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Flaffen
How to make an electromagnet?

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Hi. I've got a project going and I need to make an efficient electromagnet. The problem is that I'm pretty much a noob at this, so I could use some hints and tips at how to make it as efficient as possible.

The electromagnets I'm building are supposed to repell eachother (when putting + next to + and vice versa). The electromagnets are supposed to only be turned on for a very short time and then turned off again, and I need them to be as powerful as possible for this short period of time. The shape of the electromagnets are supposed to be tubular.

What metal should I use? Where can I get hold of this metal?
What wire should I use to wrap around the rod? Does it need to be thick or thin? What metal is best used for this wire? What batteries should I use? Is there a ratio between the diameter of the wire and the rod that would make it more efficient?
Should I make several layers of the wire wrapped around the rod or just one? Should I put insulation outside the wire? These types of basic facts is what I'm looking for, but I dont mind more advanced ideas either (tho I'm not that fluent in "electro-lingo" tongue.gif)

At the moment I have an approx. 1cm diameter iron rod, and I use 0.6mm diameter copper wire to wrap around it (it has some lacquer around it as insulation). I dont know if its soft iron or not. I have tried paralell circuiting 5x 9v batteries to the magnet but it diddent seem to make it very powerful. So if any of you have any tips or hints on how to make this as powerful as possible for a short amount of time I would greatly appreciate it. I'm planning on using a high current and high voltage to make it more powerful (as high as possible from circuiting batteries). Also it would be preferrable if the magnetic field dissapated as quickly as possible after the current has stopped.
And I'm also wondering how I can greatly increase the voltage of the current. As far as I have understood, I can make a tranformer to incfrease the voltage by wraping copper wire around two permanent magnets (facing in the opposite direction) and let the current flow throught this.

If anyone has any hints or tips or any how-to's I'd greatly appreciate it.
Michael J
Well, you would want to use copper wire for your magnets for starters, they conduct the electricity quite well. I would suggest the use of large capacitors if you only require the magnets to be on for a short period, but very powerful. Perhaps a transformer to increase voltage? If you want a serious voltage increase, you are much better off to buy one, than spend your time making your own. If you need a lot of voltage, the ones out of microwaves work real well, but those require 120v (wall plug in).

I'm new to this whole electronics thing, currently in a class this semester. Hope anyone with more experience can help you out.

Please do note, electricity does kill! I would not suggest handling transformers attached to capacitors unless you've proper safety equipment, as even though your device may be off, the capacitors will remain charged...

Good luck!
Lunarlanding
QUOTE (Flaffen+Oct 1 2009, 10:41 PM)
How to make an electromagnet?


What metal should I use? Where can I get hold of this metal?
What wire should I use to wrap around the rod? Does it need to be thick or thin? What metal is best used for this wire? What batteries should I use? Is there a ratio between the diameter of the wire and the rod that would make it more efficient?
Should I make several layers of the wire wrapped around the rod or just one? Should I put insulation outside the wire? These types of basic facts is what I'm looking for, but I dont mind more advanced ideas either (tho I'm not that fluent in "electro-lingo" tongue.gif)


Hi Flaffen;

In general, When trying to increase the magnetic field (and thus the force) its the CURRENT (NOT the voltage) that matters most as well as the NUMBER of windings about the core.

Of course the thickness of the wire must be sufficient to handle the amperage.

Thus in your example you should increase to say D size batteries to get greater current and use an many windings as possible.

For any particular size, The Magnetic field increses linearly with both current and number of windings....the FORCE increases as approximately the square of current and the square of winding number.. Thus if you want to maximize the magnetic force.you should increase the current and winding number to as much as possible without melting your wires. biggrin.gif

Yes, insulated wires should be used (enamel coating is OK)...also soft iron core is best . The length of the coil also has an effect ....make it several inches long. Overlapping many windings is fine.
Try various current increases by putting several D size (1.5 volt) batteries in series to give enough current.... ((those little 9v batteries have very little current)

That will do the trick for your type of experimentation...

Since you only want a brief surge in field the heat should not be a major problem if you disconnect rapidly.

Lunar biggrin.gif
Flaffen
Ok, so I should just increase the current by paralell coupling batteries (attaching + to + and - to - right?), and increase the windings. But voltage wont do me any good? Running the current through a stun gun wont help? Also I'm using a 0.6mm diameter copper wire, should I use a much thinner wire? I read somewhere that the resistance with this copper wire would be way to small? Or could I just up the current? (If I have to switch wire I'm gonna have to wait until I got money enough to buy it, and i'm not very patient tongue.gif) Also I've got like 30+ 9v batteries here, if I paralell connect them they still wont do any good? (I'm gonna buy D batteries from now on, but gotta wait a bit until I get money again tongue.gif, so thought it might be worth a try while waiting, they were rly cheap so wont be to much money going out the window tongue.gif)
Lunarlanding
QUOTE (Flaffen+Oct 6 2009, 02:25 AM)
Ok, so I should just increase the current by paralell coupling batteries (attaching + to + and - to - right?), ....


NO Flaffen; I said connect in SERIES.
If you want to use the 9v batteries, it will probably take 4 or 5 connected IN SERIES to get the approx amperage of one D battery.

Your wire size is OK for starters...experiment with using thicker wires later when ramping up amperage.

Get the D size later...and add more (IN SERIES) to see the difference in field strength.

Quit over analyzing it; half the fun is simply starting and experimenting with various arrangements.

...Lunar
piersdad
go to a recycle place and see if you can get the water solenoids from a fisher paykel washing machine some of the older ones were 24 volts and the newer ones had 12 volt coils.
remove the plastic solenoid from the valve part and replace the center with a bit of steel.
2 of these will ether repel or attract according to the direction of the current.
i picked up 2 from a recycle place for a few dollars.

12 volts from a car battery will work ether the 12 or the 24 volt one.
much easier than winding your own
Flaffen
Ok thanx for the info, it has helped a lot. But now I'm wondering if it is possible to "store" an electrical charge with higher current or voltage than what would flow from a bank of batteries? Kind of "charging up" and realeasing it, getting a very high current or voltage for a short moment. Or do I need to circuit a bunch of batteries to get a decent current?
Lunarlanding
QUOTE (Flaffen+Oct 27 2009, 02:32 AM)
Ok thanx for the info, it has helped a lot. But now I'm wondering if it is possible to "store" an electrical charge with higher current or voltage than what would flow from a bank of batteries? Kind of "charging up" and realeasing it, getting a very high current or voltage for a short moment. Or do I need to circuit a bunch of batteries to get a decent current?


What you need is a capacitor . If that's what you want to do ....You simply need to charge up a very high capacitance CAPACITOR with a direct current source...and then discharge it through the coil.

BTW, I think you should atke a course in basic electronics, flaffen.

More info here... http://en.wikipedia.org/wiki/Capacitor

http://electronics.howstuffworks.com/capacitor.htm

Lunar
Enthalpy
Core: iron is a good choice. What you need here is a high saturation induction, and any iron or steel (not stainless) is good. Few alloys (50 Fe +50 Co) would be slightly better but cost 50 euro/kg. Soft iron's only effect here is that the core doesn't attract iron once the current is shut off. Laminated cores aren't useful for DC current.

Windings: unless you have superconductors, copper is the best choice, and you should pack as much in the coil's volume as possible. So lacquer is better than a thick insulator, and square wire would be better if available. Thin copper sheet is excellent for the filling factor but as you wind it only in spiral, it often gives too few turns, meaning a resistance often too small.

Turns: the amount of copper determines the power needed. Then you can choose between many turns of thin wire or few of thick wire, but this changes only the winding's resistance. The same power will have to be provided at a higher voltage and a lower intensity, or the opposite. So you tune this freely to match the properties of your source of power.

Power: as much as possible, but compatible with the cooling of your coil. I used 7MW for 10ms (from 1m3 capacitors) to achieve 7T in an ironless coil.

So whether you connect your batteries in series, parallel, use thin or thick wire: combine this to extract the maximum power from your battery. A new 1.5V battery gives its maximum power when the load lets is voltage drop immediately to some 1.2V.

Form: with a limited power (from batteries) a somewhat longer core would be better. But the real improvement would be to have zero air gap in the magnetic path: if the object to be attracted is flat, then your electromagnet needs a curved iron that brings the rear pole to the target as well.

If you look at cranes that have electromagnets to lift big iron pieces, that's the form their magnet has. The iron is cup-shaped (rear pole) with a rod at the centre (aft pole) and the coil around the rod. Hard to buy in small iron part, but exists for electronics engineering as a so-called "ferrite pot".

Easier to find: get an old transformer - definitely the effective and easy method. Its iron core composes of an I-form part that you throw away and an E-form that you keep. Around the E's centre pillar are the coils which you may keep if one has a resistance that matches your power source; if not, remove the windings and put yours on the coil former you keep.

Have fun!
Enthalpy
High power for a short time:

The standard answer is a capacitor (or a bank of). Depending on the design, peak power can really be huge, like MV*MA. See the Z-Machine, various megajoule lasers...

At somewhat lower (or less huge) peak power is provided by accumulators, who store more energy than capacitors. Ni-Cd accumulators are really brutal for that, Pb accumulators (like in cars) little less - and both are authentically dangerous because of that. Their short-circuit current is huge. Be really careful. Nothing for a noob.

More exotic answers exist, like a homopolar machine, a compulsator, a (superconducting) coil... Less common.
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