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High voltage ignition, about 2us spark.

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carpenter

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I need High voltage ignition, not for gas or engine ignition, but for ionization of gas.
Spark parameters
Voltage about 6kV
Duration about 2us.

I think it will require MHz switching speed.
Am I right?

If yes, Ithing the main problem will be coil or trnsformer for this frequency.
You can help?
You know the right design?
 

Hi,

2us is a very short time for a spark. Are you sure you can ionize gas within this short piece of time?

2us ... MHz of swtiching speed ... not very useful information.
Please draw a sketch of what you need. timing, waveform, voltage, current...

Usually an ignition pulse is just one peak...no high speed switching frequency involved.
For sur you can do this - but do you really need it?

Klaus
BTW: coils and transformers are widly used for pulses in the us range. Nothing special.
 

Hi,
2us is a very short time for a spark. Are you sure you can ionize gas within this short piece of time?

The gas is for example very clear agron and for ionization just a shorter event., for example beta particle.
let physics aside, aplicacion request is
Electric ignition with voltage min 6000V (gap about 2-5mm)
length of spark about 2micro second with a repetition ratio of 50-100Hz.
That's all I know.
I got it on the table. Black box, in epoxy resin.
On oni side is inut for DC 24V and driving TTL input on second side is HV output .
for short shot on drivimg TTL this generate on output 6500V with pulse duration about 2,4us
if drive input is active generate about 62 shot every second in this mode is output voltage lower and the time between shoots and the length of the shot floats +- 30%.

My first idea is 2MHz high voltage generator, but her is problém with realizing induktance
In short I just do not know how to do it
 

If you want a 2uS spark then you are not switching at MHz.
Spark comes during your "off" phase and you need about
the same "on" phase to re-energize the core ("dwell").

For highest energy you want to run the dwell*volts as
high as won't break down insulation somewhere bad.
Every core has a maximum volt-seconds to saturate.

The output spark duration will be whatever it takes to
bring the core energy out, that you put in, across the
spark gap.
 

You think something like tyristor ignition system?
For example
Charge 140uF capactor on 96V (energy 0,65J) and this energy over tytistor discharge over primar of transforter and this energy make on sec. side high voltage pulse.
theoretically it will work.
Practically I find it difficult.
In first is need realise high voltage for chraging capacitor,
I do not know if it's good chice using ceramic capacitor , for example 14x 10uf 100V 1210 X7R chrging on 96V
or must be used PP motor capacitor for example 10uF 400V ( 0,8J )?
What energy is the right one 1/4 ,1/2 1J or ....
 

If you don't need incredibly precise control of the waveform shape, I would recommend something based on spark gaps, like a marx generator. Here's a document I found with a lot of practical info **broken link removed**.

Make sure you stay safe, these systems can be quite dangerous...
 

Thanks, I look at it.
In the meantime, I have invented this. see pic.
Three 1uF PP cap in paralele is charged on 400V (80%,60% or 45% 400V) charging make PS with DPA425R from 24V.
Capacitor is charged 100us, after charging is DPA425R OFF and capacitors is dischrage over thyristor Q1 on HV transformet TR2. TR2 make from 400V 6kV ..
400V is isolated HV (OK not full isolated have 3M ohm resistnce over R16,17,18) Voltage on this line is is determined by the ratio of the transformer threads between this and 20V auxiliary windings.
It's quite complicated, but it makes it possible to control the whole process up to individual pulses

HV Ign..jpg
 

I doubt a standard triac is going to be able to operate fast enough without destroying itself. Do you have any estimate for the arc current?
 

Is not above experimental verification.
big 10uF motor capacitor charged on 400V and dischage over TIC236N on transfomer primar 36turn sec 1000 turn on core ETD5922
sec is load 1kOhm .
Max current over primar is 128A, igmiton lenght on sec 50us (1k ohm) and max votage 8kV.
this work many years as elektric fence on my sister's pasture.
Her is measuremt on osciloscope

cign.png
 

As long as the Thyristor or triac I²t and dI/dt rating is observed, the setup will work well. I²t should be no problem, dI/dt of 50 A/µs has less margin but looks still sufficient. SCR have usually higher rating than triacs.

Pulse duration seems far from initially intended 2 µs however.
 

But your spec is about ten times that fast, right?

How much control do you need over the duration/shape of the arc? Do you need a sharp turn off?
 

Yes you are right in this measurement is the pulse time noticeably higher.
but
- this is due to the fact that the secondary is loaded with a resistance of 1k ohm and the loss of energy accumulated in the core of the transformer occurs gradually
- the current is measured at the primary
In the event of an spark discharge I thing dischrge is much faster, because sec have high isolation resistence, voltage on sec increases and exceeding the insulating resistance of the gas will result in a rapid spark discharging
 

Have you considered a neon sign transformer (power
supply), which would seem to be perfectly suited to
ionizing a gas chamber?

I'd bet you could find a beer sign, surplus or broken,
for dirt cheap.
 

Yes you are right in this measurement is the pulse time noticeably higher.
but
- this is due to the fact that the secondary is loaded with a resistance of 1k ohm and the loss of energy accumulated in the core of the transformer occurs gradually
- the current is measured at the primary
In the event of an spark discharge I thing dischrge is much faster, because sec have high isolation resistence, voltage on sec increases and exceeding the insulating resistance of the gas will result in a rapid spark discharging
It's not easy to model arc formation and quenching. The rise time on the output will be limited by leakage inductance in the transformer, as well as the switching device itself.
 

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