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)

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Step 2: Disassemble The Core

The transformer core is made of layers of "E" shaped & "I" shaped pieces which are held together with varnish.
To separate the layers use a box knife to break apart the first layer, then beat the piece out with a hammer and screwdriver. Once it breaks free it can be pulled out with the pliers.
Once you get the first couple of layers out, put the transformer on a hard surface and hit all sides of the core with the hammer to help break the varnish loose. Then you should be able to get the rest of the pieces out with the knife easily.

Step 3: Wind The Coil

Picture of Wind The Coil
I wound this coil by hand so I didn't get any pictures in the process.
I used wire that I collected from other transformers and motors.
So I ended up twisting together about 15 strands with a drill to make about 50ft (15m) of 22awg wire.

The coil form has a divider between the coils that needs to be cut out in order to wind one big coil.

This coil has 5 layers of wire in it.
The layers must all be wound in the same direction and should be wound as neatly as possible .

This coil will run at 5 volts. For a higher voltage use more turns of a thinner wire.

When using DC to run the magnet, you can estimate the current using a wire resistance chart & ohms law.
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avwerosuo9 months ago
Hello rocketman, it's a nice job you are doing keep it up! I am not a professional in this field so I'll need your help. I've a neodymium magnet of 4''diameter x 1.5''long and i want to make an electromagnet of if possible equal force for repelling purpose. I want use a larger core of 3''diameter x3'' long and the electromagnet will operate continuously. Please kindly guide me on the wire size, the number of turns and length of wire that will not generate heat and also operate at low current. Please i need a very strong electromagnet with equal force as the neodymium magnet. I'll be very grateful if you or anyone can give me any useful advice. THANKS!
rocketman221 (author)  avwerosuo9 months ago
Unfortunately you won't be able to make an electromagnet capable of repelling that super magnet using a transformer core. If you were to use an iron core, the neodymium magnet would just stick to it and be very difficult to remove.
You could try using an air core electromagnet, that would be able to attract and repel the neodymium magnet, but won't be nearly as strong as the neodymium magnet.
Be careful with those super magnets, they will crush anything that comes between them and a piece of iron or another magnet.
Thanks for your reply!
But yes i actually wants it to stick together when the electromagnet is switched off and when the electromagnet is connected (switch On), the North pole of the electromagnet and the North pole of the Neodymium magnet will cause them to repel from each other, and when switch off again they stick together.
I don't know if am correct, but i want to know if this is possible.
Thanks for your reply!
barry9211 months ago
if DC power supply is used on E-shaped ferrite core electromagnet, will the performance of the electromagnet the same as the one usign AC power supply?
How to differentiate the poles of the transformer, as i want to repel another identical transformer?
Do the armatures of the E-shaped electromagnet exert forces on the other identical one when current is supplied?
rocketman221 (author)  barry9211 months ago
The magnets are much stronger on DC. On AC the magnet's polarity is constantly changing and they will vibrate strongly when brought near metal. They will draw less current on AC and the current will decrease when stuck to a piece of metal.
The inner part of the E core is one pole and the outer parts are the other pole.
Two magnets will repel each other when the polarity is different, but they don't like to stay centered on each other. The inner core will stick to the outer core on the other magnet unless something prevents them from moving side to side.
sdhavle11 months ago
which wire did you use?
rocketman221 (author)  sdhavle11 months ago
I have used 22awg wire on my 5v magnets and 28awg wire on my 12v magnets.
ankit pundir12 months ago
Hello rocketman, I have few questions in my mind.
I am working on 12V magnet and using the 'E' shaped core having dimensions (40x26x17) mm. So can you please suggest me the diameter(or gauge no.) and the length of the copper insulated wire needed.
rocketman221 (author)  ankit pundir12 months ago
I would suggest using 28 awg (0.32mm diameter) wire.
I have an open office spreadsheet that will estimate the amount of wire you can fit on a core. Put the measurements in the yellow fields and it will tell you the aproximate length and number of turns that will fit.
The magnet will probably use about an amp at 12v dc depending on the length of the wire.
barry9212 months ago
Hi rocketman221, I'm having a problem in building a DC electromagnet for my DIY project, using 22.2v lipo battery.
I have a couple of questions to ask you.
-ferrite rod or ferrite core makes perfect electromagnet?
-When I connect my electromagnet to my DC power supply, it heats up quickly, is this a good or a bad sign?
-it is advisable to use 19 swg or 27 swg enamel copper wire ?
-From the previous comments, 'when constructing a DC electromagnet we should consider the the resistance rather than the no. of turns', what does this statement mean?
rocketman221 (author)  barry9212 months ago
If it is heating up too quickly then it's using too much power. How many amps is it pulling at 22.2v?
You can increase the resistance by using thinner wire or using more turns.
How big is the core you are using? The size cores that I used for mine work well at around 10 to 15 watts.
For it to use 15 watts at 22.2v, the coil would need to be about 32 ohms.
I would recommend the 27 gauge wire unless you are using a large core.
I haven't tried using a ferrite core, so I don't know how well they will work.

With a DC electormagnet the resistance of the coil determines how much current will flow. With AC the inductance of the coil will also limit the current used.
Well thx for your reply, I appreciate it.
The resistance across the wire is about 1 ohm, o the current flowing through the coil is about 20+ amperes. I use 10 ferrite rods each with a diameter of 1 cm and length of 16 cm to to build the core of the solenoid. Does a higher watt imply a stronger electromagnet or vice versa?
rocketman221 (author)  barry9212 months ago
20 amps is way too much power, that's nearly 500 watts. The wire insulation will burn up pretty fast. That magnet would work fine up to 5 or 6 volts, but not at 22v. You need a lot more turns
Higher wattage will make the magnet stronger to a point anyways. The core makes a big difference too. An iron core in a "E" shape or "U" shape usually works best.
barry9212 months ago
Well thx for your reply, I appreciate it.
The resistance across the wire is about 1 ohm, o the current flowing through the coil is about 20+ amperes. I use 10 ferrite rods each with a diameter of 1 cm and length of 16 cm to to build the core of the solenoid. Does a higher watt imply a stronger electromagnet or vice versa?
Machine1 year ago
Very nice, very impressive weight that it can lift and simple construction too. Thanks for showing us.
krrran0001 year ago
i am looking for such type of powerful electromagnet . finally i got it. i will try for it..
thank you
aloving952 years ago
Immagine if you did this with a MOT (microvave oven transformer)
rocketman221 (author)  aloving952 years ago
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.
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 (author)  my project box1 year ago
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.
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.
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
Mazdak672 years ago
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.


rocketman221 (author)  Mazdak672 years ago
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.
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

rocketman221 (author)  Mazdak672 years ago
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 (author)  rocketman2212 years ago
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
Thank you for your instruction.

I will try it
theloyz2 years ago
I might have missed it, but how much power are you putting into that?
sassafras722 years ago
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 (author)  sassafras722 years ago
The two wires are connected to a DC power supply.
aviatordave2 years ago
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 (author)  aviatordave2 years ago
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).
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

Just curious, do these give off high EMF? Is it safe to be by?
rocketman221 (author)  aviatordave2 years ago
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.
OK, great. Thanks!
agod2 years ago
how did you wind the wires together
rocketman221 (author)  agod2 years ago
I strung all of the wire out, then used a drill to twist them together.
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 !
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