Coil construciton: 80amp through 30aw wire?
PlayNice, Tue Dec 11 2012, 10:31PMCan anyone tell me what would happen if I make a coil from a 30 gauge wire, about 40 turns, only about 4ft of wire. 4 ft of wire should have about .4 ohm resistance. I need to run pulses of 80amp 40v through it. Can the coil survive that much amps if I keep the coil at the rated temp, say below 120c?
Seems to me that 80 amps through 30aw wire is a lot but 40v / .4ohm seems to allow up to 100amps? Whats wrong with my calculations?
I need a coil that is 1 layer, 1cm wide, with a power supply of 40v 80a max and need to figure out the best geometry for the coil.
Thanks everyone
Re: Coil construciton: 80amp through 30aw wire?
Barry, Wed Dec 12 2012, 12:41PM
This is relatively large current for a very small wire. So first look at the wire's fuse limit: at high current density the wire will melt like a fuse.
This manufacturer's datasheet at www.hmwire.com says that 30 gauge wire will melt at 7.5 amps.
Barry
Barry, Wed Dec 12 2012, 12:41PM
supak1 wrote ...
What would happen if I make a coil from a 30 gauge wire, about 40 turns, only about 4ft of wire. 4 ft of wire should have about .4 ohm resistance. I need to run pulses of 80amp 40v through it. Can the coil survive that much amps if I keep the coil at the rated temp?
What would happen if I make a coil from a 30 gauge wire, about 40 turns, only about 4ft of wire. 4 ft of wire should have about .4 ohm resistance. I need to run pulses of 80amp 40v through it. Can the coil survive that much amps if I keep the coil at the rated temp?
This is relatively large current for a very small wire. So first look at the wire's fuse limit: at high current density the wire will melt like a fuse.
This manufacturer's datasheet at www.hmwire.com says that 30 gauge wire will melt at 7.5 amps.
Barry
Re: Coil construciton: 80amp through 30aw wire?
BigBad, Wed Dec 12 2012, 02:20PM
How long do you need it to carry the current for? It can do it, for a short time.
You can get the heat capacity for the metal of the wire, and plug in the energy, and calculate the heat rise.
Make sure you allow for the rise of resistance with temperature though. Also I think that hotspots can sometimes form, and then you can get thermal runaway, so it's a good idea to allow for some leeway.
BigBad, Wed Dec 12 2012, 02:20PM
How long do you need it to carry the current for? It can do it, for a short time.
You can get the heat capacity for the metal of the wire, and plug in the energy, and calculate the heat rise.
Make sure you allow for the rise of resistance with temperature though. Also I think that hotspots can sometimes form, and then you can get thermal runaway, so it's a good idea to allow for some leeway.
Re: Coil construciton: 80amp through 30aw wire?
PlayNice, Wed Dec 12 2012, 07:07PM
Fuses are exactly what I was thinking, didn't seem right that 80a would go through 30a wire.
Its not for long, coil would rise to 80a in 1 - .01ms. Problem I see is that I may need lots of HZ so. My coil will be very low inductance, goal is to make a very fast coil.
Metal is just pure copper with 200c shielding, I wish I know how to figure out the heat, is there a calculator? What do I search for?
BTW I am planing on coiling the coil with water, this experimental setup where I am going to have my coil sit in water, the actual coil rings/wire will be sitting in water for maximum surface area.
PlayNice, Wed Dec 12 2012, 07:07PM
Fuses are exactly what I was thinking, didn't seem right that 80a would go through 30a wire.
Its not for long, coil would rise to 80a in 1 - .01ms. Problem I see is that I may need lots of HZ so. My coil will be very low inductance, goal is to make a very fast coil.
Metal is just pure copper with 200c shielding, I wish I know how to figure out the heat, is there a calculator? What do I search for?
BTW I am planing on coiling the coil with water, this experimental setup where I am going to have my coil sit in water, the actual coil rings/wire will be sitting in water for maximum surface area.
Re: Coil construciton: 80amp through 30aw wire?
Yandersen, Wed Dec 12 2012, 09:35PM
OMG, it will handle it without a problem if it is a single spike. You are building a reluctance coilgun? The thicker the wire, the longer the current will oscillate in it. Just use 2mm copper stick if you are able to bend it.
Yandersen, Wed Dec 12 2012, 09:35PM
OMG, it will handle it without a problem if it is a single spike. You are building a reluctance coilgun? The thicker the wire, the longer the current will oscillate in it. Just use 2mm copper stick if you are able to bend it.
Re: Coil construciton: 80amp through 30aw wire?
PlayNice, Wed Dec 12 2012, 10:35PM
Yes building a reluctance coilgun. My projectile is 1cm so I want to make the length of the coil 1cm. I also want a really really fast coil, so only about 10-20uH and one layer. To get 10-20uH I need to have about 40 turns and to fit 40 turns in 1cm 1layer I need to use a 30aw wire.
Yandersen are you sure I can do quick 1ms or less pulses of 80a through 30aw wire? How many HZ could I run through such coil at 40V* 80a?
2mm wire is 12aw, I'll only get 5 turns with that, that is way too low of inductance.
PlayNice, Wed Dec 12 2012, 10:35PM
Yes building a reluctance coilgun. My projectile is 1cm so I want to make the length of the coil 1cm. I also want a really really fast coil, so only about 10-20uH and one layer. To get 10-20uH I need to have about 40 turns and to fit 40 turns in 1cm 1layer I need to use a 30aw wire.
Yandersen are you sure I can do quick 1ms or less pulses of 80a through 30aw wire? How many HZ could I run through such coil at 40V* 80a?
2mm wire is 12aw, I'll only get 5 turns with that, that is way too low of inductance.
Re: Coil construciton: 80amp through 30aw wire?
Maxwell, Wed Dec 12 2012, 11:47PM
I'm with Yandersen on this one. A 1ms pulse of 80amps in 30AWG is no big deal. Although I have a feeling it'll be far less than 80 amps, and much more than 1ms.
Maxwell, Wed Dec 12 2012, 11:47PM
I'm with Yandersen on this one. A 1ms pulse of 80amps in 30AWG is no big deal. Although I have a feeling it'll be far less than 80 amps, and much more than 1ms.
Re: Coil construciton: 80amp through 30aw wire?
Yandersen, Thu Dec 13 2012, 12:48AM
Supak, didn't i told you about the spiral flat coils and flat projectiles for reluctance coilgun? Wanna try the most inefficient way to build the most inefficient type of coilguns (at such energies)? OK, go ahead. Maybe your projectile will move a little proving that your thing may "work"...
Your wire will sustain single pulse, not continuing series of those. Trying to plug your coil to the outlet, touching the wires for a little time, huh? It will burn. But be more aware about the soldering points - they may blow before the wire. Put drops of solder all around wires.
Yandersen, Thu Dec 13 2012, 12:48AM
Supak, didn't i told you about the spiral flat coils and flat projectiles for reluctance coilgun? Wanna try the most inefficient way to build the most inefficient type of coilguns (at such energies)? OK, go ahead. Maybe your projectile will move a little proving that your thing may "work"...
Your wire will sustain single pulse, not continuing series of those. Trying to plug your coil to the outlet, touching the wires for a little time, huh? It will burn. But be more aware about the soldering points - they may blow before the wire. Put drops of solder all around wires.
Re: Coil construciton: 80amp through 30aw wire?
PlayNice, Thu Dec 13 2012, 02:16AM
I didn't understand what you meant by "Just use 2mm copper stick"? Please explain. Thanks for the heads up on the soldering points, something I hadn't though about. I should be able to keep the pulse below 1ms. I'll be using IGBTs with a opto-switch for fast trigger times. Thinking about using compressed air to speed up the projectile to X speed and drop the amount of time the projectile is the the opto-switch to less then 1ms, and then the multi coils will speed it up more.
PlayNice, Thu Dec 13 2012, 02:16AM
I didn't understand what you meant by "Just use 2mm copper stick"? Please explain. Thanks for the heads up on the soldering points, something I hadn't though about. I should be able to keep the pulse below 1ms. I'll be using IGBTs with a opto-switch for fast trigger times. Thinking about using compressed air to speed up the projectile to X speed and drop the amount of time the projectile is the the opto-switch to less then 1ms, and then the multi coils will speed it up more.
Re: Coil construciton: 80amp through 30aw wire?
Maxwell, Thu Dec 13 2012, 02:30AM
That's cheating ;)
Hybrid coils have been discussed before - electo-chemical, exploding wire, compressed air, spring-start, etc....
If you're looking down that road, you realistically should switch out from HV completely. The major benefit of these CG's is that they are damn close to being silent, relying purely on electro-magnetism.
Some people have done 'injector' coils which is essentially a small coil to accelerate the armature into the main coil.
Maxwell, Thu Dec 13 2012, 02:30AM
That's cheating ;)
Hybrid coils have been discussed before - electo-chemical, exploding wire, compressed air, spring-start, etc....
If you're looking down that road, you realistically should switch out from HV completely. The major benefit of these CG's is that they are damn close to being silent, relying purely on electro-magnetism.
Some people have done 'injector' coils which is essentially a small coil to accelerate the armature into the main coil.
Re: Coil construciton: 80amp through 30aw wire?
PlayNice, Thu Dec 13 2012, 02:52AM
Yea I could do that too, use one higher inductance coil then use low inductance coils on all the rest. I was thinking compressed air because modifying a bb gun will be easy and it will give the general shape for the whole gun.
PlayNice, Thu Dec 13 2012, 02:52AM
Yea I could do that too, use one higher inductance coil then use low inductance coils on all the rest. I was thinking compressed air because modifying a bb gun will be easy and it will give the general shape for the whole gun.
Re: Coil construciton: 80amp through 30aw wire?
Yandersen, Thu Dec 13 2012, 04:40AM
IGBT for reluctance coilgun?!?!
The push-force projectile experiences is proportional to the square of the current and speed of it's rize (which is proportional to the frequency of oscillations). Reluctance coilguns are purely LC oscillators, which are easily build on non-polar caps and bi-directional thyristors. For a little current IGBT can handle and a single pulse you will not be able to push a projectile out of the coil. But we will see, good luck. ;)
Yandersen, Thu Dec 13 2012, 04:40AM
IGBT for reluctance coilgun?!?!
The push-force projectile experiences is proportional to the square of the current and speed of it's rize (which is proportional to the frequency of oscillations). Reluctance coilguns are purely LC oscillators, which are easily build on non-polar caps and bi-directional thyristors. For a little current IGBT can handle and a single pulse you will not be able to push a projectile out of the coil. But we will see, good luck. ;)
Re: Coil construciton: 80amp through 30aw wire?
PlayNice, Thu Dec 13 2012, 05:00AM
IGBT can handle 60amps and 160amps if pulses. If not IGBT then what would you use for switching? I don't have to use IGBTs I just though it was a good idea because they can produce a nice square wave. I'd love to hear your input
PlayNice, Thu Dec 13 2012, 05:00AM
IGBT can handle 60amps and 160amps if pulses. If not IGBT then what would you use for switching? I don't have to use IGBTs I just though it was a good idea because they can produce a nice square wave. I'd love to hear your input
Re: Coil construciton: 80amp through 30aw wire?
Yandersen, Thu Dec 13 2012, 05:34AM
"...easily build on non-polar caps and bi-directional thyristors." - who did just said that right above your post, huh?.. :)
Yandersen, Thu Dec 13 2012, 05:34AM
"...easily build on non-polar caps and bi-directional thyristors." - who did just said that right above your post, huh?.. :)
Re: Coil construciton: 80amp through 30aw wire?
klugesmith, Thu Dec 13 2012, 05:36AM
IMHO, a pneumatic injector for a coilgun is like using a blowtorch to light a match, except perhaps for seriously big and expensive CG's.
80 amps in your 0.4 ohms of 30AWG wire represents a power of 2560 watts, not counting thermal increase in R. If you limit the pulse duration to 1 ms, that's 2.56 joules of heat to the coil. My unreviewed calculation says the wire temperature rise would be between 10 and 15 degrees C.
So at 10% efficiency, you would add only 1/4 J of energy to the projectile.
For reference, the UK allows unlicenced air guns up to muzzle energy of 12 ft-lbf (16 J).
What's the energy of your BB gun? Is it one of those Airsoft toys?
If you have compressed air, please consider:
A projectile area of 1 cm^2, at only 120 psig (8.2 bar), receives 83 newtons of force.
In 1 meter that could impart 83 joules of kinetic energy.
[edit]
klugesmith, Thu Dec 13 2012, 05:36AM
supak1 wrote ...
Yea I could do that too, use one higher inductance coil then use low inductance coils on all the rest. I was thinking compressed air because modifying a bb gun will be easy and it will give the general shape for the whole gun.
Uh, as maxwell said, why not use the air gun by itself and skip the coil?Yea I could do that too, use one higher inductance coil then use low inductance coils on all the rest. I was thinking compressed air because modifying a bb gun will be easy and it will give the general shape for the whole gun.
IMHO, a pneumatic injector for a coilgun is like using a blowtorch to light a match, except perhaps for seriously big and expensive CG's.
80 amps in your 0.4 ohms of 30AWG wire represents a power of 2560 watts, not counting thermal increase in R. If you limit the pulse duration to 1 ms, that's 2.56 joules of heat to the coil. My unreviewed calculation says the wire temperature rise would be between 10 and 15 degrees C.
So at 10% efficiency, you would add only 1/4 J of energy to the projectile.
For reference, the UK allows unlicenced air guns up to muzzle energy of 12 ft-lbf (16 J).
What's the energy of your BB gun? Is it one of those Airsoft toys?
If you have compressed air, please consider:
A projectile area of 1 cm^2, at only 120 psig (8.2 bar), receives 83 newtons of force.
In 1 meter that could impart 83 joules of kinetic energy.
[edit]
Maxwell wrote ...
If you're looking down that road, you realistically should switch out from HV completely.
The major benefit of these CG's is that they are damn close to being silent ...,
Same goes for air guns designed for chamber pressure to match atmospheric pressure when projectile leaves the muzzle. Tuning for efficiency = tuning for quietness, as in my old CO2 mortar that used a pneumatically exploded soda bottle as propellant charge. Impressively quiet as it lofted a 16.5 lb concrete piston for more than 5 seconds. By scale & stopwatch, muzzle energy was > 2000 J.If you're looking down that road, you realistically should switch out from HV completely.
The major benefit of these CG's is that they are damn close to being silent ...,
Re: Coil construciton: 80amp through 30aw wire?
Yandersen, Thu Dec 13 2012, 05:39AM
To make bi-dir thyristor conducting, wind two coils around a little ferrite ring transformer: one coil connects between the thyristor's cathode and gate, and on a second coil oscillating wave goes. While vibrating, thyristor will be constantly triggered (in a conductive state).
Yandersen, Thu Dec 13 2012, 05:39AM
To make bi-dir thyristor conducting, wind two coils around a little ferrite ring transformer: one coil connects between the thyristor's cathode and gate, and on a second coil oscillating wave goes. While vibrating, thyristor will be constantly triggered (in a conductive state).
Re: Coil construciton: 80amp through 30aw wire?
Turkey9, Thu Dec 13 2012, 07:07AM
IGBTs can be used very effectively if you don't want to use the LC time constant to determine the pulse length.
I would strongly advise against using such thin wire. You won't notice a difference in using a single layer as compared to two or three. Thicker wire will make the entire coilgun much more durable. You don't want to spend a lot of time building something only to have it break after a couple shots.
Turkey9, Thu Dec 13 2012, 07:07AM
IGBTs can be used very effectively if you don't want to use the LC time constant to determine the pulse length.
I would strongly advise against using such thin wire. You won't notice a difference in using a single layer as compared to two or three. Thicker wire will make the entire coilgun much more durable. You don't want to spend a lot of time building something only to have it break after a couple shots.
Re: Coil construciton: 80amp through 30aw wire?
PlayNice, Thu Dec 13 2012, 07:34AM
But whats the point of having the thyristor triggered by the oscillation? Shouldn't my opto-switch be triggering my thyristor so I can have the timing right and not have suck-back?
PlayNice, Thu Dec 13 2012, 07:34AM
But whats the point of having the thyristor triggered by the oscillation? Shouldn't my opto-switch be triggering my thyristor so I can have the timing right and not have suck-back?
Re: Coil construciton: 80amp through 30aw wire?
Yandersen, Thu Dec 13 2012, 11:40AM
There is no suckback in a reluctance coilgun - it pushes the projectile away from the coil, wherever it is, but with distance increased force is weakening.
Yandersen, Thu Dec 13 2012, 11:40AM
There is no suckback in a reluctance coilgun - it pushes the projectile away from the coil, wherever it is, but with distance increased force is weakening.
Re: Coil construciton: 80amp through 30aw wire?
PlayNice, Thu Dec 13 2012, 08:20PM
The one that pushed the projectile is induction coilgun, I though reluctance coilgun pulls the projectile like this:
PlayNice, Thu Dec 13 2012, 08:20PM
The one that pushed the projectile is induction coilgun, I though reluctance coilgun pulls the projectile like this:
Re: Coil construciton: 80amp through 30aw wire?
Yandersen, Thu Dec 13 2012, 09:21PM
Funny. Reading the dictionary for the word "reluctance" made me think about repulsion way of operation...
Okay then. I thought you are building an induction coilgun. Forget what I said. :)
Yandersen, Thu Dec 13 2012, 09:21PM
Funny. Reading the dictionary for the word "reluctance" made me think about repulsion way of operation...
Okay then. I thought you are building an induction coilgun. Forget what I said. :)
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