Understanding Transformers Part 1: Inrush, Saturation and Fusing
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- Опубликовано: 20 окт 2024
- We test a transformer using a Rigol 1054z scope and a 120 volt transformer to see what current inrush we get due to saturation, and explain transformer characteristics and fusing considerations
Very good explanation! Thank you for your effort. By the way I saw your videos on Odysee. I came here because videos were buffering for a loooooooong time. But it is so much easier to find relative content on that platform.
Super helpful video, very well explained. Thank you!
Congratulations on the nice volume level - it matches the quality and clarity of the video, and the clean/organized work bench. Far too many otherwise interesting videos relied on the cheap microphone of their camera making the video unhearable/unwatchable. I wish every author had your attention to detail in this regard!
Thank you so much. One of the most helpful and effective video I have ever watched on Yotube. Much obliged.
I am a total lateral entrant in to electronics and wow this is great stuff I even dare to say that I get it.
Thank you so much!!!
Thanks for the great explanation.
Best explanation I have seen. Excellent and thanks!
Excelente explicación sobre el tema, muchas gracias.
Saludos desde Argentina!
hi, at 15:10 you say transformer primary is 20 ohms and you calculate 6A max current but scope shows 7A, I think the mistake was that 6A is maximum RMS current and you are measuring maximum peak current. So at 120V RMS, you have about 170V peak voltage and at 20.5 ohms (primary+shunt) that could produce max peak current of 8.3A.
*In this context I have a question regarding flyback transformers:*
Instead of a single coupled inductor (gapped core) with a high windings ratio, would it make sense to instead use a low windings ratio coupled inductor (to deal with inrush currents and core saturation) and connect it in series with a transformer (non-gapped, toroid) to do the majority of voltage up-stepping (=at a higher efficiency than a gapped core)?
It would be useful to show the applied voltage waveform along with the current waveform to illustrate where on the voltage waveform the current is peaking.
@@thomasmaughan4798 You can't do that yourself?
@@EETechStuff "You can't do that yourself?"
Yes, I cannot. Once the shunt resistors arrive I will be able to do this myself. So many youtube videos are ALMOST useful.
Experiments complete! Thank you (and youtube) for revealing this phenomenon. By displaying the voltage and current, I obtain understanding of that first half cycle.
*The strongest inrush* happens if you energize the transformer at the voltage crossover or zero. The polarity of the inrush depends on the slope of the voltage at that moment; rising or falling.
*The least inrush* happens if you energize it at peak voltage.
*Inrush current starts* when the voltage waveform crosses a peak. In other words, if I energize on the positive half, quarter of the way into the voltage waveform, the current just sits there until the voltage goes over the top and starts back down. That is when you get the inrush and it *catches up* to its out of phase current.
*Core magnetization* of the inrush is remembered for some cycles, about a dozen. The subsequent voltage polarity changes are not enough to immediately demagnetize the core. Eventually the current in the core becomes symmetrical but still isn't a sine wave.
*Test Conditions* : To eliminate the problem of residual magnetism from turning it OFF mid-cycle, I use a variable autotransformer to reduce the voltage to zero and thus leave the transformer in a known, non-magnetized state for the next power-on test. The oscilloscope is powered from a Goal Zero batter/inverter so as to avoid problems that can happen clipping the ground lead to the mains power.
When I first learned that a magnetic core was added to transformers to get a larger magnetic field for less primary current (less primary current compared to how much current required with air core for the same magnetic field coupling), I thought "okay, the core magnetizes and less primary current is needed to get a bigger magnetic field coupled to the secondary"
But the larger magnetic field means higher current in the secondary since current increases with magnetic field intensity.
So it seemed odd "we use the core to boost lower current in the primary to get a higher magnetic coupling to the secondary, but when the secondary current really takes off - when the core saturates - that's somehow bad."
Faraday's law, induced voltage directly depends (varies directly with) magnetic flux created by the primary, and the core boosts the magnetic flux.
Obviously, the non-linearity when the core saturates and the secondary current goes non-linear is a factor
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Thank you from the other half of the world
How does this change when there is a load on the secondary?
Greaaaaaaaat
Sir, could u tell me whether transformer always goes to saturation
A transformer should never go into saturation. Its impedance will drop suddenly allowing high current in the primary with no additional current in the secondary.
After some experiments, it isn't clear that a transformer always or ever goes into saturation BUT the inrush current can be large depending where in the voltage cycle you energize it. This inrush magnetizes the core and takes a dozen or so cycles to degauss itself.
so what to do... between switch and fuse,,, never to be answered
Max current indicate to voltage cross zero sinusoidal 120V/60Hz and blow fuse very hard to set in this point
Fuse chose to transformer slow blow and nominal current for this power rating
Outerwise don't blow fuse set high current mesurent this point in this video
This explains why microwave transformers draw so many amps from mains lol