[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

 

[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.

 

[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

 

[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.

 

[OneMalt]

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

 

[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.

 

[groggory]

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

---------

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

 

[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)

 

[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.

 

[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.

 

[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).

 

[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: [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.

 

[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?

 

[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!

 

[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.