electromagnets

[brice618]

anyone know how to make a rather large electromagnet that could pick stuff up through 4 inches of stone?

any magnet will do really but i didn't figure i could get that without going electro...

[TomK]

4 inches of intervening non-ferrous material hmmm? Law of the Inverse Square will come into play and require a pretty strong field. (1/2 the distance = 4 times the strength, 1/3 = 9 times, 1/4 = 16 times, 1/10th = 100 times, etc)

For permanent magnets, take a look at this one that will suspend 700 pounds.
The new tech rare-earth Neodymium magnets are crazy-strong compared to the old ferrite ones.
http://www.gaussboys.com/ndfeb-magnets/D7626.html



To build an electro-magnet is pretty simple conceptually, but you need to know more about the mass of ferro-magnetic material (junk) that you want to move or hold on the other side of those 4 inches.
Chunk of Iron for the core, enamel insulated copper wire for windings, run electric current thru it.

[Big E]

Tech talk, jong!





Had to be said.

[runethechamp]

I built these when I was a kid. Took 4 really large nails and spun a ton of insulated wire around them in the same direction(I got my wire from a building site where they were blasting out a bunch of rock) and just hooked up a battery to it. I think the strength is a combination of the mass of metal in the middle, the number of windings you have and the voltage (or was it current) you're sending through it.

And if I remember the theory right, you need dc to send through the wire. AC will cause the magnetic field to reverse at 60Hz. On the other hand, that might not matter since you're just picking up a piece of metal. I have no idea how much you need to have it go through 4 inches of stone, that's a lot. Maybe you need to set up your own dedicated circuit for it in your house?

[davep]

You'd need a huge copper coil and a ton of water cooling to come close to the field strength of a big neodymium magnet. Just buy the biggest one from TomK's link, or any other magnet seller.

BTW I think the magnet's force drops like 1/r^7, at least for distances bigger than the magnet's diameter... why 1/r^2?

Anyways, 4 inches distance - I dunno, might work. Have fun.

[davep]

And if I remember the theory right, you need dc to send through the wire. AC will cause the magnetic field to reverse at 60Hz. On the other hand, that might not matter since you're just picking up a piece of metal.

AC's fine. Don't kill yourself.

[AsheanMT]

Some of you guys are major fkn brainiacs!! Perhaps we should use you and let Maggots Rule The World!!!

[TomK]

DC current will permanently magnetize the iron, AC is used in bigger electro-magnets so that when you turn the current off, the magnetic field goes away. Just got to have enough wire length to give you enough resistance so as to not blow the AC fuse. (max current allowed = 80% of fuse or circuit breaker rating. 10 amp fuse = 8 amp maximum draw.)

To de-magnetize the iron after running DC thru the coil, reverse polarity and let it run the same amount of time.

DC is used in tabletop/kid friendly demos due to the shock hazards when dealing with AC. That and D-cell batteries are cheap.

Current is what creates the magnetic field.
Double the current = double the magnetic field.
Double the # of windings = double the magnetic field.
Half the distance from the magnet = FOUR times the field strength. This is also why you want to use enamal-insulated wire like what's inside a motor and not thick insulated stuff like house wire.

To get enough strength to affect fairly large objects 4 inches away thru stone I suspect DaveP is on the right track with the large current's involved creating a lot of heat in the winding.

You could always start small and work your way up.

[brice618]

I did about 15 different tests today, and the best i could do was hold stuff from about 2 inches. Almost all of the stuff you guys said went over my head, but that is ok I still appreciate your time to make the comments. I got it working well enough to make sense and given the time constraints thats what I needed. Thanks for the input!

[Dantheman]

For permanent magnets, take a look at this one that will suspend 700 pounds.
The new tech rare-earth Neodymium magnets are crazy-strong compared to the old ferrite ones.
http://www.gaussboys.com/ndfeb-magnets/D7626.html

Holy shit. Permanent is right, anything iron that comes even close to it will be permanently attached to it

[Brocktoon]

Holy shit. Permanent is right, anything iron that comes even close to it will be permanently attached to it

Yeah, plus at $115 it's not worth if for my purposes (fucking with other people).

This one is and = ordered!:

http://www.gaussboys.com/ndfeb-magnets/D3712E.html

[davep]

Yeah, plus at $115 it's not worth if for my purposes (fucking with other people).

If you're carrying it around to fuck with people, just don't let it near your wallet, you'll need a lot of new cards. I'd be careful with the cellphone/other electronics too.