EEVblog 1401 - DC Power, Efficiency, & Maximum Power Transfer Theory
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- čas přidán 7. 07. 2024
- Dave closes out the basic DC circuit series with DC Power, Efficiency, & Maximum Power Transfer Theory tutorial. Includes Ohm's law refresher.
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I must have passed a quiz on Power Transfer Law in my first circuits class, then forgot it. When I got to RF transmission lines and impedance matching I finally understood it intuitively, and was surprised to learn it applied everywhere. Just goes to show that some "fundamentals" may need to be taught more than once, and from more than one perspective. Ohm's Law, in all its many forms, RULES!
Yep, I always say, it's Ohms law, not Ohm's suggestion... :-)
@@pa4tim , OMG... soooo true!
put Omh's law before Murphys, & ya can't never go wrong....
@@keithking1985 Or put the H before the M
Another place that this happens is in the inner ear. The three bones in the ear that connect the ear drum to the cochlea are an impedance matching circuit that maximizes power transfer of sound energy.
I don't know why kids go to school anymore when they have Dave. Honestly.
@oH well,lord! I learned most of what I know in my free time. Uni is more about learning a mindset than actual knowledge or experience. But "muh piece of paper" was also my reason for obtaining an engineering degree. This was before it cost as much as a house.
I think in schools I been to they scrapped electronics or merged it in science at some point in around 2000 where they focussed on theory and curiculum test material. No wires, battteries or even a volt meter on site. Lots of writing but very little. I was told by a student who got transferred mid way about the electron flow (in the new science curriculum module) being wrong compared to an older book he was talking about and referred to it as "junk science". The teacher said it was easier to teach it like that so us students can remember it to pass the exam.
I love how the calculator is swapped out every couple of cuts, nice easter egg.
LOL..yeah, showing off some of his vintage calculator collection. 1st one looked like a Casio FX-750.
Glad you brought back fundamentals.
I was getting bored of dumpster teardowns.
Just jealous maybe :)
All of trigonometry is based on one "mother of all formulas".
Sin(x)^2 + Cos(x)^2 = 1
All other trig formulas could be derived from it.
In electronics, Ohm's law rules.
Let's all meditate, ohm
🤣
Technically every circuit is 100% efficient... as long as you want a heater to come preinstalled with every other device.
I remember some old wall sockets light dimmers 40 years ago that use to overheat and burn out and they must 100% efficient.
17:14 Maximum Power Point Tracking, a great way to think of this is one that we have all learnt intuitively from childhood with bicycle gears. Too low and your legs almost free spin on the pedals with little forwards movement, Too high and you feel your legs burn as you heave on the pedals, again with little movement. But when you use MPPT, starting in low gear to take off, click up gears as you accelerate to higher and higher speeds, you "ride" that peak efficiency, *Transducing* the most chemical potential energy into kinetic energy, with the least "wasted" energy, (~2000W Gross) Its like having a bar heater in each leg..... Feels like it to :-D
I learned all this in the '70s so this is a good refresher.
It's nice to go through it again, it is about 30 years since I was at the university and have been occupied at none electronics for 15 years, you don't forget it however it is far back in the brain and can be "hard to recall", so Thanks David 👍
The timing of these "fundamentals" videos coincided with me picking up the Art of Electronics for the first time.
I really appreciate you making them!
Great refresher course! Thank you very much.
I LOOOVE THIS SERIES!!!
Your encouraging way of explanation , encourages me to learn electronics. Thanks Dave.
Hey Dave, great to brush up on the fundamentals, and I will be giving the apprentices homework to watch your videos! I’m an auto electrician and thinking about the maximum power calculations in the automotive setting straight away made me think of a battery and a starter motor. Obviously it’s a bit different as internal resistance in a battery depends on many things including temperature. But it makes sense that having the battery and starter motor matched to get peak power across the load. When a battery ages and Sumgait on occurs internal resistance increases and the lid is no longer balanced for peak power. This can cause slow cranking, high current draw and low voltage. Through hands on experience I’ve seen the data and now you’ve shown me the theory and it made a happy match in my head! Thanks 🙏
thanks Dave!... i needed that refresher!
Ohm's law is a physical law. In physics the voltage is denoted by U. After all, we denote the current with the letter I, and not A (amper) or C (current). :)
Thank you! I have a visual type memory and seeing the visual representation of formulas is very helpful.
Dave at his best!
thanks dave
In high school, my teacher who was teaching electronic used V=C*R instead of V=I*R because it was easier to remember. Even though he did say the correct way is V=I*R.
These videos are super, happy the fundamentals videos came back
10:49 probably learned that in
school....Learn't nothing like this in school they didn't show me much apart from the material and test questions from a water down narrow changing curriculum. Thanks to you over the years I am learning things I always wanted to learn without much difficulty.
Fascinating and useful, as always....cheers.
Incandescent light bulbs are non-linear resistances. Even at the simplest analysis, they have a very distinct kink in their I vs. R graph at the point where they start to emit light.
I find square box resistor symbol much more convenient, because it has standard way to integrate dissipation power within it.
Re the Ohm's Law Triangle: Maybe a small point, but we learned that you simply put your finger over the term you want and what's not covered is the answer.
Dave's subtitle reminded me of something I read in a car forum. These guys were generally against Harley Davidson motorcycles, because they believed they were old technology, and inefficient. (not much mechanical energy out for the chemical energy one puts in. I won't get into THAT argument.) One person said "What do you mean? A Harley is almost 100 percent efficient..." After some incredulous comments, he finished "...at converting chemical energy into noise."
Thanks again!
...and this is where I have to admit that I stopped (truly) advancing in electronics. I didn't want to do (read lazy here) the messy math around max power transfer that wasn't intuitive or useful in my mind. I did continue on but never really advanced until I went completely digital. This was before personal computers and spreadsheets. I have, however, circled back around (decades later) and am continuously learning. Thanks for teaching/re-teaching...
Was hoping you'd tie this back to the practical application of MPPT solar charge controllers - oh well.
I thought that was a bit much for this video which was already long enough.
@@EEVblog2 Yes I thought that too. Power transfer is very interesting - as you say not intuitive. But back to practicality - how do MPPT controllers adjust the load, and the same for inverters that are trying to ‘push’ power into the electricity network?
@@Richardincancale , What do they say? "Clever those Chinese!"
All these thermodynamic limits, i.e Pout < Pin, were discovered in the analysis of steam engines.
OK Volts x Amps = smoke, light & sound
smoke first then fire (that's the light) and finally the bang (thats the acoustic output)
Upvoted simply because you made the point to even explain the $ sign in the excel sheet :D
Awesome video! Big thumbs up :D
Thank you very much, kind sir. /bow
I wish the maximum power transfer theory wasn’t so harsh on my cheap 5 m USB cables…
I 'solved' it by putting the DC-DC at the upstream port, but now I have unlabelled spicy 12 V USB cables…
Use USB PD, goes up to what now, 250W? 5A 50V or something crazy like that..
@Jannie Kirsten "The USB Type-C specification has also been updated to Release 2.1 to define 240W cable requirements, and with the updated USB PD protocol and power supply definition, this extends the applicability of USB power delivery to a large number of applications where 100W wasn't adequate." As per usb.org
You just explained the importance of impedance matching! 😅👍
That was mostly review, but I do like these videos for fundamentals. In the first half of my career, I never even thought about the efficiency formula, but in my last job I was working on the design of high voltage dc-dc converters. I quickly learned that, and used on a daily basis. It’s amazing how efficient low voltage dc-dc converters have become. Is as in seminar where the low voltage guys were talking about 95%+ efficiency, where in the HV domain we would it was hard to get over 75 to 80%. On another note, I’ve been playing around with Mathematica, and I was thinking it would be a good way to run the analysis you ran in Excel. That was a nice demonstration of the calculus concept of maxima, but with out getting bogged down with the calculus. Mathematica gets around a lot of the Excel limitations, but it is way too expensive, so I only use the “Home” version and it can’t be used for commercial work. Great video.
A long time ago, before I had a grasp on the very basics (electronics is not my area at all), I found the the relation of ohm's law to power and heat a little bit counter-intuitive due to how the human brain tends to simplify things.
I had the association that "more current = more power = things get more hot", and since I knew that adding resistors lowers current (given the same voltage, that was all I ever saw), I also formed the mental association of "more resistance = things get less hot". So then when you see stuff like P=I²R, the brain goes "wait, so the less hot things get, the more hot things get?" for a split second until you actually think about it 😆.
Bless you for excellent lessons to new players (and, in all humility, as long as we’re working toward our personal best, we are all new players at some point).
There’s a special place reserved in paradise for enthusiastic teachers like you. (enthousiastḗs "person inspired by a god" ).
I love the theory videos thanks dave !
I²R losses, you forgot the most dangerous one: bad contacts, loosy connectors 🔥 Most dangerous when R contact equals R load, the power will be spread 50/50. When the load is 1000 Watt, and Rcontact= Rload, the contact of a few mm² will convert 500Watt into heat.
Amazing content! Thanks for Excel chart! 👌👍💪
Ok, who else got to 12:04, where Dave asks why LEDs heat up, and immediately said, “I squared R losses”? I presume it wasn’t just me, after he hammered it home starting around 4:34. :)
You can deliver more power with less series resistance for higher loads (lower load resistance). This is shown when you changed Rs to 10.
At the point of maximum power transfer half the power is being dissipated in Rs so your efficiency (load power / power supplied by the ideal voltage source) is only 50%.
The efficiency increases as Rl increases, but that also decreases the delivered power, it is just that the power wasted in Rs decreases even faster. You only get 100% efficiency when Rl is infinite, but then you get no power at all!
You get similar results if the power supply is idealized as a current source with a parallel resistor. You once again get maximum power to the load when Rl = Rs, but now you get 100% efficiency when Rl is zero, and 0% efficiency when Rl is infinite. But almost all real-world power sources are voltage sources with series resistance.
Then there's solar panels, which have a non-linear I:V relationship which also varies with illumination. This is why you have MPP controllers which adjust the apparent load resistance to get the most power as the illumination varies.
The maximum power transfer theorem can be seen as the solution to an optimisation problem: what's the load that maximises current draw while minimising voltage drop across the source
This is maximum power transfer to a T. Maximum voltage delivered to the load = voltage divider between Rs and Rl while keeping series resistance Rs + Rl at a minimum to yield highest possible current. So what’s the highest voltage drop across Rl while keeping (Rs+Rl ) to a minimum . Well easy Rs=Rl. Nicely done.
V=IxR, P=I^2xR, derive the rest with basic algebra
Very helpful, thank you. I have always been confused by impedance matching - have you done a video on that yet? I could watch another I suppose but really enjoy your style and approach.
At the end of your day, whatever you did requiring whatever sort of energy form, it ends up in heat. Driving a car? 100% of the energy that was in your tank or batterie ended up in heat, lastely when breaking down to stop the car to 0 mph | kph. Crazy huh, when you realize this. Gives a new sight on what really is ecofriendly ^^ (renunciation, abstinence, whatever the best word is in english for that).
Can 't wait for DC transients... impulse or unit step response .. haha
sounds similar to how RF impedance matching works, Zin (Rs) = Zout (Rl) => VSWR = 1
In engineering, there is rarely, if ever an all around best way to do something. There's always some kind of tradeoff. Power vs. efficiency, etc. It seems like some vast cosmic conspiracy.
I think it's the Illuminati.
RF fundamentals or a photonics series next!
You should talk about the need to make the load resistance much larger than the source resistance if you want to transfer power efficiently. I run into way too many engineers who don't understand that power supplies must operate with a source resistance that is much lower than the load resistance, not equal to it, which will result in half the power being dissipated in the source resistance...
It's how you define the problem. I mentioned that the ideal source resistance is zero. But yes, I actually was going to mention that you shouldn't use your load resistance to determine the source resistance, but I forgot. The theory though is about "you have X source resisiance by design, so what's the maximum power you can put into any given load using that"
@@EEVblog The wiki page on MPTT shows power transfer vs power max and efficiency as two separate curves as a function of load resistance divided by source resistance. The MPTT curve is just as you describe it. The efficiency curve is at 50% when the load resistance is equal to the source resistance, and goes up monotonically. The power transfer curve goes down asymptotically to 50% as the load resistance to source resistance ratio gets very high.
I design preamps and power amplifiers for sonar systems. For the preamps, you want to minimize self noise, but maximize power transfer too if possible. Efficiency isn't important. For the power amplifier driving the transducer, you want the transducer's resistance to be much higher than the power amplifier's output impedance to obtain high efficiency. This means you need to design the power amplifier to have twice the output drive that you will actually be using. This is true for power supplies as well.
This has caused a lot of confusion over the years, including of some big names. Thomas Edison was struggled with this for several years before figuring it out...
I'm confident you could make a less than 100% efficient resistor by having some of the power converted to light (and smoke)..
At least in Europe the symbol for voltage is often U or E with your teacher hitting you if you're diving face forward into the "trap for young players", using V as the formula symbol for voltage. That seems, as far as I know, more of an American thing. Perhaps Australian as well?
Hey mate, you're a really good teacher, wish my lecturers had a 10th the enthusiasm. Just wondering if you will be covering any more complex topics in the future?
Yes
I'm grateful for my physics teacher for those triangles, saved my ass in many exams! Bit of a wanker but a good teacher.
I got them from my electronics teacher. I didn't run into them in physics until 2nd year of university.
That curve looks exactly like the power curve for solar panels. Maybe mirrored but same. :)
One thing that would be a good addition to these videos would be a real world example.
Just a simple thing on a bread board for example.
Lets say you were just powering an MCU, would you add a source resistor matching the resistance of the mcu?
Not exactly sure when you would add a matching source resistor.
breadboards are cancer
Good on you!!!!!!!!!!! No more TV repair BS. PS - more Mechinal work - those are comical.
plz make a video how to make a linear power supply using discrete components(using transistor and op amp)
Hi Dave! Thank you for all these basics videos: they're always interesting and there's something to learn anyway. 👍 Just a question: can I measure the internal resistance of a battery connecting to it a variable resistance and measuring the power? i.e. when I'll read the maximum power I'll know for sure Rs will be equal to my (variable) Rl set at that moment.
Thank you! 😊
21:31 Yes! Yes please, a video on that!
Maybe also "extra for experts" with things like resonate inductive coupling as seen in tesla coils and newer wireless phone chargers, there is also alot of impedance matching in amongst there, not just Lx Cx but also wavelengths and tesla himself states in his patents matching Lx with R in regards to designing and choosing inductive coils, I was curious to know more about the implications and reasoning as his Bifilar coil that was intended to negate "self inductance" not only became closely associated with his work but he himself replaced many of his previous project designs with his newly updated bifilar coils, as if he realised a significant advantage in their application to resonance circuits. Something that has little proffesional, indepth and sensible explanation with rational reasoning on youtube and the internet as a whole.
I have to emphasis, I'm talking about overunity,free energy (as in thermodynamics violations), or infeasible energy transfer/transduction. I cringe at the very thought and grit my teath when forced to use the associated nomenclature, but hidden away beyond the mountains of spudosciencs and absolute bullshit is legitimate intelligent engineering science, built, tested and paid for by a genius with more money than most universities, and entire hydroelectric power stations at his disposal.
The internet needs competent, well educated, well informed and well explained discussion of the intricacies of their operations and sort the garbage from the gold.
Thank you. Calculator #1 is that the Radio Shack 1982 portable computer? Then the Swiss Micro? No idea about the last one but probably a Casio?
Yes as the voltage goes up across the load, the current through it goes down. I agree, not that intuitive. My first instinct would tell me to lower the source resistance.
Calculator trolling?
Is this why you have to match the impedance of the output transformer to the speaker? If you run a 16 ohm speaker on a 8 ohm transformer, will it damage the transformer, or speaker?
As a North American, I learned the power law as West Virginea ... W = VA Watts = Volts * Amps
SCIENCE!
When discussing the P graphs, it would be nice to see the efficiency as well. For R_S=R_L, efficiency is 50%. When is efficiency maximized?
Efficiency will be maximized as R_L approaches infinity. The current will be decreased meaning both R_S and R_L will consume less power, but because P=I^2*R and R_L is getting increasingly larger than R_S, it will consume more power than R_S, with the efficiency approaching 100%.
Efficiency in this circuit would be Pl/ (Ps+Pl). This simplifies to Eff = Rl/ (Rs+Rl). This doesn't have a local maximum and grows as Rl grows (but total power transfer drops). Intuitively we can maximize efficiency by minimizing Rs.
@@mikefochtman7164 wouldn't this be Rl/Rs+Rl)?
@@pj6366 DOH! You're right of course. Edited.
@@mikefochtman7164 Interestingly, if you wish to maximize both power transfer and efficiency, the sweet spot is at Rl=3*Rs, which gives you an Eff = 75% and P = 0.75*Pmax
can you make video on how one port and two port network synthesis applied practically on designing ckts like filters and amplifiers, thank you.
Is this the same reason that you need to use the correct speaker impedance, like 4, 8 or 16 ohms? To get the power transfer matching? Or am I off the mark with that...
Hey, If you can explain radiowave spectrum circuits the same way you make these tutorials it would be like ending world hunger (literally the hunger for proper tutorials on youtube)
What spreadsheet app is that thing in the late minutes, please?
20:40 - MS Excel, as I can hear, so I have the answer now.
Would love to see this correlating with mppt?
mppt for solar is just increasing the load current until the voltage starts dropping settling on the point giving you the most power as opposed to the most current which would at a lower voltage also yield a lower power. (in broad terms)
@@notsonominal Thanks for the explanation.
There are two different optimization problems:
Finding load resistance RL to maximize load power for a given source resistance, Rs.
Finding source resistance Rs to maximize load power for a given load resistance, RL.
For example:
In the old days with transformers, the first problem was unavoidable.
With switching power supplies we can get well above 50% efficiency. Mainly due to the clever combined use of lossless components: "bucking" inductors and capacitors. ... And great switching semiconductors. Not DC, of course.
Great videos though.
Usually Rs is fixed in the design and you wouldn't go just increasing it.
@@EEVblog2 True in most cases
I should add, I know Dave knows his stuff. It was watching one of his videos that I learned that matching impedance uses the reverse reactance. I seem to have read that the same applies on the input. Apparently coil mics perform better with a “matching” capacitance? Presumably the same would apply to a magnetic cartridge for a record player?
Although true in most cases, when we CAN choose the supply, as in choosing a battery, we want the one that has the lowest internal resistance. A battery with a low internal resistance will be more efficient for the same load.
Isn't what that is actually doing is getting the maximum power from the SOURCE not actually into the load, as you are treating the series and load resistance as one?
To get the maximum power *from* the source you simply short the source of course, and all you have is Rs. But that does no useful work. The whole point is to get power into a load to do useful work, and in that case you can't get more power than when Rl=Rs. And Rs is inherent in all sources, so there is nothing you can do about it.
The phrase is "Maximum Power Transfer". One side is the source, the other side is the load. The maximum power you can transfer from the source into the load occurs when the ESR of the source equals the load resistance. The load is the object of the power transfer.
The series resistance and the load resistance are:
1. Joined in circuit as required for circuit operation
2. Two values that are used in the appropriate equations
3. Two very independent elements
"you are treating the series and load resistance as one" - not at all. They are part of the same network and subject to appropriate calculation.
Interesting. The 23 minutes just flew by.
Could you please create a vedio of power transfer efficiency using SCMR system with resonant inductive coupling
curious: why did you change the calculator on the board between 6:16 and :18? ;) sorry, I just noticed ... doesn't matter of course .. thx for all the awesome videos!!
I clicked on the video specifically for his calculator flexing.
Achievement unlocked.
@@EEVblog2 =) LOL and thx!
Are you planning to extend this to the "complex" power theory? (Power in reactance loads, Power-factor, VA, Q, S, etc )
About max power when Rs = RL, this is correct but leads to misunderstandings when you talk about hardware like transmitters. Rs from a transmitter is not 50 ohm, it is much lower. A transmitter is designed to deliver a certain amount of power (its max power without blowing up) into a 50 ohm load. If the load is not 50 ohms while using 50 ohm transmission lines you get reflections. That is in-depended from Rs. But just because a TX delivers its max continuous power (without burning or blowing up) in 50 ohms it will not say that Rs is 50 ohms too.
It is the same for DC, the max power transfer possible according math (when Rs=Rl) is only possible if the used parts can handle that power and a lot of people forget that. The max power a load can dissipate and a source can deliver is not related to the max possible powertransfer based on Rs=Rl. Simple if you think of this, if the max power of a Rs source is 100W into a 1 ohm load, the load resistor must be 100W, a 1W would still cause a 100W max power but very short, the resistor would just burn up. Everybody gets that, but when it comes to 50 ohm and RF many people forget that max power is not equal to the max power a source can deliver and a load can dissipate.
Why do you write the multiplication symbol for V = I × R but miss it out when writing P = I2R ?
Genuine question! I'm weak at maths and notation can be a hindrance. Even worse is undefined variables!!
You can do it either way. It's just about convenience/brevity versus readability. He could have written V = IR, but to emphasize there are two variables I and R, not a single named "IR" he put "×". Probably unconsciously so.
i like your teardown of marketing wankery when it comes to meme energy, like solar roads. how about heliostat 'boil salt to boil water' tower things, i hear about them on and off. some are ditched, some....work
ah yes! something simple enough for my software-guy head to understand
Ok, so when I need absolute maximum power heater in my house, it should load my 220v line down to 110v. :)
correct :) Will also heat your local substation/transformer
"of course there are inductive losses as well". What are they? There are a lot of inductors in power equipment these days. How is inductive loss calculated? What's the formula?
It's the energy needed to magnetise the core. This is what heats up those tiny linear power bricks that used to be everywhere. The transformer has some inductive (undesirable) element which is charged and discharged on every half-cycle.
@@userPrehistoricman I know that. But what are they. An ideal inductor is 100% efficient (as is an ideal capacitor). Any losses ultimately have to be resistive. Eddy currents in the core, wire resistance, skin effect etc. I'd like to see that explained. :)
superconductivity
Why didn't I send in my assignment in time? I**2*R losses.
Why is a resistor 100% efficient? Couldn't there be acoustic, vibrational, or magnetic effects which bleed energy in a form other than heat?
What has been described in this video is concerned with "ideal" models of components, this makes assumptions so that it is generally quicker easier to do go/no go calculations. Yes you are correct in that resistors do have other losses but that detail would only start to taken into consideration in very important fields generally.
Because by definition it's just a resistor. If you want to talk practical, then that's possible, but in most cases it's so close to 100% you don't care.
The max power transfer thm is blowing my mind right now... It just seems very very wrong...
Why is my I²C bus heating up? I²R losses.
At first, everyone did not believe in Bitcoin, then in Defi, then in NFT, and now someone really does not believe in the RJV12 algorithm :D
There is nothing that's 100% electrically efficient.
Some energy is lost in generating magnetic field around the resistor and conductor.
Photons galore.
This is DC *theory* remember. But yeah, there can be other energy loss mechanisms, but for most practical purposes it's 100%
Rubbish. It can absolutely be 100% efficient… the trick is to find out where all the energy went, and then tell the marketing team to list it on the front of the box!
Best to also include a big red “x” next to the competition!
If you have a lightbulb which is also supposed to act as a heater at the same time then wouldn't it have 100% efficiency? ;)
@@EEVblog A DC light bulb is a resistor filament. It loses energy both in heat and light. But I get what you mean. I thought since it's fundamentals, one needs to be more anal about facts.
@@onemanshow4116 Yes, as I mentioned in the video, it's how you define "100% efficient". A LED is 100% efficienct if you consider it's also used as a heater.
Damn. 1400 vijeos.
Tell me about it...
I don't understand why do people still make the mistake of multiplying by 100 to get a percentage? They probably mean to multiply by 100%, which is 1, and multiplying by 1 is the same as doing nothing at all. 0.85 EQUALS 85%. And no, it's not some convention that Excel invented, it's basic math. And it's not like 0.85*100 is 85% because in fact that's 8500%.
Why talk about the growth of BTC if there is NFT and the RJV12 algorithm
Sorry Dave....I just can't handle the phrase "inductive resistance" isn't it reactance?
Could you repeat that? 🤣
It is misleading to claim that max efficiency occurs when R source = R load. That may be true of power transfer (Source to Load) but not efficiency.
For instance let V=100 Rs=10 and RL =90
Then I = 1, Ptotal = ExI = 100w, Pload=90x1 = 90w.
Efficiency = Pload/Ptot = 90/100 = 90% when expressed as a percentage
As opposed to when R source = R load, the efficiency is then 50%
That's why it's called Maximum Power transfer theory and not Maximum Efficinecy Transfer theory.
Why did bitcoin crash? I2R losses!