Electromagnet magnetic field issue

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The discussion centers on a group of mechanical engineers experiencing significantly weaker performance from their electromagnet compared to a reference design, despite using similar specifications. They have ruled out issues with wire gauge and coil resistance, confirming a current draw of 0.45A at 12V. Concerns about the materials used for the core and bracket arise, with suggestions to avoid high-cost steels like stainless and instead use mild steel for better magnetic properties. The bracket's symmetry and potential gaps in the magnetic path are also considered as possible factors affecting magnet strength. Further testing with different materials and configurations, including the use of a Hall sensor, is planned to diagnose the issue.
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Hi Guys
We are a bunch a mechanical engineers trying to build a simple electromagnet. Our design is based on a very similar magnet. However, our version is about 10 times less magnetic and we are wondering why. Our coil has exactly same length, same number of layers and turns.
What is possibly wrong? PIN and bracket are made of iron and are in electrical contact, exactly like the reference design.
Any help will be appreciated.
Thanks.

edit: even same wire diameter and coil was wounded by a coil manufacturer.
Initially we thought about magnetic short circuit since the bracket and pin create a core 'loop'. We tested by cutting the bracket in half but that didn't help too.
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Is it using an AC or DC supply ?
Is the wire the same gauge or diameter ?
Can you measure the coil current ?
 
Baluncore said:
Is it using an AC or DC supply ?
Is the wire the same gauge or diameter ?
Can you measure the coil current ?
DC 12V. Yes wire gauge is same (0.24mm). Reference consumes 0.45A. I haven't measured what our coil consumes yet. I can measure tomorrow.
Resistance of the both coils are same which is 25 ohms.
 
Yes, check the current tomorrow.
Maybe the 12 V supply has insufficient voltage under load.

Is the pin made from iron, steel, or maybe a stainless steel, or a manganese steel alloy ?
 
Baluncore said:
Is it using an AC or DC supply ?
Is the wire the same gauge or diameter ?
Can you measure the coil current ?
Bracket is not symmetric at both ends of bobbin. Can this cause magnetic field leak and make the magnet weaker by ten times?
 
Baluncore said:
Yes, check the current tomorrow.
Maybe the 12 V supply has insufficient voltage under load.

Is the pin made from iron, steel, or maybe a stainless steel, or a manganese steel alloy ?
Alright.
I used the same power supply for both magnets. This power supply can delivery upto 10A.
We tried 1010 steel, SS430 and did not observe any difference.
 
Can there be a shorted turn in the coil and yet the overall resistance be as needed?
 
Zeusex said:
We tried 1010 steel, SS430 and did not observe any difference.
You should try soft iron or mild steel for the pin, not stainless or high tensile steel. The more the pin material costs, the worse it will work as an electromagnet. Test the pin with a permanent magnet to compare it with the prototype. One manufacturer, who wanted to make an electromagnet, purchased silicon transformer steel because they wanted the best. It did not work because the magnetic field was permanent, so it could not let go. Buying cheap mild steel fixed the problem.

Zeusex said:
Can there be a shorted turn in the coil and yet the overall resistance be as needed?
So long as the short is between adjacent turns in the same layer, and not between layers of the coil, a shorted turn will slow the change in field, but not change the effective field.
 
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Baluncore said:
You should try soft iron or mild steel for the pin, not stainless or high tensile steel. The more the pin material costs, the worse it will work as an electromagnet. Test the pin with a permanent magnet to compare it with the prototype. One manufacturer, who wanted to make an electromagnet, purchased silicon transformer steel because they wanted the best. It did not work because the magnetic field was permanent, so it could not let go. Buying cheap mild steel fixed the problem.


So long as the short is between adjacent turns in the same layer, and not between layers of the coil, a shorted turn will slow the change in field, but not change the effective field.
Thanks.
Tomorrow I will try to replace the pin with a cheap iron bolt.
How close the bolt diameter to be in relation to inner diameter of the bobbin?
 
  • #10
Zeusex said:
How close the bolt diameter to be in relation to inner diameter of the bobbin?
That is not critical. Use the greatest available diameter unless the magnet is switched on and off very rapidly. Use an uncoated iron bolt, avoid zinc plate or galvanised.
 
  • #11
Baluncore said:
You should try soft iron or mild steel for the pin, not stainless or high tensile steel. The more the pin material costs, the worse it will work as an electromagnet. Test the pin with a permanent magnet to compare it with the prototype. One manufacturer, who wanted to make an electromagnet, purchased silicon transformer steel because they wanted the best. It did not work because the magnetic field was permanent, so it could not let go. Buying cheap mild steel fixed the problem.


So long as the short is between adjacent turns in the same layer, and not between layers of the coil, a shorted turn will slow the change in field, but not change the effective field.
1010 is a mild steel too which is why we selected it.. I don't know what grade is the bolt I found, hopefully A36
 
  • #12
I remember turning mild steel into soft iron by heating it to cherry red than quenching in water.
 
  • #13
tech99 said:
I remember turning mild steel into soft iron by heating it to cherry red than quenching in water.
That will change the magnetic properties, but it would actually harden it, and make it brittle. If you let mild steel cool slowly, then it would be annealed, becoming softer, with bigger crystals.
https://en.wikipedia.org/wiki/Hardened_steel#Hardening_and_tempering

To turn mild steel into iron, you must remove carbon from the alloy. That can be done by pushing oxygen through the melt, like Bessemer does, or by working it in air to make wrought iron.
 
  • #14
Thank you. I think the annealing process makes the steel magnetically "soft", so it does not retain magnetism.
 
  • #15
Heating copper to cherry red, then water-quenching, would soften it, but steel would harden. However, mild steel wouldn’t harden significantly without some extra carbon (eg case hardening).

Annealing steel increases its magnetic permeability. Might you be thinking of the Curie temperature, where steel stops sticking to a magnet? That’s how you know it’s ready either to anneal or harden.
 
  • #16
I have often turned nails into "soft iron", by heating and quenching them, for pupils making magnets. This makes the core lose its magnetism when the current stops.
 
  • #17
tech99 said:
I have often turned nails into "soft iron", by heating and quenching them, for pupils making magnets. This makes the core lose its magnetism when the current stops.
I hadn’t heard of that, but I looked it up - on the same site, in two different places, it seems to say two different things (highlighted in red):

*****

https://steelprogroup.com/alloy-steel/magnetic/#:~:text=How It Works: Iron is,How Alloying Elements Affect Magnetism?

Heat Treatment​

Heat treatment can either increase or decrease magnetism depending on how the steel is cooled. Rapid cooling (quenching) locks the steel into a magnetic martensiticphase, while slower cooling can result in a non-magnetic austenitic phase. The cooling rate essentially “locks in” a magnetic or non-magnetic structure, depending on the process.​

*****
https://steelprogroup.com/carbon-steel/is-carbon-steel-magnetic/#:~:text=Heat Treatment * Annealing (slow cooling after,(non-magnetic phase) may remain, slightly weakening magnetism.

Heat Treatment​

  • Annealing (slow cooling after heating) helps restore grain integrity and improves magnetism.
  • Quenching (fast cooling) can create residual stress, making it harder for magnetic domains to align, reducing overall magnetism.
  • If steel is cooled too fast from high temperatures, some residual austenite (non-magnetic phase) may remain, slightly weakening magnetism.
 
  • #18
It is easy to try quenching the core if making an electromagnet. I have found it works on nails used by pupils as cores for making magnets. The untreated steel retains its magnetism and the quenched steel does not.
 
  • #19
Baluncore said:
That is not critical. Use the greatest available diameter unless the magnet is switched on and off very rapidly. Use an uncoated iron bolt, avoid zinc plate or galvanised.
Measured the amps on our coil, it is same as the reference, 0.45A.
Tried the bolt, but the pin made of 1010 was more magnetic compared to bolt.
But at the bracket, the magnetic forces are lower.
Any more ideas?
I think that the bracket needs to be symmetrical.
Next week we can try to build and measure the magnetic field using a hall sensor but this doesn't solve the problem.
 
  • #20
Zeusex said:
I think that the bracket needs to be symmetrical.
Symmetry is not a likely reason for magnetic differences.
Open gaps in the magnetic path, are a more likely cause.
What material is the bracket made from?
How thick is the bracket material?
Is it punched and/or bent, heat treated or plated?

The magnetic properties of ferromagnetic materials can be changed by heat treatment, or by work-hardening.

A Wiegand sensor is made by axially twisting an alloy wire. The centre remains soft, while the outside work hardens. Those internal volumes have different magnetic properties and can work together, producing sudden changes in flux when subjected to a slowly changing external bipolar magnetic field.
https://en.wikipedia.org/wiki/Wiegand_effect

To make a Wiegand sensor, get a short annealed Nichrome wire and work it axially in alternate directions with a cordless drill. Then cut an inch or two, (40 mm), from the wire, and wind on 100 turns of the finest magnet wire you have. That winding will produce a positive or negative pulse of about one volt for 1 us, each time the external axial field is reversed slowly.

Nichrome wire is common resistance wire, often found in used heating elements, so it may be annealed when you get it. I should not need to explain how you can anneal a nichrome wire with a car battery.
Stimulate your brain, experiment, but don't burn your fingers.
 
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  • #21
Zeusex said:
Measured the amps on our coil, it is same as the reference, 0.45A.
Tried the bolt, but the pin made of 1010 was more magnetic compared to bolt.
But at the bracket, the magnetic forces are lower.
Any more ideas?
I think that the bracket needs to be symmetrical.
Next week we can try to build and measure the magnetic field using a hall sensor but this doesn't solve the problem.
I assume the wire is the same gauge, copper, enamelled? If so I strongly suspect the material of the core as the problem.
 
  • #22
tech99 said:
I assume the wire is the same gauge, copper, enamelled? If so I strongly suspect the material of the core as the problem.
Yes same gauge (0.24mm), pure copper and enamelled. Core (pin) is from 1010, also tried 1020, SS430 and a random iron bolt I found. 1010 and 1020 pins were more magnetic than the rest. Brackets I have are also from 1010, 1020 and SS430. With Pin of 1010/1020, I notice that the magnetic attraction at the center of bracket (ring shape) is much lower than the pins.
 
  • #23
Baluncore said:
Symmetry is not a likely reason for magnetic differences.
Open gaps in the magnetic path, are a more likely cause.
What material is the bracket made from?
How thick is the bracket material?
Is it punched and/or bent, heat treated or plated?

The magnetic properties of ferromagnetic materials can be changed by heat treatment, or by work-hardening.

A Wiegand sensor is made by axially twisting an alloy wire. The centre remains soft, while the outside work hardens. Those internal volumes have different magnetic properties and can work together, producing sudden changes in flux when subjected to a slowly changing external bipolar magnetic field.
https://en.wikipedia.org/wiki/Wiegand_effect

To make a Wiegand sensor, get a short annealed Nichrome wire and work it axially in alternate directions with a cordless drill. Then cut an inch or two, (40 mm), from the wire, and wind on 100 turns of the finest magnet wire you have. That winding will produce a positive or negative pulse of about one volt for 1 us, each time the external axial field is reversed slowly.

Nichrome wire is common resistance wire, often found in used heating elements, so it may be annealed when you get it. I should not need to explain how you can anneal a nichrome wire with a car battery.
Stimulate your brain, experiment, but don't burn your fingers.
Brackets I have are from 1010, 1020 and SS430.
2mm thick.
Laser cut blanks and then bent.
I know that cold work on steels and stainless steels increases the magnetism.

I will have to explore the Wiegand sensor and how I can use it to solve the problem.
 
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