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Is it easy to create your own Transformer? Everything you need to know about Transformers! EB#42

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Rating: 4.0; Vote: 1

Is it easy to create your own Transformer? Everything you need to know about Transformers! EB#42 ian: Hi GreatScott, overall a very nice video, good to see this kind of education content! I would like to offer some small technical corrections if youre amenable. At 5: 00, you say that the EMF induced in the primary which opposes the applied voltage is the reason the primary current didnt agree with your complex impedance based calculation. This EMF _is_ self induction, and is exactly what your meter measured, and if the measurement were taken under the appropriate conditions, the complex impedance formula would give you exactly the mains current. The reason you didnt get agreement is that electrical steel is a highly nonlinear magnetic material: your meters excitation current simply wasnt high enough to replicate the (nonlinear) inductance that the mains voltage sees at higher excitation. You could point at the chart at 6: 30 (or a similar chart) to show this: the line approximating the slope of the 0. 3 T B-H loop is less steep than the one approximating the slope of the 1. 2 T B-H loop. Or, a current probe/oscilloscope measurement of the magnetizing (no load) current would show the extreme nonlinearity of the typical mains frequency transformer. Also, at 7: 52, you say that increased load current can push the transformer closer to saturation. This is a very common misconception. In fact, at higher loads, a transformer is operating farther from magnetic saturation. The reason is that the secondary currents flux opposes the primary currents flux, as you said. This ends up lowering the total core flux. You can work it out from the lumped element model by seeing that the load current reduces the total AC voltage across the mutual inductance part of the winding system, and causes larger voltages across the resistive (and leakage inductance) parts of the primary winding impedance. So the dPhi/dt integral of the mutual flux (which is equal to the mutual voltage) must be smaller, and peak mutual flux is actually lower. At 8: 29, the formula you show is the formula for induced voltage in terms of _net magnetizing current_ (the flux that links both windings, not primary current. Magnetizing current is the difference between primary and secondary amp turns (at least ignoring leakage inductance, which is usually fair for mains frequency transformers. So that I should really be labeled Im or Ip - Is. Referring to the T model at 5: 44, you can see how (in the lumped element model at least) the Lm element sees less voltage as the load current is increased, and so the flux linking Lm is reduced. The model is just a model of course, but the real behavior is captured correctly in this case. Edit: also, worth mentioning that the reason high power transformers use larger cores is really just so that the primary (and secondary) windings can be made with fewer turns of thicker wire, reducing the ohmic resistance and therefore reducing conduction losses, while still avoiding saturation at no load conditions. It's also worth noting that the volt-second product seen by a mains frequency transformer winding is a super fundamental parameter that drives core flux excursion as a function of winding count, and that practically we always use this method of calculating the core flux, and never use the induction formula, because the induction formula depends on the nonlinear resistance while the volt-second product applied to the winding is directly proportional to the change in flux linkage, and so tells you exactly how many turns and square centimeters you need to hit a particular operating flux.
Date: 2020-09-05

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Comments and reviews: 9

Pablo
This video is so awesome.
At my work we built a couple of Three-Phase transformers that were designed to transform 110VAC to 50VAC at 125Hz. We were struggling with saturation and we had to adjust the design of our system, thus increasing the operating frequency from 125Hz to 250Hz (not such a big deal since we were going to use a three-phase rectifier for those phase-phase voltages)
This video was very educative.
Can you please make a video explaining Generators or Alternators? That would be so awesome
reply

Jorge
I'm confused by the explanation of why the current through the primary winding is less then V/Z. Because the back EMF induced by the current in an inductor is nothing else than the phenomenon responsible for the reactive part of its impedance in the first place. And a transformer with the secondary winding open is just an inductor. So, there must be something else that is causing that discrepancy. Maybe the inductance measurement was inaccurate, or done at a frequency other than 50Hz.
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Steve
I bought a transformer with 2 x 24v secondary outputs and put a bridge rectifier on each output. Without load each output was measuring 49vdc? Shouldn't this be closer to the rated 24v power of each secondary output? Or is this simply a no load voltage. I did not put either output under load until I could get a better understanding of the dual output transformers. The bridge rectifiers used were package type and not made fr inn 4 separate diodes.
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Spatial
I have the same USB charger you showed at video start, but it was sold in switzerland with a different package!
But the PCB is still the same! Galvanical isolation of this transformer is very bad so you should protect yourself by connecting the negative output of the phone charger to the ground of a mains voltage plug!
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Aldrin
Great scott sir, please make a video describing about AC to DC smps. i. e. Str w6754 ic based smps. And also include about err amp, feed back system. Please I request you, I am very curious to know about this topic from you, since your videos have been very much attracting me from the last 3 years.
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Research
I used to make my own transformers baxk about 20 years ago, they worked well. Mine were designed for 25khz and up tho for switching power suppliy use. Calculated about 88% efficiency average on my diy transformers. Used to take the core out of commercial ones and rewind it for what i needed
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Jonas
Hi Greatscott.
I'm creating a diy spot-welder with a MOT and a timer/control board. In the primary coil there is a capacitor in series on the input of the primary coil.
Why/what does it do?
Does it need to be there? (It broke when removing the secondary coil)
Thanks
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Steam
I love your video so. much, but i want you to help me with this. i am working on ultra low voltage boost converter to light a LED by using Thermal Electric Generator but i dont know what to do please helpppp me =(
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Carlos
I've been trying to understand this in highschool but my teacher, men! I wished see this video 10 years ago
P. s. I speak Spanish so can you add subtitles in other languages this is very important knowledge
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