How to make a spark gap

[concrete_hed]

Hey, what i am trying to achieve is a small spark that will go accross a gap of about 1mm using a 12 volt car battery. I have read how car ignition systems work to make a spark, but without going down to the junkyard and buying an ignition coil, i'd like to make one.

 

Can someone please tell me how i can make an ignition coil and how i would wire it to the battery so that it will produce a high enough voltage to cross the spark gap. Or give me a diagram or equation or something?

[YT2095]

an ignition coil is Way over the top for a 1mm arc, you only need about 700volts to jump that sort of distance (needle electrodes).

as for making your own, Good luck, it`s not that easy.

you`ll still need a good core and former, Ferrite core would be the ideal.

often small HF transformers are ferrite core, and they come appart quite easily (they always have a seperation gap to stop saturation).

take one appart strip the winding off and then put your own on.

about 7-10 windings of a thick copper (insulated) wire 1`st.

then a layer of PTFE tape, and then wind on 1,000`s of turns of the thinest insulated copper wire you can get, around the tape.

when done dip the whole thing in thined down Yacht varnish and allow it to dry (takes about a week), then put on a layer of Not thinned down varnish and let that dry (takes about a day and a half).

 

you`ll need to make a simple 555 osc to switch a 2N or TIP 3055 transistor, that transistor in turn provides power for your 1`st Thick wire winding.

 

you`ll get your Arcs

[JesuBungle]

Honestly I think you're making it harder than it really is. Could you just take two wires, one on the positive and one on the negative and get em close enough together so it sparks?

[YT2095]

12v will NOT jump a 1mm gap, as I said, you need about 700v to do that.

[JesuBungle]

My mistake. Didn't see what voltage he said. Okie silly dokio, I'm an idiot lol

[YT2095]

lol, no problem

 

another Cheap-and-Nasty method would be to use a "chattering relay".

quite simply this is an ordinary relay wired in such a way that the power to activate it goes through the Normaly Closed contacts 1`st.

when power is applied the relay activates and Breaks this contact which De-Activates it, so the contacts close again and the cycle continues.

but across the relay coil, considerable Back EMF is given off into 100`s of volts!

with the right relay, your 1mm spark will be made

[concrete_hed]

thanks for the post. A question about your first reply. You said i needed an oscillator. If i had an oscillator, would that give me a repeating spark. If i just wanted one quick spark and thats it, would i need an oscillator? And a sort of off topic question. Say u have a step down transformer 240v down to 12, can that be used in reverse to make it a step up transformer from 12-240?

 

Thankyou verymuch for your reply.

[YT2095]

an oscillator will create what appears to be a continual spark, yes.

a stepdown trans at the ratios you said will give you roughly your 240v back out, if it was a 4volt transformer then you`de get about 700v out, but ONLY do this in short pulses, as you`ll burn out the 4v winding with 12v in a very short time!

[5614]

It's quite hard to get a respectable spark from a 9V battery... but I can get a decent one from a 7.5V 40,000μF capacitor. I just charge it up for about 1 min (from a ~7V battery, it's an old 9V one which now only gives 7V) and then I attach a wire to one end of the cap and take the other end and slowly move it towards the other terminal of the cap.

 

The actual spark distance may not be too large, but the spark spreads out in all directions and does seem a reasonable size. Also as soon as it begins to spark I move the wire away, as the air is already conducting it will continue to conduct for a bit as I move the wire away.

 

You can also get 12V from a computer PSU to spark.

 

These two examples are not a case of putting two wires 1mm apart and it will spark, you need to be holding the wire and getting it ever so close. Then just as you are about to touch it will spark.

 

[edit] in fact I'm just doing it now with the 7.5V cap and it is definately a lot close than 1mm, but you know how when you weld or something sparks fly off, well you get that, sure on a smaller version, but I reckon concrete_hed would like them. The spark, which only lasts for a very small amount of time (mainly because you can't hold it that close for very long) jump out a cm or 2.

[YT2095]

Hmmm... I would Strongly advise against doing that!

shorting a car battery or Switchmode PSU, may result in severe burns and possible Explosion!

the surge current on car battery when shorted is almost unlimited and will cause it to Boil almost instantly.

[5614]

I don't have a car battery available... why would a PSU explode?

 

And what's the difference between a PSU and a Switchmode PSU?

 

And I think those sparks probably could burn you, if you were not expecting them and had your fingers all over the place. But at least for a 7.5V spark it is not very hard to hold the insulated part of the wire. Also 7.5V is so low I've found that if I just place my finger across both terminals of the cap then no current will flow, at all, because the voltage is too low, so in that sense it is safe. Although a spark could burn.

 

[edit] 7.5V 40,000μF makes a much more impressive spark than 10V and 10,000μF.

[YT2095]

a computer PSU isn`t series regulated, it`s a Switchmode.

the current passed through a wire whilst you "hold it close" as you reccomended is more than ample to set it on fire and burn you! a car batt doubley so.

also a switchmode will blow in one of 2 ways (unlike a series regulated supply) they either go Open or closed cct, one way is harmless, the other will present Mains voltage directly out as DC!

 

in both scenarios, the "Spark" is the least of your worries.

[5614]

Hmm, I don't normally make a PSU spark, it just did it once by mistake. And then I repeated it a few times just to make sure I knew what had happened.

 

Basically with the PSU I've got (I got like 7... a friend was throwing out old computers and asked if I wanted anything, so I said I wouldn't mind a PSU, he gave me 6!) and I've tested this on 3 of them when it sparks the PSU just goes dead. You have to disconnect it from the mains to reset it. No mains voltage. The micro second it sparks or draws a high current (ie. doing electrolysis and having the electrodes too close) the whole thing just dies. It's not the fuse. You just need to disconnect it from the power to reset it.

 

These are all different makes between 2 and 10 years old. Why would a manufacture make a "safety" device chuck out mains voltage???

 

When you say "blow" do you mean totaly fail or just spark it (ie. drawing a high current for a micro second)?

 

And why would a spark set it on fire?

 

Either way I don't normally use PSUs for this.

[YT2095]

I`ve seen several mobos Fried! by broken PSUs, invariably they read roughly 400VDC out.

how is it a "Safety device" as you call it?

do you actualy KNOW how a switchmode works?

 

you "test them" by shorting them out??

to be entirely honest, I don`t really Care if you beleive me or not, shorting either out is a plainly Stupid act!

and even if some do respond as you say, how can you be 100% sure that the other guy has the same type?

 

and so, despite your comments, I stand by my warning, do Not short out car Batts OR switchmode PSUs!

[5614]

What I understand by switchmode is that the current is continuously altered in order to maintain a constant output voltage. [edit] I'm not "not believing" you, I just don't understand why that would throw out mains voltage. Are you saying that this device could break shorting itself and then it would effectively have no effect and mains voltage would pass straight through it?

 

I don't "test them" by shorting em. It's just the first time it happened by mistake and the whole thing turned itself off I thought maybe it was broken or something (this was a long time ago) and so by repeating with a different PSU I concluded that when a high current is drawn from a PSU (or more specifically from 2 of the ones I own) it will just turn itself off. To reset it just remove the power.

 

I don't make sparks from a PSU for fun. I mean, come on, it's 5V or 12V. Or I spose you can get 24V (from 12V and -12V rails) but I can do better than that if I want a spark for the sake of a spark.

 

If someone wanted to make a spark at home I would suggest using a 7.5V 40,000μF capacitor, althogh I appreciate that most people would not have one at home. They make a decent spark and are quite safe (unless you burn yourself on the spark).

[YT2095]

the 5v it the most dangerous rail of them all, the 12v and -12 would stop in an instant blow the -12 rail totaly (that IS series regulated and only at miliamps).

AT and ATX psu differ sure, the ATX may well reset (some may not), but remember you are Never isolated from the mains in anyway! and if it blows closed cct the mains has free reign over the entire thing!

[5614]

5V because it has the highest current, right?

 

When you say "blow" do you mean if it totaly fails or if it melts inside? And this is different from what happens when my one shuts itself down after a momentary current surge isn't it?

[YT2095]

yup, and so the power available is More than enough to melt the wires into your skin (faster than you can move).

when I say Blow, in ref to the -12 rail I mean Blow as in tiny explosion inside the 7912 substrate.

[5614]

The wire is insulated and capable of handling 5A, but thanks for the safety warning.

 

Am I right in saying there is nothing life threatening with my 7.5V cap?

[YT2095]

there`s nothing Particularly dangerous about doing that if the cap is designed for that type of duty cycle.

having said that, if it ISN`T then gasses will be produces and you risk blowing out the pressure release valve on it (not nice in your eye).

 

but then this Cap idea isn`t helping the OP much either

[woelen]

Why all these dangerous and difficult things? Making a spark periodically is very easily done, especially if sparking already starts at 700 V.

 

Have a look at the following page:

 

http://www.oberlin.edu/physics/catalog/demonstrations/em/neonosc.html

 

The idea is that a capacitor is charged to a certain voltage, until a breakdown of the gas/air occurs. Then a flash is produced (discharge of capacitor) and next the capacitor is recharged again. The principle behind this is that a certain breakdown voltage Vb is needed to start the sparking, but once the spark exists, a conductive (ionized) channel exists, which can sustain a current while the voltage across the channel becomes much lower than Vb.

 

This example with the neon bulb can easily be made with a rectifying circuit, a small capacitor and a resistor from the 220 mains line. Actually, I have one of these circuits lying around here, just for fun.

 

When you don't use a neon bulb, you need to build a cascade circuit, which multiplies the rectified voltage several times. With three cascade steps you can make 1000 V DC from 220 V AC.

 

http://www.kronjaeger.com/hv/hv/src/mul/

 

A word of warning here: When you build a rectifying circuit or a cascade circuit, which connects to the wall outlet directly, ALWAYS ALWAYS ALWAYS connect resistors in series with the capacitors. Use 100 nF capacitors in series with 100 K resistors, which can withstand the high voltages. Failing to use the resistors will result in exceedingly dangerous situations!

 

Another danger is that the cascade circuit is galvanically connected to the wall outlet. That may give an electrical shock on touching. That problem can easily be overcome by using a separation 1 : 1 transformer (these are used in many hotels etc. for making a shaver's power outlet). They are easy to obtain and it does not need to be expensive, because the transformer does not need to provide more than a few hundreds of mW of power.

 

At the n-th stage of the cascade circuit, you need to connect an additional resistor (e.g. 1 MOhm, and a capacitor of 100 nF / 1500 V). Using that, you will have a spark every second or so (probably somewhat more frequently). Using a larger capacity gives a more powerful spark, but less frequently.

 

Again, be very careful that you do not touch both ends of the capacitor, charged to 1000 V. Although the capacitance is small, I assure you, 100 nF charged to 1000 V can give a REALLY nasty shock.

[YT2095]

that`s very similar to my 10 stage Cockroft Walton Voltage multiplier, each cap 3900pf @ 6.3Kv (ex-Russian Military), with 3Kv diodes between.

it`s a fantastic peice of Lab kit.

 

but if you decide to use these as a way to make your HT instead of inductors, then be very carefull as Woelen points out, and also beware they will generate alot of Standing Static charges around the area too!

[woelen]

The latter problem is not an issue at 1000 V. I understand that it is at 6.3 kV as in your apparatus, but with 1000 V I would not worry too much about the static fields. As long as wires are kept well-separated (at least 1 cm) there is no risk of unintended breakdown.

 

However, the other warnings remain valid for 100%. High-voltage cascade circuits are no childrens toys!

[YT2095]

agreed to a point, 6.3Kv over 10 stages (20 caps) gives a good 60Kv max out (I Never drive mine that high).

and using the 10Kv per inch "rule" you can probably understand Why I never take it to full power

 

1Kv cant still cause signigicant damage though, and parts can still get charged, I know there`s a breakdown point above this level where static then becomes a REAL (non trivial) issue, but I still would be very carefull at 1kv also.

[KFC]

The clicky thing in stick lighters can make big sparks and you never have to use batteries.

 

Its fun to shock your self,