38 replies to this topic

[whoof]

Just a quick note on this. Standard electrolytic 'photo flash' capacitors aren't really up to pulse discharge duty for plasma / ebw applications unless you're careful. Yes, they'll work for a few dozen shots but given a low impedence circuit, the cap will progressively destroy itself as the internal foil is damaged.

Spot on, photoflash are too big anyway , about 10uF is needed.

Ideally you could use a mylar, oil or ceramic HV pulse cap with a fast trigger circuit but they're expensive and bulky. With electrolytics, slowing down the pulse with a long wire, added series inductance or resistance is helpful for e-matches. It somewhat defeats the point for EBW HE / shock tube work though, so it might be a bit of a balancing act...

Having said that, have you guys looked at the Maxim flash charger chips?

I had a look but even using solder resist i found them impractical/impossible to solder with available equipment.

The ZXC440 was at the limit of my ability

http://www.maxim-ic....dex.mvp/id/5323

Interesting thread...

Just met with Cooperman to discuss ST initiation methods. He trialled something along the lines of what EasyPyro has described above with some promising results. Any updates from from the other experiments?

You have a PM.

Ive had a bit of interest RE photography so have started a private thread.
PM if you are interested..

Edited by whoof, 14 March 2012 - 04:29 PM.

[Pyromancer]

Hi All,


Just thought I'd share a method of making reusable ST electric starter heads:



Take a large bore hyperdermic needle and pass a thin single insulated wire down the centre - the tighter the fit the better.


Snip off the end and clean up lightly on a grinding wheel.

Make yourself two or three of these.

Fit each one with a BNC plug, to allow you to swap them easily.

Have a BNC socket on your high energy output firing unit.



Connect the BNC of the needle to the BNC of the firing unit.



When functioned you should get a high energy spark across the end of the needle/wire assembly.



To initiate shock tube, simply insert the needle into the tube and function the firing unit.

The needle assembly will need cleaning/grinding from time to time to maintain reliability, but that's why you have two or three so you can easily swap if you have a problem.



Hope this is of use.



If anyone is willing to make me a small discharge unit with a BNC connector for the output please let me know.



Steve

Edited by Pyromancer, 14 March 2012 - 06:54 PM.

[dave]

ofca's original patent re use of shock tube for display fireworks

http://www.freepaten...com/5710390.pdf

dave

[cooperman435]

Just a quick note on this. Standard electrolytic 'photo flash' capacitors aren't really up to pulse discharge duty for plasma / ebw applications unless you're careful. Yes, they'll work for a few dozen shots but given a low impedence circuit, the cap will progressively destroy itself as the internal foil is damaged.

Id point out though that I have units made from single and multiple photo flash caps which Ive used for years without problem, if using an ematch with no pyrogen a large plasma ark is created when the wire pops and power is still left (multiple caps create MUCH bigger arks)

Ive fired HUNDREDS like this and no fail whatsoever from the cap or charging circuit?

[pyrotrev]

Just a thought, anyone tried using a piezo igniter unit (think ignition on gas cooker ) for firing shock tube? No batteries needed, and the bigger ones for commercial cookers/boilers pack quite a punch.

[exat808]

Just a thought, anyone tried using a piezo igniter unit (think ignition on gas cooker ) for firing shock tube? No batteries needed, and the bigger ones for commercial cookers/boilers pack quite a punch.

Yes, we have tried those types of device and they will initiate ST - but not with 100% certainty.

[whoof]

Ive fired HUNDREDS like this and no fail whatsoever from the cap or charging circuit?

Possibly firing into the wire has sufficient inductance to slow the edge.
I had one fail this week although my track length and inductance was very low.

These may be of interest
They are not the plastic ones but are short hollow blunt needles.

http://www.ebay.co.u...=item3f0d47481e

Some cooker ignitors do work but they tend to be electric these days 240v,
12v ones can be had for camping.

Edited by whoof, 17 March 2012 - 11:21 PM.

[pyrotrev]

Having been involved in a mega flash generator a while back I've a few ideas about how this could be done well, but it would be useful to know exactly what the initiation mechanism is. Is it the small shock wave off the spark, or is it the localised very high temperatures in the ionised gas I wonder

[whoof]

Having been involved in a mega flash generator a while back I've a few ideas about how this could be done well, but it would be useful to know exactly what the initiation mechanism is. Is it the small shock wave off the spark, or is it the localised very high temperatures in the ionised gas I wonder

Ive seen one design theat appears to have an external electrode so i am assuming / hoping it's the shockwave.

Mega flash , do tell if you can, i would be interested to know if you know of decent affordable trigger transformers , ones i have tried so far don't last long.