Transformer core saturation and imbalance

[@andrewgalbreath2101]

I need a whole series of Matthias dissecting household appliances

[@fmaz1952]

Do you know the channel Technology Connection? Lol

[@matthiasrandomstuff2221]

he doesn't get into the nuts and bolts of how they work as much, certainly never seen him dissect and measure.

[@rpavlik1]

Yeah not the the electrical stuff as much as you. It was cool seeing inside a running dishwasher though.

[@ashypharaoh8407]

@@fmaz1952 He has some decent content, but his affect is so off putting

[@jasonharrison25]

@@matthiasrandomstuff2221 he occasionally does if the reason to open it is appealing enough or there is more to learn inside. But he doesn't measure current or much of anything else other than temperature. He does go into a lot of history and other details though which can make it a good learning experience

[@thomask4836]

I used to teach electronics and told my students that another technical reason that a transformer will hum LOUD like that is because it doesn't know the words eh! On a more serious note, your passion shows through your enthusiasm. I've been retired for years now and this was an excellent video and your explanation was impeccible! Thank You Sir! What is it about us wood nuts that love the nature of electron flow and gap flux density??

[@madriverair]

One 12 min video just practically described concepts I paid thousands of dollars to attempt to learn in college. The biggest complaint I have always had is the inability of higher education to provide practical demonstration of the theory. Don't know what prompted your playing with the microwave but thanks for sharing. Neat video. Enjoyed the history too... that will be a rabbit hole for later.

[@tomharner83]

I don't think of myself as dumb, but I'm always amazed when some people are able to go this deeply into such engineering questions.

[@locke3141]

I don’t understand most of this, but I still find it interesting.

[@brianoz2brn976]

Next series in channel - Matthias will take us through Maxwell's field theorems in an understandable way. Thanks for your ability to simply visualize electromagnetism :)

[@Mrshotshell]

On two GE microwaves I've owned the timer didn't start counting down for a second or two until it actually started producing microwaves. It was nice because if you put something in for 5 seconds it would be heated for 5 seconds, not just 5 seconds of power to the transformer and magnetron

[@fredio54]

Panasonic for years, but this could convert me.

[@Kineth1]

I wish we had a specific electrics manufacturer so we didn't need to rely on all these general solutions.

[@jakobsime4190]

@@Kineth1 lol

[@charlesenfield2192]

I observed long ago that short times in the microwave didn't seem to have their expected effect. The few seconds theoretically needed to soften cold butter without melting it is a prime example. I'm often inquisitive about such things, but in this case I never gave it much thought. Just started using longer times at lower power, which gave more predictable results. I know how magnetrons work, so I'm a little embarrassed that the warm-up time didn't occur to me. Thanks for the explanation.

[@andrewsuderman]

This video is so over my head, but I love watching it

[@kentceaser4413]

I have no idea what he’s talking about, but I find this fascinating.

[@linsteadpeck9288]

Thank you for sharing your understanding of this electrical theory, I have always loved electricity and I really enjoyed this video. Also, funny enough you seem to have a better understanding than the electrical technicians that I work with. I hope you feel inspired to keep making videos like this one.

[@Alexander84129]

I’ve never wanted a Canadian all star collaboration video from matthias and mehdi more!

[@markm0000]

I’ve never wanted it less. These are two separate channels.

[@jessicav2031]

Interesting! I always assumed it was the shaded pole fan trying to start up, so vibrating at the input frequency. It seems to get worse with age, which I would attribute to more friction in the motor bearings.

[@matthiasrandomstuff2221]

could be that too on yours

[@pete3897]

Oh that was some fantastic editing Matthias where you cut in the audio saying look how safe I'm being unplugging the live exposed wires and then picking up the oven with the water still in there. Honestly you had be guffawing out loud in my workshop fella! Love your style. Keep it up and many thanks :)

[@matthiasrandomstuff2221]

the water spill was completely unplanned. Though I did boost the audio so you can hear me mutter "oh shit" better.

[@nixxonnor]

I once posted a remark on KZbinr Mr Carlson's Lab and he got really upset and stated that I was some kind of a Troll pretending to know it all. That is by far accurate. The issue was that I mentioned that during previous information searches I could not conclude that a toroidal transformer would pull the most amps (and trip the breaker) if the transformer was turned on at the exact moment of the mains voltage zero crossing or 90 degrees later. Mr. Carlson said it was obvious that if the coil was energized at the voltage peak, the amps would be the highest. He got really cross with me, even though I only wanted to investigate and get some measurement data to understand how this all works out. So Matthias, you seem to have the skills and opportunity to enter this rabbit hole that I was only touching. After the encounter with Mr Carlson's Lab I did not have the courage to continue. A part of this is that that I remember a very good analysis that concluded that the closer you were to the mains voltage peak, the less the inrush current would be. But for me today it seems very strange that energizing a transformer at peak voltage should induce a higher current than energizing at the zero volt crossing... But then again you have the current lagging/leading voltage stuff that makes it all so har do grasp... en.wikipedia.org/wiki/Leading_and_lagging_current

[@thomasmaughan4798]

There's a lot of "just not so" stories on KZbin (and elsewhere). It also depends on other factors. An unloaded transformer is just an inductor and, near as I can tell, it does not really care where on the incoming waveform you suddenly make the connection. Ideally you make it at the zero crossing of voltage. Since current lags voltage, you would think current would be maximum, and so some people say, but that's stupid; how can there be current without voltage? Well, there isn't and cannot. So what happens is the voltage starts to rise, that builds a magnetic field and the rising magnetic field opposes the applied voltage. But the voltage keeps rising and some current must flow in order to build the magnetic field. Peak current happens at the steepest part of the applied AC voltage; and the steepest part is the zero crossing. It is not AT zero that matters, what matters is dv/dt, the slope of the voltage. In fact, the concept of "zero" doesn't matter to a transformer. So, as the voltage starts back down toward zero, the magnetic field starts to collapse and resists the reduction; or in other words, "squirts" the electrons along in the same direction they already are going. This is why current lags; as the voltage crosses zero and reverses polarity, the current reaches maximum and does not yet reverse polarity. This has some implications for the source, because the current is coming from the source. The voltage reverses but the current wants to continue in the same direction. Since voltage and current don't actually HAVE to be in phase, this current ripples back up to the source still out of phase. IF the source is an inverter or generator, this out-of-phase current can confuse the voltage regulator, current limiters and other things. Not only that, in a totem-pole arrangement of power transistors or mosfets, they cannot source current, but only sink current on the negative half. So the current must stop abruptly and when that happens, instant collapse of magnetic field with corresponding voltage spike that could reach back and destroy the inverter. A *loaded* transformer will have a lot less of this effect and current will be nearly in phase with voltage.

[@-sturmfalke-]

Man your channel is a goldmine for useful things to know!

[@daniellambert6207]

10:31 that would be the instant in a Medhi video where it cuts to him cursing... Excellent video, I would watch more of this.

[@Kineth1]

Great. Now I want a whole video about magnetic amplifiers.

[@surfcello]

This channel is quickly becoming more interesting than your main one ...

[@DEtchells]

Fascinating, especially the last little bit about magnetic amplifiers!

[@kevinmartin7760]

I think one of the Ward Leonard light dimmers at one of the theatres at university used a saturable reactor. With no control current it had high inductance and the lights remained dim. A control current (I think it was DC) would saturate the iron core making the main windings act like coreless ones, giving a lower inductance and much more current through the lights. This was not used for the actual stage lights, but for the house lights. The control voltage itself came from a variac which made this unique squeaking noise as it was turned, giving the audience an interesting sound effect if they were quiet enough as the lights went down.

[@wantmp3]

This is perfect. I was just pondering this yesterday while using the microwave. I'm so happy to understand that delayed hum now.

[@rossen_nikov]

I just want to add some small point to your anyway perfect explanation. I have/use isolation transformer for my on-desk electronics and repairs. It is rated for 1kVA. As you can imagine, 99% of the time I cannot switch it on in phase and as a result the initial current is so high due to unsaturated/opposite "magnetized" core that triggers my overcurrent protection. So, I use simple, time delay circuit with inrush limiting 5W, 10ohm resistors to prevent this problem from happening.

[@AbdicateDotNet]

I love how you analyze stuff! I've not used an O-Scope for years! Too cool!

[@markwatson9816]

Thanks for the mention of magneic amplifiers, where they came from, and how they work. I'd heard about them in videos about the V2 but hadn't realized how they work. All your videos are interesting but your illustration of how makes this a Mr. Wizard video.

[@matthiasrandomstuff2221]

I had been thinking I should be able to do it by just running some DC into a transformer, but thinking about it more, the control would have too much energy feeding back into it, and realized they had different arrangements of the core and coils.

[@dtiydr]

I have followed you for some few years now, but I had no idea you were doing stuff like this. KZbins algoritm send me this one.

[@musthavechannel5262]

day x: why pocket screws are bad... next day: flux is a function of integral of voltage. Thinking matthias does this to embarrass the unsuspecting DIY woodwork lovers...

[@s0nnyburnett]

An engineer for all disciplines.

[@louco2]

This is gold! Thank you for taking the time to do these videos!

[@esepecesito]

Wow. Learned quit a bit! I thought the humm at start of a transformer was worst if catched a high voltage. It is actually the opposite. The piece of history at the end is very nice. Had no clue about it.

[@steamer2k319]

So the magnetic 'amplifiers' were essentially conditioners designed to break through the ice of magnetic reluctance around the circuit? That seems pretty neat. Thanks for leaving the water spill in. I've been there before and it gave me a chuckle.

[@WormBurger]

I never even knew I cared about old microwaves humming... but apparently Mattias did.

[@C1Ansy]

This is very random and I like it a lot!

[@noobhunter3000]

Dismembering microwaves and questionable wiring? Matthias has watched way to many ElectroBoom videos lately ;)

[@thomask4836]

Totally agree, if this video was silent, that would totally be a Mehdi setup.

[@owendodman3037]

Boredom kills

[@somewhere-else]

matthias has been getting yelled at on the internet for his dodgy wiring for far longer than most youtubers you can name have even been watching youtube :)

[@thomask4836]

@@somewhere-else - Mehditthias?

[@jasonharrison25]

I almost always compensate for the delay in heating when using a microwave unless I'm doing something longer. I just kinda instinctively knew that it took a second or two before the magnetron would be active and build a habit of adding a couple of seconds

[@s0nnyburnett]

Hyperencabulator saturation chambers decay algorithmically along a toroidal path of current dispensation. Much research has been done to eliminate this unwanted effect but manufacturers want cost effective, easy to produce solutions. A hopper dadoscope with a laminated spiral core decommutator should do the trick.

[@matthiasrandomstuff2221]

Bonus points for using jargon words that actually relate to the video

[@kv501]

Criminally underrated comment. Well done.

[@marcfruchtman9473]

Super interesting. Please do more on the magnetic amplifier...

[@TradieTrev]

What does Matthias do for a living? He's a great teacher and I loved the break down of the waveforms!

[@holbroak]

Thanks, you hit just the right operating point for me.

[@Lizlodude]

Neat, I was right in guessing it was the magnetron heating up. Would also be interesting to mess with the power levels on the microwave, since most use a ~5-30 second period PWM instead of actually varying the power level.

[@kiffing]

I've really enjoyed this video, thank you.

[@fredio54]

Thank you for this video. I've been frustrated by this in the past, too. I wish tye manufacturers would take the filament temperature into account and only start the countdown once active. Voukd be done with a simple naive mathematical model.

[@jamiemascola6614]

Cool analysis!

[@tcm4721]

Mag amps, used in miller srh welders, units, 333's,444s 555s, Dialarc units and also mp units, 30e,45e. I loved welding with the single phase Miller Dialarc 250, Mag amp tech at it's best, not a circuit board in those things.

[@roccit]

Didn’t understand any of that. Will watch more times.

[@samp-w7439]

Is this guy a woodworker or electrical engineer? So much of this went over my head.

[@JonnyDIY]

He's a mad genius! 😆💕👍

[@Elektronaut]

Very interesting! I thought that's the time it takes to get the voltage doubler charged up but the filament makes more sense (and was proven correct)

[@mckenziekeith7434]

Do you think the startup hum of microwaves gets louder as the microwave ages? It seems to me that they do but I am not sure. I thought that was what this video would be about. Very interesting video though, even though it was slightly different than what I expected. I also didn't know you could put lightbulbs in a microwave. I thought we were being trolled.

[@CBWP]

Saturable core reactor. We had a very large unit at my last job that controlled a pit furnace for carburizing. I eventually exchanged it for an SCR. 480vac 3 phase 500a

[@JohnAudioTech]

Microwave oven transformers are designed to be operated at full load. Even with an open secondary, they draw a lot of current because of saturation. The primaries are wound at over 1 volt per turn where a general purpose transformer is wound at around 200mv per turn.

[@MegaVoltMeister]

One reason they are so closed to saturation is the fact they skimp on materials to make them as cheap as possible. Use the least amount of copper and iron and some times the primary has Aluminum windings.

[@analoghardwaretops3976]

Now J.A.T. comes chipping in before MEHDI..goes BOOM 👍👍

[@analoghardwaretops3976]

J.A.T. may be studying the feasibility of subwoofer audio signal for driving the microwave tx.....

[@howardsimpson489]

The variac starts with points bounce. The nio magnet will not be magnetised along it's length but across it.

[@joshuaobelenusable]

I would love to see the scope if you had 2 transformers running, scoping one, and then slowly bring them closer together.

[@vandabo]

Man, I'm enjoying watching a video about electromagnets and microwaves, and then I get distracted for a few seconds and then he's talking about V2 rockets? Guess I'm gonna have to rewatch the part I missed!

[@elanman608]

The same idea was used to control theatre lights called unsurprisingly a saturated core dimmer.

[@GabrielNeacsu-gu6mv]

Mathias thank you for this video! Was explained very good. I would like you, if you have the pleasure and time, to do the same for a transformer in a SMPS PSU... tell us about transformer core sizing, feromagnetic materials, etc...

[@PeopleAlreadyDidThis]

I have the 15A version of that Staco variac. Unless one lucks into the magic instant in the power line cycle, its current spike trips a 15A mains breaker every time.

[@analoghardwaretops3976]

Use a suitably sized TRIAC with zero crossing optocoupler triac trigger chip...for both turning ON & OFF.....a bypass relay can be added to short out the triac a few secs. AFTER turn on & to open a few secs. BEFORE z.c.d. turn off.....that way inrush is always @zero....& there is no turnoff spike either

[@darkstatehk]

Exactly the kind of question I would ask on a Friday evening. Excellent stuff.

[@whirled_peas]

He’s really figured us out eh

[@howardsimpson489]

I reckon you are looking at the initial half wave capacitor charge current which is why it is repeated in the same phase.

[@hendrikehlers1066]

Fluxgate magnetometers also use saturation to detect external Magnetic fields. I didn't know about the amplifier!

[@eviltreechop]

Looking forward to your review of the Blackberry movie when it comes out 😆

[@matthiasrandomstuff2221]

Hmm, indeed. They did consult me for that one a bit. Though I'm sure for the sake of making it an entertaining movie, it won't be that true to reality. Fact is, some of the pivotal moments in RIM's history didn't seem that pivotal at the time they happened -- enough so that in the log I kept of what I did every day, some I didn't consider worth noting.

[@daifeichu]

You channel always brings me back to my college days which I enjoyed a lot. Thanks for doing these Matthias. I haven't owned a microwave for about 20 years now so haven't experienced the hum of one and don't miss it.

[@perrybrown4985]

I'm looking forward to his exposition of the inner workings of an Interocitor

[@blaircox1589]

I'm on my second new Panosonic microwave. A 900 watt model. It's the noisest microwave I've ever owen, the first one lasting only a few month with likely the diode going on it. This second one is a slightly better model, but still 900 watts, but it's already making noises that do not sound healthy at all. Bottom line, keep your older, better built microwave as long as possible.

[@lightdark00]

We deserve some kind of mouse video now. Mazes, traps, or whatever, I'm not picky.

[@aerogfs]

"Notice how unsafely I transported that glass of water inside the microwave."

[@nonsquid]

Many of the microwave transformers I've taken apart have permanent magnets on them to pre-bias the transformer into partial saturation. I thought they did this because they are only half wave rectified and they wanted to buck the transformer output and use more of the core volume for flux feeding the magnetron with a smaller, cheaper transformer.

[@matthiasrandomstuff2221]

that's is a very clever idea for when using a half wave rectifier. Haven't seen that on any microwave oven transformers myself though. But thinking about it, with the voltage doubler typically present, in one direction it charges the cap, in the other direction it uses the voltage stored in the cap, plus the transformers voltage, to power the magnetron

[@nonsquid]

@@matthiasrandomstuff2221 If you search youtube for "microwave magnets" you can see examples of the magnets I am talking about.

[@TheSonichedgehog8]

I would love to hear more about thoes magnetic amplifiers owo

[@ericfeldkamp3788]

"More flux than it can take".... this seems like a good spot for a flux capacitor.

[@markbrotherson]

Thank you, teacher

[@jonathandill3557]

"Hon, What are you doing to the microwave?"

[@Nick-HBC]

Towards the end there I thought we were heading towards an ElectroBoom moment!

[@T2D.SteveArcs]

Great video mate Saturable core reactor 😁 il be posting a video about my DIY version made from a old 3ph transformer and a variac controlled DC source to control the saturation level Steve

[@matthiasrandomstuff2221]

email me when you do!

[@T2D.SteveArcs]

@@matthiasrandomstuff2221 👍👍

[@unregistereduser2]

You should check out 'constant voltage transformers.' Really neat way of exploiting resonance and magnetic hysteresis to provide a regulated voltage output, without semiconductors.

[@matthiasrandomstuff2221]

Microwave oven transformers strike me as constant voltage transformers, though googling around for it, I saw no mention that they are (which is not to say that they aren't). They certainly have weird current waveforms, different from regular transformers.

[@unregistereduser2]

@@matthiasrandomstuff2221 I have a 1.2kVA ferroresonant CVT. It's got a LOT of iron in it. At least 60 or 70lbs. And a pretty large bank of capacitors. A MOT doesn't have enough mass to provide sufficient power storage at >kW outputs to act as a CVT.

[@eDoc2020]

@@unregistereduser2 A microwave transformer also isn't large enough to run a load the size of a microwave oven. Even with forced air cooling they'll still overheat if run continually.

[@peckhamian]

@@unregistereduser2 Diode Gone Wild has made a video about ferroresonant cvt a couple of months ago. Pretty good explanations there.

[@piconano]

There is a high voltage capacitor inside a microwave. I think, those humps distorting the current's sine wave, are the result of a capacitor charging and discharging. What is the power factor of that microwave?

[@eDoc2020]

When you turn on the unit the capacitor will charge up but won't discharge at all* until the magnetron warms up. *Except for the capacitor's discharge resistor.

[@MegaVoltMeister]

Have you noticed how variacs have a larger and maybe longer inrusher than conventional transformers? I have noticed that the older MOT draw less open circuit current than the newer ones. I attributed that to the cheaper cores and windings running closer to saturation. Another thing I contemplated was if a transformer was switched off during the negative cycle and then later powered up at the peak of the positive cycle, this would seem to be when the maximum inrush would happen. The residual magnetization of the core in the opposite polarity would seem to be the biggest load?

[@matthiasrandomstuff2221]

Good point, I hadn't thought about the residual magnetism contributing, but I'm sure it does.

[@analoghardwaretops3976]

In smps ..some controller ics for push pull transformer applications have internal logic sequencing for restarting on the next device in cases where such is required after clearing fault / protection conditions... This is only possible as long as the ic is powered up... In case of AC transformers etc. similar can be achieved with memory/latching relays..+ logic circuitry to allow such alternate phase sequencing on .

[@eDoc2020]

I imagine variacs are run relatively close to saturation. You need lots of turns to avoid saturation yet variacs only can have one layer of windings.

[@TheDaniel688]

I had a large old Sun Microsystems CRT monitor that did the same thing. The initial hum was huge.

[@matthiasrandomstuff2221]

Big old color CRTs have deguassing coils in them that run when the monitor sarts up. Same with TVs.

[@SinsBird]

I got startled when you moved the waveform on the transparent film. I was like, what just happened?!

[@dack42]

What happens if you set your microwave to a low power setting? It should cycle the magnetron on and off, which I expect would unload the transformer and make it hum again during the off cycle.

[@matthiasrandomstuff2221]

correct

[@c0ldc0ne]

I now know how Marty must have felt while Doc Brown was explaining how he modded the DeLorean.

[@NoirBeard]

Safety and swearing? Mehdi would be proud.

[@hansangb]

Throughout this video...Mrs Wandel /* as the house dims in phase w/ the microwave */ MATTHIAS!!! KNOCK IT OFF. I'M TRYING TO MAKE DINNER OF THE KIDS!!!!! :)

[@MaxGoddur]

Wow, you come up with some interesting ideas! While I was watching your videos I remember some folks stating you should never connect an Ocilliscope to and 115VAC line. Something to do with the ground on the AC circuit and the probe ground. Could you explain what this is about?

[@matthiasrandomstuff2221]

I just plugged my scope into a 2-prong extension cord, so no ground! And the current sensing resistor was on the neutral side.

[@dack42]

The ground clip on a normal scope probe is directly connected to the chassis of the scope and to the ground pin on the power plug. If you were to connect that to hot, you would have a direct short to ground through your scope. In some circumstances you can get away with connecting the the ground clip to neutral, but it's still risky. For example, if you break the neutral on the supply side you'll still get the full load current going through the probe ground. Disconnecting the ground pin on the scope may work, but then the risk changes from blowing your scope to shocking yourself when you touch it. You could just not use the ground clip, but that will give you noisier measurements (since the ground path is through your AC wiring instead of directly from the probe). The best solution is a high voltage differential probe, or isolate your load (such as with an isolation transformer).

[@MaxGoddur]

@@dack42 Thank you for the detailed answer that was really helpful.

[@tardigrades3184]

My microwave hums louder at the end when it's done heating the food but it still spins for a second or two as it beeps saying it's ready. I wonder if it's because the microwaves stop being produced then.

[@talhaahsan7480]

that initial peak might be because of the transformer inductance at the primary is big so it draws more current for a few mili seconds . I saw the same peak when learning about how to choose a fuse for the transformer primary. What you think?

[@talhaahsan7480]

nice solution

[@matthiasrandomstuff2221]

actually, the initial peak is as explained in the video.

[@termiterasin]

I'm watching a man flip on and off a microwave 20 times in a row and couldn't be happier!

[@SupremeRuleroftheWorld]

at least you didnt open your fuse box today. so that's a win.

[@NavinF]

Been a long time since we had fuses in north america

[@TheMadJestyr]

This is like Mr. Pete for smart kids.

[@dl5244]

1. the human ear-brain system cannot discern very short acoustic sounds such as the first cycle inrush. this is part of how the MP3 codec works to perform lossy compression of "un-hearable" sounds. 2. current out of phase from voltage does not indicate real power, but reactive or "imaginary power". 3. many power supply circuits include an NTC for inrush limiting that has a several-seconds thermal time constant ps. an older engineer taught me to never trust that toggle switch on a variac! He's shown me a few that failed in a shocking way!

[@JonnyDIY]

All I wanna know is what you're microwaving for an additional "2 seconds"? 😂💕👍

[@matthiasrandomstuff2221]

a small cup of hot chocolate for the kids

[@ramous5182]

could it also be the capacitor charging until the voltage is high enough for the magnetron?

[@wyw876]

magnetic core memory next?

[@JoseSilveira-newhandleforYT]

Interesting that you noticed the filament warming time.

[@MoShen-rk9qb]

dude i see you everywhere, here and PHAD lol. we share the same interests lmao

[@JoseSilveira-newhandleforYT]

@@MoShen-rk9qb LOL. Yep, diversified interests 🙂

[@RichardGreco]

Very interesting. I would have guessed the initial loud hum was due to the plates in the transformer vibrating but then warming up and not slipping. I hope your humor about your simple testing setups with electrical connections isn't foreshadowing.

[@Mark-dc1su]

Matthias got me with a deez nutz what?

[@pokojnitozo2360]

Mag amp is stil used in PC PSU(ATX), to regulate 3.3V!

[@matthiasrandomstuff2221]

cool!

[@AdityaMehendale]

..and a similar principle is used in fluxgate magnetometers too.

[@matthiasrandomstuff2221]

Interesting, just had to look that up!

[@AdityaMehendale]

@@matthiasrandomstuff2221 :) It's not everyday that one gets to add a droplet on knowledge to the ocean that is MW :)

[@KG4JYS]

I'd like to see some videos on toroidal transformers. Got any of those?

[@matthiasrandomstuff2221]

Just my variac.

[@honeyforce996]

@Matthias- I can't remember, but if you guys homeschool your kids, can you post the curriculum on your blog? Or, if anyone else reading this knows of something good, I'd love to hear it as well. Thanks

[@matthiasrandomstuff2221]

we don't home school

[@gregorymirsky8707]

Did you take into account that in a transformer the only current that can saturate the core is the primary winding MAGNETIZING current, and the main primary and secondary fluxes compensate for each other.

[@lwilton]

The fast hash at the start of the current waveform for the autotransformer is quite likely contact bounce in that toggle switch. Adjusting the core saturation was how SOLA "constant voltage" transformers maintained a somewhat constant output voltage despite line and load variations.

[@SenorGonzo]

I might have missed it because this is all rocket science to me, but why don’t new microwave ovens hum?

[@matthiasrandomstuff2221]

They don't use a big transformer. Switching converters instead