Novice Questions about transformers, voltage, resistance, mostly DC application

Hello, I am completely new/novice with electronic design.

What I want to build first, is a device which can take a 2.5V or similar low voltage battery like a AA (or 9V) and generate a spark with it, or even a slight tingling feeling when touching a wire. I realize I can buy a "high voltage gen" from ebay for $8 which does this dramatically; I am not after such a high voltage output (it looks painful), but rather, wish to generate a very gentle (NON painful) spark, something even a child could touch without pain or discomfort, but still able to notice/feel the output. It would be great if the power could be dialed up or down as well.

I have been doing research; It looks like I will need a transformer. I realize many of them contain cancer causing/dangerous metals so all contact with this will be enclosed off at some point. I need safety #1. I found a transformer in an electric fly swatter for example, I wonder if it will work for this. If not I can scavenge more (I would prefer using free/scavenged parts, as a DIY effort, rather than buy what I need). This is more of a learning/fun project so the aspect of DIY Is important, it has no practical application.

I have access to my schools engineering/electronics hardware storage, literally any number of free capacitors/boards/switches/diodes/ you name it. They do not have anything "high voltage" (no transformers) but the room contains tons of objects which I have no clue how they work, so you can name off a parts list and I can take it to my school and ask what they have there etc...

I kind of wish for some direction, I want to learn and read, not get "spoon fed".

It will be both educative and entertainment to design a transistor oscillator with a hand made low power transformer - the voltage can be high but the current can be low (must be very low) and you will not get a shock. Transformers (most of them) do not have cancer causing parts/ elements and they can be very small because they will not be handling much power.

c_mitra said:

It will be both educative and entertainment to design a transistor oscillator with a hand made low power transformer - the voltage can be high but the current can be low (must be very low) and you will not get a shock.

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Excellent, where should I start with this? Transistor oscillator, hand made transformer (wind the "coils" myself?) I want to do this, how can I start? i.e. where does one acquire the necessary metal to wind the coils for the transformer, and what is a transistor (besides the actual definition in the web, what it does is sometimes different than what it is)

https://www.allaboutcircuits.com/worksheets/oscillator-circuits/

thank you, I will read up about the terms

hello everyone,

I have been reading daily and think I have some good questions!

For starters, can somebody explain better the primary/secondary winding situation? What I mean is, sometimes you see them using "air cored" windings, and they will wind the secondary BELOW (I think?) the primary on the same "air core". And sometimes you see the two windings separated by iron "rods", with space between primary and secondary. I found many beginners guide(s) but they all seem to glaze over the winding part, don't really explain where or how to wind them, or on what (sometimes it is vague- "use iron core" or "powder iron core"). I found an CFL driver circuit that uses a transistor and 3 coil windings to illuminate a CFL, and it appears that ALL THREE of the windings are together on one single iron core? that that make sense? It uses "flyback voltage".

2. And then they discuss "insulating layers" and "sticky tape". Again, very vague and hard to "See" what they mean. Should I make a neat pass of windings (one layer) and then wrap painter's tape around them, then make another row and so forth? that seems to be the routine but its so vague I am not sure.

3. WOuld 0.1mm copper/enamel wire be suitable for a 50turns : 500turns ratio (approx 800volts "flyback" from a 12v battery I believe) or should I use something thicker.

4. Can I use multiple windings to take say, the 800volt "flyback" from an additional secondary winding (so 1 primary and 2 secondary windings on the same iron "core") and wire them in series for 1600volts?

So far I've learned alot about: transistors, oscillators, diodes, Zdiode, capacitor, resistor, magnetic flux, positive feedback, Integrated circuits, gating, basically all the novice/beginner terms, but I have to construct anything useful. Most of what I want to make contains capacitors and windings which I am still fairly clueless how to use effectively. The phasing of the windings is also a little bit confusing to me, because if you wind them on the same iron rod by hand it seems impossible to get them exactly straight. I am thinking of setting up a dremel to help me create my high voltage secondary windings.

My ultimate goal is to understand enough to design my own injector/ignition driver circuits for controlling a modern EFI engine (1990-2010 era engines) so I am concerned greatly with the operation of inductors, and high voltage capacitive discharge circuits for controlling combustion in an engine. Everyone keeps discussing the magnetic field, collapsing, I never see much discussion of the electric field though. Arn't the electrical and magnetic components of current flowing in a wire perpendicular?

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c_mitra said:

It will be both educative and entertainment to design a transistor oscillator with a hand made low power transformer - the voltage can be high but the current can be low (must be very low) and you will not get a shock. Transformers (most of them) do not have cancer causing parts/ elements and they can be very small because they will not be handling much power.

Click to expand...

Let me repeat this back to you the way I think you wanted me to design something (so you can check it for me)

By wiring a coil in with a transistor and capacitor/resistor in a specific way, there will be an oscillating current on the collector/emitter side as the transistor turns on and off, responding to the voltage potential held between the base and the capacitor(?). Is this the circuit you had in mind?

By manipulating capacitors and resistors the timing and shape of the waveform is adjusted, and there are probably an infinite number of ways to further adjust such oscillating circuits. The output, or amplification of the circuit (collector/emitter of one single transistor) contains the alternating current with some frequency f, with the 'basic' transistor turning on at 0.6v on the base and using about 0.2v to operate (a 9v source will show 8.8v on the turned on collector/emitter circuit).

You mentioned a transformer though. So one of the coils will have another coil on top of it(this is where Iam kind of stuck), with more turns to drive a secondary circuit at much reduced current but higher voltage? That is what I guess you meant to do, is it correct?

For starters, can somebody explain better the primary/secondary winding situation? What I mean is, sometimes you see them using "air cored" windings, and they will wind the secondary BELOW (I think?)

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A transformer is a magnetic device in which two coils that are electrically separated are coupled by magnetic field. The magnetic field is oscillating and to enhance the effect, we often use ferromagnetic materials like iron, iron power, iron oxide (ferrites; a spinel material) and sometimes none (simply air). The location of the two coils are not important but they must share the same magnetic field. Hence they can be side by side, on top of each other and even interleaved (one layer and another alternately). There are other considerations that determine the location of the two coils.

the primary on the same "air core". And sometimes you see the two windings separated by iron "rods", with space between primary and secondary. I found many beginners guide(s) but they all seem to glaze over the winding part, don't really explain where or how to wind them, or on what (sometimes it is vague- "use iron core" or "powder iron core").

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I have not see transformers where the primary and secondary are separated by iron rods but the magnetic lines of forces must cross both the coils.

Common line frequency transformers use iron plates that are insulated to reduce magnetic losses and induced current losses. The transformer in the CFL is made from a iron oxide based powdered material that is sintered into a suitable form. These materials are electrically insulating (no electrical loss) and are magnetically permeable (low magnetic loss). These ferrite core materials are very versatile- some have very low hysteresis and some have very high permeability.

I found an CFL driver circuit that uses a transistor and 3 coil windings to illuminate a CFL, and it appears that ALL THREE of the windings are together on one single iron core? that that make sense?

Click to expand...

It does not matter how they are placed except that the same magnetic lines of force must embrace both. There are secondary considerations like capacitance between the coils and the leakage flux or inductance.

And then they discuss "insulating layers" and "sticky tape". Again, very vague and hard to "See" what they mean. Should I make a neat pass of windings (one layer) and then wrap painter's tape around them, then make another row and so forth? that seems to be the routine but its so vague I am not sure

Click to expand...

Because the two coils (primary and secondary) must be electrically separate, we must ensure that there is sufficient insulation between them. Nothing more than that. If the primary and secondary voltages are sufficiently different, they must be physically separate.

WOuld 0.1mm copper/enamel wire be suitable for a 50turns : 500turns ratio (approx 800volts "flyback" from a 12v battery I believe) or should I use something thicker.

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Yes, because the current load is low. In fact, thinner wire would have been useable but they are less common and difficult to wind by hand. Your turns ratio is not good enough: you need to use 50:5000 or 50:2000 turns if you want output of 1200 or 500V approx.

thank you for all the responses,

I see that I will need an AC current to drive a high voltage (sudden field collapse in the secondary). Would a 555 unit be suitable for a beginner to this end? Or should I make my own oscillating circuit?


How can I test the oscillations without an oscilloscope. I have access to one of those machine but not at home.

A couple of projects on my mind are:
hand cranking flying magnets past a winding to generate a lighted LED, then possible a hand-cranking to generate a current good enough to charge a battery or power a larger electrical device.

The CFL lighting project. A question I have about this is: does the AC current continually send a high voltage spike to ionize the gas repeated at 50Hz for example, or does the gas only absorb a voltage spike 1 single time for the moment you turn it on, and then draws a steady lower voltage current after that? because the book I am reading makes it seem like the lamp is repeatedly striken with a 700volt zap and then absorbs what is left and repeats itself over and over with some frequency f.

An ignition coil dwell tester device. I am not sure how I am going to do this one at all... there are coils from different vehicles that ignite spark plugs, and there is a concept called "dwell" and charging time etc... I'd like to design some kind of test bench where I can experimentally determine the proper coil input to get a reliable output.

Hand built radio: I have a pre-made kit with everything included to assemble first, it was given to me by a professor at my school. I would like to get to the point where I can make my own radio from scratch next. Is it possible to avoid using IC (or is this recommended at all) or should I just use the cheap, commercially available pre-made IC (the chips that contain a bunch of transistors and pre-made circuits).



I am curious how you feel about using multiple transformers for stepping up voltages, I see sometimes this is done and I am wondering what is easier, trying to squeeze a single transformer for 5k windings (I cant imagine 5000 loops around a primary nor where I would find such a large piece of suitable iron) or doing it gradually. Can't I use capacitors to nurse the circuits for every last ounce of + current where necessary? In other words, I have lots of huge capacitors on hand free for use.