields (an intermediate single layer winding of wire or foil, connected only on one side to a fixed potential, thus producing a capacitor between each coil and the shield, but reducing the coupling from coil to coil).
I use the L measurement difference between open and short to test transformers. works perfect, for every transformer I tried. I have made a video about it some years ago.
Excellent analysis. It would be interesting to check the highly-enclosed cores like ferroxcube p-type. In theory they should give best coupling as they minimise the open areas where stray flux could escape. Also toroids should be pretty good if you keep the winding intimate to the ferrite core.
Interleaved windings are also really useful or actually needed for transformers for audio purposes, to get a nice frequency response up to 20kHz. One of the reasons why mains transformers don't work well in audio circuits, because an high isolation is more important since they only have to work at 50/60Hz.
I guess its important to add here that at 20KHz an iron core no longer behaves as well as it would at 50Hz. It starts to loose its magnetic permeability; so the way in which the coil is built will help to reduce losses as more of the magnetic flux is going outside of the core.
Inductance is the most voodoo-like phenomenon in all of electronics, in my opinion. That said, Is there a theoretical (or real-world) max-min limit for transformers whereby the coupling factor is maximized and the capacitance is minimized? I’m guessing there is, but am curious to know how this is formally characterized.
The core was a standard ETD29, honestly I don't remember where I got it from; the bobbin was 3d printed - there might be some models available online for the larger cores.
What are the advantages of simultaneous winding over split inductors? The interwinding capacity is high and the coupling coefficient is only slightly increased, so there seems to be no advantage. Are there any other considerations?
I guess the coupling factor increase was marginal only in my experiment; in general this sort of winding - also called bifilar winding, as pointed out by other viewers - will give the best possible coupling factor. In other words, there is not much more that can be practically achieved to improve on this. Its usually widely used in RF applications.
I'd love to have a list of (vintage?) books (and any other resources) to educate myself about all things transformer (and similar things like motors, alternators, etc., for that matter). Do you have any recommendations? I'm especially interested in audio transformers. I'd like to understand why for instance, pro audio electronics designers are happier with Jensen (and other premium brand) transformers than with ordinary run-of-the-mill ones. I'm also interested in designing power generation equipment (micro hydro) and would like to have a good understanding of how things like wire gauge, # of turns, etc. are to be determined, given water flow rate and volume, desired output voltage and current, etc.
Unfortunately, I don't have a specific list of documentation. Usually I try to go for Application notes and Datasheets from the actual manufacturers of such products. Usually the manufacturer knows more about their class of products and use cases than other third parties. For hydro and power generation related info, I really don't have any input, its not something I am very familiar with.
With the parallel windings example @13:20 where you state that this method is limited to a 1:1 turns ratio, would it be possible to parallel-wind say, for example, two or three or four wires for the secondary for every one wire of the primary? Granted, this would no longer be a perfectly parallel winding scheme, but the inductance geometry would seem to be mostly preserved.
Honestly I never seen that done in practice, or try that; but it should be possible. You would not get a coupling as good as for the 1:1 circuit, but it still should be better than all of the other methods discussed.
8:22 When you reduce the capacity between the 2 inductors, wil this also increase the heat development in the primary, or is that only if a inductor or the primary in this case has no core?
From dissipation point of view, the whole transformer dissipates it's loss on it's outide surface area. The main loss is usually caused by the resistance of the wire. If you choose the wire sizes so that the primary has the same power loss as the secondary, then it should not matter which winding is inside or outside. The inner layers will get more warm no matter what, as the heat resistance to the core then to the air is higher than the heat resistance from the outer layer to the air, and on top of that the inside surface area is way less, but the total dissipation will be the same.
How much "natural" isolation do these coatings provide? I just built my first flyback converter on a breadboard to step up 12v, experimenting to see how high of a voltage I can generate. I used a 68µH 3A ring core inductor and wound 12x the windings for a secondary (just directly on top/in between the thick original wires). I charged an Elko to 350V. Is this near breakdown voltage? And I guess I just discovered that I chose the worst method for capacitance...
The breakdown voltage will of course depend on the exact type of coating applied, but you should get 1-2 kV on most typical wires; a very important aspect to mention though is that if the coating is scratched or peeled of for any reason, you get no more isolation... For this sort of voltages though (350V) you should be fine.
Thank you for a great video. What is the make and model of the special, gray-colored adapter that you are using to connect the tiny wires to the meters? And, where can it be purchased?
I got the adapter together with my multimeter, it was not bought separately... The multimeter is AxioMet AX-588B. On the adapter is written "Multi function socket". Hope this helps.
Of course the dielectric permittivity will have an impact on the capacity in-between the inductors, but just how much of an impact depends on how much air there also is between the windings and isolator - the windigns are not perfectly flat...
Regardless of transformer, there will be some voltage drop as a load is added, but this can be made worse by the type of converter you have built - so if there some sort of control logic driving the primary, not just a basic sine wave.
