Forums

*small* spark generator

Started by ScottM May 19, 2012
> 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!
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: http://www.amazing1.com/Graphics/CD45.jpg . 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!
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

ScottM wrote:

> 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.
Ah, but the gap doesn't start out being a cm wide. It starts off tiny, with the two wires diverging as they go upwards in a 'V'. The air gets ionized or plasma-ized by the spark, making it a great conductor. The warm air around the spark makes it rise up the wires. I once got the spark four or five inches wide before it went out. That was with a sixteen thousand volt neon light transformer and four feet of 'rabbit ear' shaped wires, tapering from about 3/8 of an inch to about six inches wide at the top. Once the spark extinguishes itself, another one automatically starts at the narrow gap and the process repeats. You may need a glass tube to shield the arc if there are any strong drafts in the vicinity. Here's one using ten thousand volts: http://www.youtube.com/watch?v=P5KRE1nlgTc The power consumption is very low. My transformer drew under two amps from the 120 volt wall outlet. mike -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJPuYzkAAoJEDTMN7GV3zbXrGgH/A9MymtVNY3r3yVeI8D+c617 lFikpFkEm7UKvZcCNiL4uG+KwFwKk09n9FCzbN36kjIDKAm+r5tMqKi8OPvOobct E5dH5OIHHiD+TCG1wjUFNDnZ+mpRFCMRaedrhVtvECNwIh20K+IQcTWgiepMLhSc KR0vETQJ+SbIb/ety1OgUJlO6n5q3YjmkWPaJCH8YjmxUygSJPExSdpq3j6ROWIV KAjRDUT6iYsJ5G0fJ7hn3PjJp0XW0CJuwXsK+gjFjW7Ppo36GsJHwqUgFN6qJPgn azu9hE7YOypg1KE33LWUUwvvl0txXx+Ft3I+6zHdl064hoU3k/lE7MMvtVzpQsg= =n7tJ -----END PGP SIGNATURE-----
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!
ScottM wrote:
> 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!
Not to be rude but, I think it maybe just out side your abilities? You can use a Cockcroft Walton voltage multiplier.. http://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator 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. http://www.electronixandmore.com/project/4.html 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.
> =A0 =A0 You can use a Cockcroft Walton voltage multiplier.. > >.. > =A0 =A0Look up a MARX generator. >.. > > =A0 Hope that helps.
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".)
On Monday, May 21, 2012 3:17:04 AM UTC+2, ScottM wrote:
> 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!
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: http://www.powerstream.com/z/AA-100mA.png 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...
On Sunday, May 20, 2012 4:56:42 PM UTC+2, notbob wrote:
> > The text say 3A draw, the vid says 20A draw. ????? >
There's seven of them in the video.
"ScottM" <scott.a.mayo@gmail.com> wrote in message 
news:9b7ac15a-b395-4489-a39d-463713018eb7@e20g2000vbm.googlegroups.com...
>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.
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.
On Saturday, May 19, 2012 11:36:21 PM UTC+2, ScottM wrote:
> I need to generate sparks between two pieces of brass, about a half > inch apart or slightly more.
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: http://www.youtube.com/watch?v=kQN3Xys1Ilc 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...
fungus wrote:
> On Saturday, May 19, 2012 11:36:21 PM UTC+2, ScottM wrote: >> I need to generate sparks between two pieces of brass, about a half >> inch apart or slightly more. > > 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: > > http://www.youtube.com/watch?v=kQN3Xys1Ilc > > 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...
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