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MadCow257
07-27-2005, 08:42 AM
I am planning on building some em experiments, but before I buy the parts I need to confirm some things.

1) A railgun will work with ac current, correct?
2) Is stranded copper wire better than solid wire?
3) In an electromagnet, does a steel core work as well as an iron core?

B0bDole
07-27-2005, 09:16 AM
1) probably? IDK
2) I would look up the melting temps for both, and chose the one that wont melt
3) Iron would be better

no-one
07-27-2005, 09:21 AM
HOW CAN YOU NOT KNOW!!!, your ........ing MacGyver?!?!!?!!!!!??... and Bobdole?!?!?? you should know anything....

MadCow257
07-27-2005, 09:23 AM
3) Iron would be better

Will the difference be signifant? The only metals in rod form that my local hardware supplier sells are steel and aluminum.

SMurf
07-27-2005, 09:28 AM
You do realise that if you're doing what I think you're doing and you're successful, Navy SEALs are gonna come crashing through your windows and offer you a lucrative contract, don't you? :cool:

Govtcheez
07-27-2005, 09:30 AM
HOW CAN YOU NOT KNOW!!!, your ........ing MacGyver?!?!!?!!!!!??... and Bobdole?!?!?? you should know anything....
the spazzing one has a very good point.

confuted
07-27-2005, 10:29 AM
I am planning on building some em experiments, but before I buy the parts I need to confirm some things.

1) A railgun will work with ac current, correct?
2) Is stranded copper wire better than solid wire?
3) In an electromagnet, does a steel core work as well as an iron core?
1) Absolutely not, unless your goal is to weld the projectiles to the rail and blow the fuse. Rail guns rely on the Lorentz force to push the projectile along its merry way; to work, this push needs to only go one direction (DC). Alternating current will produce oscillating magnetic fields - if you're lucky, you'll get the projectile to vibrate. But really, it sounds like your approach is all wrong - you need far more current than you're going to pull instantaneously out of a wall socket, anyway. You need to charge capacitors over a period of time, and then discharge them through the rails very quickly. See this page: http://www.powerlabs.org/railgun.htm

2) Generally, but it depends on the application. Stranded wire bends more easily and doesn't break as much. I'd suggest doing the theoretical calculations for the current levels you expect in the wire (don't discount this as trivial, for your safety and mine - especially on the wires going to the rails), add 20% to that for safety, double it in an attempt to alleviate pains due to design changes and calculation errors, and then find the largest gauge (smallest diameter) wire that will carry that load or more. Overdesign? Yes. Would I do less? Not unless I knew what I was doing. Would I know what I was doing the first time? No.

3) No, a steel core does not work as well as a soft iron. The difference lies in a factor called the magnetic permeability of the material. The strength of the magnetic field in the core is proportianal to the current in the coils, the turns of wire around the core per unit length of core, and the magnetic permeability of the core. See this page (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indcur.html#c1) to learn a bit more. Double the magnetic permeability, double the strength of your field. Here's a table with some permeabilities (http://hyperphysics.phy-astr.gsu.edu/hbase/solids/ferro.html#c5). Steel, especially "high grade" steel, will have much lower permeabilities than soft iron. Also, if you're planning on using this magnet with AC, such as in a transformer, the hysteris curve may be of importance to you. It is significantly less important with DC however.

B0bDole
07-27-2005, 11:15 AM
AC -> DC inverter will solve problem to question 1

MadCow257
07-27-2005, 11:24 AM
Thanks for all the information, confuted.

My first test where I was just going to pull the power straight from the socket was supposed to just confirm that my connections where intact, and that there was indeed a magnetic field. I know that I am going to have to get some capacitors, and make a power surge.

The thing about the soft iron core will definitely improve my current design.

confuted
07-27-2005, 12:04 PM
B0bDole: I was waiting for someone to say that. If you convert your AC to DC, you're once again using DC, and not AC, just like I said. I don't care where you get the DC, but you need it. Regardless, you meant a rectifiier, not an inverter. An inverter goes from DC->AC; a rectifier goes from AC->DC and is much easier to construct.

There are a few more things to note that I forgot to mention in my previous post. For the rails, you want to optimize a combination of wear resistance and low electrical resistance. For testing that connections are valid, I'd suggest using a multimeter, rather than potentially lethal currents. Remember kids, electricity is dangerous, and it only takes one mistake to wake up dead the next morning.

B0bDole
07-27-2005, 12:39 PM
>it only takes one mistake to wake up dead the next morning.

lol

MadCow257
07-27-2005, 01:17 PM
Remember kids, electricity is dangerous, and it only takes one mistake to wake up dead the next morning

I've already ran lethal amounts of current through something I've built 4 times this week. I always just plug in a closed circuit in so I'm really not in any danger. (I'm more concerned for my equipment than myself)

Anyways,
I need suggestions on a capacitor. So far, the only one that I have found that I can buy straight from an online store is the BCAP0350.

confuted
07-27-2005, 01:22 PM
You're unlikely to get the current you need with a single capacitor. You'll need to build a bank of them. I seriously suggest reading some of those links that I provided earlier - especially the powerlabs one. I know the guy who did that (goes to my school), and he's quite capable.

That said ...
http://froogle.google.com/froogle?q=capacitors&hl=en&hs=63V&lr=&client=firefox-a&rls=org.mozilla:en-US:official&sa=N&tab=wf
http://newarkinone.com
http://digikey.com

A bit more looking and you'll find plenty of capacitors. They're anything but rare.

MadCow257
07-27-2005, 05:33 PM
My last question on the subject I hope...

Would a lot of 25 63volt 6800uf capacitors be a good deal if I get it for less than 25 dollars?

MadCow257
07-27-2005, 07:55 PM
Actually, I am also confused by the concept of a farad. I went ahead and bought that set for 16 bucks, and for design considerations I need to know what kind of amperage that set will give me.

Thanks,
MadCow

B0bDole
07-27-2005, 08:56 PM
http://en.wikipedia.org/wiki/Farad

golfinguy4
07-28-2005, 06:10 AM
Farads are a measure of capacitance. The larger the capacitance (more farads), the more energy the capacitor can store for a given voltage connected to it.

BobMcGee123
07-28-2005, 02:52 PM
1 farad is a very large amount of capacitance.