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Thread: Practical Experiment in LRC circuits

  1. #31
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    Fishn sparky:

    Most that have responded to you want you to go the simulation route. This may be very good for a lot of purposes, but I don't believe that is your desired direction based on the implication of your first post.

    A side story that may relate.

    When I was a student I also worked part time in a research group that was directly linked to the teaching staff of the EE department. The project I was heading up at a particular time was sponsored by Chrysler and related to how to improve the ignition system in the face of firing fouled plugs as compression ratios were approaching 12 to 1, mid 1950s.

    An EE student that was quite smart told his advisor that he was thinking of changing fields because all he was getting was theory and he did not see a connection to the real world. I was asked if this student could work with me and see if he might have a change of mind. For me that was OK and after a portion of a semester the student found there were exciting things to consider when he started to have connection with real engineering work. He went on to continue in EE.

    Since you don't have the resources of an oscilloscope it probably also means you are quite limited in what you do have. We need some idea of what resources you have.

    A 1000 ft spool of wire is an inductor, a transformer is an inductor. An incandescent bulb is a crude voltmeter or ammeter. So is an LED. I would like to see you have a Variac, Fluke 27 and 87 meters. A Kill-A-Watt EZ is quite inexpensive, about $30 at Home Depot. A range of capacitors and resistors may be a major cost factor. Old working motors can be useful. Ignition system components from junkyards provide much to work with.

    I have had my own Tek scopes in the past, since 1961, all presently nonworking. I made my own in 1949 in two days with some WWII surplus components. I think it may still sort of work. In the mid 40s I had my first exposure to an oscilloscope at Ford Engineering with a 3" DuMont. In the late 50s I built a Heathkit scope. While on board the USS Wisconsin in 1951 I had use of a singleshot scope. Then in 1952 at the Brooklyn Naval Shipyard I had my first exposure to a Tek scope. At the U of M I always had Tek scopes to use. Presently I have a Rigol (Chinese) DS2072A. Got this for about $800 new with many optional functions on one of their year end sales, 2 years ago. Its screen size is adequate. There are lower cost ways to get a scope function. But my Rigol scope has a lot of value for the money.

    .

  2. #32
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    Quote Originally Posted by GoldDigger View Post

    Some people just do not believe math, I guess.

    Or, more to the point, they do not remember it as well as hands on experience.
    seeing something on this subject means little
    drawing the diagram and working the problem in steps leads to understanding
    different strokes I guess



  3. #33
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    Ingenieur:

    My guess is that
    Fishn sparky is trying to teach people how circuits work so that they can use that information to troubleshoot and solve problems, rather than how to design circuits.

    Troubleshooting problems requires hands on skills with understanding what they are working on and how to make real measurements.

    Example: battleship, 16" guns, shoot 20 miles, main battery firecontrol radar is not functioning correctly, radar transmitter is on the bridge, the antenna system is on top of the conning tower which is just above the bridge, and the rest of the equipment is in CIC (combat information center) two decks below the main deck. There are a lot of RLCs, RLs, and RCs in this system. Do you use a simulator to solve the problem, I doubt that you could. So how do you attack the problem?

    .

  4. #34
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    The following is something for everyone to chew on.

    Parts and meters being played with:
    Sq-D 500 VA 60 Hz transfomer. Two 240 V windings, and two 120 V windings. Part # SV1B or something like that. Fluke 27, Beckman 4410, Kill-A-Watt EZ, 100 W incandescent, Superior Electric 7.5 A Powerstat (General Radio name for this is Variac), and a General Radio LRC bridge at DC or 1 kHz.

    Fluke R measurements (test leads 0.1 to 0.2 ohms).
    X1-X2 = 1.5 ohms, X3-X4 = 1.7 ohms, H1-H4 = 10 ohms.
    Note: 1.4 + 1.6 = 3, and 3*4 =12 which is close to 10, good balance.

    GR Bridge DC., clip leads 0.2 ohms.
    X1-X2 = 1.7 ohms, X3-X4 = 1.8 ohms, H1-H4 = 10.15 ohms.

    GR Bridge at 1 kHz, same clip leads. Non tested transformer coils (leads) are open.
    H1-H4 L = 1 H, Q = 11.
    X1-X2 L = 0.072 H, Q = 10.
    X3-X4 L = 0.072 H, Q = 10.


    GR Bridge at 1 kHz, same clip leads. Certain transformer leads are shorted.

    H1-H4 L = 0.011 H, Q = 2 on Hi-Q range, X1-X2 shorted, X3-X4 open.
    H1-H4 L = 0.014 H, Q = 2 on Lo-Q range, X1-X2 shorted, X3-X4 open.

    H1-H4 L = 0.024 H, Q = 4 on Hi-Q range, X3-X4 shorted, X1-X2 open.
    H1-H4 L = 0.022 H, Q = 3.9 on Lo-Q range, X3-X4 shorted, X1-X2 open.

    H1-H4 L = 0.0075 H, Q = 2.4 on Hi-Q range, X1-X2 shorted, X3-X4 shorted.

    Did I make any measurement mistakes, don;t know?

    Measurements made with the GR Bridge at low signal levels, and 1 kHz may not be close to results at other excitation conditions.


    The next experiments are with a 100 W 120 V incandescent alone, and in series with H1-H4 for current limiting.

    100 W bulb only.

    121 V, 0.82 A, 99.6 W, 99.7 VA, and 0.99 PF.


    100 W in series with H1-H4, and no shorted secondaries.

    120.8 V, 0.02 A, 1.4 W, 3.0 VA, 0.46 PF. Blub does not glow, bulb is probably about 10 ohms.
    Apparent Z looking into H1-H4 = 120.8/0.02 = 6000 ohms. Assuming R is negligible, then calculated L = 6000/377 = 16 H. Magnetic core and flux levels may be the reason for the gross difference.


    100 W in series with H1-H4, and X3-X4 shorted, X1-X2 open.

    121 V, 0.72 A, 87.2 W, 87.3 VA, 1.0 PF.
    Apparent Z looking into series string 121/0.72 = 168 ohms.

    Bulb voltage 95.5 V, calculated R = 95.5/0.72 = 132 ohms. bulb is quite bright.
    Approximate internal R of transformer is 10 ohms (primary DC resistance) + 4*1.7 = 6.8 ohms (secondary DC resistance reflected to primary), or a total internal seen at the prreimary of 17 ohms.

    So equivalent series resistsnce is about 132 + 17 = about 150 ohms.

    Estimate of series inductance. Internal resistance voltage drop about 17*0.72 = 12.2 V. Voltage across internal L and R is measured at 26.3 V, and estimate of L drop is sq-root of 26.3*2-12.2*2 = 23.2 V. X sub L is 23.2/0.72 = 32 ohms. Estimated L = 32/377 = 0.09 H. This quite far from 0.02 H. However, the GR bridge and this measurement are under quite different operating conditions. I don't have the time now, but there is a way without a scope to do a better measurement.

    You can do some other checks on my calculations, and the results show reasonable correlation.

    Others should be starting to provide you some suggestions, but you have to indicate what are your resources.

    I have not fully proofread the above.

    .

  5. #35
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    To try to correlate my other results.I tried a series resonant experiment. This experiment clearly showed that excitation level had a substanual effect on resonant frequency, but I won't provide any resilts on the effect.

    The experiment was the transformer 480 primary as the inductor with no shorted secondaries. The Powerstat was used to adjust the excitation into the series circuit. The circuit was the Powerstat, an 0.00 to 1.00 adjustable capacitor box in series with the 480 primary. Obviously 60 Hz excitation, and voltage was measured across the capacitor. At about 200 V peak across the capacitor the resonant point was at 0.46 ufd.

    Using the Shure slide rule L comes out at about 15 H. Good correlation with my other method at a high excitation level and 60 Hz.

    .

  6. #36
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    Consider my series RLC circuit of a capacitor and the transformer primary. No AC excitation. Initially I have the series circuit open, place a 200 V charge on the capacitor, then close the circuit.

    What happens to the capacitor voltage when the circuit is closed?

    .

  7. #37
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    Relative to my last post.

    First 1/4 cycle 3.5 mS, 71 Hz. This did not meet my expectation. What might be the rreason.
    Next 1/2 cycle 7.5 mS, 67 Hz.
    Next 1/2 cycle 6.0 mS, 83 Hz.
    Next 1/2 cycle 4.0 mS, 125 Hz.

    ,

  8. #38
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    There is much to be learned by playing with actual components that you quite possibly won't see with simulation.

    What I have experimented with using a transformer as an inductor, variable capacitor, Variac, and scope is not something that Fishn sparky can do because he lacks a scope and possibly a Variac and variable capacitor, but my results are probably very hard to simulate. For example there are some unstable nonlinearities that develop.

    Fishn sparky ask for some example circuits he could use for his students. There have been virtually no responses to that question.

    With very limited equipment how could you measure the duration of a pulse. For example if I take a P&B KUP 24 V DC coil relay and charge a 2200 ufd capacitor to 24 V, and discharge the capacitor thru the relay coil, then how long will the contacts remain closed?

    .
    Last edited by gar; 12-09-17 at 06:34 PM.

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