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Designing 2kW electromagnet

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cduma

Fri Nov 21 2008, 08:11PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

This may not be the correct forum but, I think it fits here best.

My basic question is this: What is the best way to build a very strong electromagnet.

The only purpose I have is just to amaze friends with an electromagnet stronger than they are.

What I was going to do is use a heater as a load and have several rectifyers connected to a capacitor in parelel with an electromagnet. This would all operate at 120v.

What are the best dimensions for the electromagnet itself? Do I need to rectify the current?

...

Fri Nov 21 2008, 09:18PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I would skip the heater ballast in series and just use fine enough wire so that it has enough resistance on its own, and add a bridge rectifier+smoothing cap. For added fun add a switch that lets you switch it over to strait AC into the magnet and use it for all sorts of levitating tricks. Although keep in mind that a 2kw magnet is going to need 2kw of cooling, which will at the very least mean a lot of water flowing through it.

Also, you will want to put that on some kind of core (probably a C core, although an I core would work) to help organize the field.

And finally, where did you come up with the 2kw number? You really don't need that much juice to make a strong magnet. TeslaDownUnder has made some very impressive magnets that run well under 500w (on this forum and on his site)

cduma

Fri Nov 21 2008, 10:00PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

I choose the number through a very complicated process that no body will ever hope to under stand. I choose a random number. It is true though, no body understands how the mind works.

I love sarcasm

The reason I wanted a ballest was so that I could use large wire and not need exotic cooling. Besides, I always wanted to make a contraption out of a toaster!

I want the electromagnet to be stronger enough to exert 130 lbs of force.

And what do you mean by "levitating tricks". That sounds alot better than a strong magnet.

Friend," Oh thats neat you built a stong magnet. Lets go watch TV"
Or
Friend,"OMFG that is the most awesome thing ever! Its floating in the air! Lets go take over the world." at which point I
would say," Thats immoral besides this world is lame and I dont want it."

rp181

Sat Nov 22 2008, 01:11AM

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

A simple electromanget wont make objects float. You need to incorporate power control. 1.5kW will be a more reasonable figure, most house fuse's can handle that (if your in 120v land). Use ohms law (current= volt/ohm) to find wire length and AWG. This gives a figure of .1ohms (to be on the safe side).
Look at wikipedia's table of AWG (search for the AWG listing). Its shows a current rating and resistance, find a good combo.

Dr. Slack

Sat Nov 22 2008, 07:54AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

The reason I wanted a ballest was so that I could use large wire and not need exotic cooling.

If you use large wire, then you have few turns, and a weak magnet.

Basically the more power loss in your copper wire, the stronger the magnet.

...

Sat Nov 22 2008, 04:54PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Yes a simple electromagnet can make things float, it can even make non-magnetic float through induction. See TDU's maglev disk

(although understand that you need to keep something to keep the target sliding off since it is an unstable system).

Also, your plan to use a ballast to absorb the heat is not going to work. As said before, the strength of a magnet (for a given type of wire) is pretty much proportional to how much heat it burns. You can use a few thick turns and run it at super high current, or use a ton of thin wire and run it at lower current, but the strength of the magnetic field will always end up being about the same strength for the amount of power you burn up (with the exception being for magnets wound with superconductors and the like)

uzzors2k

Sat Nov 22 2008, 11:04PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

We should maybe clarify that it's the amount of turns and current that gives magnetic force, and not the actual power lost in the electromagnet.

Dr. Slack

Sun Nov 23 2008, 08:49AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

We should maybe clarify that it's the amount of turns and current that gives magnetic force, and not the actual power lost in the electromagnet

OK, if you replace the copper with silver or superconductor and the losses reduce.

For the material constants of copper, it doesn't matter whether you use 100 turns of x diameter wire, or 10000 turns of x/10 dia wire on the same coilform, the field is poroprtional to sqrt(watts).

aonomus

Sun Nov 23 2008, 08:02PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

More turns = greater resistive losses = more heat

Perhaps even consider working in some way to cool it. Tesla Down Under made a gigantic kW scale one and had to air cool the thing.

Electroholic

Sun Nov 23 2008, 08:18PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

its not about power, its about how you couple it.
my HS physics teacher once showed me a hockey puck sized electromagnet. It was powered by a single D cell and was impossible to separate by hand.
It think it was just some ferrite pot cores.

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