I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
On Thursday, December 21, 2023 at 4:03:35?PM UTC-8, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
Sure, there's formulas; an auto spark coil takes high current from 12V on the primary
to build up field energy, then when the points open, the stored energy (less a bit for the
resistivity of the iron) blasts the spark hard. After warmup, the current limit resistor
(often a PTC type) gives a lower current for the now-hot engine.
Energy is conserved, a little under L times the square of the current, over two, per spark.
The gap size has to be small enough that the arcing doesn't occur in the >wrong place... and the conductivity of the gap determines the spark duration (low
gas denslty, lower resistivity and faster spark).
Sure, there's formulas;
an auto spark coil takes high current from 12V on the primary
to build up field energy, then when the points open, the stored energy (less a bit for the
resistivity of the iron) blasts the spark hard. After warmup, the current limit resistor
(often a PTC type) gives a lower current for the now-hot engine.
Energy is conserved, a little under L times the square of the current, over two, per spark.
The gap size has to be small enough that the arcing doesn't occur in the wrong place... and the conductivity of the gap determines the spark duration (low
gas denslty, lower resistivity and faster spark).
On 12/21/2023 8:07 PM, whit3rd wrote:
Sure, there's formulas;
The problem is quantifying the environment. The medium between
the electrodes plays a role -- as do the shapes of the electrodes,
etc.
an auto spark coil takes high current from 12V on the primary
to build up field energy, then when the points open, the stored energy (less a bit for the
resistivity of the iron) blasts the spark hard. After warmup, the current limit resistor
(often a PTC type) gives a lower current for the now-hot engine.
Energy is conserved, a little under L times the square of the current, over two, per spark.
The gap size has to be small enough that the arcing doesn't occur in the
wrong place... and the conductivity of the gap determines the spark duration (low
gas denslty, lower resistivity and faster spark).
We had a VC approach us shortly out of school (70's) asking
us to design an "electronic ignition" -- no rotor, etc.
Back then, 1MHz processors were the norm. And, only
1802's were low enough power to run in an automotive
environment.
We knocked together a prototype in short order (the code
is trivial -- as is the hardware, if you don't have to
plan for production!) and demonstrated how we could adjust
the advance and dwell based on RPM and "general performance
criteria".
The VC had hoped we could enhance the value by compensating
for plug degradation, indicating needs for service, etc.
You can't (cheaply) *look* at the plug voltages but you can
look at "characteristics" of each firing. And, if you ignore
absolutes and, instead, do relative comparisons (this plug
to that, this plug NOW to this plug a month ago, etc.) you
can make some crude inferences.
But, there are just too many variations to account for!
No two plugs are produced alike. No two coils (we had a coil
per plug). Wires get dirty and rerouted. etc.
None of us had a desire to make a career out of this -- or
ANYTHING automotive -- so we bowed out when he wanted to
present to the automakers. The only way to do ANYTHING is
in huge quantities -- which means, you do FEW things!
(We'd rather have lots of varied challenges than just a few)
Amusingly, I now find myself reviewing those (ancient) notes as I
look to design an ECU for "one last *big* ICE" (for myself).
I think it would be cool to be able to dial in operating
constraints, dynamically: performance, fuel economy, emissions
quality, etc.
[This sparked from a discussion with a colleague over designing
similar controls for race cars... let the controls "learn"
the characteristics of the track so the driver doesn't
have to tell the controls when he's entering a straightaway,
deep curve, etc.]
On Sunday, December 24, 2023 at 9:52:02 AM UTC-8, Cursitor Doom wrote:
On Thu, 21 Dec 2023 19:07:11 -0800 (PST), whit3rd <whi...@gmail.com>
wrote:
On Thursday, December 21, 2023 at 4:03:35?PM UTC-8, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
Sure, there's formulas; an auto spark coil takes high current from 12V on the primary
to build up field energy, then when the points open, the stored energy (less a bit for the
resistivity of the iron) blasts the spark hard. After warmup, the current limit resistor
(often a PTC type) gives a lower current for the now-hot engine.
Energy is conserved, a little under L times the square of the current, over two, per spark.
The gap size has to be small enough that the arcing doesn't occur in the >>> wrong place... and the conductivity of the gap determines the spark duration (low
gas denslty, lower resistivity and faster spark).
What a terribly unscientific explanation. I'm aghast, quite frankly.
If you want science, look up Georges Charpak's work (Nobel prize 1992);
the physics of a spark is nonlinear, nontrivial, and depends on... EVERYTHING. There's no simple general formula. Maybe if you
define a geometry, and a gas pressure, and a temperature profile, and an energy
budget, you can design a detector gas to equal the magic mixes Charpak was known for.
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that
is possible, I have not seen it.
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that
is possible, I have not seen it.
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that
is possible, I have not seen it.
In the older style transformer-only arc welders, the arc has to be
struck manually by momentarily shorting out a low voltage/high current secondary winding; typically 50 to 80V. This can be a messy and
frustrating process at times, even for a skilled tradesman. Newer
style inverter welders use HF AC for a 'soft start' which is much
cleaner and faster. I've not heard of a high voltage start method
either.
needs hard real time so raspberry pi is useless
an Arduino might do to implement something like what manufacturers did 30+ years ago ..
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that
is possible, I have not seen it.
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."Ah, ok, yes.
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that
is possible, I have not seen it.
It's how Xenon flash lamps are triggered. The big capacitor is
charged less than 1 KVolt, which isn't enough for such a long gap (the
length of the fused quartz flash tube). The trigger wire is wrapped
around the flash tube and when pulsed with 10 or 20 KV, causes a
conductive path to form in the Xenon gas (about 0.1 Bar) within, and
boom!
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a >>distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that
is possible, I have not seen it.
It's how Xenon flash lamps are triggered. The big capacitor is
charged less than 1 KVolt, which isn't enough for such a long gap (the
length of the fused quartz flash tube). The trigger wire is wrapped
around the flash tube and when pulsed with 10 or 20 KV, causes a
conductive path to form in the Xenon gas (about 0.1 Bar) within, and
boom!
Joe Gwinn
On 2023-12-25 17:58, Joe Gwinn wrote:
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."Ah, ok, yes.
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that >>> is possible, I have not seen it.
It's how Xenon flash lamps are triggered. The big capacitor is
charged less than 1 KVolt, which isn't enough for such a long gap (the
length of the fused quartz flash tube). The trigger wire is wrapped
around the flash tube and when pulsed with 10 or 20 KV, causes a
conductive path to form in the Xenon gas (about 0.1 Bar) within, and
boom!
But there is no conductivity between the high voltage and low voltage parts.
Carlos E.R. <robin_listas@es.invalid> wrote:
On 2023-12-25 17:58, Joe Gwinn wrote:
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."Ah, ok, yes.
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that >>>> is possible, I have not seen it.
It's how Xenon flash lamps are triggered. The big capacitor is
charged less than 1 KVolt, which isn't enough for such a long gap (the
length of the fused quartz flash tube). The trigger wire is wrapped
around the flash tube and when pulsed with 10 or 20 KV, causes a
conductive path to form in the Xenon gas (about 0.1 Bar) within, and
boom!
But there is no conductivity between the high voltage and low voltage parts. >>
Gas lasers and CFLs are started by a HV transient on the terminals.
Carlos E.R. <robin_listas@es.invalid> wrote:
On 2023-12-25 17:58, Joe Gwinn wrote:
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."Ah, ok, yes.
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that >>>> is possible, I have not seen it.
It's how Xenon flash lamps are triggered. The big capacitor is
charged less than 1 KVolt, which isn't enough for such a long gap (the
length of the fused quartz flash tube). The trigger wire is wrapped
around the flash tube and when pulsed with 10 or 20 KV, causes a
conductive path to form in the Xenon gas (about 0.1 Bar) within, and
boom!
But there is no conductivity between the high voltage and low voltage parts. >>
Gas lasers and CFLs are started by a HV transient on the terminals.
Cheers
Phil Hobbs
On Tue, 26 Dec 2023 19:52:00 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Carlos E.R. <robin_listas@es.invalid> wrote:
On 2023-12-25 17:58, Joe Gwinn wrote:
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."Ah, ok, yes.
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I >>>>> have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a >>>>> distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that >>>>> is possible, I have not seen it.
It's how Xenon flash lamps are triggered. The big capacitor is
charged less than 1 KVolt, which isn't enough for such a long gap (the >>>> length of the fused quartz flash tube). The trigger wire is wrapped
around the flash tube and when pulsed with 10 or 20 KV, causes a
conductive path to form in the Xenon gas (about 0.1 Bar) within, and
boom!
But there is no conductivity between the high voltage and low voltage parts.
Gas lasers and CFLs are started by a HV transient on the terminals.
Cheers
Phil Hobbs
Series trigger transformer?
Krytrons have a seperate trig terminal and a keep-alive electrode.
On 26/12/2023 12:06 am, Carlos E.R. wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I
have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a
distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if
that is possible, I have not seen it.
The high pressure xenon arc lamps I built my power supply to drive were
being used as UV light sources in the Photochemistry group at
Southampton University.
It took about 20kV to drive a spark between the electrodes, which dumped enough xenon ions and electrons into the gap to sustain a glow discharge
for the few microsceconds it took for the tungsten electrode surface to
warm up enough to sustain an 24A arc at about 20v or so.
They ran hot and were filled with a couple of atmospheres of xenon gas,
and relied on silica glass to keep the gas inside and the tungsten
electrodes spaced apart. Moving the electrodes wasn't an option.
Providing a third - trigger - electrode to allow easier starting was possible, but not popular.
I set up a stable constant current so the lamp provided a more or less
stable output - turbulent convection currents in the xenon gas meant
that it wasn't all that stable in the short term.
On Tue, 26 Dec 2023 19:52:00 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:It certainly simplifies things. The high voltage spike can destroy the
Carlos E.R. <robin_listas@es.invalid> wrote:
On 2023-12-25 17:58, Joe Gwinn wrote:
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."Ah, ok, yes.
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I >>>>> have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a >>>>> distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that >>>>> is possible, I have not seen it.
It's how Xenon flash lamps are triggered. The big capacitor is
charged less than 1 KVolt, which isn't enough for such a long gap (the >>>> length of the fused quartz flash tube). The trigger wire is wrapped
around the flash tube and when pulsed with 10 or 20 KV, causes a
conductive path to form in the Xenon gas (about 0.1 Bar) within, and
boom!
But there is no conductivity between the high voltage and low voltage parts.
Gas lasers and CFLs are started by a HV transient on the terminals.
As can the flash lamp - it was sometimes done that way.
The advantage of the capacitive coupling (through the fused quartz
lamp tube wall) is that the 20 KVolt pulse does not appear on the 1 KV terminal or circuit, a simplification.
On Tue, 26 Dec 2023 19:52:00 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Carlos E.R. <robin_listas@es.invalid> wrote:
On 2023-12-25 17:58, Joe Gwinn wrote:
On Mon, 25 Dec 2023 14:06:06 +0100, "Carlos E.R."Ah, ok, yes.
<robin_listas@es.invalid> wrote:
On 2023-12-22 01:03, RichD wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
That's strange, an arc lamp is low voltage, high current. The ones I >>>>> have seen needs the points to touch for an instant, then separate,
either automatically or manually. During use, the points can be at a >>>>> distance of about one centimetre.
Using a a high voltage spark to initiate the thing? I don't know if that >>>>> is possible, I have not seen it.
It's how Xenon flash lamps are triggered. The big capacitor is
charged less than 1 KVolt, which isn't enough for such a long gap (the >>>> length of the fused quartz flash tube). The trigger wire is wrapped
around the flash tube and when pulsed with 10 or 20 KV, causes a
conductive path to form in the Xenon gas (about 0.1 Bar) within, and
boom!
But there is no conductivity between the high voltage and low voltage parts.
Gas lasers and CFLs are started by a HV transient on the terminals.
As can the flash lamp - it was sometimes done that way.
The advantage of the capacitive coupling (through the fused quartz
lamp tube wall) is that the 20 KVolt pulse does not appear on the 1 KV terminal or circuit, a simplification.
Joe Gwinn
On December 21, Bill Sloman wrote:
I recall working on an arc lamp power supply, which used
a spark gap for ignition.
I wondered, and still do, are there any design techniques
or formulas, to obtain a specific desired voltage pulse
across the gap? Or is it cut and try, regarding the gap size
and current? (the current break, that is)
You can buy high voltage spark gaps - the one I bought for that job in
1972 was glass-enclosed tube with an inert gas filling.
At the tine I'd bought a copy of a 1920's text book on the conduction pf
electricity through gases, for which there was already a well
established theory - search on Paschen's Law.
https://en.wikipedia.org/wiki/Paschen%27s_law
My first spark gaps was made in the workshop, and used two steel
ball-bearings to form the gap, mounted in a silica glass tube,
The arc lamp was exposed to the UV light from the spark, and that help
start the lamp. The glass in the store-bought spark gaps wasn't UV
transparent and the light they emitted didn't start the lamp nearly as
often.
I looked at the Paschen theory, it's complicated. I find it hard to believe that Joe Engineer uses that to design spark gaps.
I'm more curious as to what precision one can achieve a desired pulse amplitude and shape. Or maybe it doesn't matter, the process is robust?
Looking at the physics, you have to specify the geometry, solve the field equations, control the transition slope of the (non-ideal) switch, etc.
Note that ionization is sensitive to the E field, not voltage.
Maybe EEsof can handle it -
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