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Strange idea:Can a transformer power a coilgun/railgun effectively?

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T_chester

Sun Aug 16 2009, 07:30AM

Registered Member #2299 Joined: Sun Aug 16 2009, 07:04AM
Location: Hong Kong
Posts: 3

As the electromagnetic accelarator use a huge amount of current to speed up the projectile,
I am thinking if a transformer (eg. 1V 3000A output) could power up a coilgun or a railgun just as
a capacitor does.
Do anyone of you heard of a design using a transformer as power supply?
Or the input energy would be to low and cause a huge resistive lose?

Killa-X

Sun Aug 16 2009, 08:17AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

I wouldn't know much, but good luck finding a house that allows 3000A. Last i thought, a transformers output in current, is the same as your house. If you have 20A plugs (like me) I can't use a transformer that uses more than 20A. Yes, time to time you find other plugs like our hot-tub, 60A. But 3000?

If you asked me I wouldn't see if fully possible. Yes you can use some nice 12V nice amp power supply to power a transformer, like uzzors 50W flyback one, and get a fast charge..But without capacitors, your stuck.

I know people have used voltage multipliers with capacitors on 120V, so it takes 120V to 480V but...Not sure. Welcome to the forums though!

T_chester

Sun Aug 16 2009, 09:28AM

Registered Member #2299 Joined: Sun Aug 16 2009, 07:04AM
Location: Hong Kong
Posts: 3

Maybe I could explain my idea further.
I have a transformer Input: 220V 13.5A 50Hz OutPut : 1V 3000A
I am sure it delivers 3000amps when shorted, but I am not sure if such current could drive a coilgun or just turn into heat in the coil.
And I am thinking if the voltage output of the transformer effect the output of the coil.

Marko

Sun Aug 16 2009, 11:51AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Well, mains powered coilguns are not a new proposal. Using transformers makes no sense though, as 1V with a 1 turn coil would work the same as mains voltage and a 230 turn coil, while getting rid of the transformer and all associated losses.

I could imagine a mains powered coilgun that could easily be much more efficient than ordinary air core and capacitor designs. The goal would be to design it like a linear motor, either LIM or LSM, with barrel made of iron cores perhaps several meters long, and rectified three phase mains as power source, with the whole system controlled with igbt's.

It certainly be a great project for someone with a deep wallet and sense of electromagnetic engineering (note that couple tens of kilograms of iron U cores or like might be required).

For a toy coilgun, one could probably use mains for maybe up to a hundred joules of energy for tipycal house feeds. Some system ofphase angle detection would be required though, to allow consistent firing, and it would have to be timed and controlled by an IGBT.

Marko

kromsson

Sun Aug 16 2009, 02:36PM

Registered Member #1444 Joined: Tue Apr 15 2008, 06:55AM
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Posts: 20

It can be done for fun, but will NOT be really effective, because the energy you get from the mains is quite low - 3000A x 1V = 3kJ/sec (3kW).

If you want to provide the projectile with 1 kJ of kinetic energy (assuming that the efficiency will be 20% !!!) you need 5 kJ of mains electrical energy, which means the projectile should be accelerated for almost 2 seconds (!!!!!) with means that if it has a terminal velocity of 50 m/sec, then you need 100 meters of barrel!

The capacitor discharge over a coil would take normaly about 2-3 msec (which is the half cycle). If the capacitor bank has about 3 kJ (which is quite large but possible for an amateur) then the average power of the capacitor is 3kJ/0.003 sec = 1MW !

So you need 300 times more power than the mains can supply - but only for a very short time.

rp181

Sun Aug 16 2009, 02:51PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I recall seeing somewhere someone trying a mains coilgun with filtered, rectified 3 phase power, but it did not work too well. Timing is also a issue.

T_chester

Mon Aug 17 2009, 10:09AM

Registered Member #2299 Joined: Sun Aug 16 2009, 07:04AM
Location: Hong Kong
Posts: 3

Thanks for the information, and I think transformer or main for coilgun is not suitable for me.
How about using main as a railgun or thompson coil, is there any possibilities?

Barry

Mon Aug 17 2009, 10:56AM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

Marko wrote ...

Well, mains powered coilguns are not a new proposal... I could imagine a mains powered coilgun that could easily be much more efficient than ordinary air core and capacitor designs. The goal would be to design it like a linear motor, either LIM or LSM, with barrel made of iron cores perhaps several meters long, and rectified three phase mains as power source, with the whole system controlled with igbt's.

A nice LIM was built by EF Northrup in 1937 and no IGBT were needed. (Good thing too, since they hadn't been imagined yet.) He had in-depth understanding of eddy currents and skin effect depth, and determined that 60 Hz was too low -- he ran the equipment at 4800 Hz from a motor-generator pair. It seems a loss the technology was never developed further.

I always enjoyed his description of a "magnetic field sweeping like a wind along its axis." What a great mental image.

Cheers, Barry
Q: Can you give me some information about hippo racing in Canada?
A: A-fri-ca is the big triangle shaped continent south of Europe....Ca-na-da is that big country to the north of U-S-A... oh forget it. Sure, the hippo racing is every Tuesday night in Calgary. Come naked.

kromsson

Mon Aug 17 2009, 11:39AM

Registered Member #1444 Joined: Tue Apr 15 2008, 06:55AM
Location:
Posts: 20

T_chester wrote ...

How about using main as a railgun or thompson coil, is there any possibilities?

Railgun, coilgun or otherwise, it is not efficient.

You need GREAT length of whatever acceleration field (in the measure of 10ths of meters), because the energy placed on the projectile is very slow.

You would need to gather the energy provided my the mains power for a few seconds (maybe 3-4), and save it in a DEVICE, then throw it altogether at the projectile in a millisecond.

The first DEVICE that comes to mind is of course, a capacitor...

Sorry friend, the mains can give you only fun, not really high velocities...

Backyard Skunkworks

Tue Aug 25 2009, 05:06AM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

The easiest way to think about this is to simply calculate the theoretical maximum energy one can get from the mains. At 240V, 400A, 96kW, you can theoretically get up to 96kJ per second of power for the gun. If a powerful coilgun can dump a 1kJ bank in 10ms, it uses energy at a rate of 100kJ/sec. By looking at this, it would appear possible in theory to make a halfway powerful CG powered off mains. All the problems outlined in previous posts still stand though, and make the prospect of making a mains powered coilgun a bit harder.

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