Help with transformer spark (probably simple if you are knowledgeable on subj.)

[mrpsychotic]

I am building this poster that is for a school project that is supposed to be about me so I decided to do it on electronics. One of the parts is a small spark that I am trying to make.

The difficult thing is that I am trying to make it from a battery supply (whilst using a transformer) and that I am presenting it so the spark needs to be pretty visible and noisy.

I had a wall power supply that took 120VAC and output 4VDC. I removed the output smoothing and rectifying circuitry so all I was left with was a transformer.

I connected a 9v battery to what used to be the output through a pushbutton switch. Then I placed what used to be the 2 input wires (there is a center tap as well I think) close together. Upon clicking the pushbutton switch I get a spark of maybe 1mm. (the spark seems to jump when I open a previously closed switch rather than when I close it.

Is there a way I can use a capacitor to get a more sustained charge? My results were faint in sound and visually. I need to present this to a room.

Is there a way I can automate the switching process? I tried to use a ceramic resonator but I have little understanding of how those work since I have only used them in embedded electronics and would just align the proper pins. I am thinking about sing a 555 timer and tying the output to a transistor which would supply the transformer with 9VDC.

Is there a way to get a spark from DC battery supply without a transformer? It seems like the transformer adds complication since it is made for AC.

I am thinking about tying the output of my current setup (which produces a small spark) to the input of another transformer. Will this work? Will the spark become even more faint if I do this?

Thanks, and I understand that I am working with HV at my own risk.

[Fraser]

I built such an item many years ago whilst at school.... it was used to demonstrate a car engines EHT spark ignition system

To create the spark that you desire in the simplest manner you can use an old car ignition coil commonly available cheaply from a car scrap yard or even a garage. The creation of a spark in air requires enough voltage to break down the insulating effect of an air gap.... in the case of a car ignition coil this will be around 12 to 30 kV depending on the model used. There is a safety warning at the end of this text.... please read it !

The ignition coil is usually driven off of a mechanical contact in the cars distributor or an electronic switching module. You will need a 555 timer IC running in astable mode at around 10 Hz driving a 2N3055 power transistor via a resistor to it's base. (~10K should do) The 2N3055 emitter is at 0V and the Collector connects to the ignition coil -Ve terminal. The +ve coil terminal is connected to the +12V supply. A diode should also be connected in reverse polarity across the coil to prevent back emf damage to the 2N3055. The output from the coil EHT terminal should be connected to the spark gap using a car EHT lead as that has appropriate insulation. The other side of the spark gap connects to 0v

Such an arrangement creates an EHT voltage cable of jumping a gap of 10mm or so with a good 'crack' and lots of ionisation odour.

HEALTH AND SAFETY WARNING !

Car ignition coil output voltages can be dangerous if contact is made with them. The circuit detailed above is capable of inflicting serious pain or injury. Appropriate precautions are required to prevent anyone coming in to contact with the coil EHT output. Your school should be consulted regarding the dangers of such a device before it is used. If you have any doubts regarding the safety of your construction or your ability to build it, you should not proceed with this design. I'm not kidding when I say that this circuit is hazardous and must be built and used responsibly.


An alternative method of creating an EHT voltage that will jump an air gap is the use of an AC power source connected to a voltage multiplier. Someone else on this forum can probably advise you on those designs or you can Google it. You would basically use the 555 circuit described above to drive the low voltage side of a mains transformer at it's rated voltage. The high voltage side would then create the 120V AC to drive the voltage multiplier that consists of diodes and capacitors. Very high voltages can be created this way and they will jump a spark gap OK. The building of such a device is more involved than the car ignition coil method but may be safer as lower currents are available.

[mrpsychotic]

Is there a way I can charge a row of capacitors in parallel (say 10) and then Switch them to series so that there voltages are added when they discharge?

[Zero999]

Is there a way I can charge a row of capacitors in parallel (say 10) and then Switch them to series so that there voltages are added when they discharge?

Yes, it's called a charge pump converter. An oscillator and a diode + capacitor multiplier will do this. The trouble is, to get 1kV from 9V you'll need 111 capacitors and as many diodes so it's not practical.

With the transformer, you get a spark when the battery is disconnected because of the magnetic field suddenly collapsing around the coil. Voltage is generated in a coil when the magnetic field surrounding it changes, the greater the rate of change, the greater the voltage. When the battery is disconnected, the magnetic field suddenly disappears so the induced voltage is very high.

If you want more voltage, use a 230V transformer (order from Europe) or get a transformer with two 120V primaries and connect them in series. Yes, a 555 timer oscillator is a good way to go but I'd advise using a MOSFET such as the IRL540 rather than a BJT because it's easier to drive and will have lower switching losses.

[Mechatrommer]

I had a wall power supply that took 120VAC and output 4VDC. I removed the output smoothing and rectifying circuitry so all I was left with was a transformer.
I connected a 9v battery to what used to be the output through a pushbutton switch. Then I placed what used to be the 2 input wires (there is a center tap as well I think) close together. Upon clicking the pushbutton switch I get a spark of maybe 1mm. (the spark seems to jump when I open a previously closed switch rather than when I close it.

how on earth a 30:1 transf being "backed/inversed-voltage" at 9V and producing a 1mm spark on the 1st winding? according my calculation, the out volt should be just around 270V? is it possible?

[Fraser]

mrpsychotic,

I have been thinking about your project.

Bearing in mind your forum name, I am left wondering what your objective is. If you hope to create a large impressive plasma arc then I am afraid that will likely be beyond your means and is unlikely to be safe in a school environment. If you wish to demonstrate that electricity can jump through air then this is a valid experiment/demonstration. Your arc length and intensity will be influenced by the applied voltage and gas through which the arc is formed. Air is a pretty good insulator hence the use of air gaps in HV PCB's. Arcs in air will be much smaller than those through rare gasses.

To create an impressive arc you may wish to consider applying a high voltage to various rare gas filled envelopes.  Xenon discharge tubes come to mind. I recall that whilst experimenting with my car ignition coil demo, I connected the two ends of a large 2" Xenon discharge tube to it's output without the trigger electrode connected.... a large arc was formed inside the tube with good light intensity.

What this comes down to is you intended effect. Arcs can be impressive especially if a Jacobs Ladder is constructed, but the high voltages used can be hazardous so they don't usually make for good school projects in uncontrolled environs. Also, consider whether an arc is a good representation of "Electronics" ? I don't usually seek to generate arc's in electronics, they are usually bad news to sensitive components. I associate arc generation with power grid testing and heavy electrical applications such as arc welders and plasma cutters.

The HT & EHT generators are electronic .... it is just that the arc product that you are intending to produce seems a little 'off message' to me IMHO.

Never, ever, be tempted to apply a DIY HT or EHT generator to yourself or others as a prank or weapon. I know cattle control fences are HT generators but they are carefully designed to not cause injury.

[Simon]

what about a 12V to  240V inverter to drive the voltage multiplier. (I'd not advise directly rectifying the mains). in any case some sort of current limiter might be a good idea even if just a lowish resistor.

I've not experimented with none of the above so be careful.

[mrpsychotic]

how on earth a 30:1 transf being "backed/inversed-voltage" at 9V and producing a 1mm spark on the 1st winding? according my calculation, the out volt should be just around 270V? is it possible?

I live in Arizona, possibly one of the best places on earth for sparks. Also the mm was not an exact measurement bu that figure is pretty close.

Bearing in mind your forum name, I am left wondering what your objective is. If you hope to create a large impressive plasma arc then I am afraid that will likely be beyond your means and is unlikely to be safe in a school environment.

Yes the name is unfortunate. I don't want some impressive and dangerous presentation, just something that is barely noticeable at 10 feet away.

[qno]

I had success with a battery operated CFL pcb.
It was used for 6 volts but when operated on 12 Volt without a load it easily created 1000 volts.
I made a small Jacobs ladder with 2 paper-clips that could make a spark of 2 to 3 mm.
You know when it works when you smell the Ozone.
Maybe an electric fly catcher PCB also works.

[Zero999]

Using a disposable camera flash charger to increase the input voltage to the transformer will give you larger sparks.

Here's how.

Remove the large capacitor from the output (it's too large and will fry the transformer) and replace it with a smaller capacitor, 100nF to 1µF. Connect your transformer to the output via an SCR with a DIAC connected to the gate and a potential divider so when the capacitor voltage reaches 200V it fires. I'll post a schematic if you like. You may have to modify the capacitor charger so it operates continuously.

[Psi]

To get a bigger spark in your current circuit of a 9V directly into a transformer you should try two things.
1) Use C or D cells instead of a 9V, 9V batteries can't handle the current. Two or three C or D cells in series is a good thing to start with.
2) Put a typical mains filter cap (eg, 0.2-1uF 400V) in series between your battery and transformer and put the pushbutton switch directly across the capacitor. When you let go the button you should get a much bigger spark than without the cap.


You could also try adding a relay to make it spark continuously.

Something like this...



The relay is setup to vibrate and continuously make and break the current flow into the transformer coil.

The 1uf cap causes ringing between itself and the transformer, pushing the voltage up way higher than the transformer is intended for.

I've not actually tried this sort of thing with a relay, but the basic cap+transformer circuit i've used to generate ~1-5mm sparks as a kid.

You can play with the value of the cap across the relay coil to make sure the contacts actually break properly instead of just twitching.

The choice of transformer will change things also, just try lots of ones you have lying around.
Normal mains step down transformers work fine. Your high voltage will come out the 230v side at a few kV.

Try one or two C or D cells as your battery first, a 9v batt wont be able to supply the current.

A heavyduty relay with large heavy contact arms and a large cap across it will vibrate slower than a smaller relay/cap.
So a bigger relay would be better suited to this kinda thing.

I'm not sure how long the relay contacts will last for tho

[Lance]

If you want to spend a little time building, I could give you the schematics for a simple strobe lamp that uses a xenon arc bulb. I made it back in high school, relatively simple project.

[Zero999]

Here's a schematic of the circuit I was describing above.