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Calculating electromagnet – magnetism vs heat

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perik

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Im making an electromagnet that will be more or less permanently turned on so I need to avoid heating problems. I have studied this a bit and came to the conclusion that:

the lower the gauge (AWG) (the thicker the wire) and the more turns around the core => the greater current it can handle and the lower the heat.

with this in mind I would have taken something like 500 turns around a 10 mm diameter screw, with pretty thick copperwire awg 20 (0.5 mm) or something similliar would be okey?

What do you say? Is there a way of calculating these heatingproblems before I decide the dimension and number of turns of my copperwire?
 

heating due to wire can be calculated by knowing the resistance of the wire wound and current passing through it.

for 20awg get the typical resistance from data sheet or measure it
and estimate the power dissipated due to coil resistance.
 

How are you powering the electromagnet?
you will need to provide a path for the current when you turn it off.
if you do not, you can get very large voltage spikes that can damage the equipment.
 

What do you say? Is there a way of calculating these heatingproblems before I decide the dimension and number of turns of my copperwire?

I suggest the following steps:

Estimate the current and number of turns (NI is more important). You need to see that the core is able to handle the magnetization without saturation.

Look at the power supply and estimate the max current you can handle.

Decide the number of turns based on the current capacity. Select the wire size and the length. Using the length estimate the resistance.

If the heat dissipation is not acceptable, use a thicker wire.

Low voltage high current power supply is important. 10mm diameter iron can saturate with a NI of 500 or so; you need to estimate from other informations.
 

Thanks for the answers. I did some research and did this calculation:
circumference of the spool: diameter of the screw * PI :: 1 * 3,14 = 3,14
Length of wire: Number of turns * circumference :: 500 * 3,14 = 1570 cm
The resistance of the wire / cm (ohm): 0,00032
Total resistance of the wire: resistance per cm * length :: 0,00032 * 1570 = 0,5024
Current:
I = V/R, I = 5 / 0,5024 = 9,95 A

Im using wikipedia to get information about the copperwire:
https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes

Two questions reagarding the cable:
1) The Ampacity - is that what temperature the current will generate? In my case than if you read the table, since my current is 9,95 A that would generate about 70 degrees? Is that correct?
2) Fusing Current - that is the current that will melt the wire? Preece is longer than 10 seconds and Onderdonk is over 1 second or 32 ms? Is that correct?


Im also using a diode to handle the EMF

So in my case I should go for a thicker wire (lower AWG) to be able to take down the heat .

Then to calculate the magentism I use this page:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html
Solenoid Magnetic Field Calculation
here I get with my values: 157 m long, 500 turns, 9,95 A in current and 200 in relative permeability = 79.64 gauss in the center of the magnet

So in my example above I will get:
heating about 70 degrees
79.64 gauss in the center of the magnet


In other words I will go for a thicker wire to get down the heating ...

Would you agree on this calculation?

Thanks
 

You will be generating about 50W (dissipation); this must be dissipated.

Your screw is 1 cm in diameter but you have not said anything about the length.

I assume the 500 turns are made in one layer (if multilayered, your length will be more)

Resistance of wire / cm (ohm): 0,00032 suggest a AWG of 20; but your mistake is elsewhere.

You need to drive the electromagnet with a current source. First fix the current and then select the wire size and number of turns.
 

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