*small* spark generator

I need to generate sparks between two pieces of brass, about a half inch apart or slightly more. I want each spark to be triggered by a logic line going high (going low would work, too.) The voltage supply is 6v or 12v from a battery. The problem is that I need the circuit to fit inside a 1.5" inside diameter PVC pipe, and not take up more than, say, 3" of the pipe length, discounting battery. I was looking at autotransformers, but I'm not finding anything that will fit in that space. I don't need more than 1-2 sparks a second, but I want the circuit to be reliable. Can anyone suggest a circuit design that fits in a small space like this?

I'm aware of the safety risks in generating a voltage high enough to cross 1/2" of air, and the spark won't be anywhere that a finger can get into it. If it wasn't for the voltages involved, I'd tinker something up by trial and error, but in this case I don't like the possible consequences of "error", so I'd rather get expert advice. I'm willing to wind my own transformer if that's needed. Thanks!

Reply to
ScottM
Loading thread data ...

May I suggest an electronic gas stove igniter?

The most common type runs fro a i.5V cell using a single transistor blocking oscillator to generate about 250V - that charges a capacitor which is dumped into a HV pulse transformer a few times a second by aa gas discharge tube - replace the tube with a thyristor and you can control it.

If you're lucky, you might find a handheld igniter, alternatively go to recycling and look on the backs of scrap gas stoves.

Alternatively; look for a tiny SMPSU (DVB-T tet top box type thing) with a little re-arrangement of the blocking oscillator wiring you can make a 5V or

12V inverter - you should be able to produce a continuous ark between the pins that were the primary at about 20kHz or more.
Reply to
Ian Field

Have you looked at a Tazer?

--
?? 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net
Reply to
Jasen Betts

Potato gun?

Reply to
fungus

[...]

ScottM,

You might take a look at this item and its associated video:

Spark Gap Igniter - 4.8V -- $15

formatting link

It's not completely clear whether their "gap

Reply to
Frnak McKenney

The text say 3A draw, the vid says 20A draw. ?????

Also, be aware Sparkfun, being a small company, doesn't have the financial/legal horsepower to fight for yer privacy. They recently got into trouble cuz some dirtbags used one of their items to make illegal credit card readers and the govt came down on them, demanding lists of all their customers. A deal was worked out and sparkfun released only the customers that had recently purchased the offending device, not the entire customer list. Not saying you shouldn't deal with sparkfun, jes that you should know what's what.

formatting link

nb

--
vi --the heart of evil!
Support labeling GMOs
Reply to
notbob

It's usually a good if the OP states the objective. For a potato gun most use a BBQ igniter.

Reply to
Tom Biasi

Fair enough. It's to make a prop for a play involving mad science. The spark will be created inside a small brass funnel, and I'd like it to be bright enough and loud enough to be noticeable at a distance, which is why I want a longish spark. I'm not igniting anything with it. I'd prefer not to use a tazer circuit, on the grounds that those are meant to knock people over; I want something less likely to cause lawsuits if there's an accidental shocking.

I hadn't considered a continuous arc, on the grounds that I figured that would eat a lot of energy, but I have to admit that would look impressive, if possible...

Reply to
ScottM

I don't think the arc will be heard any distance in the magnitudes that you are describing. If it's for "Mad Science" why not incorporate a Jacob's ladder, much more impressive?

Tom

Reply to
Tom Biasi

With a motorcycle ign coil (twin HT lead "wasted spark" type is best) and a

555 driving a reasonably "fat" MOSFET its pretty easy to get fast enough sparks for persistence of vision make it seem continuous.

After playing with the experiment for a while, my ears were left ringing!

Reply to
Ian Field

This sounds promising, but I've been digging into this, and I need

30kV per cm of air gap. Or about 45kV to get what I want. I'm not finding motorcycle coils that talk about those voltages. But I think I've found a pulse transformer that's rated to that voltage, and fits in a 1.5" tube:
formatting link
. From the scanty description elsewhere on the site, I think it wants a 300v pulse for input, so now the problem reduces to generating a 300v pulse from a 12v battery, at a rate set by a CMOS logic circuit (1/sec would be the absolute minimum, 10/sec would rock.) Suggestions appreciated!
Reply to
ScottM

I probably should clarify the problem, since people are talking about AC power sources and jacob's ladders.

The prop is a handheld device, about 6-8" long, made mostly of 1.5" ID PVC pipe. Maybe 3" inside that pipe are available for electronics. On the front is a small brass funnel, with an insulated wire inside it. I want sparks to jump from the wire tip, to a point on the inside surface of the funnel. The funnel will point at people (the audience when possible) and I want the spark to be plainly visible at a distance. (I figure the acoustics of the funnel will make sure it is audible.) The power source is a small 12v battery, probably in a backpack or pocket. (A 9v battery would be great, but I figure if I want a few thousand sparks, that's impossible.)

My guess is, this is a hard problem, which is why I'm here. If I wanted a jacob's ladder, I can find designs for those myself, online. If I had AC power available, I could probably tinker up something for myself and eventually get it right. It's the combination of small space, long spark and small battery that makes this something I don't want to just tinker up. It needs to work, it needs to be efficient, and for safety reasons I want the circuit to fit entirely within the PVC. So please, think SMALL. Thanks!

Reply to
ScottM

Not to be rude but, I think it maybe just out side your abilities?

You can use a Cockcroft Walton voltage multiplier..

formatting link

Follow the guide lines on the actual rectifier chain, you can keep adding to the string..

but for your circuit to start off with.. You can get a HV Transistor of a MOSFET or NPN and what you do is use a high frequency pulse source like a 555 timer to switch this on/off. This transistor will pull current through an inductor and when the transistor switches off, the release energy is many times higher in voltage. This output is connected to the first stage of the Cockcroft Walton multiplier.

P.S.

Look up a MARX generator.

formatting link
You can use a basic boost single coil switcher to get the voltage up to some point where a MARX circuit can the start to work.

Hope that helps.

Reply to
Jamie

It might. I'd ruled out a Marx generator because it looked like the size of the spark gaps was critical, and it didn't look easy to pack it into a small space without distorting the wiring and messing up the gaps. But the CW multiplier looks interesting.

I do have a couple questions. Since I need to get into the neighborhood of 45kV, the last few stages are going to be handling serious voltage. I've never worked with diodes that can handle that voltage - is this likely to fit into my space constraints? Can you recommend specific parts?

Secondly, I was hoping to get sparks at a regular, controlled interval. (The goal is to have a 555 drive a 4017 at 10-20Hz, with each output of the 4017 controlling an LED, except for the last, which triggers a spark. Hence flash-flash-flash-flash-flash-flash-flash- flash-flash-SPARK!) The CW circuit is clearly going to have some recharge time, and if it's a few milliseconds that's fine, but I suspect it's a lot longer. How is it calculated?

(At some point I'm expecting someone to look at this, and say something like "12v to 45kV, 2 sparks a second, in 5.25 cubic inches - give up, it's not possible".)

Reply to
ScottM

The sparkfun thing is small but needs three amps of input so you'll have to be careful with the batteries - probably need at least a couple of D cell sets in parallel to prevent them from getting hot.

You'll also have to take into account that battery voltage varies over time and also with temperature and current draw. Getting exactly five volts from a battery without extra hardware isn't easy.

Battery voltage varies over time like this:

formatting link

eg. You might have to use four D cells which have been partially discharged to work with that spark gap igniter from Sparkfun (ie. get them down to about 1.3 volts each before using them otherwise you're looking at 6V of input and it might burn out).

How long does it have to run for? If it's only short bursts then it might not matter much if the batteries warm up a bit. For continuous use it can be a problem.

The sparkfun thing definitely looks like a good starting point. Get hold of a couple and play...

Reply to
fungus

There's seven of them in the video.

Reply to
fungus

Then look for a very small SMPSU transformer as I've alreadyy suggested - you can run the blocking oscillator from 4 or 5 AA NiMh.

Anything over about 20kHz you can get an apparently continuous arc with way less than the voltages you're on about.

If you want individual sparks the BO is easy to control with a single additional transistor.

Reply to
Ian Field

Just a follow up:

I was ordering some Arduino stuff from Sparkfun so I slipped a couple of their spark gap generators into the order.

They're perfect for any kind of mad scientist machine. You can get decent sparks from a single AA battery.

This is with three AA batteries:

formatting link

Disclaimer: 3xAA is not the way to do it for more than a couple of seconds. The batteries are overloaded, they'll heat up, bad things will happen...

Reply to
fungus

Can you point to a non-private video? I'd like to have a way to generate single sparks cheaply to collect audio impulse responses.

-- Les Cargill

Reply to
Les Cargill

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.