Low Voltage Capacitor ETG
spectre, Fri Oct 31 2014, 07:47PMIs it possible to use low voltage capacitors to power a ETG/Railgun? i have i 16 Volt 50 Farad Car audio Cap bank that is collecting dust. Total stored energy i 6.4 KJ at 800 Coulombs.
If this is to low a voltage to drive the circuit properly, can i discharge it through a transformer core?
I am in the process of designing a ETG, and i am sourcing materials needed. thinking of a long barrel, large chamber, multiple electrodes and low melting-point material connecting the electrodes. lead, tin, potassium.
Re: Low Voltage Capacitor ETG
hen918, Fri Oct 31 2014, 10:32PM
Well the thing with ETGs is, the Thermal bit is caused by a thin piece of wire of other metal, vaporising when it has a multimegawatt pulse of electricity through it. More voltage = more current, with a low resistance. Basically you are trying to get the thing you want to propel the projectile to explode as violently as possible. A low voltage just isn't going to do that.
Discharging those capacitors though a transformer will cause the transformer to get hot, but nothing else: transformers work with AC, capacitors are DC.
As for the type of propellant metal needed, you want a low boiling point and low resistance (with the resistance being more important)
hen918, Fri Oct 31 2014, 10:32PM
Well the thing with ETGs is, the Thermal bit is caused by a thin piece of wire of other metal, vaporising when it has a multimegawatt pulse of electricity through it. More voltage = more current, with a low resistance. Basically you are trying to get the thing you want to propel the projectile to explode as violently as possible. A low voltage just isn't going to do that.
Discharging those capacitors though a transformer will cause the transformer to get hot, but nothing else: transformers work with AC, capacitors are DC.
As for the type of propellant metal needed, you want a low boiling point and low resistance (with the resistance being more important)
Re: Low Voltage Capacitor ETG
spectre, Sat Nov 01 2014, 03:54PM
oops, i see my mistake, was tired when i wrote that. i meant a dc-dc transformer, cant remember the name, switch-mode something something.
and i see your point about low voltage, will try to get my hands on something larger, series parallel 400 volt caps or something in that area, get up to about 800 volts
thinking of trying tin as metal, in a chamber filled with pure oxygen, or possible other gases. in the process of machining a valve that can contain the blast, in theory it should hold pressure from vacuum to 100K psi.
using tin, it has i melting point of 239 degree celsius and almost no resistance, 115 nano-ohm per meter.
easier to read: using a 1 centimeter piece of tin, it has a internal resistance of 0.000001 milliohm at 0 degree celsius
i am not sure how to calculate potential energy from capacitors. does anyone have a formula i could use??
spectre, Sat Nov 01 2014, 03:54PM
oops, i see my mistake, was tired when i wrote that. i meant a dc-dc transformer, cant remember the name, switch-mode something something.
and i see your point about low voltage, will try to get my hands on something larger, series parallel 400 volt caps or something in that area, get up to about 800 volts
thinking of trying tin as metal, in a chamber filled with pure oxygen, or possible other gases. in the process of machining a valve that can contain the blast, in theory it should hold pressure from vacuum to 100K psi.
using tin, it has i melting point of 239 degree celsius and almost no resistance, 115 nano-ohm per meter.
easier to read: using a 1 centimeter piece of tin, it has a internal resistance of 0.000001 milliohm at 0 degree celsius
i am not sure how to calculate potential energy from capacitors. does anyone have a formula i could use??
Re: Low Voltage Capacitor ETG
hen918, Sat Nov 01 2014, 04:25PM
You would have to use a switch-mode power supply (my favorite is the Mazzilli flyback driver with a homemade 3kv flyback transformer) to charge up the large 400/800v capacitors.
Aluminium works very well, because it is actually flammable as well as having the third lowest resistance of any element. (about 5 times less than tin)
The boiling point of tin is 2602 degrees Centigrade, meaning that it may not even vaporise: all of the energy would be dissipated in the connecting wires.
hen918, Sat Nov 01 2014, 04:25PM
You would have to use a switch-mode power supply (my favorite is the Mazzilli flyback driver with a homemade 3kv flyback transformer) to charge up the large 400/800v capacitors.
Aluminium works very well, because it is actually flammable as well as having the third lowest resistance of any element. (about 5 times less than tin)
The boiling point of tin is 2602 degrees Centigrade, meaning that it may not even vaporise: all of the energy would be dissipated in the connecting wires.
Re: Low Voltage Capacitor ETG
spectre, Sat Nov 01 2014, 04:35PM
well don't i feel like an idiot. should probably have read or checked, not trust my on brain. all the numbers were drawn form memory, which apparently is not that good...
back to the practical, let other people handle the theory and the science
as for charging the capacitor, i have built a variable transformer with ac and dc output. 0 to 4000 volts, 0 - 400 hertz. filtered through a custom sinus filter. use it for heat testing/drying and current/voltage supply on large generators and transformers.
spectre, Sat Nov 01 2014, 04:35PM
well don't i feel like an idiot. should probably have read or checked, not trust my on brain. all the numbers were drawn form memory, which apparently is not that good...
back to the practical, let other people handle the theory and the science
as for charging the capacitor, i have built a variable transformer with ac and dc output. 0 to 4000 volts, 0 - 400 hertz. filtered through a custom sinus filter. use it for heat testing/drying and current/voltage supply on large generators and transformers.
Re: Low Voltage Capacitor ETG
Houdini0118, Sat Nov 01 2014, 05:13PM
Why do you want a large chamber? From my experience with these they are detrimental unless you need the space to hold the electrodes the chamber should be the size of the projectile.
Houdini0118, Sat Nov 01 2014, 05:13PM
Why do you want a large chamber? From my experience with these they are detrimental unless you need the space to hold the electrodes the chamber should be the size of the projectile.
Re: Low Voltage Capacitor ETG
spectre, Sat Nov 01 2014, 07:24PM
the large chamber idea was to have enough gas/material to plasmatize(?). this went out the window since a cant use my low voltage capacitors. they have a combined power of 64 kJ. (16 Volt and 500 Farad)
the chamber size will now be reduced, will be using tungsten-alloy as electrodes, from high temp welding equipment.
what gases can i experiment with? have access to argon, oxygen, acetylen, argon, nitrogen, xenon, helium, hydrogen, carbon disulfide, propane and butane. any more suggestions??
spectre, Sat Nov 01 2014, 07:24PM
the large chamber idea was to have enough gas/material to plasmatize(?). this went out the window since a cant use my low voltage capacitors. they have a combined power of 64 kJ. (16 Volt and 500 Farad)
the chamber size will now be reduced, will be using tungsten-alloy as electrodes, from high temp welding equipment.
what gases can i experiment with? have access to argon, oxygen, acetylen, argon, nitrogen, xenon, helium, hydrogen, carbon disulfide, propane and butane. any more suggestions??
Re: Low Voltage Capacitor ETG
hen918, Sat Nov 01 2014, 08:32PM
well if you want a big bang, why don't you just fill the chamber with hydrogen and oxygen? :)
hen918, Sat Nov 01 2014, 08:32PM
well if you want a big bang, why don't you just fill the chamber with hydrogen and oxygen? :)
Re: Low Voltage Capacitor ETG
Houdini0118, Sat Nov 01 2014, 09:02PM
Any amount of material will turn into plasma and as i understand it the less material the hotter what is there gets and the more it expands. With plasmas negative temperature coefficient you are better off with less material. I am not an expert on this however so i could be completely wrong.
Houdini0118, Sat Nov 01 2014, 09:02PM
Any amount of material will turn into plasma and as i understand it the less material the hotter what is there gets and the more it expands. With plasmas negative temperature coefficient you are better off with less material. I am not an expert on this however so i could be completely wrong.
Re: Low Voltage Capacitor ETG
spectre, Sat Nov 01 2014, 11:20PM
so what you are saying, i should apply vacuum to the chamber and fill it with whatever gas to somewhere between 0.1 and 0.9 bar (assuming normal pressure is 1 bar.)
and yes, a hydrogen/oxygen mix could be fun. maybe a chamber filled to 0.5 bar with the mixture.
will design the chamber to be excessively strong, made from chrome-moly steel or titanium...held together with bolt for easy dis-assembly for replacing electrodes and inspecting blast chamber. 6 or 8 M6 bolts, 8.8 grade, each bolt have a tear strength of around 2 metric tonnes.
spectre, Sat Nov 01 2014, 11:20PM
Houdini0118 wrote ...
Any amount of material will turn into plasma and as i understand it the less material the hotter what is there gets and the more it expands. With plasmas negative temperature coefficient you are better off with less material. I am not an expert on this however so i could be completely wrong.
Any amount of material will turn into plasma and as i understand it the less material the hotter what is there gets and the more it expands. With plasmas negative temperature coefficient you are better off with less material. I am not an expert on this however so i could be completely wrong.
so what you are saying, i should apply vacuum to the chamber and fill it with whatever gas to somewhere between 0.1 and 0.9 bar (assuming normal pressure is 1 bar.)
and yes, a hydrogen/oxygen mix could be fun. maybe a chamber filled to 0.5 bar with the mixture.
will design the chamber to be excessively strong, made from chrome-moly steel or titanium...held together with bolt for easy dis-assembly for replacing electrodes and inspecting blast chamber. 6 or 8 M6 bolts, 8.8 grade, each bolt have a tear strength of around 2 metric tonnes.
Re: Low Voltage Capacitor ETG
hen918, Sun Nov 02 2014, 12:55PM
You have to be very careful with hydrogen and oxygen; under pressure they can spontaneously combust, leave them at RTP or below.
You need everything as strong as possible (better over-engineered than under-engineered); I would use 12.9 bolts, they are hardly more expensive than 8.8 ones, and a lot stronger.
hen918, Sun Nov 02 2014, 12:55PM
You have to be very careful with hydrogen and oxygen; under pressure they can spontaneously combust, leave them at RTP or below.
You need everything as strong as possible (better over-engineered than under-engineered); I would use 12.9 bolts, they are hardly more expensive than 8.8 ones, and a lot stronger.
Re: Low Voltage Capacitor ETG
spectre, Sun Nov 02 2014, 01:08PM
That was what i meant with 0.5 bar. On a pressure gauge set to 0 at normal the oxygen/hydrogen mix would read -0.5 bar
reason for 8.8 was that is our standard bolt, but yeah 12.9 is better... would making the blast chamber and barrel from titanium be worth the hassle of machining? it is not that expensive as a material, it is the machining that jacks the price up. (b*tch to work with)
spectre, Sun Nov 02 2014, 01:08PM
hen918 wrote ...
You have to be very careful with hydrogen and oxygen; under pressure they can spontaneously combust, leave them at RTP or below.
You need everything as strong as possible (better over-engineered than under-engineered); I would use 12.9 bolts, they are hardly more expensive than 8.8 ones, and a lot stronger.
You have to be very careful with hydrogen and oxygen; under pressure they can spontaneously combust, leave them at RTP or below.
You need everything as strong as possible (better over-engineered than under-engineered); I would use 12.9 bolts, they are hardly more expensive than 8.8 ones, and a lot stronger.
That was what i meant with 0.5 bar. On a pressure gauge set to 0 at normal the oxygen/hydrogen mix would read -0.5 bar
reason for 8.8 was that is our standard bolt, but yeah 12.9 is better... would making the blast chamber and barrel from titanium be worth the hassle of machining? it is not that expensive as a material, it is the machining that jacks the price up. (b*tch to work with)
Re: Low Voltage Capacitor ETG
hen918, Sun Nov 02 2014, 01:23PM
Oh I know, I'm a maintenance engineer that works in a company that machines titanium, nimonic, stainless, aluminium and brass for aerospace. The machines that breakdown most often are the ones that often machine titanium. Everyone moans when they get a job in titanium.
I don't think titanium would be worth, it stainless steel would probably be best: not too difficult to work with, not too expensive. The last thing you need is a titanium fire!
hen918, Sun Nov 02 2014, 01:23PM
Oh I know, I'm a maintenance engineer that works in a company that machines titanium, nimonic, stainless, aluminium and brass for aerospace. The machines that breakdown most often are the ones that often machine titanium. Everyone moans when they get a job in titanium.
I don't think titanium would be worth, it stainless steel would probably be best: not too difficult to work with, not too expensive. The last thing you need is a titanium fire!
Re: Low Voltage Capacitor ETG
Shrad, Sun Nov 02 2014, 07:09PM
if I was to make an ETG propelling charge, I'd use a tab of aluminium dipped in some kind of wetting agent which would leave only a pellicul, then dip it in sulfur powder and either dry or bake gently to make it stick (at safe, 50°C temp I'd say, but take care to verify it won't self-ignite)
this will make the same result as a flash powder mix if you have made sure to get the right ratio
maybe a dip in Fe2O3 would also prove to be of some use ;) and you'd be able to stock it safely
Shrad, Sun Nov 02 2014, 07:09PM
if I was to make an ETG propelling charge, I'd use a tab of aluminium dipped in some kind of wetting agent which would leave only a pellicul, then dip it in sulfur powder and either dry or bake gently to make it stick (at safe, 50°C temp I'd say, but take care to verify it won't self-ignite)
this will make the same result as a flash powder mix if you have made sure to get the right ratio
maybe a dip in Fe2O3 would also prove to be of some use ;) and you'd be able to stock it safely
Re: Low Voltage Capacitor ETG
hen918, Sun Nov 02 2014, 07:21PM
hummm, thermite ETG, interesting...
hen918, Sun Nov 02 2014, 07:21PM
hummm, thermite ETG, interesting...
Re: Low Voltage Capacitor ETG
Thomas W, Sun Nov 02 2014, 07:26PM
Hmm, this might be a little over complex... but what about this:
Bore out a barrel in stainless steel, then insert a strong ceramic tube inside, drilling holes in the bottom of the barrel for electrodes and a magnatron end. Fill up the tube with aluminium fileings and activate the magnatron, causing all those bits of aluminium to heat up, possibly even close to the plasma stage, then dischage your energy into there. The ceramic would be needed to keep anything from shorting out.... Its just an interesting idea.
Thomas W, Sun Nov 02 2014, 07:26PM
Hmm, this might be a little over complex... but what about this:
Bore out a barrel in stainless steel, then insert a strong ceramic tube inside, drilling holes in the bottom of the barrel for electrodes and a magnatron end. Fill up the tube with aluminium fileings and activate the magnatron, causing all those bits of aluminium to heat up, possibly even close to the plasma stage, then dischage your energy into there. The ceramic would be needed to keep anything from shorting out.... Its just an interesting idea.
Re: Low Voltage Capacitor ETG
spectre, Sun Nov 02 2014, 07:30PM
So, by using Fe2O3 on aluminium, i will be igniting and plasma-ing(?) thermite? sounds fun, will give that a go.
how about gun cotton?
to make it clear, this is a fact finding and ideas thread, i will start a build and fire thread when the parts are ready.
is there interest for a build thread, or do you guys just want to see things being shot?
and if a build thread, how detailed?
spectre, Sun Nov 02 2014, 07:30PM
Shrad wrote ...
if I was to make an ETG propelling charge, I'd use a tab of aluminium dipped in some kind of wetting agent which would leave only a pellicul, then dip it in sulfur powder and either dry or bake gently to make it stick (at safe, 50°C temp I'd say, but take care to verify it won't self-ignite)
this will make the same result as a flash powder mix if you have made sure to get the right ratio
maybe a dip in Fe2O3 would also prove to be of some use ;) and you'd be able to stock it safely
if I was to make an ETG propelling charge, I'd use a tab of aluminium dipped in some kind of wetting agent which would leave only a pellicul, then dip it in sulfur powder and either dry or bake gently to make it stick (at safe, 50°C temp I'd say, but take care to verify it won't self-ignite)
this will make the same result as a flash powder mix if you have made sure to get the right ratio
maybe a dip in Fe2O3 would also prove to be of some use ;) and you'd be able to stock it safely
So, by using Fe2O3 on aluminium, i will be igniting and plasma-ing(?) thermite? sounds fun, will give that a go.
how about gun cotton?
to make it clear, this is a fact finding and ideas thread, i will start a build and fire thread when the parts are ready.
is there interest for a build thread, or do you guys just want to see things being shot?
and if a build thread, how detailed?
Re: Low Voltage Capacitor ETG
Shrad, Sun Nov 02 2014, 08:23PM
I guess the vaporization of the aluminium pad will also vaporize the deposit it holds, and that the reaction occuring between aluminium and the other product will be catalysed by vaporisation and pressure buildup...
another go would be to make a barrel bottom out of ceramid and a separate barrel, with electrodes at the bottom of the barrel cup, and ram flash or thermite powder in the cup to replace the fuse
Shrad, Sun Nov 02 2014, 08:23PM
I guess the vaporization of the aluminium pad will also vaporize the deposit it holds, and that the reaction occuring between aluminium and the other product will be catalysed by vaporisation and pressure buildup...
another go would be to make a barrel bottom out of ceramid and a separate barrel, with electrodes at the bottom of the barrel cup, and ram flash or thermite powder in the cup to replace the fuse
Re: Low Voltage Capacitor ETG
hen918, Sun Nov 02 2014, 09:36PM
sounds like this ETG will end up shooting iron vapour. I'd like to see it!
The thermite reaction does not release any gas though, so it wouldn't accelerate the projectile much, and you would have to use a non-oxygen gas to stop it reacting with the aluminium instead of the iron oxide.
hen918, Sun Nov 02 2014, 09:36PM
sounds like this ETG will end up shooting iron vapour. I'd like to see it!
The thermite reaction does not release any gas though, so it wouldn't accelerate the projectile much, and you would have to use a non-oxygen gas to stop it reacting with the aluminium instead of the iron oxide.
Re: Low Voltage Capacitor ETG
Shrad, Mon Nov 03 2014, 08:25AM
haha I guess you're right
as far as I know, the flash powder mix will release a decent amount of gas when used with KNO3 or KMnO4 due to the oxygen, so I guess that the aluminium pad can be dipped in KNO3 paste before it is in sulfur...
do not try this with KMnO4
Shrad, Mon Nov 03 2014, 08:25AM
haha I guess you're right
as far as I know, the flash powder mix will release a decent amount of gas when used with KNO3 or KMnO4 due to the oxygen, so I guess that the aluminium pad can be dipped in KNO3 paste before it is in sulfur...
do not try this with KMnO4
Re: Low Voltage Capacitor ETG
Ash Small, Sat Nov 29 2014, 01:24PM
If you use stainless I'd recommend at least grade 316 which is a lot stronger than the common 304 grade due to added molybnum and more nickel. Stronger types are available, but 316 is one of the more common ausenitic stainless steels.
Ash Small, Sat Nov 29 2014, 01:24PM
If you use stainless I'd recommend at least grade 316 which is a lot stronger than the common 304 grade due to added molybnum and more nickel. Stronger types are available, but 316 is one of the more common ausenitic stainless steels.
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