Electromagnets - I could electrocute myself?

I bought a 100m roll of copper earth electrical wire - 2.5mm single strand which cost 90 dollars so I want to make sure it DOESNT burn through from the power source.


Im planning to wrap the wire in MANY coils around my iron water tank which has a surface diameter of .8m (80cm) and a height of 1m (Clear in the middle). And I'm going to get my electrician cousin to strip the wires and insert it into an electrical socket in my back yard - 240V for my experiment.


Someone I know suggested I use a resistor in the form of a light bulb but this will drain the overall strength of the magnet and (a) I'm wondering what else I can do so it will maintain power?


(b) Im wondering if theres any one I can talk to in regards to this. I'm sure if I called a more qualified electrician who I dont know about magnets he'd think im weird. Are there experts I could see about specifically this subject?


(c) How much would a powerful industrial lifting magnet cost?

Electromagnets - I could electrocute myself?
Warren has what looks about right, Though I would measure the resulting inductance with an LCR meter to make sure there is sufficient reactance to not burn out the wire or trip your breakers.





Then again, if your purpose is to make an electromagnet, I would ask if you intend on filling the tank with iron or other ferromagnetic material? Because if you do, there will be 2 major results-





1- the inductance will be significantly higher due to the higher permeabilty





2- the mag field will be stronger, though not near as strong as if the magnetic path were continuous through a high-permeabilty core.





And if you are attempting to build a lifting electromagnet, there are much more effective shapes than a solenoid (what you are doing), such as a simple horseshoe or (even better) an offset rotated horseshoe. This is how the big boys do it. 8^)





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Oh yes, another biggie - if you really are building a serious lifting magnet, you will use iron core, but the core material will have to be laminated to reduce eddy losses. Otherwise most of your power in will be burned up heating the iron. 1/16" plate might be appropriate, fully varnished before stacking for electrical isolation between the stacked plates, in plane with the flux but insulated somewhere in the magnetic path. One way you might do this is by using 2 sizes of rectangles for the plates in which you alternate the laminations such that you end up with an interleaved U-shape. It's ok to have bolts going through the stack for assembly if the bolts are wrapped in mylar tape so that they do not short the laminations together. Email me if not clear.
Reply:Actually, it isn't the resistance of the wire that you should be too concerned about, considering the amount of wire you have. The inductive reactance of the coil will probably dominate and keep the current down.





I am a little off my grid, when it comes to computing the inductance of your device, but I figure about 400 turns in one meter length gives you .074H or 74 milliHenry of inductance with a single layer.





2 x pi x f x L = 23 ohms inductance reactance. 220v/23 ohms = 9.5 amps to start with. The steel core will make it more efficient, maybe by a factor of two, to be safe, which still gives you 4.5 amps. If you wrap two layers of 400 each, you will get .3 Henries, which will give you a current without a core of 94 ohms, and a starting current with the two layers of 2.3 amps, so when you add the core it should be much less.





If you don't kill yourself and everyone around you, you should be ok.





Disclaimer: I did not say you would be OK. ☺
Reply:First to answer your "headline":


Yes, you could always electrocute yourself if you work with 240VAC and don't know what you are doing....





But most likely, you won't have the voltage standing at your "magnet" for long, because your fuse in the distribution box will blow immediately.


You see, a 2.5mm dia copper wire has only a resistance of about 3.3 Ohm per kilometer. You have 1/10th of that (100m)


and so your coil will have a resistance of 0.33 Ohm. At 240 Volt, that translates into a current of 727 Ampere !!!


You need your own power station for that.....


So yes, you need to limit the current somewhat, and I suppose that is where the light bulb (in series to your coil) comes in (working like a resistor, which would also get very hot). Yes you could do that, but your magnetic field will not be very strong (heaven knows what you are trying to achieve....)


You see, the strength of a magnetic field is mainly determined by the number of windings, not by the thickness of the wire. I think you made a mistake buying such a thick wire. You should use 1km of 0.5mm diameter wire (have fun winding that around your water tank!) and that wire should be coil winding or magnetic wire (with the lacquer insulation which doesn't melt - and cause short circuit - when it gets a bit hot).


Then you have a strong magnet, and you pull "only" 3 Ampere or so.


Put your earth wire on eBay.....

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