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Wessel

Wed May 20 2009, 03:41PM

Registered Member #2127 Joined: Wed May 20 2009, 03:35PM
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Posts: 8

I'm not trying to make a gun, just a ringlauncher or sorts. Wrap a coil around an iron core, then fire it up and launch a washer. My coil is about 8 inches long, used 10 guage wire and has 3 layers of 20 turns each. It balances to about 300 turns/meter. I was planning on hooking it up directly to a wall outlet, 110 volts at 60 Hz, but I was wondering if

a) the wattage would vaporize the coil
and
b) the kickback form the inductor would blow a fuse

Also, would it be wise to attach a capacitor to allow the circuit resonance, or would that put too much power through it?

Bonehead

Wed May 20 2009, 04:38PM

Registered Member #2046 Joined: Sun Mar 22 2009, 01:12PM
Location: Stockholm, Sweden
Posts: 23

You're probably gonna blow a fuse even without the added kickback unless you have enough resistance in the coil.

hotcrazyfruit

Thu May 21 2009, 12:07AM

banned on 5/26/2009
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about the capacitor and making the circuit resonate, it already WOULD be if you plugged it straight into the wall AC. also, you would need quite a bit of turns to make it not draw enough to trip a breaker. also, if you just wrap it around the iron core, it would just make an electromagnet, which the poles would be switching 60 times per second, no good for ring launchers. with ring launchers, you need LOTS of power in a VERY short time period. the idea is to create eddy currents of the same polarity in the ring or projectile, and as any electrical energy flowing through a wire does, it produces an magnetic field. this causes the ring and coil to repel each other as they are of same polarity, launching the ring. Also, the wall AC would not come close to vaporizing 10 gauge wire, and it would not be the inductive kickback to trip the breaker / blow the fuse, it would be the coil drawing to much current due to low resistance. Read up on the wiki for more details before experimenting.

Nick.

Wessel

Thu May 21 2009, 04:04PM

Registered Member #2127 Joined: Wed May 20 2009, 03:35PM
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My physics teacher has one that just runs the 110v 60Hz power through it, and it works, if you leave the switch down the ring will just levitate there. It's only .5 ohms. I'll have to add a few more layers of higher guage wire to raise the resistance.

hotcrazyfruit

Thu May 21 2009, 07:41PM

banned on 5/26/2009
Registered Member #1877 Joined: Mon Dec 22 2008, 02:03AM
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Wessel wrote ...

My physics teacher has one that just runs the 110v 60Hz power through it, and it works, if you leave the switch down the ring will just levitate there. It's only .5 ohms. I'll have to add a few more layers of higher guage wire to raise the resistance.

it is likely the coil has some sort of ballast as well as a rectifier. i have not seen electromagnetic levitation device running off of AC.

klugesmith

Thu May 21 2009, 09:43PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1715

O ye of little faith, Wessel has seen a common physics demonstration that requires no rectifiers nor external ballasts.
For a variant see http://www.youtube.com/watch?v=WX1fkfJPWpY

Suppose the iron-core coil has L = 30 mH and R = 0.5 ohm.
Total impedance at 60 Hz is 11.3 ohms.
Plug it into the wall, it will draw 10.6 amps and dissipate about 56 watts (I^2*R).
Good example of a low-power-factor load.

Of course the magnetic flux path isn't all iron, it's open on top so an alumin[i]um
ring can be placed close to the coil. Ring is stabilized by a vertical rod in the middle.
Induced current circulates in the ring, opposing the current in coil and partly canceling
the magnetic field. Viewed from wall plug, L goes down, R and I and P go up.
The Al ring is lifted and heated.

In order not to blow a fuse, Wessel's coil needs to have enough inductance.
This forum is a good place to find help to analyze the design.
I am guessing it will need to have at least a few pounds of Cu and Fe.

To hurl a ring or disk against the ceiling you need lots more ampere-turns. Around here that's
usually achieved with a much smaller L and somewhat higher V, with charge stored in a capacitor.
Magnetic fields reach a level where the iron core doesn't count for much.

Wessel

Thu May 21 2009, 11:47PM

Registered Member #2127 Joined: Wed May 20 2009, 03:35PM
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I gave up on using that high guage wire, moved down to 5 layers of 40 turns each. I plugged it directly into a wall (hotwired an AC adapter so it doesn't change current). Fuses are all good, and it went about 3 ft in the air. I have 4 more lengths of the same wire, and was wondering what would happen if I added more layers either in parallel or in series with the first set of layers?

klugesmith

Fri May 22 2009, 12:13AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1715

Good work, Wessel. Experimental evidence trumps theory & simulation!

If you add more winding layers, it would be good to bring their wires out separately.
Then you can try serial and parallel configurations by changing the connections
instead of rewinding.

WARNING: if your original configuration depends on its inductance to limit the current,
and your additional winding is connected backwards, then you have turned the
coil into a non-inductive resistor and could easily blow a fuse.

Can you provide a picture or more detailed mechanical description?

And does your quoted 0.5 ohm resistance apply to your teacher's demonstration coil or to your own original configuration?
It looks as though the wall-pluggable LR numbers I quoted above, though commonly attainable, would require a few lbs of Cu & Fe even with a closed core, e.g.

and with an open core, the scale is more like

The teacher's coil is OK for intermittent operation, but for manageable size it probably has at least 5 ohms of resistance
and rather less inductance than my first guess.

Wessel

Fri May 22 2009, 12:43AM

Registered Member #2127 Joined: Wed May 20 2009, 03:35PM
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Posts: 8

My new and old coils, and a battery for size.

Wessel

Fri May 22 2009, 02:02AM

Registered Member #2127 Joined: Wed May 20 2009, 03:35PM
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Posts: 8

The big one on the left has the .5 ohms. I'm not sure about the small one on the right, but it sent the ring about 4 times as high.

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