Home made electromagnet

[Rgillard]

Hi guys,

Just wondering if anybody has ever built an electromagnet. I am thinking of making one for the lifting blocks in my shed so that workpieces could be lifted easily. I seen on scrapheap challenge (UK version of junkyard wars) that they lifted a 600kg mini cooper car out of a lake using two twelve volt batteries wired to a coil wrapped around a piece of metal (http://www.channel4.com/4car/ontv/scrapheap/challenges/06_car_fishing/science.html). I was just wondering if anyone has done this how many volts and whether AC or DC? Any replies would be muchlt appreciated

Ronan

 

[Paddy]

I work in the High Voltage industry. We use magnetic actuators to open-close large circuit breakers. This is a solenoid type device with a permanant magnet holding once closed. To open, a pulse from a coil in flux circuit reverses the polarity. This kills the strength of the permanant magnet momentarily and allows for the wieght to drop.

The addvantage of this concept is the current need is for 20ms, a very short time. The magnets I use have holding strength of 1200kg and weight less than 0.5 kg.

The device; a 3" dia round bar 6-10" long with a round magnet at one end and a coil at the other! As you energize the coil it will either hold better or release, depending on pos or neg direction.

Magnets are cool

 

[TMcD_in_MI]

To answer your last question first, you need a DC power source. AC will cause the electromagnet to reverse its field 120 times per second, if you have 60 cycle AC, and that won't pick up much of anything.

Electromagnets are easy in principle. Take a piece of iron, wrap it with a hundred or so turns of insulated wire and connect the wire ends to a battery. More turns will make a stronger magnet. Higher voltage will make a stronger magnet, assuming the voltage source can supply more current as well.

I have only made small electromagnets. My biggest one had an iron rod about .5 inch diameter with around 200 turns of maybe 18 guage wire. I hooked this to a 15 volt power supply that would put out 1 amp of current. With this I could pick up several pair of pliers at once, or a small steel table weighing less than ten pounds. This could be scaled up by using more turns, bigger guage wire, and a power supply that could supply more current, like a car battery.

Things to worry about include heat buildup in the coil of wire, and the danger of electrical shock if you get the voltage up beyond the twenties. There may be other worries that I haven't thought of, so please do more research before you try this, and be careful. Remember, I am just a voice on the internet, and you can't necessarily trust me. /forums/images/graemlins/grin.gif

ThinMan

 

[have_blue]

Here are some tips:

A laminated soft steel armature is more efficient than a solid core. They can be cut out with tin snips or a plasma cutter, stacked, drilled, and bolted together.

A singele 12v battery will work fine, but your wire gage will have to be pretty heavy.

A pair of 12v batteries in series work better than a single, and the wire can be thinner with many more turns.

Solid core wire is better than stranded.

The more amperage, the more power in the magnet.

 

[chim]

The strength of the electromagnet depends greatly on the number of "ampere turns". An oversimplification is the magnet with 2 turns of wire with 1,000 amps will hold about the same as a magnet with 1 amp and 2,000 turns of wire. The latter would be a whole lot easier to wire /forums/images/graemlins/grin.gif.

AC works pretty well for some applications. AC is almost exclusively used for the electromagnets that close large sets of contacts in motor starters.

I'd be nervous about using an electromagnet for lifting a load that would have people under it, or anything expensive. Scrap yards use large electromagnets on cranes to move scrap, but I'd bet they have some serious rules about keeping personnel away from the loads.

There are door locks (strong electromagnets) that we have installed that have a holding power of 1,200 pounds. These have #18 wire feeding them with 12volts. They measure about 8" x 3-1/2" x 1-1/2" and bolt to the door frame. A steel plate is fastened to the door so the magnet has something substantial to grab. Have a look at this site, and go to PRODUCTS, MODEL 62 for a look.............chim

http://www.securitron.com/products.asp

 

[Charlie_in_TX]

As chim said, the important thing is ampere turns. You multiply the amps by the number of turns to get the magnetic field (there are other factors that go into as well but to KISS just think ampere*turns). A bit of an oddity comes about in the math (given an strong enough power supply), for a given gage wire at a given voltage the ampere turns remain constant. It comes from the fact that the wire resistance per turn is the same for a give wire gage. If you want to increase the ampere turns you must increase wire size.

Example: (I will use exagerated values to make the math easier. Do both of us a favor, don't try to run more currents thru a wire than it can stand. Roughly 20 amps for 12ga, 15 amps for 14ga, 10 amps for 16ga, 7.5 amps for 18ga)
lets say you use a wire that is 0.01 ohm with one turn and 10vdc. The current thru the wire is V/R. In this case that is 10/0.01 or 1000 amps. 1000 amps times one turn gives 1000 ampere turns.

Same wire and power supply as above but 1000 turns instead of 1 gives a total resistance of 10 ohms. 10V/10ohms is 1 amp. 1 amp times 1000 turns gives 1000 ampere turns.

Now if you go from 0.01 ohms per turn to 0.005 ohms at 10 volts you go from 1000 to 2000 ampere turns.

 

[MikeD74T]

It's not clear what you're trying to lift. i.e. how much weight. The Securitron magnets are very powerful. Ebay sometimes has magnetic drill presses that have a bad drill motor and are sold for parts. My old Black & Decker holds well enouth to drill 1 " holes with a heavy feed rate. It has a nice feature where the magnetic field comes on seeming instantly but decays off somewhat slowly when releasing. handy when adjusting the drill position on vertical or overhead projects. I paid about $200 delivered for it. One of the best tool purchases I've ever made. Don't see why the magnet couldn't be used for other things.

 

[TruChaos]

I've played around with small electro magnets and have made a few observations. First, it takes an amazingly small amount of power to lift realtively heavy loads. For example, I had a small hand held electro magnet with a handle on each end. When it was energized with only a 1.5 volt D battery (flashlight battery) two strong men could not separate the two halves. This magnet has at least 300+ pounds of lifting strength before breaking.

My second observation is, aside from the current and magnet size, the contact surface of the electomagnet is critical. If the magnet face (contact surface) is very smooth and flat and is mating with another smooth flat surface, it was nearly impossible to break the attraction. The more rough and irregular the mating surfaces, the weaker the lifting strength.

I agree with the comments about using DC however, since DC current is more troublesome to obtain (batteries, power converters, etc) than AC wall power, if you build your electromagnet to plug into the the wall outlet and place a high current diode in series with the coil, it will work just fine. This will give you a pulsating half wave, sometimes referred to as pulsating DC. If you go this route, you may be able place a light dimmer in series with the electromagnet and control the current to the magnet.

Just my two cents.

 

[MizztaPeppa]

I wanted to know if there was a way to use a homemade electromagnet to make something push away from the magnet instead of pull. Is there a way to reverse the power? I do not know at all alot about currents and diodes resistors ohms and all that. Ideally i want to make a flat electromagnent about 20inches wide by around 25 inches long and probably about no less then an inch or an two inches in height, that can plug into a portable battery jump starter which has dc car plug power or ac power. and i would like it to push another flat metal, or iron, whatever works, away from the magnet. And i was planning on having fishing wire on the edges to hold this plate in place so it would look like it was floating. Is this possible? and around how much would you estimate it would cost. Please someone respond! Cant find alot of information ANYWHERE!

 

[bobodu]

You could possibly get repulsion from having a permanent magnet magnet attached to whatever you are trying to push and using a linear electromagnet with the opposite polarity aligned with the permanent magnet. Don't have a clue as to how you would determine the size of the two though because I DID NOT stay at a Holiday Inn Express last night...

EDIT: Here is a Google search using "electromagnetic repulsion" as keywords.Maybe something here will help you.

http://www.google.com/search?hl=en&...sult&cd=1&q=electromagnetic+repulsion&spell=1

 

[GuglioLS]

Solenoids can be made to push or pull, electromagnets are pull only. What exactly are you trying to move and how far are you trying to move it? DC solenoids are easiest to wind by hand. AC solenoids can be made but the winding scheme and armature are a little more complicated best done by machine. Electro magnets are best for holding ferrous metal tight. With low power magnets, the gap between the magnet and the object being pulled toward it, can not be more than a inch or two at most, same goes for repulsion you can't get more than an inch or two of motion. Here is a home made solenoid I once made in an attempt to automate a locking pin for a TPH implement. A linear actuator may be a better choice as they are much more powerful and predictable. The basic concept of making a solenoid is simple enough, putting theory into a home made working solenoid is a bit more challenging:






If interested, check out my original post 360* rotating back blade project PAGE 18 check out page 19 as well, heck, check out the entire project if your really curious.






Google - electro magnets, home made solenoids, How stuff works, Magnetic levitation, etc.. there are tens of thousands of articles of how to make solenoids and electro magnets. So you want to levitate something 20" X 25" ? that's huge, How much does it weigh? Something that big is gonna take quite a bit of power and hundreds of $$$ worth of copper magnet wire. Magnetic levitation is difficult and a huge power hog. Under the best of circumstances, you might get 1/4" to 1/2" height at most of levitation.

Larry

 

[MizztaPeppa]

Solenoids can be made to push or pull, electromagnets are pull only. What exactly are you trying to move and how far are you trying to move it? DC solenoids are easiest to wind by hand. AC solenoids can be made but the winding scheme and armature are a little more complicated best done by machine. Electro magnets are best for holding ferrous metal tight. With low power magnets, the gap between the magnet and the object being pulled toward it, can not be more than a inch or two at most, same goes for repulsion you can't get more than an inch or two of motion. Here is a home made solenoid I once made in an attempt to automate a locking pin for a TPH implement. A linear actuator may be a better choice as they are much more powerful and predictable. The basic concept of making a solenoid is simple enough, putting theory into a home made working solenoid is a bit more challenging:


Google - electro magnets, home made solenoids, How stuff works, Magnetic levitation, etc.. there are tens of thousands of articles of how to make solenoids and electro magnets. So you want to levitate something 20" X 25" ? that's huge, How much does it weigh? Something that big is gonna take quite a bit of power and hundreds of $$$ worth of copper magnet wire. Magnetic levitation is difficult and a huge power hog. Under the best of circumstances, you might get 1/4" to 1/2" height at most of levitation.

Larry

Thanx for the info Larry, Yes basically i want something thats 20 inches by 25 inches to levitate estimated weight between 150 to 180 pounds.
So copper wire around lets say a piece of iron, is the best thing for a basic homemade electro magnet? And if that is true can I get lets say multiple pieces of iron and wrap them all seperately but still be powered from the same source for a stonger push/pull force? Or could i wrap around all them together to get a greater force. Also how big of gauge of wire should i be using.

 

[MizztaPeppa]

Thanx for the info bobodu,I like your joke and also yes i was thinking of having a magnent on the surface of the floating piece of metal or whatever it would be.
So copper wire around lets say a piece of iron, is the best thing for a basic homemade electro magnet? And if that is true can I get lets say multiple pieces of iron and wrap them all seperately but still be powered from the same source for a stonger push/pull force? Or could i wrap around all them together to get a greater force. Also how big of gauge of wire should i be using.

 

[bobodu]

180lbs???

You're sucking a lot of juice!!
I'm not implying you're a drunk...but you are going to be broke from the electric bill.
Watch Modern Marvels "Magnets" and see how much power is required to levitate a frog.

 

[MizztaPeppa]

180lbs???

You're sucking a lot of juice!!
I'm not implying you're a drunk...but you are going to be broke from the electric bill.
Watch Modern Marvels "Magnets" and see how much power is required to levitate a frog.

lol ok i will watch it tonight. ok so heres the thing. maybe itll help you get you guys to see a little more of what im getting at.

This is the hover chair.

HOVERIT - Changing the rules of conventional furniture.

I want that but not a chair. Just a flat surface i can stand on. but i dont want big bulky magnets i want magnets that is flat but about 20 by 25 inches or smaller, whatever necassary to get me able to stand on it. I was trying to get it to be electric so i can turn the hover on and off ya know so when i hit on it raises up. And i will have fishing line at the edges of the magnets or surrounding surface of the magnent so it doesnt fall off when i turn it on. Ya know what I mean? going for the hoverboard look.

 

[MizztaPeppa]

O and also i found these. Would they be strong enough if i had two just like the chair. or could i have an electro magnet on the bottom and one of those on top pushing away.

http://www.magnet4sale.com/home.php?cat=355

 

[rScotty]

I wanted to know if there was a way to use a homemade electromagnet to make something push away from the magnet instead of pull. ........... Please someone respond! Cant find alot of information ANYWHERE!

OK. Here's a definitive answer. BTW, designing magnetic devices is how I make a living so it's a subject I know well. The answer is, "No you can't. Magnetism doesn't work that way". Actually that's not quite true. I should say that you can't make it do any useful work. There are a few materials that are repelled by a magnetic field regardless of polarity. But those materials aren't common and the effect is very weak.
Magnetism isn't the only basic force that works in this lopsided fashion; gravity is another. You can have it as an attractive force, or no force at all...but no one has yet discovered a way to reverse its effect.
rScotty

 

[MizztaPeppa]

OK. Here's a definitive answer. BTW, designing magnetic devices is how I make a living so it's a subject I know well. The answer is, "No you can't. Magnetism doesn't work that way". Actually that's not quite true. I should say that you can't make it do any useful work. There are a few materials that are repelled by a magnetic field regardless of polarity. But those materials aren't common and the effect is very weak.
Magnetism isn't the only basic force that works in this lopsided fashion; gravity is another. You can have it as an attractive force, or no force at all...but no one has yet discovered a way to reverse its effect.
rScotty

im not trying to make something just levitate and stay in one spot by itself im going more along the lines of the hover chair which i put in a reply earlier thats obviously floating but its being held by the plastic parts of the chair. so i want to do that but with an electromagnet to turn it on and off and if i cant turn it on or off and have to use just basic magnets then thats what ill have to do, but ill still need to find strong enough magnets to support 150-180 pounds. Which according the magnets 4 sale website the magnets i was looking at have a pull force of 210 lbs which im assuming that the push force would be the same if i had two magnets of opposite polarity. If you respond to this message please respond to everything i said not just one point.

 

[GuglioLS]

The fishing line to hold it all together will not work. Use at least two rigid guide rods (four guide rods, one at each corner would be best) Take a close look at the maglev lounge chairs in the link you provided. They clearly show rods with guide holes to keep it aligned above the magnets. I hope they have a warning about not sitting in them with your wallet or the magnetic strips on your credit cards will be wiped out! Same goes for a pace maker, which you might need after you learn of the cost of copper magnet wire, and the electric bill to power your contraption. Sitting in one of those maglev chairs would be the same as if they were conventional chairs. Gravity will still pull you body down against the chair just the same as any other chair. To me they look like some gimmick for cool-aid consumers with money to burn.

If your really serious, I suggest sixteen of those $88.99 4X4X1 closeout Neodymium magnets with 335 pounds of holding force. Stack 4 of them on top or each other, then place one stack at each corner of your platform. Then make 4 corresponding electromagnets placed above the permanent magnets. Hook the electro magnets to a couple of 12 volt car batteries connected in series and viola - magnetic levitation. As far as how big and how many windings those electro magnets need to be, and just how much force it will lift and how high it will lift it will require some serious Quantum electrodynamics and mechanical calculations. I suppose your budget for this is unlimited and your just wanting to make some sort of magic trick? A little effort on your part in some on-line google searching will reveal the reality of how many windings and how much power your really going to need. rScotty nailed it with "I should say that you can't make it do any useful work." The most practical use of magnetism is to produce electricity, the second is electromagnetic radiation (radio waves) the third practical use is solenoids. The amount of mechanical power provided by magnets is very week and somewhat limited to small solenoids and electromagnets to hold doors closed and moving / separating steel in scrap yards. The Mag Lev train is a waste of money and power, it is very inefficient. The trouble with magnets is they have two equal but opposite attracting poles, so the magnetic radiation is a closed loop that does not reach out very far. Now if you could somehow invent a single pole magnet, you may have something that would revolutionize the world.


Larry

 

[rScotty]

the magnets i was looking at have a pull force of 210 lbs which im assuming that the push force would be the same if i had two magnets of opposite polarity. If you respond to this message please respond to everything i said not just one point.

The push or pull force is maximum when the magnets are touching. Is that what you want? Otherwise the force falls off as the square of the distance between them. As Gugliols says, the big problem is going to be keeping the magnets centered above each other. On the calculations, I don't know whether that supplier is quoting force between two magnets or one and some ferritic material. Either way, go to Arnold - Technology Center and download the spreadsheet on magnetic field strength calculations. That will give you a handle on magnetic strength via calculation....or just buy two magnets, thread them on a rod and graph how much weight it will support and how the gap between them decreases as the weight forcing them together increases. BTW, summing magnetic forces by stacking depends on the magnets and the geometry & diameter to length ratio- but using two won't double the forces. A rule of thumb is that the second one is worth 50% of the first.
Many magnetic buffs use a freeware program called "FEMM". If you have time to model your magnetic circuit the program will answer all of your questions. You can find it at femm.foster-miller.net
rScotty