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