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~50KV from 1 CR123 3V Battery

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LAN_403

Legit_bacon

Mon Aug 15 2011, 05:08AM

Registered Member #4034 Joined: Thu Jul 28 2011, 10:41PM
Location: somewhere in the Southern hemisphere
Posts: 138

Hello hotwired! you wouldn't happen to be the hotwired of spudfiles? love this little circuit you've got here very nice!

Hotwired

Mon Aug 15 2011, 02:57PM

Registered Member #4049 Joined: Sun Aug 07 2011, 03:50AM
Location: UK
Posts: 14

Yes I hang about on Spudfiles too.

It's why I made this. Combustion potato guns need a high voltage ignition source. Sometimes stunguns are used. Stunguns are illegal where I am so I saw that as a challenge to make an equivalent.

It has far less power than an actual stungun but still loads for gas ignition. Your average commercial ignition for a BBQ or whatever puts out 10mJ sparks, this does 13mJ sparks and at a much higher rate too.

Forty

Mon Aug 15 2011, 03:25PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

lol stun guns are illegal but potato guns aren't?
this is a nice little use for all the camera transformers I've scavenged. Do you have any info on the transistor? I don't have any still assembled flash boards so i'll have to use a transistor from my collection. it's too bad those hv pulse transformers aren't more common. i'll have to try making one. I like that you've used one of those gas discharge tubes for your mini spark gap. I haven't read in to mov's or avalanche diodes yet, but when I do, i'll help you out. since the voltage is only ~400v, i'm sure you could get away with a hv transistor triggered by a 555 timer. then you could tune the frequency until you get the desired pulse energy/repetition rate.

Hotwired

Mon Aug 15 2011, 06:25PM

Registered Member #4049 Joined: Sun Aug 07 2011, 03:50AM
Location: UK
Posts: 14

Yes potato guns are as well.

I don't fire much these days. Don't have the space or privacy and feel depressingly responsible.

I've been checking and a MOV or TVS is unsuitable.

They conduct very quickly when an overvoltage turns up but stop conducting when voltage drops to correct levels.

On the other hand a SIDAC or GDT will start conducting on an overvoltage but won't stop conducting until the current drops enough.

Basically the TVS/MOV acts as a pressure relief valve, only opening enough to let off excess pressure and the SIDAC/GDT act as dump valves. They'll let the entire capacitor discharge before they reset.

I've had some 330V SIDACs with me for the last few days but I've been feeling really lousy and haven't got round to trying them yet.

As for the transistor, I'll see if there's any markings and get back to you.

Arcstarter

Mon Aug 15 2011, 06:26PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Cool project! I love pulse transformers.

I have recently been messing with the idea of large pulse transformers (and ignition coils being forced to spit out 100's of kv). It is much easier on HV transformers to output pulses than CW, so i think a homemade pulse transformer would be feasible if you want bigger sparks. A primary of a few turns, and then a secondary with hundreds or if possible thousands of turns over a ferrite rod. However i think a pulse transformer with a spark output around the size of itself would need to be vacuum potted with some paraffin wax or oil.

A more efficient way of switching the cap into the primary of the pulse transformer would use an IGBT and a diac/sidac (can be found in a light dimmer). I would use a circuit like this:

It's reffered to as SISG (sidac IGBT spark gap) and it is typically used to replace the spark gap on Tesla coils. The sidacs could be replaced with anything that will reliably break down at the voltage you want the circuit to fire at, which charges the gate of the IGBT and it acts like a closed spark gap. The difference is that it will only drop a few volts when it is on, while a spark gap has high resistance when it is on.

Hotwired

Mon Aug 15 2011, 06:58PM

Registered Member #4049 Joined: Sun Aug 07 2011, 03:50AM
Location: UK
Posts: 14

Spent all of 2 mins setting up the circuit and the 330V SIDACs work fine in place of the 350V GDT.

Mind you the 20V difference seems to be an issue on the HV coil, the terminals are ok for the 350V GDT but when using the SIDACs they are too far apart to arc.

Nevermind, can always put a few in series for higher voltage pulses.

The SIDAC didn't seem to heat up during prolonged use as I was worrying.

Arcstarter wrote ...

A more efficient way of switching the cap into the primary of the pulse transformer would use an IGBT and a diac/sidac (can be found in a light dimmer). I would use a circuit like this:

Looks like that would double the component count of the circuit by itself :P

As far as the original intention of the circuit, that doesn't add anything over a SIDAC or GDT switch aside from size and added complexity. There's a fixed spark gap and the goal is for it to arc that using the smallest possible device with enough energy for gas ignition.

Not sure what you mean by high resistance in a spark gap when its on, plasma is high resistance?

Hotwired

Thu Aug 25 2011, 10:53AM

Registered Member #4049 Joined: Sun Aug 07 2011, 03:50AM
Location: UK
Posts: 14

Thought you might like an update, I boxed the circuit into a usable form and it's now powered by a rechargeable lithium CR123 which charges to 3.8V.

Shell is made of 2.5mm PVC and the circuit is essentially in a brick of hot melt glue.

Again, I'm using the word stungun simply because that's what people are more likely to understand. It has 3-7 times lower energy output than a proper stungun and is for ignition purposes.

I've revised my estimate of the voltage after rummaging about for the breakdown of air using sharp electrodes.

Source here claims 42.6KV to 51.0KV at 3cm for a 50% chance of a breakdown of air using pointed electrodes: http://www.eurojournals.com/ejtaer_1_06.pdf Tmpl

What do you reckon? Is 50KV realistic?

radhoo

Fri Aug 26 2011, 09:38AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

very nice, compact design.

LE: you can actually use this for a highly portable x-ray generator, see:

radhoo

Sat Aug 27 2011, 06:51PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

I need to build something similar for auto-ignite my flame thrower:

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