EEVblog 1469 - AC Basics Tutorial Part 2 - Phasors

[@thegreenxeno9430]

Your tutorial on Op Amps was essential to me helping my friend graduate an electrical technician program. These are great!

[@thosewhowish2b693]

I need to point out the convention for the sign of the angle. In AC, φ is positive (anti-clockwise) for inductive loads (current lagging the voltage), and φ is negative (clockwise) for capacitive loads (current leading the voltage). To accomodate the convention, the equation actually becomes v(t) = Vp*sin(ω*t - φ). In your drawing, as you said, V2 is leading V1. While your phasor diagram checks out with the equation on the white board (summing φ inside the sin()), convention-wise, V2 is lagging V1 on the phasor diagram. The phasors should be reflected about the horizontal axis, or V2 should lag V1 on the plot against time. This distinction is very important when designing power factor correction, single-phase machines, and the likes. Btw, great video!

[@martinda7446]

Ha, ha brilliant Dave. I admit, I almost didn't watch, but thought I may as well look through to see how you were doing. Well I'm glad I did because your 1/10th of a Smoot had me in stitches. The community just couldn't be any luckier, to have such a wonderful ambassador. I've thought about doing a first principles series...Just thought about it. Done nothing! Dave does it and keeps on giving. His energy and generosity are legendary as far as I'm concerned.

[@mastershifu23]

Great work Dave. It comes both as a refresher and a lession for me! Thank you so much for starting this series 🙌

[@keithminchin1817]

Dave this is awesome. I’ve been scratching my head for a while looking at some brushless motor control theory. Always a fan of the way you explain things.

[@BenChilds]

Well explained, Dave. In less than 7 minutes I now understand how the analog video vector-scope I used in college to color calibrate NTSC video decks to cameras works. I never could figure out why the target locations were at different distances from the center of the scope - it appears it's because it's showing the amplitude and the phase simultaneously.

[@karlm9584]

I needed this about 8 years ago when i was doing electrical tech in my ee degree. Confused the heck out of me at the time. Thank you!

[@sandromoscati7380]

Same for me, but 25 years ago, I learn more in 20min then sometimes days/weeks/months in the classroom... Dave is awesome!

[@MattHollands]

Just to be completely specific about what you said at 15:20, any two sinusoidal waveforms *of the same frequency* that are added together will you give you another sinusoidal waveform.

[@ct1igu401]

One of the best explanations of this that I've seen. Thanks

[@radman999]

THANK YOU for producing this technical content, Dave. If you don't get hundreds of immediate viewers, consider it invaluable for the archives for students to refer back to when they need to visit this particular topic. Don't change a thing man!

[@IanScottJohnston]

"CIVIL".....wow that takes me back many years......thanks for refreshing my brain Dave!

[@pj6366]

Never heard of "CIVIL" before. It was always ELI the ICE man.

[@janeklof2769]

Extremely good explanation - very pedagogic ! Many thousand thanks for your honesty and piece of excellent work ! You have a great knowledge and experience of electronics. It is nice to learn from a person who knows what he is talking about !

[@fg2996]

Great video, as always! I want to point out that a lot of this is only true if the sine wave have the same frequency though. If the frequencies are different, then the sum of two sine is not a sine. In that case, phasor are not too useful (but complex numbers still work of course).

[@EEVblog]

Yep, I should have made that clear.

[@JarzanX]

@@EEVblog This just proves that even the best can always improve ;)

[@Peje1953]

Thats in the chapter about Fourier analyses, I presume?

[@garypoplin4599]

@@EEVblogWhen discussing ‘phase shift’ between two waveforms, they are necessarily the same frequency, right? Did I miss something here? Doesn’t the concentric circles diagram represent the same frequency at different amplitudes?

[@scottholmes4388]

Great video. No mucking about, just good ole fashioned physics. You could easily explain power factor with this video, and magnetic theory.

[@KidCe.]

Finally some more teaching videos 😍😍😍

[@Sahko123]

Great video! I would also love to see a video on how these phasors and the complex numbers relate and can be used to calculate inductance and capacitance values!

[@EEVblog]

Editing the video now!

[@TheZanger]

You probably didn’t expect this but this is also very interesting for audio engineers to better understand phase. Say you have to mic’s picking up one instrument, one close and one a bit further away and things start sounding funny. Or with peaks and dips in certain frequencies with speaker placement and room reflections. A lot of audio engineers struggle with understanding this when they start. Great explanation!

[@kratz9]

I'm saving this to watch later. As a comp sci major that took an AC analysis course from the physics dept. ('cause I thought it'd be fun), I'm excited to try and remember how in the hell I passed that class.

[@sandromoscati7380]

Thank you so much Dave for this perfect explanation. You are awesome!

[@gregorymccoy6797]

Ah the memories. These were always the busiest looking graphs in the textbooks. First time I saw them my jaw dropped. Turned out it was pretty simple 😀.

[@andreavergani7414]

Thanks you. I really appriciate this series

[@richardgrier4721]

OFine. I was a university freshman 55 years ago and haven't forgotten these concepts. However, I find value in your channel(s), so I'm here to passively (get it?) support you.

[@JohnSmith-bb2np]

That was exactly the same lesson I learned about two years ago in an amateur radio class for the extra class license. I expect the complex (imaginary) numbers tutorial will be the same too. I know radio doesn't excite you, but you would make a great guest speaker at classes like that. I really like these kinds of tutorial videos from you. 👍👍

[@joeyjustin6895]

Thanks Dave You Are Always My Number one Teacher. 💯💯

[@Kombivar]

Great stuff, I had it earlier in course, now on the 3-phase systems, would be great to see the simpler explanation of star and delta connections. All the best!

[@protocolfree]

i love and miss that small whiteboard , i like how you break down complicated stuff . you are a great teacher . keep it in the educational realm (ps I thought I is scalar and J is the vector )

[@TheDefpom]

@11:40 I’m pretty sure the circle is called a vector diagram, I vaguely remember this stuff from when I learned about 3 phase AC during electrical training a dozen years ago.

[@tookitogo]

No, it’s called the unit circle.

[@llamafrhd]

Thank you for finally uploading part 2

[@bertblankenstein3738]

Even though phasors might not be used thar much, they are still a great way to understand. Thank you for the fundamentals Friday video.

[@punchar4161]

fundamentals back baby., Wow! Thanks Dave!

[@a.x.marcus4627]

You are an amazing teacher. Thank you.

[@jdlives8992]

Last night I thought a lot about your videos. I suggest you use music / waves to show the masses all of this juicy stuff. I hated the math in the 7th grade till my science teacher sat me down and played some reggae music on a old school korg and showed me the way the wave was formed and 2 weeks later I was making beats and he was dancing to my math….

[@IGobzter]

Lovely explanation Dave! It really helps after most of my university class got whopped on our first math exam of 2. semester, it was hard to grasp phasors based on our book.

[@MaciejMiklas]

This is a really very good explanation - thank you!

[@allanoommenkurian9128]

waiting for part 3 my exams are in a week this really covered the first module of FACS for me Thank you very much 🥰

[@lilstubthumb]

I went more of a programming route after I graduated with my EE. It sucks how much you forget when you don't use a skill. I remember the concepts of course but a lot of the details are gone. These kinds of videos are almost nostalgic.

[@selectnull4459]

Good job Dave :), basics are fundamental, kids should be happy watching this :) I, m waiting for Laplace transform :)

[@marcfruchtman9473]

Thank you for a concise review!

[@allthegearnoidea6752]

Holly shit on skates I enjoyed this video. Not enough people know about how the sine wave is generated and always worth mentioning. It’s a shame that whenever I do math in my videos 80% of the audience switch off. Thanks Dave nicely done.

[@siddharthmali5841]

Excellent explanation.

[@gregsullivan7408]

Just as an aside, I'd be interested in a presentation on AC inverter design, especially with regards to how inverters handle reactive loads.

[@Turbochargedtwelve]

Someone was listening to the latest amp hour!

[@gregsullivan7408]

@@Turbochargedtwelve eh? I wasn't, if that's what you're suggesting. (but I suppose I should!)

[@Turbochargedtwelve]

@@gregsullivan7408 it’s episode 583, not the newest, but they talk about four quadrant inverters that can produce vars and lots of other good power stuff. Check it out!

[@drjenschn]

Great show, but at 15:30 "any two sinusoidal waveforms you add up or subtract; you end up with a sinusoidal waveform" seems quite wrong to me. To prove: The Fourier transform exists, and it's real-valued counterpart (cosine transform) is essentially a weighted add of sines phased all at pi. I first thought that was a special case for same-magnitude phasors, but I don't think you even have that semigroup property for such constrained additions. Multiplications are different, though... If you could comment on that? I could be more easily convinced for convolutions of sines... I think you can even see it from your sketch, where the central "negative" lobe should be ending up at a much narrower frequency than its neighbord.

[@wilburt6131]

Interesting. Hope we don't have to wait another 7 months for part 3!

[@McTroyd]

Star Trek Pedantry Warning: The show uses "phasers," not "phasors." 😁 Cool stuff. I've seen those diagrams before in old aerospace stuff and wondered what they were for. Now I know! 👍️

[@isettech]

Some precision motion control I work with uses a rotary transformer to create the Sin and Cos of the reference. They don't call it a Phasor in that application. They call it a resolver. An IC is built to support this and provide a real time absolute encoder out of the signals with 12 bit resolution and includes a real time velocity signal for PID processing. The Analog Devices AD2590 IC is relatively inexpensive decoder for absolute shaft angle.

[@seanm2511]

Thanks Dave. I feel like I could show this even to mechanical engineers :)

[@uni-byte]

@ 4:30 your notation shows a vector quantity equal to the dot product of two other vectors. Nahhh.. the dot product between two vectors is a scalar. You needed to use the cross product notation. It's actually an important distinction.

[@Theo0x89]

That's not the cross product. It's the product of complex numbers.

[@uni-byte]

@@Theo0x89 Complex variables are not written using a bar over them. Bars over the variable denote vectors. You can use a preceding bar to denote the conjugate of a complex number, but that bar goes before the variable name, not over it. One way or another, what he wrote was wrong.

[@victortitov1740]

@@Theo0x89 yes, and that "complex" vector product is useful even in geometry, so i wonder why there is no proper symbol/name for it.

[@hadibq]

so love that casio!! great tutorial too Dave if needs to be said ;-)

[@triode3582]

Took you long enough to make part 2 Dave!

[@polaraligned1]

Great video. Thanks Dave.

[@jp040759]

In MERICA we learned it as ELI the ICE man. Volts Inductor Current (volt leads current in inductor) vs Current Capacitor Volts (current leads voltage in capacitor).

[@JoannaHammond]

For me the most important thing to understand is e^ix ... x being the paramter. :D You suddenly understand so much, including a lot of the math in quantum mechanics.

[@rafakordaczek3275]

17:25 - fun fact: in Poland, we call this "Reguła Ciula" or "Prawo CIULa". The hillarious thing is, that "Ciul" is a bad word, calling sb a douche, or an idiot. That's a fun way of remarking how current behaves in response to AC signal depending on inductance or capacitance.

[@birchtree5884]

Got a final on AC circuits tomorrow, video coming in clutch

[@SwordQuake2]

4:27 the dot product of two vectors is not a vector...

[@peterjeffery8254]

I love how voltage and current can be calculated using geometry.

[@darthvader3177]

Great explanation , very informative Thanks ; )

[@dhpbear2]

11:21 *DaveCAD* works as well, in spite of its severely limited workspace! :)

[@williamtell1477]

I have kind of a dumb question, this is the only place I know where to ask. I work on vintage synthesizers (amateur) mostly from the '80s and '90s and they always seem to use a soldered in battery. This is typically a bit a pain to service of course compared to swapping out a battery in a holder. I was wondering if anyone here knows why they do it that way? I would guess either cost or encouraging a trip to the repair shop every 10 years?

[@erikdenhouter]

Rechargeable ? That will be the answer I think. Charging will need .5 - 1 Amp, and a holder for a rechargeable battery is not reliable for that current. Almost every appliance in that period I saw with a rechargeable in them was soldered. Today I have an electronic gas lighter, and there's one normal AA alkaline battery in it. It is a crappy design for the battery holder (though it is a reliable spark maker), and it draws a pretty current when turned on. The first years I had always problems remaining a good battery contact, repairing it every two months, and putting a new alkaline cell in every 9 months.. Until I had enough of it, and with a 75 Watt solder iron just soldered one alkaline battery in. Never had any troubles with that again, and the battery lasts for two years now. Takes me 10 minutes to replace it.

[@garypoplin4599]

13:46 - That would be precisely 6 and 3/4 inches (plus or minus the tenth of a Smoot’s ear)!

[@landonwilliams565]

ELI the ICE man. Some may have heard the saying

[@tedcuff9155]

That's how I learned it. :)

[@EEVblog]

It was always CIVIL here.

[@SystemX1983]

That's the equivalent to the following German sentences/rhymes: "Kondensator - Strom eilt vor" "Induktiviät - Strom zu spät" 😎

[@DarkMatterX1]

Not a single one of my professors ever gave us that civil mnemonic.

[@tookitogo]

11:00 the circle is called the “unit circle”.

[@str8_krillin_it470]

You should do a video on the laplace transform

[@Philip-KA4KOE]

My old textbook on AC circuit analysis....Phasors....whilst in university, I was bored and drew a Star Trek original Phaser 2 on the page. Oooooo.....about 1983.

[@MishTheMash]

Yayyy! a fundementals video. Return of electric julius sumner miller.

[@moddquad8362]

I thought that phasor that only changed in angle, not magnitude represented a DC signal. An AC signal would need the magnitude to track the voltage and would look like a figure 8 in this example. But if you add two vectors 90 degrees out of phase, as you would for an inductor or capacitor impedance calculation (or an FFT bin that I am more familiar with), you end up with a circle again.

[@eebaker699]

Great video, thanks for all your hard work. There's lots in here for a newbie. I'll have to watch it a few times. Question, is this how 3 phase power supplies can provide more voltage than a single phase? Would it be possible for you to conduct an experiment demonstrating this phenomena in the next video, please? Thanks again.

[@baghdadiabdellatif1581]

At 4:19 Z not a vector. and I.Z not a cross product

[@clems6989]

Dave, Are we confusing Theta with Phi. I understand that Phi is a angle with reference to vertical. And Theta being the representation of an angle referenced to another point. Like phase angle, I have always heard it called by "Theta" (E*I* COS(Theta)). for AC power as an example..

[@jorgealzate4124]

Sorry for being nit picky (or being wrong) but the product between the vectors I and Z shouldn't be cross product (X) instead of dot product? because the cross product between two vector results in a scalar, and instead the cross product between two vectors results on a ortogonal vector to the plane defined by the two vectors on the product, so V can't be a vector with a dot product, but it can be with a cross product. am I wrong?

[@nvirevolution2235]

Wish I had this a year ago D: . But I am glad I have it now!

[@NickBR57]

Somebody's probably asked but I didn't see it... Isn't s phasor diagram just a special case of an Argand diagram, so that the note saying you were technically drawing a phasor diagram is incorrect? Too long since I did this stuff but it feels to me as if a normal integer (for example) is simply a complex number where the imaginary part is 0?

[@KeritechElectronics]

As the Zen of Python says: complex is better than compicated, haha :) Set your phasors to stun! Now, on to the real and imaginary part, resistance, reactance, impedance, then harmonics and Fourier...

[@kd1s]

Interesting I recall studying for my amateur license i encountered phase angles. Yeah RF has it too. And why do I get the feeling this is coming up to Fourier transforms.

[@vasilemarius7649]

Hello and thank you for the hard work on these videos. I think you are referring to the trigonometric circle. Maybe I'm wrong? Thanks for the feedback.

[@atkelar]

Funny coincidence; all this talking aout phases and sine waves... right when I'm fixing up an old tube RF generator... and trying to find out why the upper two bands are only half way working. Diving into the medium deep end here, going from mostly DC and digital into the MHz range... 😁

[@GJackie24]

ELI the ICE man :)

[@manu808]

Lovely!

[@50Hz]

Casio FX100 is the best basic calculator for AC calculations

[@aldob5681]

was said that the frequency must be the same for all signals?

[@sarbog1]

Very cool!

[@rimmersbryggeri]

I got some aligator clips with my handheld scope. Can those be used as 1x probes (Automotive sensors) or are they exclusively for the signal gen?

[@nichijew2441]

at my uni we use cosine instead of sine. really doesn't matter too much, as you can convert between the two. any idea why this is?

[@demoncloud6147]

I used to hate this stuff back in the grad school.

[@striderskorpion]

Physics grad student here. You seem to be using vector differently here. Voltage, current, and impedance* are scalars (though they can be complex numbers) while electric fields and current density are vectors. *I should mention that resistivity and permittivity, which are used to calculate resistance and capacitance, are tensors.

[@tookitogo]

Differently from what? The way he’s presenting it is how I’ve always seen AC circuit theory presented.

[@striderskorpion]

@@tookitogo A vector as typically used in physics describes a magnitude and direction in space. These complex numbers don't really have that. Current, voltage, and impedance are scalars in a complex number space.

[@tookitogo]

@@striderskorpion I get that, but this notation is completely widespread. It’s technically a “phasor” (phase vector). (Wiki has a nice overview of that.) In any case, my point is that Dave isn’t using some strange “private” definition here, it’s the standard way of referring to AC with a phase component.

[@striderskorpion]

@@tookitogo I wasn't saying it was "private" or anything like that. I was just saying that I, personally, hadn't heard it used that way. Presumably because the vectors of physics, I would argue, are much more widespread. On the other hand, I am aware of phasors. To mathematicians, I do realize there are vectors outside of Euclidean ones, but that usage is not as common.

[@tookitogo]

@@striderskorpion And let’s not get started on the term “vector” in computer science, where it means a whole smattering of things, none of which seem to me to have anything to do with vectors as we’ve been discussing so far! :p (Other than perhaps “vector graphics” in computer graphics.)

[@DiogenesNephew]

You simply don't age, my old friend. ;)

[@arisakathedappergoose4796]

Yep, my calculus trig teacher called them 'reference circles'

[@PampostReturning]

Thank you.

[@nrocobc581]

What is a smoot? SI units: 1.702 m?

[@275drago]

Damn, was hoping that Dave invented phasors.

[@mdavidhandler]

ELI the ICE man

[@BogdanSerban]

Years of maths now make sense

[@wow1022]

this is my life as an electrical power systems engineer

[@johncoops6897]

It's great to see Dave is finally getting back into the kind of content that made this channel so successful. He really seemed to lose his way for a few years there, which was a real pity.

[@Marin3r101]

Isnt it phasers?

[@rodericksibelius8472]

ELI the ICE man: Voltage Leads Current in an Inductor / the / ICE man Current Leads Voltage in a Capacitor = CILVIL.

[@masaharumorimoto4761]

I'll go back and watch part 1 again, can't remember shit, too much weed here lol.

[@lmwlmw4468]

Nice.

[@kfitch42]

Nitpick: I think there are two typos in the chapter titles. "Hop an AC ..." "Radiands"

[@EEVblog]

Oops