Practical Experiment in LRC circuits

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Fishn sparky

Member
Location
Washington State
Good evening gents,

Do any of my established colleagues here have any classroom experiments that I can perform with my students regarding the use of inductors and capacitors? More in particular LC,RLC both series and parallel applications, circuits?

I would like to show practical uses in everyday environments where these three electrical components work together. I can teach the numbers and calculations side of these but it doesn't really show how we use these components in everyday life. It would be good for my students to be able to put the calculations that I have taught them to use in a real life scenario and see how they work.

Doing it on paper is one thing but being able to apply what we learn in putting it together is another. Like I tell my students, IMO, there are three types of people in the electrical field. Those that are book smart but can't build it, those that are "street smart" that can build anything with no book smarts and then those that can put both of the previous two together to engineer and build it at the same time. AKA - Nikola Tesla.

Thanks and look forward to everyone's responses!!
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Fishn sparky said:
Good evening gents,

Do any of my established colleagues here have any classroom experiments that I can perform with my students regarding the use of inductors and capacitors? More in particular LC,RLC both series and parallel applications, circuits?

I would like to show practical uses in everyday environments where these three electrical components work together. I can teach the numbers and calculations side of these but it doesn't really show how we use these components in everyday life. It would be good for my students to be able to put the calculations that I have taught them to use in a real life scenario and see how they work.

Doing it on paper is one thing but being able to apply what we learn in putting it together is another. Like I tell my students, IMO, there are three types of people in the electrical field. Those that are book smart but can't build it, those that are "street smart" that can build anything with no book smarts and then those that can put both of the previous two together to engineer and build it at the same time. AKA - Nikola Tesla.

Thanks and look forward to everyone's responses!!
Click to expand...

I don't know if you have a budget for classroom materials, but you might look into Snap Circuits. The level 500 kit has a ton of stuff. My oldest got the set when he was 10 and just kept going at it. It has all the components you are looking for and you can use lights and buzzers to see the outcome of your circuit. I would have used the Snap Circuit web site but it's not operating properly now.
 
I

Ingenieur

Senior Member
Location
Earth
you might look at a modelling program like matlab

you can build any ckt and plot their response
you can change parameters to see the impact
use motors, xfmrs, contactors, etc
do pf correction
as simple or complex as you like
I believe student versions are available
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Ingenieur said:
you might look at a modelling program like matlab

you can build any ckt and plot their response
you can change parameters to see the impact
use motors, xfmrs, contactors, etc
do pf correction
as simple or complex as you like
I believe student versions are available
Click to expand...

Matlab can certainly get the job done, but even the student edition runs $99. They also restrict it to degree-granting institutions, so if the OP is at a trade school or doing a union-sponsored training course he may be out of luck. Individual copies are currently at $2,150. Yikes! I have an old copy I got back in the 1990's floating around somewhere. It might have been $99 or $199 back then. Wish I could make it run on my Vista machine.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
171130-2000 EST

There are a tremendous number of different possibilities. Broadly transient, steady-state, and transient on into its steady-state.

You need an adequate scope, function generator, meters, loadcell, torque transducer (possibly rotary), pressure transducer, regulated voltage power supply, at least over a limited range a current source, a no-bounce switch, AC solid-state switch with turn on phase control, Ohmite power resistors, incandescent light bulbs, a true DC shunt wound motor with separate shunt excitation, current shunts for current measurement, capacitor start and run single phase motor, polypropylene capacitors, a transformer, a Variac, and an old automotive ignition coil and capacitor from early 1960s, a spark gap, possibly a 12 V drycell, and more.

Somehow you need to simplify what you work with.

I would start with a battery to a switch to an RC, RL, or RLC circuit. Do RL both turning on and off, and with and without a snubbing diode.

Phase controlled turn on of a sine wave to an RLC circuit off resonance and at resonance.

Phase controlled turn on of a voltage to an incandescent bulb. Same to a transformer.

Half-wave rectifier to an RC load with and without a transformer. Same with a full-wave rectifier.

Auto ignition coil is a double tuned circuit with a spark discharge. Need a 30,000 V 1 MHz scope probe.

What do you want to narrow it down to?

Just some experiments:
http://www.beta-a2.com/EE-photos.html
http://www.beta-a2.com/cat-5e_photo.html

.
 
I

Ingenieur

Senior Member
Location
Earth
he may only need the educational version
matlab and simulink $1000 per yr

just so flexible
can be put on a projector
can change freq and see the Z of an L change
can do a LC and see the notch as freq sweeps
make 2PiL = 2PiC = 1 and see total Z ~f
nice simple graph

with discrete components hard to 'see' responses
need a scope, etc
and difficult to make changes

not sure what level of student he teaches
just a thought
 
Last edited:
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
171130-2353 EST

Ingenieur:

What you suggest has some merit, but it is still a theoretical approach.

I believe the intent of the original post was to do some experiments with real world components and real instrumentation.

Thinking about my suggestion of an ignition coil, it is apparent that in one transient cycle one can simultaneously perform several experiments, and other tests can obtain other data.

These would be --- (1) LR charging, (2) LRC on opening charging current, (3) Inductive coupling to a secondary, (4) Breakdown of an air gap, (5) Spark voltage drop, (6) Measurement of primary and secondary resistances, (7) Measurement of primary and secondary inductances, (8) Estimate of primary and secondary self resonant frequencies, and (9) Measurement of leakage inductance primary to secondary.

In the real world I can measure the source voltage, and the transient current to a resistance in series with a real inductor. But I can not measure the voltage drop across either the resistive or inductive components. These I have to calculate from the current measurement.

Change this to a high quality RC circuit and I can make the direct measurements.

How to get valid measurements with a scope or other instrumentation takes real world components and equipment.

.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
gadfly56 said:
Matlab can certainly get the job done, but even the student edition runs $99. They also restrict it to degree-granting institutions, so if the OP is at a trade school or doing a union-sponsored training course he may be out of luck. Individual copies are currently at $2,150. Yikes! I have an old copy I got back in the 1990's floating around somewhere. It might have been $99 or $199 back then. Wish I could make it run on my Vista machine.
Click to expand...

Run a virtual machine which is running an earlier Windows OS. You can get a free open source VM environment called VirtualBox to do the job. Then all you need is a licensed copy of the old OS. :)
 
I

Ingenieur

Senior Member
Location
Earth
gar said:
171130-2353 EST

Ingenieur:

What you suggest has some merit, but it is still a theoretical approach.

I believe the intent of the original post was to do some experiments with real world components and real instrumentation.

Thinking about my suggestion of an ignition coil, it is apparent that in one transient cycle one can simultaneously perform several experiments, and other tests can obtain other data.

These would be --- (1) LR charging, (2) LRC on opening charging current, (3) Inductive coupling to a secondary, (4) Breakdown of an air gap, (5) Spark voltage drop, (6) Measurement of primary and secondary resistances, (7) Measurement of primary and secondary inductances, (8) Estimate of primary and secondary self resonant frequencies, and (9) Measurement of leakage inductance primary to secondary.

In the real world I can measure the source voltage, and the transient current to a resistance in series with a real inductor. But I can not measure the voltage drop across either the resistive or inductive components. These I have to calculate from the current measurement.

Change this to a high quality RC circuit and I can make the direct measurements.

How to get valid measurements with a scope or other instrumentation takes real world components and equipment.

.
Click to expand...

Honestly, that is not really practical and it is difficult to see the results and impacts of changes and is very time consuming.
Until we know the level of instruction it is hard to determine the best path forward.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
171201-1043 EST

Whenever I reread post #1 I get the idea that Fishn sparky wants his students to work with real components and instruments.

A more limited list:

A range of stable resistors, and some resistors that change resistance with temperature (thermistors and incandescent bulbs).

A Sq-D QO 15 A breaker.

A 7.5 A Variac.

A half horsepower capacitor run motor. This is RLC and some core saturation and counter EMF.

A control transformer with two 240 V primary coils (parallel or series connection), two 120 V secondaries (again parallel or series), and about 200 to 500 VA. For transformer, inductance, and core saturation experiments.

A range of polypropylene capacitors.

A 100 ft roll of #14 with EGC. Outlets distributed along the run with various switchable breaks and/or high resistance joints. Purpose to show capacitive coupling to different loads (DVM vs low resistance meter). Estimate length of wire from main panel to an outlet. Show effect on motor starting from line impedance. How to troubleshoot problems by knowing something about the circuit.

A 1500 W heater with no fan and continuous duty, 800 W if you can not find 1500.

An old AB #2 motor starter. AC RL circuit with varying inductance.

An 8ft magnetic ballast slimline fluorescent fixture. This is an inductor to generate large voltage transients on the line.

An MOV transient voltage limiter.

A Corcom 5 A line filter (LRC) to show reduction of broadcast band RF noise from the 8ft fluorescent.

Your supply transformer with some knowledge about it, your distribution lines with some knowledge, a wire from the ground rod at the transformer to your test bench, this is just a long test lead, #18 or smaller is OK, and your main panel with measuring test points at the panel.

.




 
junkhound

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
LTSpice is free also. One can also just put the equations into any spreadsheet and graph the results of varying requency, L, R, or C>

Easiest to put together for an electrician is an old motor with the rotor pulled (L), a 50 uF motor run cap (C), and a 60 W light bulb (the R) .

Hook all in series across 120
vac 60 Hz.

The motor core of an old 1/4 HP motor IIRC is around 50 mh. 50 uF and 70 mh resonate about 60 Hz.

Light bulb somewhat dim to start, slowly put the motor rotor near the core, and inductance increases (or a big bar of iron)

The light gets brighter as inductance increases to resonanace of L&C, then as you inser the rotor further the bulb will dim as the inductive reactance limits the current.

If you have a 100 W or greater audio amp and signal generator, you can drive the LRC series at different frequencies and differenct LRC values and note how the light changes - the same as the current for PSPice or LTSpice or matlab will show.
 
GeorgeB

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
gadfly56 said:
Yikes! I have an old copy I got back in the 1990's floating around somewhere. It might have been $99 or $199 back then. Wish I could make it run on my Vista machine.
Click to expand...

Off topic somewhat, but load Virtual Box (free) and an old copy of Win98 or WinXP that you might have. That;s how I run my AutoCAD LT2002 on Win7 and Win10. (All licenses are legal)
 
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