Sine Wave

Discussion in 'General Electronics Chat' started by Yoda, Jan 5, 2010.

  1. Yoda

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    Thank you for your help so far I think I am getting close to understanding this. In the second photo is one sign wave a voltage sign wave and the other current sign wave.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I guess you are referring to the photos VoodooMojo posted in this thread:
    http://forum.allaboutcircuits.com/showthread.php?t=32356
    They are both voltage waveforms.

    It would be a good idea to continue the discussion in the same thread; otherwise people will not know as to what photos you are referring to.
     
    Last edited: Jan 5, 2010
  3. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    for phase shift representation purposes.
    I had an email asking about the circuit I used to get the phase shift. I posted it here.

    the signal from the function generator and the scope will be sharing a ground so I wired it with basically a floating ground on the signal generator.

    the red and black jumpers at the left are from the signal generator, the black coming from the ground.

    the scope leads are grounded at the capacitor/resistor junction
    and the clamps are on the capicitor and the resistor.

    the wave forms are voltage representations with the second demonstrating the voltage lagging the current as we know it does in a capacitive circuit.

    the values of the capacitor and resistor were determined by what was sitting on the bench in front of me within reach at the time.

    http://forum.allaboutcircuits.com/showthread.php?t=32356
     
    Last edited: Jan 6, 2010
  4. Yoda

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    So one is the voltage wave form from the incoming power and one is generated from the motor. So if I understand correctly If the voltage wave form from the motor and from the source are close together than there is not much torch. But if you put in a run cap then that pushes them further apart creating better torch.
     
  5. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    Last edited: Jan 6, 2010
  6. Yoda

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    Ok, I think I am allmost there. The first wave form is a voltage wave form feeding the motor from a generator. The second wave form is the voltage wave form from the capacitor. Is this a 120 single phase example?
     
  7. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    this is a phase shift representation.It was put together with components of convenience.

    it is a 60Hz sine wave coming from a function generator. all the circuit parameters are in the "parameters" screen shot attached here.
    it is not 120 volts.

    I have included a photo of the circuit I constructed to achieve this phase shift.
    it has a .1mfd capacitor in series with 26.7kohms.
    the signal is coming from the left side with the red and black jumper leads and the output is on the right side going to channels 1 and 2 on the scope.

    Run Capacitors on a 120vac motor will display like characteristics but will have different component values depending on torque and application requirements.


    I think an important thing here is to see what a motor would see (or better yet, what a motor would feel) and appreciate the important role a run capacitor plays.
     
    Last edited: Jan 17, 2010
  8. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    yoda, if that is your real name;)

    Learn a basic definition of any electrical or electronic part. Be it a resistor, a diode, an inductor, a capacitor, a transistor, a SCR, a triac, a relay, or any other discrete component. Then experiment with them. singly at first and then in circuits with other discrete components. Then replace components with different values and see the outcome. Be prepared to damage some of them. Measure different parameters at various locations within your circuits. Become very comfortable and confident with the measurement process. Learn what you are measuring. Then start injecting the mathmatical concepts into your thought process. It will explain all your measurements. This is the beginning of circuit modification and design.

    At this point you will see that the basic description of an electric or electronic component at times doesn't have a darn thing to do with what it was put into a circuit for.

    Take a resistor for instance. Typically defined as a "component used to limit current". And it can. But at times a resistor is put into circuits to increase current.
    A diode is commonly defined as "a component that restricts flow to one direction". What the heck does that tell you why a diode is put into any specific circuit?

    This brings me to why I responded to this phase shift thing again.

    The common definition for a capacitor is listed by many as a "component that stores an electrical charge". Armed with that profound knowledge, how does that help explain why it is advantageous to install a run capacitor on an electric motor? It would be a stretch to come up with the phase shift explication.
    A more concise characterization of the capacitor is to state that a capacitor is a device that resists a change in voltage. Now we can see a light in the darkness as to why it is said that Voltage lags Current in a capacitive circuit.

    This definition I copied and pasted right from Wikipedia:
    "An inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it."
    How in any deluded imagination can one explain with that definition why I am always having to replace microswitches, transistors or control cards that control a relay or valve coil that does not have a suppression circuit.?
    You will always hear or read someone experienced with this outcome stating that a diode should be placed across a coil (relay, solenoid, etc). How in the world does:
    "An inductor or a reactor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it." help with this dilemma?
    Again, what is the characteristic of the inductor (coil) that would warrant the need for a diode placed in parallel to it?
    An inductor is a device that resists a change in current. Now this light in the darkness will reveal the condition why it is said that Current lags the Voltage in an inductive circuit.
    And the definition of a diode being a device used to limit current flow to one direction will not go far with understanding why we put a darned diode across the coil of wire.

    I remember the first time I was reverse engineering a circuit board that was using a gang of diodes as voltage divider / dropper circuits. I thought: "what the heck are they doing here?" I use them quite often now for just that purpose.
    What does using a diode for a voltage drop got to do with the typical definition of a diode? Not much.

    Understanding the characteristics of components in circuits comes more and more natural the more we experiment with them. Like this phase shift thing.

    One part of this experience we are having with this is the charging each cycle of the run capacitor. We can see the results and advantage of it. The next logical question would be what is causing it to discharge?

    The more we think, the more we learn. The more we learn, the more we earn. The more we earn, the more we yearn for the simpler times......

    .
     
    Last edited: Jan 8, 2010
  9. Yoda

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    Thank you for taking the time to work with me on this.
     
  10. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    we live for this stuff
     
    Last edited: Jan 8, 2010
Loading...