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Registered Member #1397
Joined: Mon Mar 17 2008, 12:47PM
Location: Finland
Posts: 43
Hi guys its been for a while since ive last posted here!
But anyway, my new project will be as the title says, fully portable etg rifle. I havent started the project yet but i will soon, atm i only have 4 caps that will be used in this project.
Here is a little scetch from it and this was drawn very quickly so :D...
So the rifle will have total 4 x 400V 1500uF caps in parallel, totals 400V 6000uF and when charged to 400V, this equals about 480J.
The ignition system will be HV-triggered. It uses homemade air core pulse transformer with ratio 1:1. Input will be 10-20kV from spudgun ignition system and ratio being 1:1, this equals about the same out put(10-20kV). There will be a little air gap inside the chamber and when that gap will be ionized with hv-spark, it comes conductive and and therefore gap will be ignited. There will be also some aluminum foil inside the chamber so the air isnt only thing to vaporize :D!
And even though there will be some little extra inductance and resistance because of the pulse transformer, i think it will be so little affect to this that it doesnt matter that much.. Secondary will only be about 5-10 turns of at least 10mm2 wire and primary from hv-source will be wind onto it.
Barrel will be 30-50cm long and it may be even good thing to be little longer, because the inductance that exists will limit little bit of the current rise time so the long barrel just gives time to make sure that pressure has rised to its maximum.
My goal is to connect caps together during this weekend and maybe buy some plexiglas.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I would use polycabonate, not plexiglas (acrylic) if a transparent plastic is required. Plexiglas shatters very easily compared to polycarbonate and could pose a safety hazard. At least per my understanding.
Constructive answer: Put a small ferrite ring with smg like 3 turns in primary and secondary winding them on separate sides of the ring instead of air core transformer - this will greatly increase coupling factor at small ignition currents and will saturate instantly as soon as kAs will blow through. Air gap must be as small as possible if it is used only to prevent physical contact between electrodes and aluminum. But if you plan to try to work with air gap only heating up the plasma channel, then you need to space electrodes as far as possible - the bigger the gap the more heat will be dissipated with the same current (will be limited mostly by inductance of the wires). Aluminum recommended, of course - air gap sucks. You may try plastic projectiles with aluminum foil ring or some other shape glued at the back of it used as vaporisator, so you will not need to put this material separately. Try different configurations, investigate what happens, give us pics. Barrel does not need to be that long, probably - try the system before assembling the cage.
Registered Member #1397
Joined: Mon Mar 17 2008, 12:47PM
Location: Finland
Posts: 43
Havent done much yet but i connected the caps together with homemade busbar system(6mm id copperpipe :DD) :
And i also bought 120cm x 30cm x 0.4cm piece of polycarbonate, which was pretty expensive indeed.
I dont have much time to do this in summer but my goal is complete that busbar system and make the hv-pulse transformer by the end of week.
Hmm..i am not sure which one to use in this, the aircore or ironcore transformer, is it really true that ironcore saturates pretty easily and it acts then as pure resistive load?
Don't you have high permeability ferrite rings (u=10000 or so)? Ferrite core will act as air core after saturation which will happen as soon as spark will establish a path for high current from caps which will blow through it. Separating primary and secondary on two opposite sides of the ring will also help to brake the coupling between them after triggering happened.
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Fully portable ETG-rifle
