Plastic Insulated Wire Usable For Coil In A Coil Gun?
evilgecko, Thu Apr 13 2006, 06:07AMI building a relativly large coil gun (3.5kJ stored energy) with currents travelling through the coil at (3000 to 6000A). The largest enamled wire I can source is 18SWG (1.0mm). I need about 10SWG to handle a 3000A current. I was wondering if I could use plastic insulated copper wire instead of the traditional without sacrificing to much efficiency. I know the primary reason why enamled wire is used is because you can fit more turns in the same space. But if i found thin insulated wire it wouldn't effect the coil diameter and length that much would it?
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
Bjørn, Thu Apr 13 2006, 06:18AM
If the insulation is very thin compared to the diameter of the wire it will not make a large difference. You can also use several strands of thinner wire in parallel.
Bjørn, Thu Apr 13 2006, 06:18AM
If the insulation is very thin compared to the diameter of the wire it will not make a large difference. You can also use several strands of thinner wire in parallel.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
evilgecko, Thu Apr 13 2006, 08:29AM
So if I ran two strands of 18SWG side by side on the coil it would be equal to the diameter doubled, no thinking about it wouldn't it be the cross section doubled? But since they are lineraly related it doesn't matter what you use.
So using 2 strands of 18AWG (not SWG) would equal about one strand of 12AWG.
Is there any difference between the resistances? I calculated it and it seemed that the resistance of two strands of 18AWG is about twice that of a 12AWG strand of equal length!
evilgecko, Thu Apr 13 2006, 08:29AM
So if I ran two strands of 18SWG side by side on the coil it would be equal to the diameter doubled, no thinking about it wouldn't it be the cross section doubled? But since they are lineraly related it doesn't matter what you use.
So using 2 strands of 18AWG (not SWG) would equal about one strand of 12AWG.
Is there any difference between the resistances? I calculated it and it seemed that the resistance of two strands of 18AWG is about twice that of a 12AWG strand of equal length!
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
Bjørn, Thu Apr 13 2006, 08:57AM
If you double the number of wires you will double the area and halve the resistance for DC current. Only the total area is interesting.
Because of the skin effect (http://wiki.4hv.org/index.php/Skin_effect) using several insulated strands can in some cases be more efficient than one thick wire.
Bjørn, Thu Apr 13 2006, 08:57AM
If you double the number of wires you will double the area and halve the resistance for DC current. Only the total area is interesting.
Because of the skin effect (http://wiki.4hv.org/index.php/Skin_effect) using several insulated strands can in some cases be more efficient than one thick wire.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
Simon, Fri Apr 14 2006, 06:27AM
Using insulated wire will have a significant impact on current density. If you think about it, for just a typical bit of insulated wire the density is probably something like half. If you're an amateur, however, sometimes you just have to work with what you have.
Simon, Fri Apr 14 2006, 06:27AM
evilgecko wrote ...
So if I ran two strands of 18SWG side by side on the coil it would be equal to the diameter doubled, no thinking about it wouldn't it be the cross section doubled? But since they are lineraly related it doesn't matter what you use.
It does matter but you got it right with the area. Remember, area is proportional to the square on diameter.So if I ran two strands of 18SWG side by side on the coil it would be equal to the diameter doubled, no thinking about it wouldn't it be the cross section doubled? But since they are lineraly related it doesn't matter what you use.
Using insulated wire will have a significant impact on current density. If you think about it, for just a typical bit of insulated wire the density is probably something like half. If you're an amateur, however, sometimes you just have to work with what you have.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
evilgecko, Fri Apr 14 2006, 12:38PM
Hmmm ok plastic insulated wire isn't seeming such a good coice then. I'm looking to make a powerful gun with 3% efficiency (I'm hoping for a 15g bullet to exit at 140ms-1). Is it posible to insulate your own wire? Maybe a nitrocellulose kind of laquer which is flexible.
evilgecko, Fri Apr 14 2006, 12:38PM
Hmmm ok plastic insulated wire isn't seeming such a good coice then. I'm looking to make a powerful gun with 3% efficiency (I'm hoping for a 15g bullet to exit at 140ms-1). Is it posible to insulate your own wire? Maybe a nitrocellulose kind of laquer which is flexible.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
rupidust, Fri Apr 14 2006, 02:31PM
Dont dispmiss without actually trying. 3% is small and I see no reason as to why plastic insulated wire could not get 3%. Also see no reason not to wind the coil, test, measure, then wind enamel coil whenever such wire becomes available. You migh end up winding 4+ coils regardless of insulation. Now as for this power level you want, 15 grams at 140 meters/second = 147 Joules of kinetic energy. This will require 4,410 Joules of potential energy for 3% conversion. If this will be in a single stage, then you will need a fast pulse and very high voltage. Single stage or multiple stage, you are going to need skills above and beyond posting about which wire insulation to use to get a 15 gram slug to that energy level.
rupidust, Fri Apr 14 2006, 02:31PM
evilgecko wrote ...
Hmmm ok plastic insulated wire isn't seeming such a good coice then. I'm looking to make a powerful gun with 3% efficiency (I'm hoping for a 15g bullet to exit at 140ms-1). Is it posible to insulate your own wire? Maybe a nitrocellulose kind of laquer which is flexible.
Hmmm ok plastic insulated wire isn't seeming such a good coice then. I'm looking to make a powerful gun with 3% efficiency (I'm hoping for a 15g bullet to exit at 140ms-1). Is it posible to insulate your own wire? Maybe a nitrocellulose kind of laquer which is flexible.
Dont dispmiss without actually trying. 3% is small and I see no reason as to why plastic insulated wire could not get 3%. Also see no reason not to wind the coil, test, measure, then wind enamel coil whenever such wire becomes available. You migh end up winding 4+ coils regardless of insulation. Now as for this power level you want, 15 grams at 140 meters/second = 147 Joules of kinetic energy. This will require 4,410 Joules of potential energy for 3% conversion. If this will be in a single stage, then you will need a fast pulse and very high voltage. Single stage or multiple stage, you are going to need skills above and beyond posting about which wire insulation to use to get a 15 gram slug to that energy level.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
evilgecko, Fri Apr 14 2006, 11:13PM
Sorry that speed was calulated for a 10g projectile. But I deicided to make both the coil and projectile 30mm long and the projectile turned out to weigh 15g.
Total stored energy = 3645J
3% efficiency = 109.35J and a speed of 121ms-1
The problem I'm facing is that yes, I need short pulses but no the maximum voltage my SCR's can handle is 600V. I have got only 2 SCR's which can handle a pulse of 3300A. If I make it two stage the projectile will be accelerated to 85.4ms-1 in the first coil (assuming each coils efficiency is 3% and cap bank is halved).
If I make the coil 30mm long then it will take 0.35ms (assuming constant acceleration t=2d/v) to travel from outside the coil to the center. This should be the maximum pulse width!
Using the MGC calculator the pulse width is 1.83ms and peak at 1.07ms. It is quite over dampened.
How can I prevent this. One way would be to use a bigger projectile, but that would decrease velocity. Is 120ms-1 unrealistic? I guess a larger projectile will have some momentum. I aiming for the gun to give the most punching power (ie can piercing).
Or decrease the capacitance but that seems self sacrificial.
Any ideas?
evilgecko, Fri Apr 14 2006, 11:13PM
Sorry that speed was calulated for a 10g projectile. But I deicided to make both the coil and projectile 30mm long and the projectile turned out to weigh 15g.
Total stored energy = 3645J
3% efficiency = 109.35J and a speed of 121ms-1
The problem I'm facing is that yes, I need short pulses but no the maximum voltage my SCR's can handle is 600V. I have got only 2 SCR's which can handle a pulse of 3300A. If I make it two stage the projectile will be accelerated to 85.4ms-1 in the first coil (assuming each coils efficiency is 3% and cap bank is halved).
If I make the coil 30mm long then it will take 0.35ms (assuming constant acceleration t=2d/v) to travel from outside the coil to the center. This should be the maximum pulse width!
Using the MGC calculator the pulse width is 1.83ms and peak at 1.07ms. It is quite over dampened.
How can I prevent this. One way would be to use a bigger projectile, but that would decrease velocity. Is 120ms-1 unrealistic? I guess a larger projectile will have some momentum. I aiming for the gun to give the most punching power (ie can piercing).
Or decrease the capacitance but that seems self sacrificial.
Any ideas?
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
The Zander, Sat Apr 15 2006, 01:26AM
Just out of curiosity what are your capacitor banks apecs? 6000A does seem a little optimistic, and even if it's not 18AWG wire should be able to handle that for the length of a pulse (probably < 1mS with a projectile that light). we can use high school chem to prove this:
lets assume your coil has an inner diameter of 1/4" is 1" long and is comprised of 5 layers of 18AWG wire (these numbers are completely arbitrary, with no real bearing on your project, once we have specs for your coil we can derive more conclusive results).
the specific heat capacity of pure copper is ~380J/KG-K, using barrys inductor simulator (thanx barry, you apps are awsome) you see that you have 20g of copper in your coil. lets calculate the power dissipated using I^2R, where I will be 4000A (to account for the fact that the current ramps up then down, and i really don't feeling like doing any integration), and R (again from barry) is 0.062A.
[(380)(0.02 Kg) / ((4000^2 A)(0.062 ohms)(0.001 seconds))]^-1 = Delta T (degrees)
After everything is said and done, after one shot using 18AWG wire and the coil described above you would see a temperature increase of ~130 degrees C, and this also assumes the coil is in a vaccum (aka: no heat is dissipated to the environment). i think if you space your shots far enough apar your coil will easily survive.
Just my $0.02CDN
-TheZander
[edit]
in regards to achieving the most punching power, i would tend towards a heavier projectile (1/2" diamater maybe and inch long), from what we seen, because of the inherently long pulse times big caps like your yeild heavier = more efficient
The Zander, Sat Apr 15 2006, 01:26AM
Just out of curiosity what are your capacitor banks apecs? 6000A does seem a little optimistic, and even if it's not 18AWG wire should be able to handle that for the length of a pulse (probably < 1mS with a projectile that light). we can use high school chem to prove this:
lets assume your coil has an inner diameter of 1/4" is 1" long and is comprised of 5 layers of 18AWG wire (these numbers are completely arbitrary, with no real bearing on your project, once we have specs for your coil we can derive more conclusive results).
the specific heat capacity of pure copper is ~380J/KG-K, using barrys inductor simulator (thanx barry, you apps are awsome) you see that you have 20g of copper in your coil. lets calculate the power dissipated using I^2R, where I will be 4000A (to account for the fact that the current ramps up then down, and i really don't feeling like doing any integration), and R (again from barry) is 0.062A.
[(380)(0.02 Kg) / ((4000^2 A)(0.062 ohms)(0.001 seconds))]^-1 = Delta T (degrees)
After everything is said and done, after one shot using 18AWG wire and the coil described above you would see a temperature increase of ~130 degrees C, and this also assumes the coil is in a vaccum (aka: no heat is dissipated to the environment). i think if you space your shots far enough apar your coil will easily survive.
Just my $0.02CDN
-TheZander
[edit]
in regards to achieving the most punching power, i would tend towards a heavier projectile (1/2" diamater maybe and inch long), from what we seen, because of the inherently long pulse times big caps like your yeild heavier = more efficient
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
evilgecko, Sat Apr 15 2006, 01:54AM
I've always wondered what 20g of vaporised copper would look and sound like. 130 degrees C! Almost seems impossible for that amount of copper tor reach that in 1 millisecond. My cap bank consists of 20 450V 1800uF caps which I picked up for $4 each. I could only reach 6000A if i paralleled the two SCR's and I'm tending towards the multi coil technique. My projectile is 10mm in diameter (nearly 1/2 inch like you said) and 30mm long from point to base.
evilgecko, Sat Apr 15 2006, 01:54AM
I've always wondered what 20g of vaporised copper would look and sound like. 130 degrees C! Almost seems impossible for that amount of copper tor reach that in 1 millisecond. My cap bank consists of 20 450V 1800uF caps which I picked up for $4 each. I could only reach 6000A if i paralleled the two SCR's and I'm tending towards the multi coil technique. My projectile is 10mm in diameter (nearly 1/2 inch like you said) and 30mm long from point to base.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
The Zander, Sat Apr 15 2006, 02:53AM
i does seem quick, but you are dissipating alot of power, and it was a purely theorectical calculation to demonstrate that given atmospheric heat dissipation, and perhapes slightly lower current (4000 rather than 6000) your 18AWG enameled wire should suffice, not to mention you eliminate the plastic insulation (which will fail at a lower temperature than the enamel, and you increase your magnetic flux density considerably).
-TheZander
The Zander, Sat Apr 15 2006, 02:53AM
i does seem quick, but you are dissipating alot of power, and it was a purely theorectical calculation to demonstrate that given atmospheric heat dissipation, and perhapes slightly lower current (4000 rather than 6000) your 18AWG enameled wire should suffice, not to mention you eliminate the plastic insulation (which will fail at a lower temperature than the enamel, and you increase your magnetic flux density considerably).
-TheZander
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
Sulaiman, Sat Apr 15 2006, 06:56AM
Since you need to use more than one switch/thyristor due to Peak current,
rather than using one thick wire or a few thinner wires per coil
you could make multiple coils with one thyristor per coil.
You could make each coil length similar to projectile length .... conventional multi-stage CG
OR
You could make each stage using coils of 1/2 (1/3, 1/4...) the length of the projectile
and use 2 (3, 4...) thyristors, with an adjustable delay per thyristor.
In other words, each stage (maybe only one stage) is made of a multi-stage accelerator.
I imagine less 'suckback' so possibly better efficiency.
Just an untried idea for you to ponder ;)
(If it works I name this Multi-Mini-Coil-Gun MMCG just for the sake of confusion)
P.S. You could treat each multi-coil stage as a single stage
and 'fire' all thyristors for one stage simultaneaously,
OR
Have precise variable delays per thyristor (monostable timers etc.)
OR
you could trigger the first thyristor per major-stage as required
and use a few turns of wire on each coil to trigger the thyristor of the next sub-stage
a resistor in series with the trigger coil and a capacitor across the gate to ground
could give a little delay per sub-stage.
e.g. 400V supply, 40-turn accelerating coil, 1-turn pickup-coil for about 10V trigger voltage.
Sulaiman, Sat Apr 15 2006, 06:56AM
Since you need to use more than one switch/thyristor due to Peak current,
rather than using one thick wire or a few thinner wires per coil
you could make multiple coils with one thyristor per coil.
You could make each coil length similar to projectile length .... conventional multi-stage CG
OR
You could make each stage using coils of 1/2 (1/3, 1/4...) the length of the projectile
and use 2 (3, 4...) thyristors, with an adjustable delay per thyristor.
In other words, each stage (maybe only one stage) is made of a multi-stage accelerator.
I imagine less 'suckback' so possibly better efficiency.
Just an untried idea for you to ponder ;)
(If it works I name this Multi-Mini-Coil-Gun MMCG just for the sake of confusion)
P.S. You could treat each multi-coil stage as a single stage
and 'fire' all thyristors for one stage simultaneaously,
OR
Have precise variable delays per thyristor (monostable timers etc.)
OR
you could trigger the first thyristor per major-stage as required
and use a few turns of wire on each coil to trigger the thyristor of the next sub-stage
a resistor in series with the trigger coil and a capacitor across the gate to ground
could give a little delay per sub-stage.
e.g. 400V supply, 40-turn accelerating coil, 1-turn pickup-coil for about 10V trigger voltage.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
FastMHz, Sat Apr 15 2006, 05:43PM
My induction launcher is feeding 3.5kj into 14awg coil with minimal heating after a shot - I don't think you need 10awg. I got the wire at www.bulkwire.com.
FastMHz, Sat Apr 15 2006, 05:43PM
My induction launcher is feeding 3.5kj into 14awg coil with minimal heating after a shot - I don't think you need 10awg. I got the wire at www.bulkwire.com.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
Electroholic, Sat Apr 15 2006, 06:08PM
A disk launcher coil? pancake right?
whats the total lenght of the wire?
whats the surface area?
coil gun coils have a lot more turns,
and have more layers.
If you are not planning to do more than 1 round every 5 min,
~14 awg is ok.
Electroholic, Sat Apr 15 2006, 06:08PM
A disk launcher coil? pancake right?
whats the total lenght of the wire?
whats the surface area?
coil gun coils have a lot more turns,
and have more layers.
If you are not planning to do more than 1 round every 5 min,
~14 awg is ok.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
FastMHz, Sat Apr 15 2006, 10:05PM
Yes, dual layer pancake coil, with each layer paralleled...the coil is 3.5" in diameter using 14awg wire, so there isn't as much as in the average CG, which means the amps are even higher. I do have a few CGs made with the same wire and they can be fired about 3 times before needing a cooling period. The disc launcher can be fired every couple of minutes.
FastMHz, Sat Apr 15 2006, 10:05PM
Yes, dual layer pancake coil, with each layer paralleled...the coil is 3.5" in diameter using 14awg wire, so there isn't as much as in the average CG, which means the amps are even higher. I do have a few CGs made with the same wire and they can be fired about 3 times before needing a cooling period. The disc launcher can be fired every couple of minutes.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
Quantum Singularity, Sun Apr 16 2006, 12:15AM
I myself would go ahead and try the plastic insulated wire. Its cheap, at worse your out about $1 and a half hours work (approximate of course). You will loose efficiency probably, so thats up to you and your goals, although I like to prototype stuff first and build a more refined final design later. I have built flat spiral coils for induction launchers like fast MHz and due to my budget at the time (poor college kid). They were #12awg and #8awg standard houshold wiring from Home Depot (probably a dollar or two worth of wire). I had a real blast launching stuff, it was way more powerful than I needed, and I didnt not have any means of calculating efficiency or reason too for that matter. On my next design I am going to use some #13 awg magnet wire since I got some locally at a motor repair shop. And hopefully I will have a chrono so I can measure speeds and calculate velocities.
Quantum Singularity, Sun Apr 16 2006, 12:15AM
I myself would go ahead and try the plastic insulated wire. Its cheap, at worse your out about $1 and a half hours work (approximate of course). You will loose efficiency probably, so thats up to you and your goals, although I like to prototype stuff first and build a more refined final design later. I have built flat spiral coils for induction launchers like fast MHz and due to my budget at the time (poor college kid). They were #12awg and #8awg standard houshold wiring from Home Depot (probably a dollar or two worth of wire). I had a real blast launching stuff, it was way more powerful than I needed, and I didnt not have any means of calculating efficiency or reason too for that matter. On my next design I am going to use some #13 awg magnet wire since I got some locally at a motor repair shop. And hopefully I will have a chrono so I can measure speeds and calculate velocities.
Re: Plastic Insulated Wire Usable For Coil In A Coil Gun?
evilgecko, Sun Apr 16 2006, 11:17PM
Yeah I'll give it a go. Dare to be different. iAlthough I'm building it because I find it interesting, I'm trying to incorporate it into a school science fair project as well. And using plastic insulated wire could put an spin on the whole joe average design.
evilgecko, Sun Apr 16 2006, 11:17PM
Yeah I'll give it a go. Dare to be different. iAlthough I'm building it because I find it interesting, I'm trying to incorporate it into a school science fair project as well. And using plastic insulated wire could put an spin on the whole joe average design.
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