Understanding Electronics Basics #1

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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.
 
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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.
 
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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.
 
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.
 
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
 
cowboybob said:
Hello! Anybody home??...
Click to expand...

You noticed I'd gone then**broken link removed** sorry seem to have been unindated with jobs to make up for my playtime on bike
**broken link removed** 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 **broken link removed** 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

KeepItSimpleStupid said:
Another example with your trying to say that a negative wave does nothing. Take a three phase motor
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erm, yeah, maybe we'll leave that a while **broken link removed**

It's nice to be back **broken link removed**
 
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!!
 
Muttley600 said:
What's this Triac thing your playing with then?
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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...
 
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cowboybob said:
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).
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What are you going to use that for then **broken link removed**

cowboybob said:
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...
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On the morrow it is & raring to go when you get up **broken link removed**

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 **broken link removed**
 
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.
 
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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
 
ok, have been playing after refreshing window for ages with nothing new, then finally realsied that you had edited exsisting post **broken link removed**

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
 
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 **broken link removed**

p.s. thanks for getting up early to give me sim **broken link removed**
 
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Muttley600 said:
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
Click to expand...

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..
 
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cowboybob said:
Now we'll go back to DC,
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You don't get away with it that easy **broken link removed** so how many VG is it possible to have within an AC signal **broken link removed** What is 3 phase electric **broken link removed**

cowboybob said:
so we can see how an AC signal is converted to DC and then smoother by including the effect of "filtering", literally the elimination of any AC component from the "pure" DC we are looking for..
Click to expand...

Cool, sure we can get back to it in a minute or two **broken link removed** 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 **broken link removed**

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

Oops, forgot to name sims
 
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