On Thursday, June 7, 2012 12:27:15 AM UTC+2, Les Cargill wrote:
> >
> > http://www.youtube.com/watch?v=kQN3Xys1Ilc
> >
> 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.
> 

Should be public now...I thought I made it
unlisted (link only) but something's broken
on youtube (I can't select that option).

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

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...

"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 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.

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...

> =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".)

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.

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!

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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












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