How can I teach transformer theory in an innovative and interesting manner in a class room; not a laboratory?
P = EI (Power equals voltage E times current I) Many electrical properties can be explained as analogous to water flow. For example, a transformer "transforms" high voltage and low current into low voltage and high current, keeping the power constant (except for minor losses) at full load. This would be equivalent to a high pressure water pump supplying low water flow to the primary winding and taking out high water flow at low pressure from the secondary winding to drive a low pressure water turbine. You could represent the transformer core as a hollow square of wood or even thick cardboard. On one side wrap say ten turns of thin clear plastic tube around the core to represent the primary (first) winding. On the other side wrap say five turns of larger diameter plastic tube around the core to represent the secondary (second) winding. Fill the primary tubing with water and red food coloring to represent "hot" high voltage and the secondary tubing with water and blue food coloring to represent "cooler" low voltage. The explanation of course is that the high voltage primary winding will have more windings of thin tube (similar to more thinner copper wire windings) because the current will be less than in the secondary winding. There will be less windings for the secondary coil using larger tubing because the current will be higher at low pressure. Supply the secondary tube with a shut off valve (or clip) to represent the fact that there will be no current unless the circuit is open. In the formula, if current is zero power is also zero (on both sides of the transformer). You can represent the pump and turbine with pictures (or drawings) of same but it would not be impossible to rig an actual pump and turbine, just not necessary to "see" what is happening. The turbine can use up more and more power until the maximum power of the primary winding is reached but not more. The magnet of the core will be "saturated at full power." The rest is explaining magnetic flux in the core and how it is produced by the primary winding and cuts through the wires of the secondary to produce voltage and current if there is a load. Each winding of a coil adds to the effect. A transformer with equal primary and secondary windings would have the same voltage and current under load. I believe that the phase would shift 180 degrees because of lead/lag. Good luck.
Can I use a copper wire instead of magnetic wire?
Sure you can use a copper wire.Just don’t be trying to make an electromagnet or transformer out of it.The spacing of the plastic insulation will reduce the magnetic permeability of the windings, so there will not be as many(windings) per length of bobbin.If you were to use plain copper wire, then there would be no insulation, and the current would short across the coil, and not keep the current confined inside the loops of wire.No loops of wire, then no reactance. No reactance, then no resistance (very little) to current flow.(Reactance is only relevant with AC, and a single shorted loop will cause the magnetic field to collapse, but probably have little affect on the resistance of the coil)Copper wire , has a certain resistance at 20C, for the size(area) of the strand. The insulation of ‘magnet wire’, has a voltage rating, based on the gauge of the wire, and how thick the varnish(coating) is applied to the copper.(Voltage rating has nothing to do with the gauge of the wire, ONLY the thickness and material of the insulation)If you are mis-understanding the use of iron, and its characteristics, then you may be referring to iron wire as ‘magnetic wire’.Any conductor, can be ‘magnetic wire;, be it aluminum, copper, gold, silver, tin, lead etc. It is the current through it, and the shape(coil, spiral) that determines the magnetic effect.
You want to wind a coil so that it has resistance but essentially no inductance. How would you do it?
Wind a coil round the core and take another wire of same length, material and cross section and wind up it again round the core but in opposite direction of the previous wound coil. Wind up the second coil in gap between two loops of previous coil with same no. Of turns.So you will have 4 terminals total, 2 on both end. Connect each pair on both side (short the coil terminals) and give supply. You will get almost zero inductance but double resistance.It is so because inductor is a unipolar element i.e, property depends on polarity whereas a resistor don’t understands polarity.
How do I identify the primary and secondary winding of a transformer?
Allow me to answer your question in a precise manner:Transformers are of two types(i)- Step Up transformer(ii)- Step Down transformerOn a step-up transformer there are more turns on the secondary coil than the primary coil which means induced voltage across the secondary coil is greater than the applied voltage across the primary coil. That is voltage has been “stepped-up”.And a step down transformer has less turns on the secondary coil than the primary coil which means induced voltage across the secondary coil is less than the applied voltage across the primary coil. That is voltage has been “stepped-down”.Now coming to the point that how to identify which one is primary or secondary .Clearly in a step down ,we want less voltage high current, high current means less resistance. And to minimise resistance we have to-1.) decrease wire length (that is less number of turns )2.) Increase the area ( Thicker wire)Therefore in a step down transformer when you will see Thicker wire winding then it will be the secondary coil of that transformer and the thin wire winding will be its Primary coil.Reverse in case of Step up transformer.Please let me know in case you need further clarification.Thank youAhmed
What is the difference between primary and secondary windings?
An AC transformer’s “winding direction” determines whether or not the transformer is “additive” or “subtractive” from a polarity perspective. Generally, this is caused by each winding occurring in the same direction (subtractive), or in opposition to each other (additive). Why is this imporant? Good question! Keep in mind that these magnetic fields can (and do) cause the windings to physically move! Have you ever heard the “hum” of a transformer? If there were zero movement, there would be no hum. This winding movement is stressful on the wires and a significant cause of their eventual failure. To reduce this failure mode, it was discovered that subtractive windings were less subject to these stress (vibration) forces.This nature of winding direction can be deduced by measurement. First, connect one end of the primary with it’s nearby secondary (on the same side of the transformer). Now apply a small, current limited AC voltage to the primary wires. The measurement of the resulting voltage on the other side of the transformer (the non-connected wires) will either be larger-than or smaller-than the input voltage. You’ll also note the transformer’s winding ratio by what the difference voltage is compared to the voltage being applied to the primary. For example, if you apply 120VAC, and see 108VAC, you have “subtractive” windings (wound in same direction) and a 10-to-one ratio because the difference is 12-volts. Voila! With one test, you’ve learned two important characteristics.
What is the difference between copper wire and magnet wire?
I am late to answer, without repeating what others have written.Copper is used in motor windings, transformer windings, induction coils, The insulation may be a thin film of varnish called enamel, a fibrous polyester or fiberglass yarn; or a combination of both enamel and fibrous insulations. The fibrous insulation may be impregnated with a varnish to bind the insulation to the conductor and enhance thermal endurance. If it is bare copper then, windings will result in short circuit, so an enamel coat is applied which acts as insulator & makes winding possible. This is done by making the copper dip in to enamel solution as it is “drawn” to required thickness / diameter and allowed to cure. Such enamelled / insulated copper wire is called magnet wire.However, Bare copper is used in electrical wiring & connections including grounding / earthing.Magnet wire is also called winding wire. There are a number of film insulation types ranging from temperature Class 105 to Class 240. Each film type has its own unique set of characteristics to suit specific needs of the applicationMagnet wire shelf life is not established in commercial specifications. As long as the wire has been carefully stored it may be usable for years to come. Bondable wire should not be stored at temperatures exceeding 100°F. Electrolytic tough pitch copper (ETP Copper, UNS C11000) exceeds 99.9% purity and is the most widely used type for magnet wire production. It is intentionally oxygenated (200-400 ppm) to achieve the best combination of conductivity, capacity for being cold worked and economy. MWS can also supply wire made from high purity (99.95%) OFHC Copper (UNS C10200) or Certified (99.99%) OFHC Copper (UNS C10100).
What is the maximum vrms output of a single coil guitar pickup?
You're getting conflicting information on this, because there's no standard for measurement. To come up with a meaningful number, you would have to specify, - The distance from the pickup to the string - The diameter of the string - The amount of deflection of the string (how hard did you pick it) - The magnetic properties of the string itself - The loading on the pickup (value of the pot or fixed load) All of these variables would affect the output of the pickup. Remember, you're essentially dealing with a generator. The pickup forms the lines of magnetic force, and the string cuts across them. The frequency of the output is proportional to the speed at which the lines are cut (Faraday's Law Of Induction). We've just talked about what it would take to standardize a test for pickup output. We haven't even addressed the individual pickups. The output of a pickup is dependent on the number of turns of wire, the gauge of the wire, the magnetic material, and the field geometry. The frequency response of a pickup is usually inversely proportional to the output. In other words, as you add windings to increase the output, you're also increasing inductance. And what's an inductor in an audio circuit? Yep, a low pass filter. So as output increases, frequency response decreases. Finally, I've been playing for a lot of years. I've NEVER seen a passive pickup put out more than a few hundred mV's. Anything that's putting out 1V rms, much less 5v pk (3.54v RMS) has got to be an active circuit. And that's yet one more variable. Oh yeah...the wood has absolutely no effect on the output of the pickup. It affects tone and sustain, but does not alter the electrical characteristics. The only way to answer your question is if it's constrained to one pickup specification. Greetings from Austin, TX Ken