Episode 18: Obey the Laws(of power)

[drandolph]

Calculating resistance and power isn't hard... and, as David explains, knowing Ohm's Law and the Power Triangle can be darn useful when you're designing a project, sorting out power supply issues, or want to keep from burning your car down.

[vincent12234]

Awesome, I'm working with this in collage right now, great to be able to enjoy it for once, awesome episode thanks!

[mawic]

I had to stop watching this episode within the first 5 minuts or so. The AC/DC battle wasnt between Westinghouse, and Edison. It was between Tesla, and Edison; Westinghouse was just a financial geniuis who took advantage of Teslas great mind. Edison used around 6600 VAC to kill the elephant to show that AC was more dangerous. Now I'll return to the show....

[drandolph]

Well you said it. Westinghouse was the financial backer for Tesla but actually the fight was between Edison and Westinghouse. Westinghouse was fighting for Tesla. We should have made that more clear I agree. I would consider it to be in the same class as Jim Louderback and Neil Tiles going at it for Patrick Norton and Kevin Perria as the king of television.

We should have made the fact of Tesla being the man behind the man more apparent.

[marklar]

http://www.uoguelph.ca/~antoon/gadgets/resistors/ohmslaw.gif

The real ohms law

[scienceking]

Sorry, but as a 4th year Computer Engineering student and someone who has worked with formal electromagnetism derivations since my 3rd year of high school in AP Physics, this episode is by far the worst episode of Systm ever, and probably the worst "day 1" orientation to electronics I have ever seen. Some of the terminology used is awful("wattage" "amperage" in equations, everyone in engineering uses Power and Current). Not discussing the most useful power formulas V^2/R and I^2R.(this is probably the worst part. For ohmic systems P=IV is harder to work with) Not mentioning the R/L + Z linear approximation for line impedances.(I have never heard of anyone using a chart before outside of n00b Mechanical Engineers)

Also whats so hard about finding the energy in a signal? You can just integrate p(t)=i(t)v(t) at the very worst case, and most of the time easier models that fit your situation can just be done by inspection. Also, if you want to talk about not frying your electronics projects, the idea of line impedance over just resistance is important, as line inductance or capacitance can imply nearly infinite(in the model) transient voltages and currents, and these can burn out a PSU easily. See www.physics.princeton.edu/~mcdonald/examples/igct.ps for a great example of this big problem.

I'm not sure if this episode is a production value casualty of the new hectic weekly release schedule at R3, but I have to say, after some episodes i thought were great for new electronics learners like the PCB etching episode and the tools episode, this was truly disappointing. Best hope for the future.

[spmion]

I really enjoyed systm when the show was more project-focused. These new theory tutorials have been really hit-or-miss. In the older episodes, I really felt like the hosts dominated the subject matter being presented (eg. MythTV Episode), but lately, it just seems like maybe David and for sure Patrick are operating outside their area of expertise. I've seen enough of David's projects to know that he knows his stuff, and Patrick made it clear to me in the wifi episode that up to the "fresnel" point he's got a lot to offer from his experience base. I just wish David and Patrick would stick to topics they are authorities on, because episodes like this one make me question what I'm really gaining from this podcast.

Looking forward to more great systm projects...

[tempesta]

"not systm, a new show thats coming out on revision3"

gee pat, whatever could you be referring to? :P :D

[kdwebsol]

Patrick said "if you are watching the HD version....". Is systm going to be in HD soon?

[firefalcon]

Sorry, but as a 4th year Computer Engineering student and someone who has worked with formal electromagnetism derivations since my 3rd year of high school in AP Physics, this episode is by far the worst episode of Systm ever, and probably the worst "day 1" orientation to electronics I have ever seen. Some of the terminology used is awful("wattage" "amperage" in equations, everyone in engineering uses Power and Current). Not discussing the most useful power formulas V^2/R and I^2R.(this is probably the worst part. For ohmic systems P=IV is harder to work with) Not mentioning the R/L + Z linear approximation for line impedances.(I have never heard of anyone using a chart before outside of n00b Mechanical Engineers)

Also whats so hard about finding the energy in a signal? You can just integrate p(t)=i(t)v(t) at the very worst case, and most of the time easier models that fit your situation can just be done by inspection. Also, if you want to talk about not frying your electronics projects, the idea of line impedance over just resistance is important, as line inductance or capacitance can imply nearly infinite(in the model) transient voltages and currents, and these can burn out a PSU easily. See www.physics.princeton.edu/~mcdonald/examples/igct.ps for a great example of this big problem.

I'm not sure if this episode is a production value casualty of the new hectic weekly release schedule at R3, but I have to say, after some episodes i thought were great for new electronics learners like the PCB etching episode and the tools episode, this was truly disappointing. Best hope for the future.

Scienceking, while you are correct that the show was sloppy in the way it expressed ideas and often incorrect, the majority of your post was tantamount to the ramblings of a self-diluted retarded person. First, you cite the hosts for their choice in terms while most of your terminology is non-standard for academia or industry. You appear to be trying to think of the biggest words you just learned in class and writing them in your post because you think it makes you look smarter... it doesn't. You say the hosts didn't address, "the most useful power formulas." If you had any experience besides your homework assignments, you would know that the most useful power formulas are dependent on which problem domain one works in. Apparently you also have little experience with the types of projects Systm does. They have little need to ever think of the non-ideal properties of the wires they use. The communication speeds are slow, the voltage levels are low, and current draw is low. The paper that you cited, which I wasted my time reading, had no bearing on anything dealing with this show or Systm in general and appears to me to be a feeble attempt on your part to show that you can find (but apparently not understand) a formal paper. Good luck in getting a job after you graduate.


---Matthew Hicks


University of Illinois
Dept. of Computer Science
Ph.D. Candidate
Real-time, Embedded, and FPGA-based system consultant

[scienceking]

I already have several job offers, but am going to attend graduate school. I also have about 1.5 years of combined work experience at 2 different fortune 500 engineering firms. ^_^

Yeah, my feeble attempts to understand basic "papers" that are geared toward freshman year physics and engineering students...

Have fun with your VHDL hacking. :p I am however very disturbed that an embedded systems expert(my area of expertise) would not identify the risk non-ohmic impedences would have in systems at ANY power level, as our systems are much more fragile than the thyristors, and can have problems with cross-regulation far more easily too. In fact, I can highly doubt that you have ever designed any component of a commercial product in this area without analyzing those concerns in some way, or perhaps copy-pasting a coupling transistor or something that you didn't understand...

Also, what terminology did I use that was nonstandard? Perhaps the Faculty of Rose-Hulman and the engineers at the companies I have worked have been misleading me all this time or something!

PS: also, what big words did I use? Pretty much everything in my post is from our Electrical Systems class, which is a freshman class that all engineering majors have to take. There is nothing very technical here at all. <_<

[kosmoe]

Edison's PR stunts were designed to scare people of AC power, not to win them over. He wasn't demonstrating the potency of his DC system, instead he was demonstrating the dangers of Westinghouse's AC system. He was doing this for two reasons: one - he didn't want to loose all that potential royalty money from his invention, and two - he didn't understand AC power. Early on Tesla worked for Edison and Tesla's polyphase generator (same thing we use today) was his for the taking, but because he didn't understand it, he shunned it. Along comes Westinghouse. He seizes the opportunity to buy Tesla's patent rights and the Edison/Westinghouse battle begins. Edison fought hard for DC. His proposal of the electric chair was to associate death and AC. He wanted people to say "He got the Westinghouse" much like we say "He got the chair" today.

[firefalcon]

I already have several job offers, but am going to attend graduate school. I also have about 1.5 years of combined work experience at 2 different fortune 500 engineering firms. ^_^

Yeah, my feeble attempts to understand basic "papers" that are geared toward freshman year physics and engineering students...

Have fun with your VHDL hacking. :p I am however very disturbed that an embedded systems expert(my area of expertise) would not identify the risk non-ohmic impedences would have in systems at ANY power level, as our systems are much more fragile than the thyristors, and can have problems with cross-regulation far more easily too. In fact, I can highly doubt that you have ever designed any component of a commercial product in this area without analyzing those concerns in some way, or perhaps copy-pasting a coupling transistor or something that you didn't understand...

Also, what terminology did I use that was nonstandard? Perhaps the Faculty of Rose-Hulman and the engineers at the companies I have worked have been misleading me all this time or something!

PS: also, what big words did I use? Pretty much everything in my post is from our Electrical Systems class, which is a freshman class that all engineering majors have to take. There is nothing very technical here at all. <_<

Apparently your fellow employees were to nice to tell you that you sound like a pretentious jack@$$ when you used "big" words that didn't pertain to the subject at hand.

While I know and use both VHDL and Verilog, if I were to "hack" I would do so in Verilog thank you very much. Which is the language I used to develop the FPGA hardware portion for the Illiac 6 supercomputer. But, you're right, I did use some VHDL while "hacking around" on a DARPA project. But, I digress from my complete lack of real-world experience. I only hope I can be like you and proudly claim to have 1.500001 whole years of experience under my belt one day.

List of words and other inappropriate stuff:
ohmic systems
line impedances
R/L+Z
formal electromagnetism derivations
Making fun of mechanical engineers
Transient voltages

Now before you go on a rant about how smart you are and how these terms are all from Freshman year of college, I will agree that you may have not used of them incorrectly in the technical sense. But who will be able to tell? The problem is that you got caught up in trying to make yourself appear to be smart by using the most dense words (highly expressive in a compact form) you knew. The problem is, as a writer, you are attempting to convey an idea to an audience. The Systm audience generally (not everyone) isn't even of age to be a Freshman in college (not to mention most schools don't cover this stuff, if at all, until Junior year). Remember, you aren't talking to your friends who are just as smart as you are and who have taken the same classes, so choosing words that may make your explanations longer, but will help everyone understand is best. In the end you will appear to be both smarter and a better writer.

Additionally, making fun of other disciplines, especially other engineering disciplines, is in really bad taste. As you get older, you will find there are many more really capable, intelligent people in professions you had previously discounted, while at the same time realizing there are far fewer in professions you hold in high esteem.


---Matthew Hicks

[kosmoe]

Way to go Marklar. I was looking for this chart. It's the best little reference chart for DC circuits.

Note to newbies to electricity: Don't try to apply this to AC systems, you will kill yourself. AC power is much more complex. Seriously.

[scienceking]

Heh, I go to a small engineering school, and all the majors make fun of each other...its a running joke. Ran into the same thing industry.(I have worked mainly in robotics, so have worked with MEs quite a bit) Of course, MEs aren't dumb, and they are way better in electronics work than EE's are in ME work for that matter. Was just making a joke, especially as we all know ME's love to use charts to interpolate from, so we sorta have a war going on with them with out more quantitative approach.

Also, I don't have time to write about what each of those terms mean. And really, how could you accurately describe some of them in a few sentences(like the idea of line inductance and line modeling). But this is the internet, so learning all about a term you don't understand is as easy as highlighting it and using your browser's context menu to search. And still, I am certain anyone who has had high school physics could have understood most of that post, and someone who hasn't should be worrying about that type of stuff before delving into electronics theory.

Also, I would be very scared if a student didn't know about these ideas at least by midway through their Sophomore year. How can they start to understand more advanced electronics like Opamp design and High Speed Digital Systems/VLSI without them in just 1 more year! I don't see why anyone would hire you if you didn't get into any of the actual useful stuff...

Actually, as a research student, you should know that after a certain level of learning, you can't be expected to know everything, and should take the time to look things up as you go: its the best way to learn. I am not a professor or a teacher, nor am I being paid to lecture, so I feel I have a right to make an accurate arguement in whatever style I prefer, regardless of my "audience".<_<

[firefalcon]

Heh, I go to a small engineering school, and all the majors make fun of each other...its a running joke. Ran into the same thing industry.(I have worked mainly in robotics, so have worked with MEs quite a bit) Of course, MEs aren't dumb, and they are way better in electronics work than EE's are in ME work for that matter. Was just making a joke, especially as we all know ME's love to use charts to interpolate from, so we sorta have a war going on with them with out more quantitative approach.

Also, I don't have time to write about what each of those terms mean. And really, how could you accurately describe some of them in a few sentences(like the idea of line inductance and line modeling). But this is the internet, so learning all about a term you don't understand is as easy as highlighting it and using your browser's context menu to search. And still, I am certain anyone who has had high school physics could have understood most of that post, and someone who hasn't should be worrying about that type of stuff before delving into electronics theory.

Also, I would be very scared if a student didn't know about these ideas at least by midway through their Sophomore year. How can they start to understand more advanced electronics like Opamp design and High Speed Digital Systems/VLSI without them in just 1 more year! I don't see why anyone would hire you if you didn't get into any of the actual useful stuff...

Actually, as a research student, you should know that after a certain level of learning, you can't be expected to know everything, and should take the time to look things up as you go: its the best way to learn. I am not a professor or a teacher, nor am I being paid to lecture, so I feel I have a right to make an accurate arguement in whatever style I prefer, regardless of my "audience".<_<

The whole point of these series of introductory shows, at least as I see it, is to give people enough of an idea and the basic formulas needed to understand later shows better and maybe even work on their own small projects. I don't believe they are trying to teach the theory, but trying to give some rules of thumb. Many cool projects(as in I show my wife and she says wow, not as in I show a practicing engineer and he says how?) can be done by just utilizing a few simple rules. Understanding isn't always required (I myself prefer understanding not just memorizing). The hosts are trying to instill rules in those that haven't had the chance to learn them yet. Maybe people will learn these rules, do some small projects, and start working on bigger projects and begin looking things up for themselves. Babysteps.


---Matthew Hicks

[marklar]

Way to go Marklar. I was looking for this chart. It's the best little reference chart for DC circuits.

Note to newbies to electricity: Don't try to apply this to AC systems, you will kill yourself. AC power is much more complex. Seriously.

Actually this chart is for single phase ac systems as well, when you are working with three phase its a little different. For example to find amps you take your three phase voltage and multiply by the square root of 3 which is 1.732 and divide that by watts. Its the same basic formula but you have to use your voltage factor.

Stop your bickering you two, this show isn't teaching you how to build a motherboard or other very complex device. This is really the basic of the basics and thats all there is to it.

[i-and-lt-u]

I was taught P=IxE or PIE for short. We used E (Electromotive force) in place of V (Voltage) in our Ohms Law charts.

[scienceking]

EMF or E as you call it(I would not recommend that, as the Physics and EE guys use E for the Electric field, which is not the same, but related) times the current is the power, you are right. EMF is just another word for Voltage, meant to standardize the vocabulary better.(people don't like to use units in property names, as it is confusing) So really, you are better off for being familiar with it as EMF, as I am one of the cursed ones who can't help but utter "voltage" naturally.

[roguex]

scienceking, you remind me of some of the kids back in my intro engineering classes who were majoring in the area of the class but insisted on fighting with the TAs about topics that were beyond the scope of the class we were in, (and were being glossed over for a reason). Nobody really liked those kids...

Trolls aside, I've gotten a little worried about the way Systm has been going lately. I understand the idea of trying to go over the very basics of electronics, and think its a really great idea. But really, you guys need to know what you are talking about, and SOUND like you know what you are talking about. The conversations have really been taking on a confused, rambling tone lately.

Also, you do jump around quite a bit, sometimes not fully explaining something, or just touching on some interesting topic and not explaining anything about it. Like, you talked for such a long time about the AC/DC debates, but never actually said much about what the difference is! Some structure would be great.

Regardless, I really love the concept of this show, the mini-projects are great, and i really think you guys are up to the job. Just try to get your ideas together so you don't confuse the people you are trying to help!

[kosmoe]

Actually this chart is for single phase ac systems as well, when you are working with three phase its a little different.

I disagree. When it come to AC circuits there are rarely simple resistances R. Instead you start dealing with complex impedances Z. These impedances can have inductive and capacitive characteristics and are frequency dependent. For a pure resistor Z = R but it is important to understand that there can be a big difference between Z and R and don't apply Ohm's law for DC circuits to AC circuits.

[scienceking]

Yup, you are right. These properties even apply to dynamic DC-level systems, especially with higher clock speeds going into stuff. And of course, even a DC steady state transistor will never follow ohms laws or its derivatives(it will follow p(t)=i(t)v(t) though), because it is a non-linear, or ohmic device in its response. Diodes are also not ohmic, but linear approximations usually work "well" for them. Good places for ohms law here:
1) Resistor networks
2) simple loads like LEDs
3) wires that don't behave like transmission lines(again, you won't know this unless you check, but its a good guess that your wire is OK)
Things never to use ohm's law for:
1) BJT transistors, and unless the design you are following says otherwise, transistors in general(yes, FETS can have linear like responses when installed to have them)
2) Light bulbs(these throw everyone off)
3) Capacitors and Inductors(however, you can read up how to model these with pre-built formulas and not have to do DiffEqs or laplace transforms or whatever, although they are good to know about if you have the time), but again, certain circuit instructions you might be given might give you assumptions to treat these like a source or a short or an open circuit.
4) IC's (this is probably just a special case of the transistor rule. remember, the beauty and horror of ICs is you just pretend like you cant know how they work outside their Spec sheet, and so you cant assume that they are ohmic in any way), but even this can be worked around. Some microcontrollers or the like might have registers you can set to control internal resistors, and you can assume these follow ohms law obviously.

So the moral of the story is, ohms law is mostly useful, but never try to apply it when you aren't sure it will work. As a follow up, your multimeter R functions will tell you nothing useful if you measure across non-ohmic devices(well, they might, but you'd need more than one data point at least). If you do really want to analyze something that isn't ohmic, you can take a look here to see how(its not as hard as you think): http://circuitscan.homestead.com/files/idxpages.htm

[marklar]

2) Light bulbs(these throw everyone off)

Umm what?? a 120volt 60w bulb pulls .5 amps you can use an amp probe or ohms law and get the same result. I have been in the electrical trade for 14 years and used parts of ohms law among many other formulas to find loads in order to design a proper power distribution center and maintain load balancing for many industrial and commercial facilities.

Get out of school and get a job after years of work and learning from your mistakes you will then be able to handle the power of the force.

Goto home depot and buy a book called "Ugly's Electrical Reference Book" It has all the formulas you need.

[kosmoe]

2) Light bulbs(these throw everyone off)

Umm what?? a 120volt 60w bulb pulls .5 amps you can use an amp probe or ohms law and get the same result.


I believe Scienceking is referring to the fact that the measured resistance of a light bulb is not the same as the calculated resistance. If you use your example the resistance of the bulb is 240 Ohms but if you take the bulb and measure the resistance with a multimeter it will measure around 16 Ohms. This is because the resistance of the filament rises as it gets hot.

[scienceking]

Hahaha, you are an idiot. P=IV is not ohms law. Ohms law is V=IR.
Search for lightbulb and ohmic device to see that I'm right. Or because you don't trust us "academics", prove it to yourself in your lab: http://tinyurl.com/2ng32g

Also, I am an Electrical Engineer, which is quite a different type of field than what you do. I design components of the products you install/maintain. I have ready developed some embedded controls hardware for a popular color laser printer, and also developed a system that company uses for QA. I also worked in EMC( http://en.wikipedia.org/wiki/Electromagnetic_compatibility ) modification for another printer, which is really crazy stuff if you think that what you do takes a brain. :p

And yes, kosmoe is exactly right, but lightbulbs also have a little bit of non-ohmic behavior caused by the fact that the filament is not purely metal conductor. This can get very useful with the most useful non-ohmic materials there are: semiconductors! In fact, semiconductors are weird, because up to an extent, their resistance goes DOWN as their temperature goes up. This can be good or bad. This can cause "thermal runaway" in transistor amplifiers that deliver a big load current, like push-pull amps, if they aren't designed right. But this effect can be useful too.

For example, the thermistor is just a chunk of semiconductor that uses this effect to stop non-ohmic devices like our lightbulb from burning out due to their non-ohmic effects(basically, our lightbulbs' resistance starts out pretty low, and that might be too low for the filament to handle the resulting current). The best example of these are CRT monitors, which will always have them. And, if you feel up to it, hook one up to one of your old fashioned light bulbs and watch it almost last forever, until the filament depletes! Its a neat trick.

[marklar]

Hahaha, you are an idiot. P=IV is not ohms law. Ohms law is V=IR.


Obviously you missed my first post ohms law is more than one formula ****ING MORON!!

http://www.uoguelph.ca/~antoon/gadgets/resistors/ohmslaw.gif

You will find both of those formulas plus ten others on the "ohms law" graph twelve formulas = ohms law

[scienceking]

That chart is inaccurate. Ask anyone with an engineering or physics degree. And actually, a more formal designation of "ohms law" does not even use the more EE style properties, but rather conductance, electric field, and current density. The physics description is better, because it can be more easily applied to all moving charge systems, like electrons in a particle accelerator.

http://en.wikipedia.org/wiki/Ohm's_law or go to your local university library. That chart is famous, and is a joke among engineers. Of course, if you had chosen to get a college degree before going out and working as a janitor or whatever, you'd know that. ^_^

Man, now I know why engineering schools make students take a test to get in. :)

Sorry for acting like kind of an ass, but i never expected this level of hostility here. I mean, I'm not even one of the best students in my class or anything, but I am an EE student at the #1 ranked undergrad school in the field, and also am a member of the IEEE and IEEE Computer Society. I don't know everything, not close, and as I age more, I become all too aware of that. But I know all these more basic electronics quite well, and like to help people in them. I mean, frankly, this is low level stuff to an engineer or physicist, and thats not bad for you. In fact, its incredible that people want to learn this stuff just for fun, and not to make a career out of it like I plan to do. But really, I just want to help. Yeah, I can be wrong sometimes. Yeah, I might be a jerk sometimes.

But I really just want to be helpful, and I'd appreciate not being so openly attacked. o_o I might be wrong and learn something. You might be wrong and learn something. Sometimes both are wrong. Sometimes there is no "right"(like in EMC :p ) But in the end, the important part is to learn.

If you want a great book to really start to learn practical electronics while skipping all the school stuff, but to still learn electronics right and really be making real projects, i recommend:
https://secure.aidcvt.com/mcp/ProdDetails.asp?ID=9781598290684&PG=1&Type=RLMa&PCS=MCP

Its by a professor at my school, Dr. William Eccles, who is perhaps the best teacher I have ever learned from. He is down to earth and nice. He worked at the Telephone company for 30 years before becoming a professor, and you can tell. Just like his class, this is a "non-idealistic, practical, and opinionated introduction to circuits. "

[marklar]

So basically your saying that version of ohms law is limited to a tiny area of electrical calculations?? Not very helpful without all the others when your working on a complex project. I guess they let you design a few traces on a board with that.


DIRECT CURRENT

AMPS= WATTS÷VOLTS I = P ÷ E A = W ÷ V
WATTS= VOLTS x AMPS P = E x I W = V x A
VOLTS= WATTS ÷ AMPS E = P ÷ I V = W ÷ A
HORSEPOWER= (V x A x EFF)÷746
EFFICIENCY= (746 x HP)÷(V x A)

AC SINGLE PHASE ~ 1ø

AMPS= WATTS÷(VOLTS x PF) I=P÷(E x PF) A=W÷(V x PF)
WATTS= VOLTS x AMPS x PF P=E x I x PF W=V x A x PF
VOLTS= WATTS÷AMPS E=P÷I V=W÷A
VOLT-AMPS= VOLTS x AMPS VA=E x I VA=V x A
HORSEPOWER= (V x A x EFF x PF)÷746
POWERFACTOR= INPUT WATTS÷(V x A)
EFFICIENCY= (746 x HP)÷(V x A x PF)

AC THREE PHASE ~ 3ø

AMPS= WATTS÷(1.732 x VOLTS x PF) I = P÷(1.732 x E x PF)
WATTS= 1.732 x VOLTS x AMPS x PF P = 1.732 x E x I x PF
VOLTS= WATTS÷AMPS E=P÷I
VOLT-AMPS= 1.732 x VOLTS x AMPS VA=1.732 x E x I
HORSEPOWER= (1.732 x V x A x EFF x PF)÷746
POWERFACTOR= INPUT WATTS÷(1.732 x V x A)
EFFICIENCY= (746 x HP)÷(1.732 x V x A x PF)

[marklar]

Oh I'd also like to add this the electrical "theory" there is no science.

[kosmoe]

Hahaha, you are an idiot... if you think that what you do takes a brain.

Scienceking, don't belittle people. The subject matter of this discussion is basic DC theory and you continue to take the conversation into the stratosphere. It seems self-serving and certainly isn't helping or impressing anyone.

[scienceking]

Yes, you are right. In fact, ohms law only really applies to resistors, and even then, only at low frequency where their line capacitance and inductance are irrelevant. For anything else, you should use a differential equation of the form:
i(t) = Cdv/dt + r(t)
V(t)=Ldi/dt + r(t)
You can also look up the way to do this by integral transform if that is easier than integrating for you, or use a computer to do it.
For more complex networks, you use nodal analysis(KVL) or loop analysis(KCL) with the ohmic equations and DiffEq solutions to build a system of equations to solve. Thats the way tools like PSPICE do it. (which by the way, everyone should have a copy of. Its nice for drawing pretty schematics if anything, and if you get things like Digikey's part libraries for it, you can draw almost anything. Its simulations are very nice too, but be careful to set things like transistor parameters right for your devices... http://tinyurl.com/bnvnc )

Three phase power is not very special at all, it just means that you will have different phases, or j-components, of your voltages and currents in the system. You can use a phaser representation which is useful if you are careful to break up non-linear responses into a magnitude and phase response. Be careful in analysis of the network as these can be hard to calculate by hand without making errors.

Again, that site i listed earlier can start you on applying these principals, but I'd recommend taking the "Circuits 1" style class at your local community college or university, as this is the type of stuff you don't want to get wrong ideas about, especially if you want to move out of basic circuits and into electronics. Transistor analysis will require a solid grasp of all these concepts as the small and large signal models require you to analyze the different terminals of the transistor separately.

I want to make it it clear that none of this is ohms law. Ohm's law only relates conductance/current density/electric field or current/EMF/resistance. Nothing more. There are many more physical laws of nature than Ohms law though, which use use in these cases. However, its worth noting that most of these are derived from the same Maxwell's equations(http://tinyurl.com/qsrgl ) that prove Ohm's Law. Indeed, anything in electronics can be reduced to a solution of those equations, and sadly sometimes, especially the RF guys have to do that.

Hmm, I've designed my own Microprocessor architecture(based on a 16-bit MIPS design), and IO driver electronics for it using this type of theory, and implemented on an FPGA, some GALs, and a breadboard for the electronics. Yeah, I guess that did take a few traces. :p

Oh, and I just want to say sorry for acting immature. Kosmoe is right(again). Hmm, I guess my main point is:
1) Ohms law is V=IR . Period.
2) There are many other useful laws that you can use with ohms law to analyze networks Like Kirchoff's laws
3) Some(most) devices do not follow ohms law, and so you need to model them differently
3*) These models' effects can be harmful or helpful
3**) Some of these models, namely those for inductors and Capacitors are very similar to the linear ohms law model, but require a DiffEq solution which may or may not be trivial to do depending on your level of math ninja-ness.(frankly, I am not good at solving them, but my comptuer is)
4) Get PSPICE

[kosmoe]

That chart is inaccurate. Ask anyone with an engineering or physics degree... That chart is famous, and is a joke among engineers.

That chart is not inaccurate and is not a joke among engineers. It is a perfectly good tool for DC circuits and some AC circuits (as long as you realize its limitations for AC - see my earlier post).

[scienceking]

What I meant is that the Power laws are not Ohms law. Thats what I meant by inaccurate. And yes it is a joke, its in my schools' ECE department window next to the Fry's ad for a "digital capacitor".
If you mean all the laws are correct, thats right. Maybe I wasn't clear about that, sorry. What I mean't was referring to the power laws as ohms law is inaccurate. Actually, it IS accurate for AC too, minding that it just assumes a zero impedence. This can actually be a decent assumption sometimes, like if you had a 10 khz signal going on 50 ohm impedence coax. Not so good if that signal is 5mhz though.

Ohms law is the linear maxwell equation solution. The power laws come from V*A=J/C*C/s=J/s=W, or a simple energy conservation equation. Note that expression does not say anything about the medium that our Efield exists in. Thats really important, although I'd rather not ramble on about why since my ramblings do not seem appreciated here, save to say it would make no sense for that to be considered part of ohms law as its totally unrelated, and also must apply to any model that uses the EM-field model, regardless of it being ohmic.

[kosmoe]

Maybe you consider it a joke because you've seen it on a teacher's window or because it's too simple for you but I've always found the simple things to be the best. I stand by my original statement, for most things that the average person will do around the house, it's a good tool.

[scienceking]

Oh no, its a good tool for anyone. The joke is the title. I'm sure the guy who made it knows what he was doing...its just one of those things that came out weird. Engineers are generally very cynical and biting people. But pretty much, if we don't just ignore something, it shows appreciation.
I just want to make clear that the Power equations are not part of ohms law, being there was confusion on the topic.
Trust me, in engineering, we ALWAYS use the simplest solution that works. Not doing that is death. So nothing is too simple for me. However, sometimes things that may be easier for a beginner to do are not a simple to someone who has more experience. Just like the CLI on a computer... doing things like sorting files on a CLI is simpler than on a GUI, but may not be easier for all people. There is a difference.

[kosmoe]

We also expect much heckling of Patrick for the fear in his eyes whenever it's time to do math (it's hard, he'd rather go shoppiWe also expect much heckling of Patrick for the fear in his eyes whenever it's time to do math (it's hard, he'd rather go shoppiWe also expect much heckling of Patrick for the fear in his eyes whenever it's time to do math (it's hard, he'd rather go shoppiWe also expect much heckling of Patrick for the fear in his eyes whenever it's tmps from Watts and Volts. (So our 1000W amp running on a 12V system would draw 83A... who knew algebra would be so useful!)

Dave/Patrick, you seem to have the text equivalent of a scratched record happening here on the show description for Episode 18.

BTW, you should remove the last section regarding "Watts Law". The equation P=I x V is referred to as the Basic Power Formula, not Watt's Law.

[cygnus1]

Oh no, its a good tool for anyone. The joke is the title. I'm sure the guy who made it knows what he was doing...its just one of those things that came out weird. Engineers are generally very cynical and biting people. But pretty much, if we don't just ignore something, it shows appreciation.
I just want to make clear that the Power equations are not part of ohms law, being there was confusion on the topic.
Trust me, in engineering, we ALWAYS use the simplest solution that works. Not doing that is death. So nothing is too simple for me. However, sometimes things that may be easier for a beginner to do are not a simple to someone who has more experience. Just like the CLI on a computer... doing things like sorting files on a CLI is simpler than on a GUI, but may not be easier for all people. There is a difference.

i just want to say there bud, you come off as being one of the most arrogant, pompous asses i've ever met.

good job

[masherscf]

You guys should be way less defensive about these basic electronic formulas. They're pretty universally applicable. Just because tech-wannabes can second guess your formulas over Wikipedia doesn't mean you don't know what you are doing.

One of my degrees is a BS in physics so I'm a little acquainted with the work/energy theories around these things. However, as a professor of Mathematics, I understand the experience of trying to speak about technical things without sounding idiotic.

As a matter of speaking in public about technical things, usually it is good to be several levels above your target audience. This helps you emphasis the right points and avoid saying anything blatant stupid.

If you guys feel uncomfortable address these formulas a concepts, you might consider reaching out to someone in local academia. I'm sure you can find some knowledgeable Professor who will appear in exchange for a letter of appreciation in his/her file. Such a public appearance is excellent professional development and helps a professor get promoted.

[hyperandy]

In reply to the formula wars:
Who cares what you call it in your circle of friends! The simple fact of the matter is most people tinkering around with systm projects are just trying to get their feet wet and learn something new. I applaud these guys for getting out there and trying to show people less familiar with electronics, something fun to do with the technology around them. If the viewer is passionate about that subject, they will research more on there own and who cares if they call Kirchhoff’s voltage law, ohms law, or the formula for power, ohm's law as long as they're considering it and not blowing their projects up. You can run numbers all day, but real life experiments are the only way to learn.

[pcguy]

Think someone might want to fix the following paragraph:

"We also expect much heckling of Patrick for the fear in his eyes whenever it's time to do math (it's hard, he'd rather go shoppiWe also expect much heckling of Patrick for the fear in his eyes whenever it's time to do math (it's hard, he'd rather go shoppiWe also expect much heckling of Patrick for the fear in his eyes whenever it's time to do math (it's hard, he'd rather go shoppiWe also expect much heckling of Patrick for the fear in his eyes whenever it's tmps from Watts and Volts. (So our 1000W amp running on a 12V system would draw 83A... who knew algebra would be so useful!)"

[ormej01]

Watching an early systm episode was my first contact with Revision3, and I thought it was amazing. The content was directed towards a common technical issue, and introduced new ideas to me. By contrast this episode brought nothing new, and was very poor in it's presentation.

Patrick/David, please go back to how earlier episodes were done, identify a project and work through that. Best to leave basic electronics teaching to those that specialise in that. These days we mostly seem to work with various kinds of modules or kits, not at the basic manufacturing level. In particular it is not a great idea for the hobbyist to get into etching their own circuit boards - why not go through how to use one of the online PCB services such as ExpressPCB or PCB123? More cost effective than buying all the etching gear.

Some project suggestions.
1. Fix up a solar cell on the side of your house/flat, with enough capacity to drive a laptop, and DSL router.

2. Go through hooking up a mobile phone to a PC, explore the internals and get it setup to fully exploit it's features.

3. Demonstrate how to measure the quality of audio and video systems, and techniques for removing noise from videos etc

[ormej01]

Watching an early systm episode was my first contact with Revision3, and I thought it was amazing. The content was directed towards a common technical issue, and introduced new ideas to me. By contrast this episode brought nothing new, and was very poor in it's presentation.

Patrick/David, please go back to how earlier episodes were done, identify a project and work through that. Best to leave basic electronics teaching to those that specialise in that. These days we mostly seem to work with various kinds of modules or kits, not at the basic manufacturing level. In particular it is not a great idea for the hobbyist to get into etching their own circuit boards - why not go through how to use one of the online PCB services such as ExpressPCB or PCB123? More cost effective than buying all the etching gear.

Some project suggestions.
1. Fix up a solar cell on the side of your house/flat, with enough capacity to drive a laptop, and DSL router.

2. Go through hooking up a mobile phone to a PC, explore the internals and get it setup to fully exploit it's features.

3. Demonstrate how to measure the quality of audio and video systems, and techniques for removing noise from videos etc

[scienceking]

Great idea ormej01 on reviewing things like PCB fab services. I think that is totally unexplored territory. Most people don't have the time/money to explore all their options with such services, and just find something that works and stick with it. Even major corporations fall into this category. It would be neat to try a few of the leading vendors, and report back on quality, speed, customer service, etc.

[scienceking]

I found some lectures from Michigan Tech on iTunes for free that are pretty good for those who want a formal introduction to the world of circuits, without too much theory(although I personally view that as a bad thing...)

http://deimos3.apple.com/WebObjects/Core.woa/Browse/mtu.edu.1257718509.01257718515

[thebear91]

That show was the most convoluted explanation of Ohms law I've ever seen. :D

Sure, there are many factors to weigh in when you need precision measurements, but if you are dealing with a vehicle, your voltage varies between 11.5 Volts and 18 Volts.

Ohms Law, according to wiki and my electronics background, is simply E=IR.

P=IE is power law. Where power is useful is when converting voltages. A real loose example of this is power inverters. Power adaptors that take 12 Volt DC and turn it into 120volt AC. If your 12 Volt circuit can handle 20 amps, using the power formula that comes out to 240 Watts. This is the absolute perfect world most you can get from a 20 amp circuit, otherwise it will blow the fuse.

So 240 watts at 120 Volts = 2 amps.

Since this is not a perfect world, that is a bad way of figuring out exactly how much you can drain your battery. :)

I typically take 80% of that wattage as the max. Some inverters get up to around 94% efficiency, but it would be a very bad inverter if it got less than 80%.

To sum this up, I'm saying that for this type of a podcast, keeping things basic and everyday use is a better way to explain things. No need for anything more than P=IE and E=IR.

Basic rule of thumb for LEDs is they have a .5 volt voltage drop.

[masherscf]

That show was the most convoluted explanation of Ohms law I've ever seen. :D

Ohms Law, according to wiki and my electronics background, is simply E=IR.



It reads V=IR in all my very old textbooks. The E or V stands for Electromotive force which is measured in Volts. So, It's known colloquially as Voltage.

The old-timer tried to understand electricity through physical analogy to familiar kinetic equations.

Anyhow. Here's a little primer on SI units if anyone is interested.

Mass: Kilogram - canonical standard
Length: Meter - canonical standard
Time: second - canonical standard.
Force: Newton = kg.m/sec^2 - The force needed to accelerate a 1kg mass at a rate of 1 m/sec^2 (F=mass.acceleration)
Energy: Joule= N.m - the work done by a force 1 N moving an object 1 m. (W=F.d)
Power: Watt=Joules/sec The power required to do one Joule of work in one second. (P=W/t)

The unit for electrical charge is Coulomb which is rather circularly defined as the charge that runs by a current of 1 amp in second. This is a bit of a chicken/egg thing to me. They knew about static electrical charge before experimenting with current. Indeed the Coulombs law is a formula for computing electrostatic force between two charge bodies. Nevertheless, 1 coulomb is the amount of electrical charge in 6.241506×10^18 electrons or other elementary charged particles. I don't recall how they arrived at that value. Someone could fill that in for me.

the rest they covered.

Electrical current: Amps = Coulomb/sec
EMF : Volts = Joules/Colomb
Resistance: ohm = Volts/Amp

[thebear91]

I'm not sure what that last post was for. I think we all agree that E=V. All my text books past and present use E.

It really doesn't matter how or why they chose particular letters as long as everyone understand what they mean.

[scienceking]

Hmm, have to disagree on the 0.5V being typical for discrete LEDs.
First you need to know the LED voltage drop. It is safe enough to assume 1.7 volts for non-high-brightness red, 1.9 volts for high-brightness, high-efficiency and low-current red, and 2 volts for orange and yellow, and 2.1 volts for green. Assume 3.4 volts for bright white, bright non-yellowish green, and most blue types. Assume 4.6 volts for 430 nM bright blue types such as Everbright and Radio Shack. Design for 12 milliamps for the 3.4 volt types and 10 milliamps for the 430 NM blue.


The variables in this are the color, composition of the LED and it's size(the little surface mount ones tend to use a bit less). But 0.5 would be very low for an LED drop voltage, and unless you have some weird LEDs, I'd guess you've been under operating them. Even the diode drop between the base and emitter of a BJT is usually 0.7V, and the light those give off(if you use it outside of the casing, of course) is usually infrared!(and of course, our physics geeks who have learned of the photoelectric effect know that potential and the wavelength of light that can be releases are very related)
Of course, a spirited discussion on this topic is not really useful, as your LED's will have a spec sheet you can just use to look it up, or you can measure it yourself if you got them from something. Also a cool note about LEDs: because of the way they work(and this goes for all simple photoelectric effect devices), you can have them work backwards! They do a horrible job as they are designed by your friendly's electronics company to be good emitters which restricts their generator capability, but if you hold one up to a really bright light and use some decent DVM probes to measure it, you will see voltage from the ether.

[masherscf]

I'm not sure what that last post was for. I think we all agree that E=V. All my text books past and present use E.

It really doesn't matter how or why they chose particular letters as long as everyone understand what they mean.

Relax, my friend, I wasn't correcting you. I was just musing. Besides, it's been almost 20-years since I got my physics degree. I haven't had much use for it since then. I'm sure they've swapped the letters around a bit.

[scienceking]

Relax, my friend, I wasn't correcting you. I was just musing. Besides, it's been almost 20-years since I got my physics degree. I haven't had much use for it since then. I'm sure they've swapped the letters around a bit.

I've even seen it called P before in some journal articles for "potential".(which was a totally horrible choice IMO) You will see these things called everything and anything if you read enough. The important thing as an author is to try to make your work as clear as possible, but after the author is done, its the student/reader's job to try to figure out what the heck he was trying to say...

[masherscf]

but after the author is done, its the student/reader's job to try to figure out what the heck he was trying to say...

You haven't read a pure Math paper recently. Sometimes, I think the goal of the other is to make things as opaque as humanly possible.

[scienceking]

Well, we are assuming that the authors of these things aren't forming some evil "boys club" to protect their jobs etc etc. But trust me, we have some mucking around in the more specialist journals for engineering, too. I guess the one good thing about engineering is if we confuse ourselves too much, things don't get done, and CEOs throw chairs at us. While the math guys seem more laid back and self policed. If I were a bit better at maths(I'm minoring in it, so I'm not clueless, but I don't think I could ever contribute anything to the field), and less excited by electronics, that would seem like a great gig.

[masherscf]

If I were a bit better at maths(I'm minoring in it, so I'm not clueless, but I don't think I could ever contribute anything to the field), and less excited by electronics, that would seem like a great gig.

It's a living...

[grendelprime75]

The whole point of these series of introductory shows, at least as I see it, is to give people enough of an idea and the basic formulas needed to understand later shows better and maybe even work on their own small projects. I don't believe they are trying to teach the theory, but trying to give some rules of thumb. Many cool projects(as in I show my wife and she says wow, not as in I show a practicing engineer and he says how?) can be done by just utilizing a few simple rules. Understanding isn't always required (I myself prefer understanding not just memorizing). The hosts are trying to instill rules in those that haven't had the chance to learn them yet. Maybe people will learn these rules, do some small projects, and start working on bigger projects and begin looking things up for themselves. Babysteps.


---Matthew Hicks
Thats it exactly man.