Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Basic RLC Circuit Design

  1. Aug 27, 2014 #1
    I've been trying to teach myself electronics. I have read a lot of introduction books and now want to build a circuit. However, I have not been able to find good books on how to assemble simple circuits. In other words how the parts (resistors, caps, coils, diodes, transistors) go together. I understand all the parts but need to learn to assemble circuits.

    For instance, I want to plug into a 120v AC outlet and create an RLC circuit where the R is an incandescent light bulb inside the tank circuit. I figure by putting the light bulb inside the LC tank I will pass the same electricity thru the bulb multiple times and save on electricity consumption. I would somehow push a little more electricity into the circuit to maintain resonance.

    Is this idea feasible? How do I get to the next step to building simple circuits? Any good books?

  2. jcsd
  3. Aug 27, 2014 #2


    User Avatar
    Science Advisor
    Gold Member

    This web site will not let me post the answer I want to since the single word "No" is not enough characters. Basically it cannot be done. You can't get more energy out than you put in.

    BTW, the phrase "pass the same electricity thru the bulb multiple times" does not indicate to me that you 'understand all the parts' at all.
  4. Aug 27, 2014 #3


    User Avatar

    Staff: Mentor

    No, you don't want to do that! You don't want to go anywhere near lethal voltages.

    Start with circuits that operate off low-voltage batteries, so that you are not imperiling your life (and that of others who may try to extricate you from your experiment). There are plenty of perfectly safe circuits to construct, without cooking up something dangerous whose hazards you don't understand.

    We value our PF members too much to not decry senseless risks through such misadventure!

    Live long, live safely, and enjoy science.
  5. Aug 27, 2014 #4


    User Avatar

    Staff: Mentor

    Start with beginner electronics kits like these:

    https://www.google.com/webhp?source...v=2&ie=UTF-8#q=electronics kits for beginners

    You will learn a lot from putting together the kits and reading their "theory of operation" information that comes with them. :smile:
  6. Aug 27, 2014 #5
    Thanks for the safety concern. But can you answer the question as to if I put a light bulb inside the tank, Ie. between the capacitor and the coil, when the current (I) is at resonance maximum, the current flows back and forth between the capacitor and coil. The same electricity is surging back and forth across the filament. Is it not?

    My supply would simply pulse in a small amount of current to maintain the state of resonance. Like a person pushing a swing analogy.

    I'm not saying I would get something for nothing. What I'm saying is that in a conventional bulb the current only goes thru the bulb once, but with my technique, the current would oscillate across the bulb multiple times while in the tank. Perhaps DC would be easier to visualize.
  7. Aug 27, 2014 #6
    I have done several kits, but most are really weak when explaining "Theory of Operation". It's the why we put a capacitor here, why is a diode there, here's what's happening as the electrons flow around the circuit kind of stuff that I need more of.

    It amazes me how ham operators,many of whom have no electrical engineering degree, can build a transmittor or radio from scratch. I wonder how they learned this field. I have hit a brick wall in trying to educate myself on this subject.
  8. Aug 27, 2014 #7


    User Avatar

    Staff: Mentor

    Can you post what kits you've built so far, and what they and their docs look like? I'd like to get calibrated on what you've seen so far, and what may be the best thing for you to work with next.

    And on the HAM Radio Handbook -- it's a good reference if you want to build legal transmitter/receiver units, but it's not a general EE development resource.
  9. Aug 28, 2014 #8
    Last edited: Aug 28, 2014
  10. Aug 28, 2014 #9


    User Avatar
    Science Advisor
    Gold Member

    No, because light bulbs use ENERGY not current. This is why they have a power rating (power in Watts is the same thing as energy per second ).
    Setting up a resonant circuit does not "create" energy, it just means that the current reaches a maximum at a given frequency. If the quality factor of the circuit his high enough (which it won't be if you put a light bulb in there) you can also temporarily "store" some energy in the circuit but that energy still had to come from somewhere in the first place, meaning there is absolutely no way to save energy using a resonant circuit.

    Also, remember that the power companies bill you for the ENERGY you use, not the amount of current and/or voltage.
  11. Aug 28, 2014 #10
    I've got the Elenco 150 in one kit, i've done a radio kit, buzzer, etc. I got my Ham license and went thru all that training. I've read the ham radio handbook. It was way too technical for my level.

    All the books I can find that are introductory just explain what a capacitor is, what resistor bands mean, parallel and serial analysis techniques, how batteries work, how inductors work, transformers , capacitive reactance, etc.

    But now I want to build circuits of my own. For example, I want to create a circuit that outputs a signal at a particular frequency and voltage. Ideally one where I can vary the frequency and voltage of the output.
  12. Aug 28, 2014 #11
    If you have several electronic kits, does that mean you've actually built simple circuits with a low-voltage supply/battery, a bunch of resistors etc., and probed the voltages around the circuit to figure out how it all works?

    Maybe used a breadboard before?


    I would think that would be the very first step to getting into electronics.
  13. Aug 28, 2014 #12
    Yes, the kits include a breadboard. But mostly they are just putting pieces into place, with very little in the way of explaining in detail what is happening in the circuit.

    For example, say I want to experiment with electrolysis, so I want to plug into a 120v AC main, then be able to change the output current to different frequencies, different voltages and be able to toggle from ac to dc output. Say i want to change the frequency from say 10hz to microwave frequencies to see if the electrolysis is more efficient at particular frequencies. If microwaves heat water better than lower frequencies, perhaps they will be more effective at electrolysis.
  14. Aug 28, 2014 #13
    That seems odd, if the kits are meant to teach you something about electronics.

    Why not breadboard up some simple circuits with LED's, 555 IC's etc.? There's tonnes of neat stuff you can start out building. Do you like audio projects? Building small amplifiers and such is a great way to start out. Fiddle around with opamps, filters - all sorts of great stuff.

    This paragraph raises so many red flags, it's like you're intentionally trying to build something dangerous. High-voltage, low-impedance outputs, water, hydrogen/oxygen gas mixtures. As far as I know, electrolysis of water is only done using DC/pulsed DC. If you want to separate the hydrogen and oxygen gas, then generally you'd want to keep the polarities of the electrodes fixed, otherwise, if it even produces any reaction, you'll just end up with a mixture.
  15. Aug 28, 2014 #14

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    You ought to read up on resonance.
    Search on "resonance Q"



    Do you believe in conservation of energy ?
    Q in a resonant circuit is the ratio of energy stored to energy dissipated every cycle.

    Don't try to resonate at 60 hz because you need a big inductor and a big capacitor and you can easily kill somebody with such a resonant circuit.

    There's plenty of Tesla coil plans that start with an old car or lawnmower ignition coil. You're not nearly so apt to kill yourself or a family member with one of those.
    Tesla became obsessed by resonance and went bonkers, so be aware there's a lot of crackpottery about him on the internet. Resonance doesn't amplify power it just stores it.

    Plenty of hobby sites on the internet.

    amasci dot cm
    discovercircuits dot com
    sparkfun dot com

    search on electronic hobby parts
  16. Aug 28, 2014 #15


    User Avatar

    Staff: Mentor

    Take a look at this book when you get a chance:

    The Art of Electronics by Horowitz and Hill: https://www.amazon.com/Art-Electron...248078&sr=1-1&keywords=the+art+of+electronics

    Maybe you have a technical library nearby where you can check it out? It should be at a level where you can understand it, and if you read it cover-to-cover and build some of the circuits in it, you will be very far along in learning electronics, IMO.
    Last edited by a moderator: May 6, 2017
  17. Aug 28, 2014 #16


    User Avatar
    Science Advisor

    That paragraph makes me think this guy might be subtly trolling the forum.

    To the OP: If you really want to "learn electronics" start with simple op-amp based audio projects or LED-flasher type things with a 555. These are fun, educational, and safe. Also, if you're being sincere, your RLC circuit won't work because any light you generate is due to power dissipation in the light bulb. Therefore, whatever energy you use to light the bulb will need to be supplied to the RLC circuit. You gain nothing.
  18. Aug 28, 2014 #17
    I may have confused the issue by mentioning resonance. I guess it is not necessary to be at resonance for this. Let me restate: Assume simple battery connected to 12 volt light bulb. The current flows thru the light bulb and the bulb dissipates some of the energy as light and heat. However, some of the energy of the current flows thru the bulb and is not used.

    What I am suggesting is putting the bulb between a capacitor and inductor. Now as the first pass of the electric current thru the bulb,not all of the energy will be disippated, so it will go into the capacitor and stored as energy, then will be returned across the bulb and any excess energy still not consumed by the bulb with be stored as a magnetic field in the coil, then released back across the bulb as the energy sloshes back and forth between capacitor and inductor. Resonance is not necessary only LC tank. What am i missing?
  19. Aug 28, 2014 #18


    User Avatar

    Staff: Mentor

    No, you are just confused. All of the energy delivered by the battery is dissipated in the load in the single pass of current through the bulb.
  20. Aug 28, 2014 #19
    Either that or he is clueless & wants to kill himself.
  21. Aug 28, 2014 #20
    you should really start with simple battery circuits before you start working with wall power.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook