# Making electromagnet and not burn the Magnet

#### Amar Ram

Joined Dec 13, 2021
13
Hi All, I have made an electromagnet of using 1 mm diameter wire appx 60 turns.
here is the problem... i have 600W smps(computer power supply) and i want to use that to power my electromagnet.
On smps it shows 3.3V with 25A and 5V with 18A. If i connect my electromagnet to one of these terminals will my coil burn ? How to not burn my coils ?

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Joined Jul 18, 2013
28,519
Read the resistance of the coil and work it out!

#### Audioguru again

Joined Oct 21, 2019
6,614
The 90W of heat will produce a temperature that depends on the size of the total surface area of the wire plus the electromagnet core at each end. If the electromagnet is small then it will get very hot.

#### MisterBill2

Joined Jan 23, 2018
17,843
The current flowing will depend on the resistance of the wire in the electromagnet. And the resistance of the wire will depend on it's length, which we do not know, and the resistance per foot, which can be looked up in a wire resistance table. So that will tell you how much current will flow, and the current multiplied by the voltage will tell you the watts of power dissipated in the coil. Calculating the heat that the coil can radiate will then allow you to determine the temperature rise, and that will allow you to decide if the coil will overheat, and if it will in fact burn up, which depends on the insulation material.
Of course, I have guessed that the wire is copper, and that it is insulated. Those are only guesses, and they may or not, be correct. But the process is the same no matter what the material is, except that for many metals and alloys there are no convenient wire resistance tables.

So the missing information is the length of the wire and the material of the wire.

My guess, based on only the information that you have given, is that indeed the wire will get very hot, based on the guess that the power supply will not shut down because of the overload.

#### Audioguru again

Joined Oct 21, 2019
6,614
He said the power supply is rated at 600W and the currents he measured produce 82.5W and 90W at two voltages.
The wire resistance increases at 90W because the heating is very high.

#### Dodgydave

Joined Jun 22, 2012
11,250
1mm copper wire is approx 17.4 ohms per Km, .

Joined Jul 18, 2013
28,519
It sounds like poor design criteria used.
To obtain the same magnetic strength, slightly more/larger core area and more turns.

#### Audioguru again

Joined Oct 21, 2019
6,614
1mm copper wire is approx 17.4 ohms per Km, .
5V/18A= 0.278 ohms which might be (0.278/17.4=) a length of 0.016 of a km if the wire did not get hot.

#### MisterBill2

Joined Jan 23, 2018
17,843
0.016 kM =16 M, not that much wire. almost 50 feet. We have no clue about the diameter or any core material.

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Joined Jan 15, 2015
7,453
During my much, much younger days, circa 1960 or so I made my first electro magnet. Using a large nail and maybe AWG 20 wire I wrapped it with I have no clue how many turns. Battery was an Eveready #6 I think, the ones with the screw terminals on top. With a new fresh battery I could pick up a few paper clips. Learning the math came years later. Batteries had a very short life, go figure.

I suggest you start reading about electro magnets and how they work. There is more to it, much more, than you may think.

Ron

#### Amar Ram

Joined Dec 13, 2021
13
i understand sorry for my incomplete information. i will write all the information i have.
one electromagnet = 1 mm diameter copper wire having 60 turns on a 7cm diameter cylinder of 2 cm
I have two electromagnet both the coils are connected in series to each other. so if we add together that would 120 turns of 1mm copper wire on a 7cm diameter cylinder of 4 cm .

can i use either one of the power supply and not burn the magnet ?
want to run this magnet for like half an hour

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#### Amar Ram

Joined Dec 13, 2021
13
The current flowing will depend on the resistance of the wire in the electromagnet. And the resistance of the wire will depend on it's length, which we do not know, and the resistance per foot, which can be looked up in a wire resistance table. So that will tell you how much current will flow, and the current multiplied by the voltage will tell you the watts of power dissipated in the coil. Calculating the heat that the coil can radiate will then allow you to determine the temperature rise, and that will allow you to decide if the coil will overheat, and if it will in fact burn up, which depends on the insulation material.
Of course, I have guessed that the wire is copper, and that it is insulated. Those are only guesses, and they may or not, be correct. But the process is the same no matter what the material is, except that for many metals and alloys there are no convenient wire resistance tables.

So the missing information is the length of the wire and the material of the wire.

My guess, based on only the information that you have given, is that indeed the wire will get very hot, based on the guess that the power supply will not shut down because of the overload.
i understand sorry for my incomplete information. i will write all the information i have.
one electromagnet = 1 mm diameter copper wire having 60 turns on a 7cm diameter cylinder of 2 cm
I have two electromagnet both the coils are connected in series to each other. so if we add together that would 120 turns of 1mm copper wire on a 7cm diameter cylinder of 4 cm .

can i use either one of the power supply and not burn the magnet ?
want to run this magnet for like half an hour

Attachments

#### Amar Ram

Joined Dec 13, 2021
13
He said the power supply is rated at 600W and the currents he measured produce 82.5W and 90W at two voltages.
The wire resistance increases at 90W because the heating is very high.
i mean i can use either of the power supply does not matter as long as the electromagnet does not get very hot . of course due to resistance heat is dissipated that cannot be avoided

#### Audioguru again

Joined Oct 21, 2019
6,614
82.5W and 90W of heat are almost the same. They each will draw a higher current until it gets hot.

You said the coils are wound on cylinders. Usually an electromagnet is wound on a solid or laminated iron core.
A "U" shaped core produces higher magnetism if the parts it lifts touch both north and south poles.

#### MisterBill2

Joined Jan 23, 2018
17,843
We still do not know the length of the wire in the coil, 7 cm x 3.14x 60=23 x60 cm =1300cm=1.3 M approximately So the resistance will be about 17.4 ohms/1000M x(1.3/1000) M= not much resistance.
So the current will be limited by the supply, and all that power will be dissipated in the coils.
So the coils will get very hot indeed.

#### MisterBill2

Joined Jan 23, 2018
17,843
Please tell us what is the purpose of these electromagnet coils . Energised for half an hour, there must be a specific application in mind. Perhaps we can suggest an alternate approach. There is a whole lot of experience available in this site.

#### Alec_t

Joined Sep 17, 2013
14,225
23 x60 cm =1300cm=1.3 M
13m actually. So resistance = 17.4 x 13/1000 = ~ 0.22Ω
The 5V supply will try to drive ~23A through that ! No wonder the coils get hot.

Joined Jul 18, 2013
28,519
@Amar Ram You need to find out the weight anticipated to be lifted and work back from there.
Usually DC powered magnets are very efficient when designed properly.
The largest I have worked on is on scrap yard cranes and these magnets operate at 100amps!
Down to small steel sheet material lifting of a around 8amps.

#### Audioguru again

Joined Oct 21, 2019
6,614
Amar Ram never said what is the core in the electromagnet so it is probably air or a small rusty nail then it barely produces any magnetism even at the extremely high current.

#### BobTPH

Joined Jun 5, 2013
8,671
Put about 600 turns and you might have something.

Bob