# Building a light but powerful electromagnet.



## Kelvie1234

I have to build an electromagnet for project.. the only restrictions on it is that it must pick up a lot of quarters.. and it uses a supplied 12V DC power source.

 I was wondering how would I go to do this?

 I'm thinking about using just the regular coiled wire method.. with a few other things, and I want some opinions + ideas of some DIY experts over here 
	

	
	
		
		

		
			






 It it scored by two methods.. picking up the most amount of quarters for a bonus..

 And the ratio of the mass of the quarters picked up over the mass of the electromagnet itself.

 I was thinking of using some extremely light batteries.. (lith ion perhaps?) to bump the power up and get power through the wires; I can safely do this by just putting the DC voltage in series with the batteries, correct?

 Also.. what kind of batteries are the lightest, and where would I go to obtain some?

 And I was just wondering about things like.. wire composition, weight of the wire, and just wondered if any of you great head-fi DIY enthusiasts would have any idea concerning these matters.

 Any other ideas that I haven't thought of.. or words of caution, would also be greatly appreciated.

 Thanks in advance,
 K


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## ServinginEcuador

I only have one thing to add: lithium batteries are the lightest around. They weigh so much less than standard NiMHs and any other battery I have ever picked up. They also last like 5 years of typical use, so in something like this they might do quite well. They aren't cheap, but if light and powerful are criteria, try some of these.


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## Stephonovich

SiE, I think you're thinking of their shelf life; Lithiums can last for 10 years on the shelf. Alkies are about 5 years, IIRC, and NiMH/NiCD are only about 30 days (if charged) before most of their usefulness is gone. Lithiums do last longer than Alkies and rechargeables in most applications, but not 5 years
	

	
	
		
		

		
		
	


	




 (-:Stephonovich


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## ServinginEcuador

Actually, it is usable life, not shelf life. Lithium batteries in my Nikon film camera will last a godo 5 years of USE, not shelf-life. They don't have the oomph of NiMHs, so for applications like a flash unit they don't work well. But, in things like a film camera they are simply unbeatable and last for several years of use.


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## OneMalt

You say that the requirement is "that it must pick up a lot of quarters"? Good luck!


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## usc goose

Quote:


 _Originally posted by OneMalt _
*You say that the requirement is "that it must pick up a lot of quarters"? Good luck! * 
 

exactly what i was thinking. that's some powerful electromagnet.


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## groggory

Just playing around on google.....few little facts for you to play with

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 The force between two magnets equals B2A/(2KU0)
 where:
 B is the magnetic field (measured in teslas), 
 A is the cross-sectional area (in square meters), 
 K is the relative permeability of the magnet (non-dimensional), 
 U0 is the permeability of vacuum (4(PI)E-7 henry per meter).

 taken from http://www.islandone.org/LEOBiblio/SPBI1EM.HTM
 ----------------------------

 Efficent power supply suitable for inductive loads

 --------------------

 Superconductors lose all resistance to electricity when cooled to near absolute zero -- about 459 degrees below zero Fahrenheit. They make compact, energy-efficient electromagnets that use far less energy and create more powerful magnetic fields than larger, heavier magnets that use conventional materials.

_So if you can get your hands on a superconductor and maybe some liquid oxygen, nitrogen, or hydrogen then you are set to go.

 taken from http://www.anl.gov/OPA/news96arch/news960831.html

 ----------------------

In short, you need to change the core of the inductor, increase the number of turns, and/or increase the current.
 Changing from an air core to iron core has the most astound effect.

Making magnets stronger

 -----------------
Inductance of a coil is a factor of:
 The number of turns in the coil (we want alot of turns
 The area of the cross section of the coil (we want a large cross section, note: also tied to ratio of cross section / # turns)
 The permeability of the core (we want high permeability)

Electricity and magnetism
 -----------

 Some near optimum materials
Alloy 49 Iron-Nickel High Permeability Alloy[/url]
Magneperm high permeability cores
High permeability ferrites

 -----------------

 Notes on permeability_


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## groggory

ok, here are some other thoughts of mine....

 because inductance increases with diameter of the coils, using a larger coil diameter is in your favor. However, this also means you need a larger core.

 I would suggest finding a high permeability piece of iron stock, machining it into a reasonable diameter, then drilling out the center (not particularly in that order) so basically you have a thinwalled pipe.

 Correct me if I'm wrong, but I don't think, the forces change if the core is a pipe or solid. But I took those classes a few years ago so I could be wrong.

 Another thing to note. Make sure to use quarters post 1965. These quarters are (8.33% Ni and the balance Cu) weighing 5.670 g whereas quarters pre 1965 are quarters contained 90% silver, 10% copper which as far as I can find will be heavier by aproximately 2x (based on silver being aprox. twice as heavy)

 As to how to suspend it most efficently I have an idea.

 Electromagnet:
 -Iron tube
 -Thin gauge magnet wire wrapped very tight held tight with masking tape (lighter than scotch or electrical tape)
 -power source (light battery capable of delivering the current needed. Test current needed by experimentally using a batter capable of ALOT of current, measure with an ammeter, and then find a lightweight battery barely capable of that current)(voltage doesn't matter as long as you can develop the proper amount of current, but then of course voltage and current are linearly related. We might be able to figure out some circuitry to fix this though***I think***)
 Holding apparatus:
 -Thin iron disk the exact diameter of the core
 -ziplock sanwich bag (lightweight plastic cheap kind, chosen so the gap between the plate and electromagnet is minimized)
 quarters:
 post 1965 US currency

 Procedure:
 -place quarters in the ziplock
 -put one layer of the sandwich bag under the electromagnet
 -place small iron disk on other side of electromagnet
 -turn electromagnet on
 -make sure to keep electromagnet perfectly vertical (so that the disk only needs to overcome gravity, and an edge does not slip off the electromagnet, thereby reducing efficency)
 -verify results
 -promptly turn off electromaget so that batteries do not become damaged (don't forget you are pushing their current capabilities to their limits) and coil does not melt down (don't forget you are using as tiny guage of magnet wire as you can)


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## Voodoochile

Quote:


 _Originally posted by OneMalt _
*You say that the requirement is "that it must pick up a lot of quarters"? Good luck! * 
 

Canadian quarters can be picked up with a magnet. I was thinking the same thing until I saw where Kelvie hails from.


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## groggory

Quote:


 _Originally posted by Voodoochile _
*Canadian quarters can be picked up with a magnet. I was thinking the same thing until I saw where Kelvie hails from. * 
 

True, but I still like the method I came up with. That way you have no bumps on the quarter to increase the gap, and you have a more efficent system as there is not a loss from quarter to quarter.

 Any thoughts on what I came up with? Remember that all the requrement is is that he needs to pick up quarters, it doesn't specify how he has to pick them up.


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## kwhead

Well, since niether silver nor copper is ferromagnetic I'm guessing those old quarters would be pretty difficult to pickup regardless of their weight 
	

	
	
		
		

		
		
	


	




.

 One thing that can help *a lot* is to guide the flux from the end of the magnet not pointed at the quarters back down near them. This can generate a much larger flux density, which is what is needed to hold the quarters. Something like this:

  Code:


```
[left] _________ | H | | H | | H | | H | Q[/left]
```

Where the H's are your rod and coil, the lines represent a bent piece of steel or some other ferromagnetic thin bar, and the Q is the quarters.

 It's worth a shot trying on any implementation you do since it wieghs almost nothing and can be thrown on any existing solenoid. Experiment with the width of the U shape and the length of the arms (extending them a little past the quarters might help if that is compatible with the rules for picking them up).


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## groggory

Quote:


 _Originally posted by kwhead _
*Well, since niether silver nor copper is ferromagnetic I'm guessing those old quarters would be pretty difficult to pickup regardless of their weight 
	

	
	
		
		

		
		
	


	




.

 One thing that can help *a lot* is to guide the flux from the end of the magnet not pointed at the quarters back down near them. This can generate a much larger flux density, which is what is needed to hold the quarters. Something like this:

  Code:



		Code:
	

[left] _________ | H | | H | | H | | H | Q[/left]


Where the H's are your rod and coil, the lines represent a bent piece of steel or some other ferromagnetic thin bar, and the Q is the quarters.

 It's worth a shot trying on any implementation you do since it wieghs almost nothing and can be thrown on any existing solenoid. Experiment with the width of the U shape and the length of the arms (extending them a little past the quarters might help if that is compatible with the rules for picking them up). * 
 

That's a really great idea.

 You were talking though about the quarters not being ferromagnetic, my idea completely does away with that problem in that it picks up a helper disc to actually pull, and the quarters are just held in a little ziplock bag.


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## Kelvie1234

Wow.. these are really great ideas.

 Also to note.. where would I be able to find most of these materials? We may use any materials except permanent magnets, and sticky materials.

 Also.. only the electromagnetic attraction should be able to be used to pick up quarters, and yes, these are Canadian quarters.

 Also.. here's a link to the composition of the quarter:

http://www.mint.ca/en/collectors_cor...l_specs_25.htm

 It's not specified which quarters will be used.

 Also.. the power problem.

 Would it be worth it to go get some lithium and put it in series with the supplied 12 V power?

 And where would I go to get decent enough batteries also?


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## kwhead

Whoops groggory, I didn't read your post closely enough. With a helper disc it would be a moot point like you say.

 Kelvie1234: I'm not sure batteries will help you given you have supplied power already. The real question is how much current that 12V supply can give you. If you have access to the supply see if there are any current specs on it or anything. For a given gauge of wire the advantage of extra voltage provided by say another 12V battery could be realized with no battery by spliting the coil into two windings hooked in parallel to the original 12V supply (again assuming it can provide enough current).

 For your rod materials most steels/iron will work just fine. But be advised their magnetic properties can vary a lot. Stainless steels are not a good choice. You might get a rod out of an old solenoid from someplace as a good starting point. Or, for style points, make your rod out of pre-2000 canadian quarters which are made of nickel, a wonderful ferromagnetic material.

 You can get away with a tube instead of a soild rod only up to a point for the core. At some point the material saturates. Once you get there you have two choices, fill in the tube by making a rod, or go to a higher permeability material. Without going and looking for all sorts of materials I'd suggest just experimenting with whatever you can get your hands on. Emperical experimentation is probably going to be faster for you than a lot of theory and numbers.

 Good luck, sounds like fun!


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## aerius

Get a u-shaped bar or rod, in effect, a horseshoe magnet. Both poles of the magnet get used and thus you can pick up almost twice as much stuff for a given sized magnet.


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## Kelvie1234

So would using extra batteries be completely useless, even if I put them im parallel? (also do I have to match the voltages?)

 I'm thinking the more current I can get through it, the more quarters it'll pick up.

 And with more power in lightweight batteries, I can win the most quarters... and highest (mass) efficiency.

 I was also reading up on superconductors a while back.. although not feasible 

 I'm going to probably stick it in the freezer.. and bring it in a big ice box.


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## amisdad

I cant beleive nobody has mentioned Lithium Polymer Batteries. Lithium Ion is junk technology. LiPos are smaller and lighter LiPo cells have a lower internal resistance, so they're able to provide higher amp draw. Individual LiPo cells have a nominal voltage of 3.7 volts (vs. 1.2volts per cell for Ni-Cds). Cells are wired in series to give the following pack voltages: 1 cell = 3.7 volts 2 cells in series = 7.4 volts 3 cells in series = 11.1 volts. You often see these cell's wired in series and parallel together. A battery pack that has three cells in series (giving 11.1 volts) and 2 of these 3-cell packs are wired in parallel is commonly referred to as a 3S, 2P (3 series, 2 parallel). These cells can discharge at about 20 amps no prob.


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## kevin gilmore

quote
 I was also reading up on superconductors a while back.. although not feasible 

 Sure it is feasible. Depends on how creative you are.
 Besides which, once charged it needs no current whatsoever.
 This will pick up a whole lot of quarters. Several hundred
 killograms worth.

 Here are some neat pictures of the insides of one of my
 cryomagnets...

http://www.jeol.com/nmr/mag_view/mag...struction.html


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## jamont

Quote:


 _Originally posted by kevin gilmore _
 Sure it is feasible. Depends on how creative you are.
 Besides which, once charged it needs no current whatsoever.
 This will pick up a whole lot of quarters. Several hundred
 killograms worth.

 Here are some neat pictures of the insides of one of my
 cryomagnets...

http://www.jeol.com/nmr/mag_view/mag...struction.html 
 

Very cool 
	

	
	
		
		

		
			





 Just curious, have you ever seen one of these things quench?


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## kevin gilmore

quote
 Just curious, have you ever seen one of these things quench?

 I quenched a 500 about 2 months ago charging it
 for the first time.

 A 400 quenched in december.

 I deliberately quenched a 400 last week.

 Really impressive especially when you can hit the
 mains heater button and get it to quench on command.
 Scares the crap out of people who have not seen it
 before.

 About 100 liters of helium liquid turn into gas very
 quickly and exit the 1 inch safety hole at about
 200 miles per hour. Sounds very similar to standing
 next to a steam engine that is starting at full blast from
 a dead stop. Actually louder than that.


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## groggory

wow kevin, that is seriously impressive

 Plus the "This magnet contains approximately 12 miles (19 km) of superconducting wire." "dissipating the heat generated from the 85.5 kJ of energy that is stored in the energized magnet"

 Those little specs in themselves show the sheer enormity of these experiments


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## Kelvie1234

Hmm... they dumbed down the voltage to 6V, with an unknown current.

 Would it be a good idea to go out and spend on a few lith. polymer batteries to get it up to 6V.. then create a circuit that would put it in parallel with the supplied 6V charge?

 Or would that fry the batteries?

 And I think I'm going with the "horseshoe magnet" idea.. where both poles are doing the picking up. I'll probably stop by a metal supply shop, or an auto body shop and see what kind of metal they can shape me up.

 Also with that.. how would I design that "guide" for the horseshoe magnet?

 And I'm lost at finding the right wire.. what's the thinnest gauge wire (magnet wire?) at digikey? Also it has to have extremely thin insulation too.

 Thanks again,


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## Kelvie1234

Well.. alright.

 I got some 30 gauge magnet wire from the RatShack.

 A few problems remain..

 I don't know where to get an iron rod. I was thinking to get a 4cm diameter 30cm length iron rod (preferably the 49 Iron-Nickel Alloy composite), bent into a U shape; but I do not know of any places to get this in such short time (most places don't open on weekends either). Is a steel rod good enough? Or is it no good at all?

 Also.. the magnet wire. I have two rolls of 200'. I don't know if that's enough, and connecting them together will be a problem.

 How is it to be stripped? I'll have to hook up 30cm long leads to hook up to the power supply also.. and it seems tough hooking up regular hookup wire to 30g magnet wire.

 And last thing, is it worth it to have the core hollowed?

 (note: 2.54cm = 1 inch.. for those that don't use metric )


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## groggory

I don't know if you've ever used magnet wire before, but it doesn't have traditional insulation. It has a sort of oxidized (or something similar) coating. You can 'strip' this coating off with a cigarette lighter. Just make sure that whatever gauge magnet wire you choose, it can handle the currents your planning on using.


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## Born2bwire

In relation to what Groggory was saying, you would want a solid core.

 Using a solenoid as an example of a core of air, your magnetic flux density would only be proportional to the magnetic permeability, the number of loops per unit length, and the magnitude of the current (B = unI). By inserting a core into the solenoid, you now make the magnetic flux density through the metallic core proportional to current and the magnetization of the metal (B = u(nI+M). Plus if you could choose a material to have a magnetic permeability that is greater than that of freespace as another way of boosting the magnetic flux.

 Really I think just doing a horeshoe magnet out of a iron rod would work. Just wrap it tightly with thin wire and put a high current through it and that should do fine. You were mentioning that you were having trouble finding material, what about a piece of rebar... though that's steel.


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