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

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Jasonr

Tue Aug 25 2009, 06:10PM

Registered Member #167 Joined: Mon Feb 13 2006, 06:41PM
Location: Waterloo, WI
Posts: 54

The only use I could think of would be to augment a railgun.
Augment Link

Jordan aka Axiom

Thu Aug 27 2009, 02:16AM

Registered Member #2317 Joined: Thu Aug 27 2009, 01:45AM
Location:
Posts: 27

Let's do a thought experiment:

An idealized shorted circuit producing 3000A at 1V would require that said circuit has an impedance of 0.0003333 ohms.

If we increased the voltage in this equation to 1000V, but increased the impedance so as to maintain the 3000A current, our impedance would be 0.3333 ohms.

Both circuits exhibit 3000A current, with one operating at 1V and the other at 1000V with impedance varying as required.

The power levels of these circuits are are 3000W and 3000000W.

Using these circuits to power an electromagnetic accelerator, being that propulsive force is a function of current, the force produced would be the same.

Is this correct?

klugesmith

Thu Aug 27 2009, 02:51AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Jordan aka Axiom wrote ...

Using these circuits to power an electromagnetic accelerator, being that propulsive force is a function of current, the force produced would be the same.
Is this correct?

Nope. To keep it stupidly simple, the fields depend on current times number of turns (and how close the turns are, since they each need room). In your example, the HV coil could have many more turns & generate lots more force.

Generally, for a given coil size and material, you can choose the wire size to match the desired voltage.
Low voltage: thick wire, few turns, high current.
High voltage: thin wire, many turns, low current -- for exactly the same power dissipation and field strength.

Jordan aka Axiom

Thu Aug 27 2009, 03:08AM

Registered Member #2317 Joined: Thu Aug 27 2009, 01:45AM
Location:
Posts: 27

Klugesmith wrote ...

I forgot to specify that the inductance of the propulsive apparatuses is maintained as well. As such, the increased resistance in the 1000V circuit comes from some internal resistance such as ESR.

Then, would not the propulsive force be the same?

M_Gargantua

Mon Sept 07 2009, 02:41PM

Registered Member #276 Joined: Thu Mar 02 2006, 04:40PM
Location: NY
Posts: 5

Barry wrote ...

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.

I think I might do a project, using this for a needle gun.

Dr. Resonance

Sat Oct 31 2009, 04:25PM

Registered Member #1670 Joined: Mon Sept 01 2008, 08:32AM
Location:
Posts: 19

yes, you can. I use an 900 Volt, 1,000 mA xmfr to charge my HV DC power supply. It quickly charges up my large 1,200 volt cap bank, and then fires thru a standard 1,600 volt SCR. I use a 5 section coil gun with each section triggered by an IR beam. The first SCR stages is triggered manually via a standard pushbutton on the SCR trigger gate. Using a 4" long x 1/2" dia steel projectile and getting measured velocities of 650 ft/sec. after stage 5. It shatters a standard concrete building block approx 50 ft from end of the gun.

Dr. Resonance

Dr. Resonance

Sat Nov 07 2009, 10:59PM

Registered Member #1670 Joined: Mon Sept 01 2008, 08:32AM
Location:
Posts: 19

A few tips for projectile accelerator designers:

One of the factors many coil gun designers miss is the necessity of getting the coil very close to the projectile. We use a stainless steel tube, with very thin wall thickness, .040". Then we use a very thin layer of kraft insulating paper, .003" thick. This allows us to wind the coils very tight on the tube giving max coupling to the projectile.

Energy goes up as square of the voltage, so keeping the voltage high, in my case 1,200 Volt, it keeps the overall energy high.

A third trick is to make slots all along the tube directly under the part covered by the coil. I also go 0.25" each side of the coil with the slot. (milling machine, 1/8th" slot). This prevent eddy current formation (losses), and, again, increases the energy in the projectile.

Use a reasonably large guage wire (I use 10 AWG) to keep overall coil resistance low and thus peak current high.

Contact me off-list if you wish to see a photo of my 5 stage gun in action shattering a concrete block at 20 ft from the gun.

Dr. Resonance

Dr. Resonance

Sat Dec 26 2009, 05:54AM

Registered Member #1670 Joined: Mon Sept 01 2008, 08:32AM
Location:
Posts: 19

yes.

I use a 1,200 Volt xmfr rated 2 Amps to rapidly charge up my 1600 VDC cap bank prior to firing. It charges 5 stages which, after the first stage, or triggered with
I-R optics of each stage. I use a 0.5" x 4 inch long projectile to shatter concrete blocks at 60 ft.

Dr. Resonance

Turkey9

Mon Dec 28 2009, 05:57AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

wow! 650 ft/s is over half the speed of sound. And assuming a plain steel projectile, that's way over 7kJ of kinetic energy! That's impressive indeed. No wonder you can shatter thost concrete blocks!

DYI

Mon Dec 28 2009, 10:49PM

Registered Member #1917 Joined: Fri Jan 09 2009, 02:38AM
Location:
Posts: 62

Looks closer to 2kJ to me. Either way, that would be a very impressive coilgun. Probably inductance rather than reluctance, unless he's got an absolutely vast capacitor bank powering those stages.

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