Strong Electromagnet From An Old Transformer

This is a very strong electromagnet made out of an old transformer.
The materials used are recycled from transformers and motors.
This magnet can lift over 30lbs (14kg)

This instructable is in the Epilog Challenge. Don't forget to pick your favorite.

Step 1: Parts & Tools

Parts:
1 Transformer
Enough magnet wire to fill the core.

Tools:
Box Knife
Pliers
Slotted Screwdriver
Small Hammer

Comments

[Machine]

Very nice, very impressive weight that it can lift and simple construction too. Thanks for showing us.

[krrran000]

i am looking for such type of powerful electromagnet . finally i got it. i will try for it..
thank you

[aloving95]

Immagine if you did this with a MOT (microvave oven transformer)

[rocketman221]

I was thinking about that, but I have never taken one apart. I don't know if it would come apart very easily.
The small electromagnets are hard enough to pull off of something. I would like to seen what a mot would do.

[my project box]

I have found that microwave ovens are a very good source for copper wire, the main problem is the varnish that that is used on the coils when they are made is very tough leaving sharp fragments stuck to the copper wire as it is unwound, which can act like a saw if pulled over unprotected hands.
Never the less around 1/2 a kilo of copper magnet wire from an old microwave oven destined for the garbage bin can't be all that bad, and if any one knows of a way to soften the varnish that is used to hold the coils together 'with out damaging the wire's insulation' ........

[rocketman221]

Wrap the wire around a metal rod or a screwdriver and pull it tight over it. It will straighten the wire and break extra bits of varnish loose.

[50-50]

WARNING
please don't try this with a MOT
I alredy have and it killed preaty much evrything electronic around it when I hooked it up to my electric fence power supply.(10 000 volts)
It also sucked the ring I was waring to it and I started getting zapped by the current.ouch.

[aloving95]

I Found a MOT that was messed up and the lamanations were bolted together. ill try and post a pic when i finish winding the giant bobin

[Mazdak67]

Can anybody help me how can I build such above powerful electromagnets with the same size of transformers and connect 8 of them in parallel to a 4.5 amp 24 Volt DC power supply?
The temperatures should not goes above 80C.

Please tell me the wire turns and diameter in mm.

Thanks

Mazdak

[rocketman221]

What size are your transformer cores? That will determine how much wire you can fit on them, and magnet with more surface area will be able to dissipate more heat.
My 12V magnet has about 650 turns of 0.3mm wire (about 66 meters).
A 24V magnet will need a lot of wire. 200 meters of 0.3mm diameter wire has a resistance of about 48 ohms which will draw 0.5A @ 24V. You could use thinner wire, but anything much smaller is very fragile.
24V @ 0.5A = 12 watts which will need a larger core than I used in order to run continuously.
The cores I normally use are 35x25x15mm which run at 10 watts intermittent or 5 watts without heating up quickly. The largest core I have used is 57x38x25mm and it runs at 13 watts and produces very little heat.
Are the magnets going to run continuously? I have never needed to run any of mine for more that 10 or 15 minutes, so I don't know how they will work for extended periods of time.

[Mazdak67]

Dear Rocketman

Thank you ! It seems you have so many experiences for making powerfull electromagnets with low cosumption.

Would you please guide me for making elatromagnets with both sizes: 57x38x25mm and 5x25x15mm

My application is continious(24hr) and power supply is 24Volt.

The power consumption ( W<12 watts) and temperature raise( T< 70C) should be as low as possible.

Can you tell me what is the total turns and size of wire in mmfor each size?

Thank you

Mazdak

[rocketman221]

The smaller core will not hold enough 0.3mm wire to make a 24V magnet. It would need thinner wire that I wouldn't attempt to wind by hand and would be limited to around 5 watts for continuous use.
The larger core will hold the 200 meters of wire needed for the 48 ohm coil.
I am away from home right now and don't remember the inside measurements of the core, but it should hold approximately 100 turns of 0.3mm wire per layer. I think it would be around 10 meters of wire for the first layer. I can get a better estimate when I get home in a few days.

[rocketman221]

Provided that my math is correct, the 57x38x25mm core will hold 86 turns per layer with its coil form. You will need 23 layers which is 1,978 turns and is 208 meters long. It will have a resistance of 49.37 ohms which will draw 486mA at 24V which is 11.66W.
The actual magnet will differ a little bit because the windings probably won't be perfect and the wire probably won't be exactly 0.3mm diameter.
The core has room for 26 layers with the plastic coil form in place, so it will be mostly full

[Mazdak67]

Thank you for your instruction.

I will try it

[theloyz]

I might have missed it, but how much power are you putting into that?

[sassafras72]

So how do you power this? I'm assuming you connect the power source to the two ends of the copper wire, but I want to be sure. If you added one more step showing that, then this would be a perfect instructable.

[rocketman221]

The two wires are connected to a DC power supply.

[aviatordave]

Thanks for the tutorial. I have found that the wire wound around nails and such is too weak for my experiments. I have a 24 v 2.5 amp DC supply. could it be possible to use this? And by magnetic wire, are you referring to copper varnished wire of small gauge?

[rocketman221]

Yes, a 24 volt power supply will work. Although using the full current would heat up the magnet quickly unless it is rather large. I would suggest winding it between 32 & 48 ohms, which would use between 12 & 18 watts.
It will need rather thin wire.

The magnet wire is enamelled wire (most of mine came from other transformers).

[aviatordave]

Just wanted to say that this worked great. I used a 24 volt supply. Taking apart the xfmr was kind of a pain, you need alot of patience.

thanks for the tutorial

Dave

[aviatordave]

Just curious, do these give off high EMF? Is it safe to be by?

[rocketman221]

I assume you mean electromagnetic field not electromotive force, and yes there is an electromagnetic field created by them. When powering them with DC power it is basically the same as a permanent magnet, so they are safe to be around. Just keep them (any powerful magnet) away from anyone with a pacemaker though.

As for electromotive force, it is a large inductor, and will emit a high voltage pulse in the opposite polarity when power is suddenly removed. Use a flyback diode if you are switching it with a solid state device (MOSFET, transistor, etc). You will notice a spark when disconnecting power.

[aviatordave]

OK, great. Thanks!

[agod]

how did you wind the wires together

[rocketman221]

I strung all of the wire out, then used a drill to twist them together.

[ElectroFrank]

DC is better than AC because the magnetic field becomes constant, instead of changing direction all the time.

The advantage of using thin wire is that it has higher resistance, therefore less current will flow, and less energy will be wasted as heat

For every two turns of thin wire at 1/2 Amp, you get the same magnetic field as one turn at 1 Amp.

So (up to a point) more turns of thin wire will give much greater efficiency than less turns of thick wire.

Very simply, the magnetic field strength is proportional to the number of wire turns times the number of Amps going through it.  (The scientific unit is "Ampere-Turns",.)

It's worth checking the wire resistance per metre, measuring the coil diameter and doing the math in advance, to get the greatest magnetic field strength for the power you are putting in.

And it helps to avoid blowing up your power supply.

The steel core strengthens the electromagnet by improving the magnetic circuit, so the "E" shaped laminations are best, with all three ends touching the item to be lifted.

Have fun !

[tledgerwood]

actually, heat is caused by friction between electrons and the copper atoms. the friction is higher when there is more resistance, as the electrons are "hitting" impurities and atoms are releasing heat energy.

if you had a copper wire and a copper pole then you would be able to pass the same amount of energy through each and the wire may melt, due to higher resistance, and the pole would be able to take more energy because of the lower resistance.

this high release of heat energy is why a strip heater uses a thin wire.

[ElectroFrank]

Yes, we all went to school. But, well done for paying attention !

It's wonderful that you are taking an interest in the depths of the science, but it is rather irrelevant for the purposes of the average instructable.

If anyone really wants to know that the thermal motion of ions is the primary source of scattering of electrons (due to destructive interference of free electron waves on non-correlating potentials of ions), and is thus the prime cause of metal resistance, they look it up on Wikipedia.

But it's not actually very useful here. Please don't be offended, I'm just trying to keep you from aeronautically ascending at figurative hyperbolic tangents. ;-)

Please let me correct your post slightly:
If you pass the same current, say 1 Amp, through a pole say 1 Ohm, and a thin wire say 100 Ohms, the pole dissipates 1 Watt, the wire dissipates 100 Watts. (Power, not energy.) The pole would dissipate less power due to it's lower resistance. 

[schumi23]

Hehe, Good Job correcting the correcter.
I do, however, disagree with what you said about what we should look up on Wikipedia, for two reasons:
One is that i might not know what to search up, if i had no knowledge at all about it.
Second is that people do not have to read it, but a lot will,because a lot care. I know that i especially love instrutables that explain why something happens. and the more in-depth, the happier i am

[Ralphxyz]

Now there's another important detail!

so the "E" shaped laminations are best, with all three ends touching the item to be lifted.

Thanks,

Ralph

[John.Henry.]

Hello, I have a couple of questions. First, is your strand of 22 awg wire insulated? I believe that for the electromagnet to work properly, each turn has to be insulated from the adjacent turns and from the subsequent layers. Also, I think that the way to go in order to determine the necessary voltage for a magnet would be to calculate the total resistance of you wire and search for the maximum amount of current it can carry and find the voltage using ohm's law. Also, I feel stuid about this question but I want to be sure; I experiemented with a couple of basic electromagnet designs (wire wraped around a nail) and I hook it up to a 12V battery and I got sparks and it started to heat quickly. I assume that this is not a normal nor a desired effect and I would like to know if this happends because of too much voltage or too much current. I beleive that it is too much current and my coil had a too low resistance which would have let a much higher current flow causing a type of short circuit.

Anyway, thanks

Btw verry nice instructable. I, myself, am trying to build a magnetic sheet metal with a couple of your electromagnets. Got any tips? I will kee you updated on the project if you would like.

[rocketman221]

The stranded wire I used is made from insulated magnet wire.

When I made my 12v electromagnet it needed 650 turns of thin wire which was probably around 200 feet.
The electromagnets will get warm, but they shouldn't get hot immediately.
If you get big sparks when you connect the magnet, then it is probably pulling way too much current.
Try using a couple of D cell batteries instead of a 12v.
Multiple magnets can also be wired in series.

[John.Henry.]

thanks for the quick answer i will keep it in mind. One last thing thaugh, you said you used the wires of different transformers to make your strand and i was wondering if the insulation on the wires from used transformers is still reliable because when i unwinded the thin wire of the transformer it was stickty and i thaught it was the insulation stripping away.

[rocketman221]

I haven't had any problems with the reused wire, but I wouldn't use it for anything involving high voltage either.
The cheap transformers are dipped in varnish to hold them together and that is probably what was chipping away. The enamel insulation is pretty tough stuff.

[John.Henry.]

All right, sounds good.
Thanks for everything

[sguy1]

if we use thin wire what happens to the magnetic field created. will it be stronger or weaker? and how does magnetic field change with the thickness of wire?

[rocketman221]

Thinner wire has more resistance so less current will flow, which will make the magnetic field weaker unless you use a higher voltage.
One of my magnets has thick wire and runs at 2 volts and another has thin wire and runs at 12v. They both use about the same wattage and lift about the same amount of weight.

[takide]

what power source are you using?

[rocketman221]

I am using this modified computer power supply.

[Ralphxyz]

Nice Instructable, thank you.

I am still working on determining the voltage.

I would use the standard "by guess and by golly" method.

I'd guess at a voltage and by golly it might work.

If you used 100ft of 22awg wire what voltage would you use?

What about 50 feet of 32awg?

I thought thicker wire higher voltage but you seem to imply thinner wire higher voltage.

I suppose you can make more turns with a smaller gauge wire.

I'd to see something definitive beyond the best guess method, or using experience since I do not have any experience.

It seems most coil projects use experience "this worked in the past" for 12 volts so I'll just do it again.

Thanks again,

Ralph

[sudharma]

Actual calculations depend on lots of factors, but generally 6 turns of windings per volt is a good value. ie for a 12 volt supply, 72 turns of windings are sufficient. You could add a couple of additional turns to be on the safer side. ofcouirse the thickness of the Magnetic wire will depend on the size of the laminations and the current .

[Ralphxyz]

sudharma, great, 6 turns per volt that I can understand. That's the voice of experience. Thank you. Ralph

[sudharma]

Sorry, I forgot to mention that the 6 turns /volt works out for AC Electromagnet only If you apply DC the coil will burnout.Its the inductance of the coil whill limit the current.

[rocketman221]

That works well running it from AC power.

[rocketman221]

Thicker wire has less resistance, so more current will flow at a lower voltage.
100ft of 22awg is 1.9 ohms. It should work with 5 or 6 volts. Just watch the temperature. 32awg is rather hard to work with.

I just made a 12v magnet with 0.3mm wire which is between 28 & 29awg. It has 650 turns which is probably around 200ft.

If you are using DC you can use a wire resistance chart & ohms law to estimate the current the coil will use.

When using recovered parts that you don't know the ratings of, there can be some experimentation. It helps to have an adjustable power supply for testing though.

[tledgerwood]

i love ohms law and how the unit "ohm" is a product of it's own law, and how the symbol is omega in the Greek alphabet or a horse shoe to simpletons

[Ralphxyz]

rocketman221, thanks a lot!
I just made a 12v magnet with 0.3mm wire which is between 28 & 29awg. It has 650 turns which is probably around 200ft.

650 turns blows sudharma's 6 turns per volt out of the water.  

The "length" of the wire effects the ohms so it doesn't seem it is only the number of turns to determine voltage.

I think I'll just have to experiment to gain the experience. At least now I have something to start with, again thank you for the Instructable.

[rocketman221]

When running the magnet from DC the resistance is more important than the number of turns.
When running from AC the number of turns is more important than the resistance.

The 650 turn magnet is very strong running from 12v DC, but barely holds its own weight running from 12v AC.
6 turns per volt works well for AC magnets.

[Ralphxyz]

Ah, now that's a important little detail.

When running the magnet from DC the resistance is more important than the number of turns. When running from AC the number of turns is more important than the resistance.

Thank you

Ralph

[Tanmcnew]

what was that big transformer out of???

[rocketman221]

That one was from a 30V DC 500mA power brick. I don't know what it was for, but the rectifier board was burnt to a crisp.

[Tanmcnew]

Oh wow, but thats pretty cool. good instructable!

[scharnchaleo]

cute cat!

[Green Silver]

Not a single f*** was given by the cat that day...
Btw, I find getting the metal plates off the transformer really hard with out damaging it..

[rocketman221]

Sometimes you have to bend and pry out the first plate. The magnet won't mind missing one of them. Besides it's very difficult to get them all back in anyways.

[oilitright]

Many years ago I worked for a 'magnetic's" company, basically it produced custom transformers of all types and shapes, sizes, functions etc. making everything from tiny toroid 0ower supplies that went into the Apollo backpacks to enormous 3 phase transformers that went on the USS Enterprise after the fire. Anyway the point I wish to make is that the material used to hold lamination's together varies a great deal and the method by which they are applied varies as well. Many transformers are not going to be easily taken apart. Once some of the harder materials have been applied and then been in a vacuum chamber then baked in an oven, they are impregnable. So when looking for transformer candidates look for those that probably just had a light dip in thin "varnish" and drip dried in air.

Also if you can find a coil winding facility chances are you can purchase cheaply or even get free wire spool ends. An even easier method to get some wire without trying to disassemble a transformer. A task which I personally in light of my experience, would not be my first choice of options. However adventures from trying new things and achieving new victories should never be undervalued.

[rocketman221]

Wow that sounds like a cool job.

I haven't come across a well made one yet. The ones I use come from power supplies that I usually get at yard sales and swap meets for free or very cheaply. The larger ones usually find there way into some project or another.

[oilitright]

It is an unfortunate reality that the power supply section of many devices receive the tail end of the design effort. This leads to many a device failing, either as a direct failure of the power supply or some other component because of inadequacies in the power supply design. Personally I think designers should reply of guys who specialize in power supply design rather then rely on their skills in this area.. I've had to just about beat engineers over the head to convince them that their power supply specifications would fail in real use, irrespective of how they looked on paper. The next time you pull a wall wart out of the receptacle and it feels hotter then you think it should, you'll have a perfect example.

[rocketman221]

So true.

[7862Tony]

There are different formulas for winding transformers. Of course if one changes the laminations the formula changes.There are more number of turns per volt for open ended laminations inductors( electromagnets). lenght of wire is not part of any formula , but number of turns per volt for a certain area of laminations.

[rocketman221]

I simply calculated the DC resistance based on the length and wire gauge. For DC it comes fairly close to what I actually measure.

[nmoraga]

hmmm mind if i ask? where do you plug that magnet?? and can you add some pictures too? thanks

[rocketman221]

I am running the magnet with this power supply.
I have also used super capacitors and batteries to run them.

[preddy6]

good work....bro
it is very usefull

[vishalapr]

Nice! Very nice trick to avoid buying those highly expensive electro-magnets!

[fegundez1]

how do you decide what voltage to use

[rocketman221]

The voltage you wind it for depends on what you are using to power it.
I used 50ft of 22awg and get 5 amps @ 5 volts.
It could be wound with 100ft of 26awg and get 2.5 amps @ 12 volts.
I just used what I had in my junk bin.
If the voltage is too high for the coil, it will overheat too quickly.

[rimar2000]

Very useful! The electromagnets are expensive.