Initiating capacitor discharge with a spark

[Piotrne]

Hello,

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V. Is it possible
to initiate the discharge with an "external" spark?
I have tried without success to use a high voltage
generator, approximately 3 kV. This "high voltage
spark" jumps between the electrodes of the capacitor,
but does not initiate its discharge. Maybe it is
too weak.

I suppose that research on this subject was conducted
a hundred years ago, but it is difficult now to find
those details... Maybe someone has experience
with sparks (?) and could answer:

- is it possible to keep an electric arc at a distance
of 1 millimeter at the voltage of 30 V? If not,
what is the minimum voltage in this case?

- is it possible to initiate the discharge using
a "high voltage spark"? What parameters should
the additional spark have (voltage, duration, current)?

It could be experimentally measured, but I do not have
enough equipment... I hope someone has measured this
and can help.

Regards
Piotr

 

30 volts is not enough to maintain ionization. Add some zeros to the
voltage or make a direct connection.

John

On Fri, 29 Oct 2010 18:20:07 +0200, Piotrne <piotr23ne@poczta.onet.pl>
wrote:

Hello,

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V. Is it possible
to initiate the discharge with an "external" spark?
I have tried without success to use a high voltage
generator, approximately 3 kV. This "high voltage
spark" jumps between the electrodes of the capacitor,
but does not initiate its discharge. Maybe it is
too weak.

I suppose that research on this subject was conducted
a hundred years ago, but it is difficult now to find
those details... Maybe someone has experience
with sparks (?) and could answer:

- is it possible to keep an electric arc at a distance
of 1 millimeter at the voltage of 30 V? If not,
what is the minimum voltage in this case?

- is it possible to initiate the discharge using
a "high voltage spark"? What parameters should
the additional spark have (voltage, duration, current)?

It could be experimentally measured, but I do not have
enough equipment... I hope someone has measured this
and can help.

Regards
Piotr

 

[George Herold]

On Oct 29, 12:20 pm, Piotrne <piotr2...@poczta.onet.pl> wrote:

Hello,

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V. Is it possible
to initiate the discharge with an "external" spark?
I have tried without success to use a high voltage
generator, approximately 3 kV. This "high voltage
spark" jumps between the electrodes of the capacitor,
but does not initiate its discharge. Maybe it is
too weak.

I suppose that research on this subject was conducted
a hundred years ago, but it is difficult now to find
those details... Maybe someone has experience
with sparks (?) and could answer:

I am not a spark expert.

It is the electric field that is important. You might start here,
http://en.wikipedia.org/wiki/Electrical_breakdown

- is it possible to keep an electric arc at a distance
   of 1 millimeter at the voltage of 30 V? If not,
   what is the minimum voltage in this case?

Wiki says 3 X10^6 V/m... but this is at atmospheric pressure... if you
reduce the pressure you can reduce the field strength.

- is it possible to initiate the discharge using
   a "high voltage spark"? What parameters should
   the additional spark have (voltage, duration, current)?

It could be experimentally measured, but I do not have
enough equipment... I hope someone has measured this
and can help.

Regards
Piotr

Why are you trying to do this with a spark? Seems like there must be
easier ways. It's not at all clear how much of the capacitors energy
is going to be deposited into your dot of metal. (Lots goes into
making the spark.) How about a laser pulse to heat the dot? Or maybe
an induction heater? Spot welder?

George H.

 

[whit3rd]

On Oct 29, 9:20 am, Piotrne <piotr2...@poczta.onet.pl> wrote:

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V. Is it possible
to initiate the discharge with an "external" spark?

Yes, Marconi did that successfully. It doesn't much
matter that there's a 30V capacitor, he used what we
now call radio frequency energy (RF).

I have tried without success to use a high voltage
generator, approximately 3 kV. This "high voltage
spark" jumps between the electrodes of the capacitor,
but does not initiate its discharge. Maybe it is
too weak.

If you want the discharge not to quench, at 30V/mm, it has to
be in something other than atmospheric-pressure air. Low pressure
neon/helium mix is typical (which is why multi-kilovolt neon lights
in meter-long tubes are not unknown). Cold metal electrodes
next to the glow discharge are ... unhelpful, so the volts/mm
number doesn't scale down very well.

- is it possible to keep an electric arc at a distance
   of 1 millimeter at the voltage of 30 V? If not,
   what is the minimum voltage in this case?

It is possible, but you need to (1) have a chemical reaction to
generate
free ions, or (2) use radioactive materials or (3) use tricks like gas
mixtures with odd power supplies (ballasts) that prevent the Geiger
effect. Geiger tubes give one 'click' then it takes a while to
recharge
the capacitor so it can click again. In air, at anything close to
thermal equilibrium, a 30V source doesn't discharge across a 1mm air
gap.

 

[Phil Allison]

"Piotrne"

- is it possible to keep an electric arc at a distance
of 1 millimeter at the voltage of 30 V?

** Certainly possible under the right conditions.

Eg: If you open a switch while it is passing say 25 amps of current from a
30 volt DC supply, an arc will form across the contacts at distances of
about 1 mm or so.

The process involves heating of the contact surfaces to produce metal vapour
which sustains the arc PLUS the fact that the distance being jumped is
initially VERY small.

If not, what is the minimum voltage in this case?

** Likely several thousand volts is needed to simply jump a 1mm air gap.


.... Phil

 

[Winston]

whit3rd wrote:

(...)

In air, at anything close to thermal equilibrium, a 30V source
doesn't discharge across a 1mm air gap.

I take it that once the air is energized to a plasma
state, it's easy to maintain current flow across
a 1 mm gap with only a 30V gradient?

My excellent Miller welder has no problem with that.
(Note the 150 A rating at 16 VDC)

http://store.cyberweld.com/mitigwema150.html

--Winston

 

[Michael A. Terrell]

news@jecarter.us wrote:

30 volts is not enough to maintain ionization.

Really? I had an entire batch of circuit boards that were arcing
between the + 5V and ground traces. Some early buzzers operated on a
single 1.5 volt cell and arced across the contacts.


--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

 

[Jamie]

Piotrne wrote:

Hello,

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V. Is it possible
to initiate the discharge with an "external" spark?
I have tried without success to use a high voltage
generator, approximately 3 kV. This "high voltage
spark" jumps between the electrodes of the capacitor,
but does not initiate its discharge. Maybe it is
too weak.

I suppose that research on this subject was conducted
a hundred years ago, but it is difficult now to find
those details... Maybe someone has experience
with sparks (?) and could answer:

- is it possible to keep an electric arc at a distance
of 1 millimeter at the voltage of 30 V? If not,
what is the minimum voltage in this case?

- is it possible to initiate the discharge using
a "high voltage spark"? What parameters should
the additional spark have (voltage, duration, current)?

It could be experimentally measured, but I do not have
enough equipment... I hope someone has measured this
and can help.

Regards
Piotr
Look up Plasma welding..

Small ionized gas paths do not produce the volume you most likely
are looking for.. You could get a pulse signal from it maybe!. You
know, RF?

 

[John Larkin]

On Fri, 29 Oct 2010 18:20:07 +0200, Piotrne <piotr23ne@poczta.onet.pl>
wrote:

Hello,

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V. Is it possible
to initiate the discharge with an "external" spark?

Unlikely at 30 volts on the cap. 3000 is more reasonable. One
configuration is to have a sharp point with the HV from the cap on it,
near the work, within a distance that's close to breakdown. A trigger
electrode, like maybe a washer around the tip, is pulsed to very high
voltage, which causes ionization at the tip and breakdown of the main
arc.

Series triggering is sometimes done, but that's a little more
difficult.

John

 

[Winston]

Piotrne wrote:

Hello,

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V. Is it possible
to initiate the discharge with an "external" spark?
I have tried without success to use a high voltage
generator, approximately 3 kV. This "high voltage
spark" jumps between the electrodes of the capacitor,
but does not initiate its discharge. Maybe it is
too weak.

I believe a single HV spark won't be enough to
establish an ionized path in the air.
You require many, many arcs to strip sufficient
electrons to provide the ionized path for your D.C.

Consider using ~15 KHz sparks instead of
0.00001 Hz sparks!


http://www.youtube.com/watch?v=vl2Y7BqXCmo

Here is the opportunity to build that Tesla
coil you always wanted!

--Winston

 

[Winston]

whit3rd wrote:

On Oct 29, 9:20 am, Piotrne<piotr2...@poczta.onet.pl> wrote:

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V.

An automotive ignition makes about the size of spark
you're looking for. Energy is stored in the spark coil
inductance (conventional) or in a storage capacitor
(CDI == capacitor discharge ignition) , and the coil
boosts the input to get to ignition voltage.

Higher frequency would be better.
A 6 cyl engine running at 10,000 (!) RPM is moseying
along at a spark rate of only ~28 Hz.

The HF used to start an arc in a TIG welder is in
the vicinity of >10 KHz.

--Winston

 

[Winston]

Winston wrote:

whit3rd wrote:
On Oct 29, 9:20 am, Piotrne<piotr2...@poczta.onet.pl> wrote:

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V.

An automotive ignition makes about the size of spark
you're looking for. Energy is stored in the spark coil
inductance (conventional) or in a storage capacitor
(CDI == capacitor discharge ignition) , and the coil
boosts the input to get to ignition voltage.

Higher frequency would be better.
A 6 cyl engine running at 10,000 (!) RPM is moseying
along at a spark rate of only ~28 Hz.

Well, OK. 1000 Hz. But you get what I mean.

The HF used to start an arc in a TIG welder is in
the vicinity of >10 KHz.

--Winston

--Winston

 

[Winston]

Winston wrote:

whit3rd wrote:
On Oct 29, 9:20 am, Piotrne<piotr2...@poczta.onet.pl> wrote:

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V.

An automotive ignition makes about the size of spark
you're looking for. Energy is stored in the spark coil
inductance (conventional) or in a storage capacitor
(CDI == capacitor discharge ignition) , and the coil
boosts the input to get to ignition voltage.

Higher frequency would be better.
A 6 cyl engine running at 10,000 (!) RPM is moseying
along at a spark rate of only ~28 Hz.

Well, OK. 1000 Hz. But you get what I mean.

The HF used to start an arc in a TIG welder is in
the vicinity of >10 KHz.

--Winston

--Winston

 

[whit3rd]

On Oct 29, 9:20 am, Piotrne <piotr2...@poczta.onet.pl> wrote:

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V.

An automotive ignition makes about the size of spark
you're looking for. Energy is stored in the spark coil
inductance (conventional) or in a storage capacitor
(CDI == capacitor discharge ignition) , and the coil
boosts the input to get to ignition voltage.

 

[Piotrne]

Thank you for all your responses. I'll consider what to do:

- use higher voltage (but not 3000V! Maybe 50V),
- use some gas,
- lower the pressure (difficult),
- ...

I'm trying to build a small welding device, a simplified
version of such a thing (which costs about $6000):
http://www.youtube.com/watch?v=2tf5wzBvrA4
It contains a battery of capacitors charged to about 36V.
May change the duration of the pulse from about 2ms
to 30ms, at 600A. Uses a special gas around the welding point.
Requires to touch the metal with a needle-shaped electrode.
I just wanted to use another way of initiating the discharge
then touching. But it really seems to be difficult...

Regards
Piotr

 

[Rich Grise]

On Sat, 30 Oct 2010 23:27:39 +0200, Piotrne wrote:

Thank you for all your responses. I'll consider what to do:

- use higher voltage (but not 3000V! Maybe 50V),
- use some gas,
- lower the pressure (difficult),

I'm trying to build a small welding device, a simplified
version of such a thing (which costs about $6000):
http://www.youtube.com/watch?v=2tf5wzBvrA4
It contains a battery of capacitors charged to about 36V.
May change the duration of the pulse from about 2ms
to 30ms, at 600A. Uses a special gas around the welding point.
Requires to touch the metal with a needle-shaped electrode.
I just wanted to use another way of initiating the discharge
then touching. But it really seems to be difficult...

You're looking for a TIG welder. SOMEBODY should have one

for considerably less than six big ones!

Can you afford a couple hundred bucks?

Good Luck!
Rich

 

[Jamie]

Piotrne wrote:

Thank you for all your responses. I'll consider what to do:

- use higher voltage (but not 3000V! Maybe 50V),
- use some gas,
- lower the pressure (difficult),
- ...

I'm trying to build a small welding device, a simplified
version of such a thing (which costs about $6000):
http://www.youtube.com/watch?v=2tf5wzBvrA4
It contains a battery of capacitors charged to about 36V.
May change the duration of the pulse from about 2ms
to 30ms, at 600A. Uses a special gas around the welding point.
Requires to touch the metal with a needle-shaped electrode.
I just wanted to use another way of initiating the discharge
then touching. But it really seems to be difficult...

Regards
Piotr
That welding that is on that link is most likely using Argon..

also, that welder looks like it's actually detecting the short
when the probe touches the metal then retracts back and energizes
the tip, to give you a short burst.

 

[bw]

"Winston" <Winston@BigBrother.net> wrote in message
news:iahn6j04vo@news5.newsguy.com...

Winston wrote:
whit3rd wrote:

Higher frequency would be better.
A 6 cyl engine running at 10,000 (!) RPM is moseying
along at a spark rate of only ~28 Hz.

Well, OK. 1000 Hz. But you get what I mean.

The HF used to start an arc in a TIG welder is in
the vicinity of >10 KHz.

6000 RPM /60 seconds per minute is 100 revs per second.
For a 6 cyl, there are 3 sparks per rev, thats 300 Hz

 

[Jasen Betts]

I have a question about air ionization. The problem
is as follows: a large capacitor is to be discharged
"by a spark" to melt a "dot" on metal. The spark
has to go through the air, about one millimeter.
The capacitor is charged to 30 V. Is it possible
to initiate the discharge with an "external" spark?

that is how a thyratron works

I have tried without success to use a high voltage
generator, approximately 3 kV. This "high voltage
spark" jumps between the electrodes of the capacitor,
but does not initiate its discharge. Maybe it is
too weak.

possibly something else.

On 2010-10-29, news@jecarter.us <news@jecarter.us> wrote:
30 volts is not enough to maintain ionization. Add some zeros to the
voltage or make a direct connection.

60V is plenty to maintain an arc
(most arc welders operate in that ballpark and can maintain ars of
several milimeters, I've heard of people arc welding with as low as
24VDC

--
ɹǝpun uʍop ɯoɹɟ sƃuıʇǝǝɹ⅁


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