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Zombie
Forum Hillbilly
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Think of it this way. A diode is a one way passage. Any power will only flow in one direction thru it. A rectifier is a group of diodes to change
back, and forth flow (AC) into one direction flow (DC).
A resistor is just like a knot in a hose. It only allows a set amount of power to flow thru. The more "resistance" the lower the flow. It also does
it's job in both directions so it can pass both AC, and DC current.
A capacitor is like a bicycle ramp. Current has to jump across a gap to reach the other side. It will only allow a set current just like a ramp will
only allow you to cross if you have enough speed.Too fast, and you know to slow down. too slow, and you know to speed up.
That ties into the phrase Sine Wave. That is neither current or voltage. That is like the pedals on the bike. It is the frequency of the power or the
up, and down movement of the pedals. Capacitors allow a set amount of up, and down movement to pass, while blocking the movement that will not work.
Just like the ramp.
Did you notice how all of this is just like water flowing? Least resistance is correct. Start at the source, and follow the flow.
IF your LED does not light... Where do you look first? The source!!! Start at the wall outlet. Go to the next place... The switch then at the
transformer, It flows like water. It changes pressure, and flow rates but it MUST follow the path you set up for it.
When it doesn't? start at the source.
I hope this is helpful. The fellas here want to teach you the correct way of learning this. I want to make it easier for you to see in your head what
is happening.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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I Like Dots
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Hey guys, quick heads up. Radioshacks across america are going out of business, which means they are having HUGE closeout sales on electronics. I got
a grab back of components (resistors, diodes, fuses, led... etc) valued at $500 for $3. I also got This kit (and number 2) for only $4. I also picked up a ton of Arduino peripherals for like 90% off!!!
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Magpie
lab constructor
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Mood: Chemistry: the subtle science.
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I'm going to ramble/rant a bit here.
Ramble: You can assemble an electronics circuit by following someone elses schematic and it should work as advertised. And this is a perfectly
acceptable way to begin learning. But to truly learn how an electronic circuit works you must learn how the basic components of the circuit function,
ie, resistors, capacitors, inductors, transformers, wires, batteries, generators, etc. In fact, if you just learn about resistors, capacitors, and
inductors you will have taken a giant leap and gained a solid foundation. This all will take time: take it one step at a time, and enjoy your latest
victory in comprehension. Don't expect to learn this overnight!
Now, to really understand these concepts you must have some math skills. Basic algebra is a must. This will allow you to manipulate Ohm's Law,
understand current flow through parallel resistance paths, etc. Understand a sine wave (trigonometry) and then you can move on to AC circuits. I
recommend mastering DC circuits first, by all means - they are much simpler.
Electronics is like math: you build on the basics, giving you a solid foundation. If you try to jump into something without understanding the basics
you are screwed as far as having a true understanding.
Rant: The demise of RadioShack is a true catastrophe. Where else will I be able to drive to a nearby shopping center and buy electronic components.
Some of the clerks (though not many) even understand electronics! Fortunately for me only 1 of my 2 stores is going to close. The remaining one will
likely become a smarmy Sprint, only interested in selling consumer gadgetry. Then they might well get rid of their component drawers altogether.  I hope not.
The single most important condition for a successful synthesis is good mixing - Nicodem
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IrC
International Hazard
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"The remaining one will likely become a smarmy Sprint, only interested in selling consumer gadgetry. Then they might well get rid of their component
drawers altogether."
After they accomplished the demise of Lafayette (vastly superior in component product line for experimenters) they started this trend (doubling or
more all prices compared to the competitors they destroyed) from the early 80's on, and this idiotic business model is exactly what did them in. I
asked a suit in Tandy Corporate one day in the 90's why they kept discontinuing every single item so much in demand by people like myself. He
explained all marketing decisions were based upon sales numbers at a single company store in downtown Manhattan. He even agreed with my point that
people there were not an example of hobbyists in the rest of the country. Sad that the decision makers were not interested in sound business
practices.
"Science is the belief in the ignorance of the experts" Richard Feynman
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woelen
Super Administrator
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What happens to Radioshack in the USA now already happened 10 years ago where I live. At that time, there were three electronics shops in the city
where I live and you could buy resistors, capacitors, many types of semiconductors, many types of integrated circuits and also all kind of equipment
and kits. Nowadays we only have one electronics shop left and they are mostly sell complete devices and gadgets. You can buy some basic electronic
parts (e.g. resistors from the E12 series, 0.25W and a few somewhat larger power resistors, some capacitors, some LEDs and some types of wires, clamps
and so on), but all of the specialist components are gone. For me, the only serious source of electronic components is the internet (e.g. eBay).
This is a general trend. The big shopping centers carry less and less specialist stuff. Clothes, mobile phones, standard consumer electronics and a
lot of perfume, cosmetics, life style products. The special hobby, arts and electronics shops are gone 10 years ago already.
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Zombie
Forum Hillbilly
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Same here. I have not seen or been in a proper electronics shop in at least 10 years. All of the Radio Shacks were sold as franchise stores years ago.
They are mainly cell phone chargers, and as Woelen said, gadgets.
Everything I use comes off the net or catalogs.
[Edited on 8-2-2015 by Zombie]
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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radiance88
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Ok WGTR - I performed both of the tests you instructed me to earlier in the thread. I don't have a 9 volt battery lying around, so instead I used the
9 volt tap. I constructed the circuit on my breadboard (to the best of my knowledge), and more or less it seems to work.
I'm not so sure about the results of these tests though.
At 9 volts AC input, testing for voltage at the DC ends on the other side of the rectifier gives me 11.12 volts. Same amount is obtained by flipping
my two AC wires.
At the same 9 volts, measuring for current with my multimeter gives me .07 millivolts/.7 microvolts either way. I measured twice with both my milli
and micro settings to make sure that it wasn't screwing with me.
Somehow these don't seem to add up to your original estimates of 7.5V output voltage, and 7-8 millivolts. I thought since the current was off a couple
of decimal places that there was something wrong with the resistor, and so I checked it, but it gave me a very close cut to the rated 1000 ohms, so
the resistor seems to work fine.
I must be doing something wrong here?
[Edited on 8-2-2015 by radiance88]
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Fulmen
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Have we covered RMS yet? It is basically the "average" or more correctly the equivalent DC voltage, meaning that a 9V RMS AC will produce the same power as 9V DC.
The reason for not using "average" is that since AC fluctuates between positive and negative the average voltage will be zero. But since power depends
on the magnitude of the current and not the direction an average of zero can still produce power.
The peak voltage will be higher than the RMS by a factor of 1.4 (square root of 2), for 9V this will be 12.7V. But since the current passes through
two diodes the peak voltage after the rectifier will be slightly lower, ~11V sounds about right.
You also have to take voltage drops in a transformer into account. Since voltage drops with current (U=R*I) the output voltage is usually chosen for a
given load, below this load the voltage will be slightly higher. The actual mains voltage also fluctuates, all this makes transformers inherently
imprecise voltage sources.
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WGTR
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1. The circuit looks good. The diodes look like they are pointed the right way, and the capacitors are the correct polarity. Also, I see the 1k
resistor on the output.
2. I made an assumption that your meter can measure current. Current is measured in amps (or milliamps,microamps,etc.), not volts. Would you mind
posting a picture of the meter; something close enough that we can read the settings on the front?
3. I suggested a 9V battery, because the measurements are simpler that way. If you want to use the 9VAC tap, then Fulmen is right.
9VAC is not exactly the same as 9VDC. Imagine that you had an oscilloscope for a moment. When looking at 9VAC on the display, you would see that the
voltage actually swings up to a maximum of 12.7V+, and then down to 12.7V- when it reverses polarity. This delivers a 25.4 peak-to-peak
voltage. If you run this voltage through your bridge rectifier, the negative peaks get converted to positive ones, and the peak-to-peak
voltage of 25.4V gets converted to a peak voltage of 12.7VDC.
A diode only allows current to flow in one direction, as you may already know, but a diode is not a perfect device. Even when current is flowing
through it, there is always a voltage drop across it. This voltage varies depending on the diode, but is usually 0.6 to 1.0V per diode.
What this means, is that your 12.7V ends up being the 11.1V that you measured. For example, 12.7V - 0.8V - 0.8V = 11.1V.
Your voltage measurement of 11.1V looks correct. The only thing that I see wrong is the current measurement, because you tried measuring it in
voltage instead of current (there is a way to measure it that way, using Ohm's Law, but that is "Plan B"). Also, the current at that point is AC, so
you would have to measure it with an AC current setting.
So the burning question is, why is 9VAC actually 12.7Vpeak? The reason is that the power company charges you only for the energy that you
use (as a "residential" user), and not for the voltage or the current. If you apply 9VDC across a 1k resistor, it heats the resistor exactly the same
amount as if 25.4VACpeak-to-peak where applied across the resistor. In other words, 9V is the root mean square value of
25.4VACpeak-to-peak. Are you thoroughly confused yet?
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radiance88
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Sorry, my bad. I meant . 07 milliamps and .7 microamps as my readings via the AC current reading on my multimeter, not volts. I got my units mixed up.
Is this supposed to be another thing associated with rectified voltage? because it really isn't anything close to what you gave me. .
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Fulmen
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What exactly are you measuring? the current through the circuit with the led shining? Make a sketch of the circuit and point to exactly where you are
measuring.
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radiance88
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The lower part of the diagram constructed by WGTR in the beginning of the thread.
diagram
My breadboard in the previous post is my replication of this schematic. Notice that there is a red wire and a white wire which aren't connected to the
board - that's where I put my multimeter leads towards and measured with the millamp and then microamp settings.
AC and DC seem to be very different critters. I might as well just go ahead and finish the circuit, build it in the box and be done with it until my
self-study allows me to understand a bit more what's going on.
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Fulmen
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Well, something is off. 0.07mA is the same as 70uA, not 0.7uA. You should get the same value regardless off the range, are you sure you've connected
the multimeter correctly? Perhaps a pic of the meter?
AC vs DC? Yes, there are some significant differences to take into account. For a resistor it doesn't matter, RMS AC and DC gives the same (RMS)
current. But since you flip polarity and current direction continuously a lot of components behave fundamentally different.
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Magpie
lab constructor
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Yes, very much so in many ways. With normal DC circuits everything (current, voltage drops, power dissipation, etc) remain the same with time, ie,
are at a steady state. With AC everything changes (in cycles) with time, at least on an instantaneous basis. If the power supply is US household
120VAC, 60 Hz, then the cycles are happening 60 times/second!
Earlier I said that understanding 3 fundamental components: resistors, capacitors, and inductors would be an important step. This is true, but
capacitors and inductors normally only come into play when using AC. DC usually only deals with resistors.
A capacitor never really passes current, it only builds or stores charge (electrons). Placing a capacitor in a DC circuit having a steady voltage
source is useless. It just forms an open circuit. Ie, no current will flow.
An inductors passes current but if the current is changing it causes a form of resistance to this change.
Quote: Originally posted by radiance88  |
I might as well just go ahead and finish the circuit, build it in the box and be done with it until my self-study allows me to understand a bit more
what's going on. |
Sounds like a good plan. There's only so much you can learn by assembly alone. Alternating this with tutorials on electrical theory is a good
strategy, IMO.
[Edited on 9-2-2015 by Magpie]
[Edited on 9-2-2015 by Magpie]
[Edited on 9-2-2015 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Fulmen
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I must object to this, especially capacitors are commonplace and indeed crucial to DC circuits. How would you build something like a multivibrator
without a capacitor?
Inductors are less common in DC operations, but they still have a wide range of uses.
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Magpie
lab constructor
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That's why I used the qualifier normally. I'm trying to explain these concepts at a fundamental level without writing a book.
The single most important condition for a successful synthesis is good mixing - Nicodem
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radiance88
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This first pic is my replication of the lower diagram, leads hooked to the "hot side" with the multimeter set at its mA, AC setting. The second is the
uA setting.
I'm not really sure what to say. If my multimeter is defective then that also leaves me screwed, as I'm pretty sure I'm out of scope of the store
return policy. If we can't figure this one out, I'll just build the circuit, place it its pretty box and leave this be.
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Fulmen
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I still maintain it's wrong and misleading. Now I'll agree that capacitors isn't the first ting one should focus on, but you won't get far in the
world of DC without understanding capacitors. I also think one should be familiar with capacitors in a DC setting before looking at how they behave in
AC.
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alive&kickin
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radiance88, since you are just starting with electronics, I have some LEDs and 8 segment displays that I can send you if you're in the states and
interested. I'll be more than happy to send you a couple dozen to play with. I posted it over in apparatus acquisition and just U2U me with the
address to send them to. This goes for anyone else who may be interested as I have about 30 8 segment displays and about 1000 LEDs, all brand new and
free for the asking.
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Magpie
lab constructor
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| Quote: Originally posted by Fulmen | | I still maintain it's wrong and misleading. Now I'll agree that capacitors isn't the first ting one should focus on, but you won't get far in the
world of DC without understanding capacitors. I also think one should be familiar with capacitors in a DC setting before looking at how they behave in
AC. |
I understand where you are coming from. I'll explain where I'm coming from:
I learned about electricity in a basic electrical engineering course in my junior year in college (1963). The text we used was "Basic Electrical
Engineering" by Fitzgerald and Higginbotham, 2nd ed (1957). The first chapter, "D-C Circuits" consisted of 29 pages covering "Basic Electrical
Quantities," "Electrical Circuit Constants," "Resistance; "Ohm's Law," "Fundamental Circuit Laws; Kirchoff's Laws," "D-C Circuits," "More Complex D-C
Circuits," "Network Simplification," "Principles of Superposition," and "Thevenin's Theorem." It was not until Chapter 2, "Alternating Currents and
Voltages" the 10th page in, after describing sinusoidal voltage and current, did the book introduce capacitance.
That's why I don't naturally think of capacitors as part of a DC circuit. But, as you say, they are certainly necessary for many circuits powered by
DC voltage.
But once you start chopping and making the voltage pulses non-steady state (cyclic transients) do you really have a DC circuit anymore?
The single most important condition for a successful synthesis is good mixing - Nicodem
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Fulmen
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Yes. Alternating currents implies a reversal of flow. One can always subdivide DC into steady and non-steady state, and your statement does make a lot
more sense in that context. In a steady state circuit a capacitor has little use.
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WGTR
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| Quote: Originally posted by radiance88 | | I'm not really sure what to say. If my multimeter is defective then that also leaves me screwed, as I'm pretty sure I'm out of scope of the store
return policy. If we can't figure this one out, I'll just build the circuit, place it its pretty box and leave this be. |
Both readings are near the bottom of their respective scales, and the accuracy may be rather poor at that point. What happens if you unplug the
transformer with the meter still connected in the circuit? Do the values change, or stay where they are?
I have, on more than one occasion, accidentally tried to measure voltage while the meter was set up to measure current. What happens at this point,
is that a lot of current will try to flow through the meter. This blows the protection fuse inside the meter. The voltage measurements are
still good, but the meter will not measure current until the fuse is replaced. Sometimes, there is an extra fuse inside the cover, because everyone
makes this mistake at some point. Just popping the cover off the back of the meter and looking at the fuse should tell you if this is the problem.
Heck, you can even take the fuse out and check it with your ohmmeter. It should be almost 0 ohms.
The only other thing I can think of, is that perhaps one-half of the bridge circuit is not making a good connection. You could try measuring DC
current to see if you get a stable reading.
[Edited on 2-9-2015 by WGTR]
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IrC
International Hazard
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"multimeter is defective then that also leaves me screwed"
Either I am not understanding your circuit or your meter was fine until you connected the meter across the rail in a current setting. Very bad idea.
As magpie suggested go look at your fuse. I am assuming the red and black banana jacks are your plus and minus rail? If so why are the meter leads on
them with the DVM clearly on a current scale? Only measure voltage in such circumstances, always put the meter in series with the circuit when
measuring current. Second, on the first couple pages of this thread links to very good sites with great tutorials were posted. With this in mind why
are you still asking simple questions (covered in depth in the links provided) instead of spending at least some time studying in lieu of asking
people here to take time answering? Hopefully I am not coming off too negative here but there is a point at which one would begin to wonder if you are
taking any time to study on your own.
Concerning capacitors and some comments by magpie and fulmen two things; even in a so called steady state circuit capacitors have use. For example a
7808 regulating from a 12 volt source, capacitors here prevent oscillation of the regulator even though we have a steady 12 volts in and a steady 8
volts out. Also in many other circuits whether to prevent oscillation or to reduce the noise on the rail. Other examples apply as well. Second, even
in a fairly steady state circuit, say a medium to long duration timer, a capacitor charging slowly provides a time reference. Depending upon the time
frame being considered one could say the circuit was 'steady state'. I am kind of with magpie on the learning in the AC section of the book for
similar reasons as he. I'm old and my learning started with the same and similar books. Notwithstanding capacitors are important to understand even in
the beginning with DC theory for many reasons, a couple of which I just discussed.
"Science is the belief in the ignorance of the experts" Richard Feynman
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WGTR
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IrC, he had the meter in series with the bridge (to measure input current), so there shouldn't be a problem with that measurement
configuration.
I don't mind answering questions as I have time. When I first started out, I bothered people incessantly with dumb questions. They were quite
patient with me. Even with books, it took me several years to figure out the transistor. Since transistors "amplify", at first I thought that meant
they created their own energy. I envisioned building a car powered by thousands of transistors. Around this time I dreamed up an electric motor that
would supply its own power by turning a geared-up generator. I tried explaining this concept to a relative of mine (who is an engineer). He kept
trying to explain to me why it wouldn't work, and I kept thinking that he didn't understanding what I was trying to do. After all, it was obvious to
me that the idea would work. At the age of 11, I had a creative imagination, but I was as dumb as a box of rocks.
Once I figured out the purpose of the transistor, I labored ineffectively at trying to get one to amplify something. Either I messed up the biasing,
or I hooked the transistor up backwards, or had bad parts...I don't know, but somehow it took me several years of frustrated tinkering before I
finally figured it out. Vacuum tubes were the only thing I could get to work during that time. An older friend of mine was befuddled by my
difficulties. After all, transistor biasing was the easiest thing in the world to him. Had someone sat down with me and built a transistor circuit
with me, walking me through the design process, showing me that transistors do in fact "work", it would have helped an awful lot.
Anyway, I don't mind walking someone through their first circuit. It's usually that first circuit that determines how one looks at electronics going
forward.
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IrC
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Had to study the images real close, no depth in 2D. I see your point the black lead is slightly above the post hooked to a wire to the top of the
bridge. But I do not see where the bottom of the bridge (AC side) goes back to the other transformer winding. One side goes to the red lead through
the meter back to the bridge. Is the other winding connected?
I realize you like helping him so do I but I thought it good to prod him into spending time studying the tutorials (and the math) in the links.
"Science is the belief in the ignorance of the experts" Richard Feynman
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