# Thread: Making a strong electro magnet

1. I am new to this but I have a basic understanding of building a simple electro magnet. I was wondering what materials can I use in order to make a strong magnet with maybe a high distance?

2.

3. Two questions, over what range do you wish it to be effective, and how big is the power cable to your home?

4. you want to build an electro magnet

Okay........ here is what you will need.....

Grab yourself an iron bar about 6 feet long and about 1/2 foot in diameter. (you MIGHT get one from the scrappies but it has to be iron and and it has to be solid)

The get yourself some insulated wire (about the same thickness that you get in a normal house-hold live wire).....

now take the wire and coil it round the iron bar, obviously the more coils you make the more wire you will need. If your mates can help you out on this project then aim for around 2 million coils around the wire.

NOW.......Get yourself 50 car batteries and line them up in your garden.

Join all the positive battery terminals up to one single wire and do the same for the negative terminals.

Now attach one end of the wires coming off the bar to the positive terminal (doesnt matter which) and the other to the negative terminal.

Now throw paper clips at it.

Have fun with your 600 volt DC 2 million coil electro-magnet.

5. If you join all the Pos terminals together and all the Neg terminals together you will get er 12 Volts not 600. If you aim for 2 million turns of house wire, and put 12 volts across it, I'll wager the current would be so small as to not even deflect a compass needle. 6Ft long 6" in diameter eh? Hmm somehow I don't think so.

6. Oh right. Yes.........Okay, How about conntecting the batteries up this way: End of coiled wire to battery 1 negative terminal; then positive terminal of battery 1 to negative of terminal of battery 2, positive terminal of battery 2 to negative terminal of battery 3, all the way up to battery 50 where you would then connect the remaining terminal up to the other end of the coil.

This should give you 600 volts, right ?

7. Yeah but it's a lethal combination, you then have near enough the same voltage that drives electric trains, and the current is such that if you made it only 1 thousand turns and made it a really high 'Q' coil when you take the lead off you'll end up with a voltage of about 20,000 volts on the coil after it has been disconnected (this is how your ignition coil works, it is NOT a transformer as many people think). So either you'll kill yourself when you connect it or when you take it off! (Ever noticed how big and bright the sparks are from electric trains).

As we say "Do not Fry this at home" - Seriously unless you are an expert with the wires DON'T!!!!

Look up "Back EMF" on wiki or somewhere...

8. Seconded. Spartadrive, making a strong electromagnet is the sort of thing that can get you killed. Make a little one first:

http://www.sciencebob.com/experiment...tromagnet.html

9. Yes I know......I worked for a short while as a guard for south west trains. During my inital training we had to casually step over the live 850 volt DC rail. We also had to create a short circuit by using a piece of metal with a wooden and rubber handle by touching the live rail and the running rail simultanously. OH MY GOD !! the bloody noise that thing made !!!

I can still remember an almost lethal mistake, when during another day in training we were practicing with something called TCOS (Track circuit operating clips, basically a piece of wire with two metal clips either end, you connect the two running rails together (incase of a derailment) and this lets the signal box know that the line is blocked. As I beant down to clip on the first clip the instuctor yelled at me "NOT THAT ONE !!!!!"

I think you can guess what I was about to do

Anyway, going back to the subject............

How about incorporating 2 simple switches so you didnt have to get a shock....1 to open and close the circuit and a second to send any residue current to earth once the circuit has been opened ?

If you had one end of the coil connected to a + terminal and the other to a - terminal, then you switched them around, I am asuming that the magnetic poles of N and S would now also be swtiched ?

If this is the case; how does an alternating current serve an electromagnet without flipping the poles 50 times a second ?

Nice electromagnet farsight.....im not suire if it would even register on the tesla scale though.

10. It ain't that simple. The Back EMF occurs because the voltage is disconnected, at that instant you still have a magnetic field, this collapses very fast, in collapsing it 'cuts' the coil at high speed and the higher the 'Q' the more voltage is 'generated' - the switch will arc as you open it - in fact it'll probably explode as you will have a very short 'lightning bolt' - this voltage is also in reverse so it's 20,000 volts applied the wrong way across your batteries - just what will it take to convince you it's bloody dangerous, lethal at the power you are suggesting - if they are auto batteris it probably won't harm them but it won't do them any good.

As for alternating voltages on coils they [usually] follow a sinusoidal voltage and, taking back EMF into account + wire resistance gives you a 'phase lag' of up to 90 degrees between V & I. the current never instantaneously dissapears and is always connected to a source impedance - big sparks don't arise, and that's why transformers can handle AC. And yes, the mag field does 'flip' at 50/second or whatever the supply frequency is.

Look up 'Back EMF & 'Q' Factor'

If you just want a very strong magnet, go to an army surplus store and buy an ex-radar 'magnetron' if you can prize the magnets out of it you can save yourself a lot of dosh - be careful A radar tech playing with these and some sheet steel had 2 fingers sliced completely off.

http://www.ee.surrey.ac.uk/Workshop/...ower_loss.html

My advice would be if you do not understand this article then leave well alone and instead play with Farsight's "patented Heavy duty compass needle magnetiser" :wink:

11. I see. what do you mean by high "Q" ?

Anyway...So...Lets say if you had an electromagnet running from an alternating current, and next to the pole of the electomagnet you put an ordinary bar magnet with a whole through the centre, where it sat on an oiled pole "bearing" if you like. Turn on the electromagnet and with its poles flipping at the rate of electrical frequency common sense tells me that the ordinary bar magnet will spin on its bearing. Is this the case ?

12. Nope it will ignore the electro magnet as 50% of the time it will be 'pulled' and 50% pushed. In order to make a motor you need a rotating field - your AC electromagnet will only produce a sinusoidal alternating field - it decreases to zero, reverses direction then rises to a peak and pepeats it does not rotate. an electric motor [for the sake of simplicity] has lets say 12 magnets aranged in a circle each is switched on in turn a 'free to rotate bar' in the middle will move around as the magnets are switched on.

If you 'unroll' the magnets you produce a thing called a 'linear motor' - look up 'MAGLEV' to see an example of this (moves a train along by magnetic levitation).

'Q' = quality factor it is a property of induction coils, transformers and the like - again it is a very specific term to Electronics/electrical Engs.

See
http://www.ee.surrey.ac.uk/Workshop/...ower_loss.html

I know you are not into maths, and the links I post are heavy on it, but these are qualities which can only be expressed mathematically - they do not physically exist, they are properties of materials not the material itself.

13. I see......

By the way, not understanding "Back EMF" that much, not even on wikipedia. Is it caused by some sort of electrical inertia ?

Rather like when you are in a vehicle which stops, just before it stops you can feel yourself being pulled back a little bit. Is this something similar ?

14. I do not know how to explain it other than mathematically. I have thought of several analogies but none are completely analogous

So:

Suppose you have an invisible tank above your head which only appears when you turn on a water supply to it.

OK you turn on the supply, the tank appears and starts to fill, it fills very quickly and when full the extra water does not overflow but turns to steam.

Now switch off the supply - the tank dissappears, but the water is still there, result it all falls to the ground in a great lump.

It goes the opposite way (from when it was being filled hencs 'back' emf)
It is the suden release of a quantity of stored energy.

15. oh i see......

instead of pushing on itself it takes the path of least resistence. Makes sense.

Anyway....with my version of an electro-magnet (as dangerous as it is)

Any ideas what kind of magnetic flux it would be likely to achieve ?

16. Absolutely no idea, if you looked at the link:

http://www.ee.surrey.ac.uk/Workshop/...ower_loss.html

You'll see some of the problems, there are many, it's a specialist subject, There are standard tables to guide designers. I did the maths a long time ago, I remember it as being long and tedious using many complex formula - I swore never to go near the bloody things again but buy them 'off the shelf' like EVERY other Electronics design engineer does!!

Here's an example it's online.

http://acc-physics.kek.jp/soken/CORECARRI'00/Electro-magnets.pdf

Maybe Farsight would like to hazard a guess....

As you propose a 6" steel bar and 'house wire" I'd say the field generated would be about as powerful as a fridge magnet per cubic area.

HOuse wire has very thick insulation - if you look at a motor winding or transformer wire you will see it just looks like dark shiny copper - ifn fact it is enamel plated, the plating is of the order of microns thick - this helps 'concentrate the field, a thin bar will have all the lines of flux 'squeezed' into it therefore it will have a higher field density - if you use hexagonal or square copper there's even less gaps between the conductors - gaps = losses. If the insulation is to too thin then the voltage between any conductor and it's neighbours may cause breakdown - a long coil will result in higher differential voltages and a higher possibility of breakdown - the type of iron core you use (if AC) will have an enormous effect on efficiency. The type of copper - the operating temperature - the list goes on.

If you can get your hands on an old auto starter motor - strip it you'll get an idea of things. If you statr playing with magnets of the power of an auto starter look at what they do - turn a bloody great engine over with ease - shredding you would be childs play if things got out of hand.

Ever heard of 'bar stool racing' ? - As I remember it a starter motor and battery were attached to a bar stool and small wheels added - they would accelerate to 30MPH carrying a guy with no sweat.

http://www.barstoolracing.net/

Try building one of these instead, but do remember the Centre of gravity is well 'outside the envelope'....

17. Trying to think of a possible analogy for back emf that would make a bit more sense to me......

Let say the EM field is a cage and the free electrons are a lion.......

On that account Back EMF would be like opening the cage BEFORE you shoot the lion dead.

right ?

18. Sorry leo,

As an engineer I can only explain it for what it is, and that has to be in terms of fields and conductors - Maybe if you think of pumping up a cylinder to a high pressure and then opening the end all the air comes back out - well instead of air think electricity.

If you still don't get it maybe Farsight can offer a different analogy...

19. Yeah sure. Is this analogy enough for you leo?

20. Yes, now i understand it.

so with back emf, does ALL of the flow collapse in the opposite direction, or does it just collapse everywhere and under entopy you get some flow in the opposite direction ?

21. Originally Posted by Farsight
Yeah sure. Is this analogy enough for you leo?

Caption = "Man you should'a seen the coil I made"

22. Originally Posted by Megabrain
Two questions, over what range do you wish it to be effective, and how big is the power cable to your home?
I just want it able to maybe pull/grab something from across a small room.

Power cable in my home?

24. Um.............

Riiiiiiiiight

25. Okay a 24 volt 100 mA relay attracts a pole from 2.0 millimeters (thats 2.4 watts of power) Now your magnet is going to follow a square law so if you want to attract something from 2 metres then you'll need around

2.4*( 2/0.001)^2 watts or about 2.4 million watts - On average that's more than enough to feed a small town of several hundred houses.

Now you know why Farsight posted a picture of a guy with frazzled hair - and burnt black.

26. .......So to attract something from 2 meteres away what you are saying is that wou would need a magnet even MORE powerful than my design ?????

27. Your 'design' as I remember had 2 million turns and 600 volts, and 6 inch diameter core, thats about 3000 turns per volt, and as I said would probably not deflect a compass needle. So even farsight's nail would beat that. NO leo, you'd really have to study how to do it from the links I provided, otherwise well, it's about the same as trying to build a moon rocket by strapping a couple of fireworks onto a dustbin. Sure, anybody can make an electromagnet but to do it properly takes a lot of maths and research. The magnets they use in particle accelerators cost zillions of bucks and for a very good reason.

28. Why not just buy a permanent magnet and have some fun, and put the time you save into learning stuff? I remember when I was a kid at school another kid called Roly brought this magnet in. It was about the size of a half brick, and CLACK, when it attached itself to the metal side of the desk you could not get the buggar off. You'd be there squeaking as you dragged this desk around until Roly showed you how.

http://www.neotexx.com/

29. OK then let me change my question.
What are the best(good) materials to make an electromagnet with? i.e., wire guage/type, core material, battery voltage/size, etc.

thanks again. lots of good info.

30. Look up 'resistivity' of materials and choose the one with the lowest value you can afford (say gold or platinum, now extrude it into a hexagonal cross-section wire, next 'sputter' a layer of insulation on it 1 atom thick, now find and infinitely thin steel core, and wrap the wire around it taking care not to leave any air gap. Next buy a good fridge, (one that goes down to 0 Kelvin), drill a couple of holes in it for the supply wires and bingo - you have one of the most powerful electromagnets in the world, and as a bonus it uses no power to keep it going! - Make sure though that you change the fridge door, otherwise you'll never get it open...

Or, experiment, and if you do, then buy 'enamelled copper wire' the sort that is used in motors, transformers. If you are using a battery then the type of /iron/steel core makes little real difference (For AC though it's very different). As for how much 'juice you use' most electromagnets operate at two distinct voltages 'Energise voltage' - that needed to attract the target and 'hold voltage' - that needed to keep it, You'll burn out an Electromagnet if you do not switch from Energise to Hold, as you are effectively putting a short across the battery, remember after the EM field has been 'set up' pretty well all the rest of the energy you put in just turns to heat. In previous posts in this thread I have provided links to sites which explain how to design these things.

31. What is a tesla coil ?

That is some kind of electro-magnet, yes ?

32. No it's not an electromagnet as such, it is a transformer that is 'tuned' ie is very efficient at one particular frequency and used to produce very high voltages, google "Tesla coil wiki' for a look.

I am new to this but I have a basic understanding of building a simple electro magnet. I was wondering what materials can I use in order to make a strong magnet with maybe a high distance?
These are two very interesting magnets I made from a reprint of a book and design from the early 1900's.

You can see that I am working with aluminum. And at first a niobium magnet. And then repulsing the aluminum washers with an electromagnet. And in the second movie I use another magnet design in that book, to actually lift aluminum washers that are really not effected by the niobium magnet.

Both these magnets are basically wound with #14 magnet winding wire. The one that lifts aluminum has a double core. The cores are separated with copper washers basically.

(Edited), actually I used a much smaller wire for the aluminum attracting magnet in the movie. I forgot I wound two different magnets like that.

I made these movies for another forum actually, but I figure they might be interesting to scientists too.

http://www.Rockwelder.com/WMV/Magnetism/Magnetism.html

http://www.Rockwelder.com/WMV/AlumEl...tromagent.html

Sincerely,

William McCormick

34. A fellow on another forum told me that if I cut the washer it will not repel from the regular electromagnet.

He was right. Once cut into an almost closed "C" it will not repel. I can understand that though. Because the electricity is met at the slit, with the dielectric force of the air.

Sincerely,

William McCormick

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