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Understanding Electronics Basics #1

Discussion in 'General Electronics Chat' started by cowboybob, Feb 16, 2012.

  1. Muttley600

    Muttley600 New Member

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    Good man, glad we didn't lose you :)
     
  2. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    A circuit consisting of a 12 V voltage source and two 6 ohm resistors can be analyzed as follows.
    12= 6I+6I ---> I=1 or 0=-12 + 6I +6I which is the generic form of the equation

    This also means the the voltage across each resistor is 6V

    Now Power = VI
    If we did the same thing we would have (12)(1)W = 6(1) W+6(1) W
    In the generic form of the equation
    0=-12 W + 6W + 6W

    Power is a negative quantity.

    Power generated, by convention has a negative sign. Power dissipated, a positive sign.

    Yea, it might make sense to have it the other way, but just like conventional current that's the way it is.

    The analysis is generic and is generally known as a "loop equation". The algebra gets messy, but it is appropriate for multiple adjacent loops.

    We don't talk about -10 MW generators, but when we analyze, they are negative. Your 100 W light bulb dissipates say 100 W of energy as heat.
     
    Last edited: Feb 18, 2012
  3. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Alright!!. Now where were we...

    All very true. However:

    Any motor, for instance, by its very nature, while turning, is also a generator. Electric Motive Force (EMF) is said to be the "power" that causes the motor to turn. All well and good. But as it turns, it's also generating what's called a Counter-EMF (CEMF) that flows in opposition to the EMF (this can set up so called "Standing Waves", [which are really bad for causing energy losses] but that really is down the road).

    Anyway, as in KISS's example, yes, there is power generated that does no useful work due to losses that are abundant. But keep in mind that a 10MW plant does not always produce at full capacity. The main power producing apparatus is throttled to the load. This does not eliminate losses, but it does reduce unnecessary loses. And, in essence, CEMF can be a power saving phenomenon.

    So, for DC, since by way of a bridge rectifier system (and other ways) we can move the negative element of the sine wave to the positive side of ground we are, thereby, now making it part of the "power" side of the equation. This is as you saw in the excepts you introduced in a previous post.

    It's good to see that that your curiosity is leading you to search out the answers to some of the questions you have.

    Sometimes it's necessary to explain a fundamental concept in such a way is isn't exactly complete or in all cases true. Certainly in a number of fields thee are ambiguities and nuances that are difficult to grasp until a certain underlying concept is understood.

    That's when you know better what questions to ask.

    And you are rapidly getting there.
     
    Last edited: Feb 18, 2012
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  4. dave

    Dave New Member

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  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Another example with your trying to say that a negative wave does nothing. Take a three phase motor which as 2 windings energized with 3 sine waves 360/3 degrees apart. When the sine wave is negative it could be pulling rather than pushing or vice versa, hence it is doing work.
     
  6. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    A DC motor can act as a generator as well as a motor. In fact the voltage produced by an unloaded generator is proportional to speed so V =k(rpm) or some constant k times the rpm. The motor also has a DC resistance, so there is an IR drop across the windings.

    So the Voltage V across the motor is V = Vm - IR; where Va is the Voltage across the motor. If you can compensate that IR drop, you can gain speed control of the motor.

    A recent application note from Linear Technology illustrates the earlier fact. The motor is pulsed for nearly the entire time. When it's coasting the voltage is measured and fed back to the speed control.

    At the same time torque is proportional to current.
     
  7. Muttley600

    Muttley600 New Member

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    Sorry guys, baled & had one of those rare visits to pub
    Back on it tomorrow
    CBB, tried to self help when site was down but I know you know the way forward, never could there be amore eager student :)
    Night all
     
  8. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Hello! Anybody home??...
     
  9. Muttley600

    Muttley600 New Member

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    You noticed I'd gone then[​IMG] sorry seem to have been unindated with jobs to make up for my playtime on bike
    [​IMG] it was maybe a tad too early in the year but had a great day out although the cold took it's own toll on me, then Lou decided if I had enough time to go out riding, I needed more jobs to do [​IMG] most out the way & the rest can wait until weds morning, so finally, I feel whacked before I start but can sqeeze in a start to kick this along again

    ok, totally agree with you on that, please proceed

    erm, yeah, maybe we'll leave that a while [​IMG]

    It's nice to be back [​IMG]
     
  10. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    CBB:

    Now you have time to work on your triac stuff. You shouldn't be complaining. <G>.
     
  11. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    See, Graham? Another addiction to deal with...

    Your right, KISS. Prob has been that our DSL link to the world has gotten very bad, lately. Keep checking the stupid thing and wasting time doing it.

    On to Triac play, yeah!!
     
  12. Muttley600

    Muttley600 New Member

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    Addictions can be good as long as they don't include triple chores. lol

    What's this Triac thing your playing with then?
     
  13. Muttley600

    Muttley600 New Member

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    Well short & sweet but got the ball rolling again, back in the morning eager as ever
    Night both
     
  14. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    It's like an electronic relay for AC. Very slick device but somewhat limited in the type of load it can handle (as I have learned the hard way).

    They're made of, essentially, a dual-diode configuration. Another little electronic wonder.

    We'll get to them in due time. (KISS is giving me a hand on this, thank goodness).

    On the morrow...
     
    Last edited: Feb 20, 2012
  15. Muttley600

    Muttley600 New Member

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    What are you going to use that for then [​IMG]

    On the morrow it is & raring to go when you get up [​IMG]

    I have read back & we'd got as far as waveforms & phases of cycle before I jumped ahead guessing, I think I've got sillyscope under control now, so I'm presuming there is still a lot more to AC than I know at the moment, what is the next step after last sims [​IMG]
     
  16. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Hey Graham,

    Just got up. Need a cuppa...

    Next up is taking two AC signals and adding them together (mixing), in the jargon. We'll start with signals of equal characteristics and then branch out to varying potentials, frequencies and phases.

    Cool stuff...

    I'll add a sim here in a bit.

    View attachment 61307

    ERROR in VG2 config!! Should read "VG2 = "Sine Wave, 500m VAC", 1KHz. (note "K"). NOT 1Hz.

    Enjoy.
     
    Last edited: Feb 21, 2012
  17. Muttley600

    Muttley600 New Member

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    Thanks CBB, morning :)
    Just watched a vid on site about lumped something or other, basically cutting the jargon, hence values. Hoping it will mean more once I have basic understanding in place :)

    Cuppa sounds good, will join you I think
     
  18. Muttley600

    Muttley600 New Member

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    ok, have been playing after refreshing window for ages with nothing new, then finally realsied that you had edited exsisting post [​IMG]

    I'm even trying to get used to this attachment thingy

    So I altered VG2 as follows:

    Sim 1: 500m - original ampitude/ 50hz
    sim 2: 500m - original amipitude/ 2k
    sim 3: 500m - original amipitude/75hz

    so by altering the frequency you are basically stretching/shortening the wave along along time line (bit like a spring) altering the time/div evened the signal back out
     
  19. Muttley600

    Muttley600 New Member

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    ok, on VG2 again, putting frequency back to 1k we have as follows:

    Sim 1: 200m/1k
    Sim 2: 1V/1k
    Sim 3: 2V/1k

    So altering the voltage your not actually altering the pull on length of the spring but the actual hieght/width , aside from playing with these different waves & pretty patterns, your actually showing me that you can have a wave/signal/frequency (whatever you want to call it) within another.

    So to relate this to something I have a vague idea about, my pmr radio for my motorbike has channel 3 = 446.032125Mhz but then has a sidetone of channel 13: 103.5hz

    Am I understanding this correctly [​IMG]

    p.s. thanks for getting up early to give me sim [​IMG]
     
    Last edited: Feb 21, 2012
  20. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    With this schematic, what you're seeing is that by mixing the two AC signals, the VG1 part is being "imposed" on the VG2 part, as evidenced by the faster (higher frequency) "ripple" of VG1 seen on the lower frequency signal of VG2.

    As you increase the frequencies of either VG1 or VG2, observe the general wave shape changes.

    Essentially, yes. Not so much as "within" as "mixed" with. Very good.


    Now we'll go back to DC, so we can see how an AC signal is converted to DC and then smoothed by including the effect of "filtering", literally the elimination of any AC component from the "pure" DC we are looking for..
     
    Last edited: Feb 21, 2012
  21. Muttley600

    Muttley600 New Member

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    You don't get away with it that easy [​IMG] so how many VG is it possible to have within an AC signal [​IMG] What is 3 phase electric [​IMG]

    Cool, sure we can get back to it in a minute or two [​IMG] is there anything else I need to know about AC before playing with DC, or are we still on AC just adjusting signals to mimick DC, or is that all DC really is, just an adjusted AC signal, which seems to make sense in my world [​IMG]

    So what was all this stuff I'd read about, real, reactive & appharent power, sorry for all the questions

    Oops, forgot to name sims
     
    Last edited: Feb 21, 2012

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