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electromagnetism

meedo74

Sep 4, 2016
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Hi all,

Kinda new to electronics, I majored in mechanical engineering so taking my first steps here :) what is the difference between an inductor and an electromagnet? For me from reading they are exactly the same components or o_O If so can I use an inductor as a tiny electromagnet? hence not as chock but to have it actuate based on magnetic energy? :rolleyes:

your help is much appreciated :D:D
 

OBW0549

Jul 5, 2016
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An electromagnet is simply an inductor with a mission: attracting ferrous objects.

I imagine you could use an inductor as an electromagnet provided it can safely pass enough current to generate a strong enough magnetic field, and further provided it has an external magnetic field; some, like inductors wound on a toroid core or cup core or E-I laminations, do not.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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An inductor with an air core is not going to make a good electromagnet.

An inductor with a toroidal core will not act like an electromagnet (neither will one with any other form of closed magnetic circuit).

An electromagnet will be designed with sufficient resistance to limit the current when operated with DC, a typical inductor is designed to have minimal resistance.
 

Alec_t

Jul 7, 2015
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Any electromagnet is an inductor but, as indicated above, not all inductors are electromagnets.
 

CDRIVE

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This is probably being overly pedantic but I think it's better stated that any electromagnet is an inductor but not all inductors are 'effective' as electromagnets. After all even a small DC current flowing in a length of wire produces enough magnetic field to move a compass placed close to it.

Chris
 

meedo74

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Thanks you all for the great info on this, so it seems that the inductor although has the same components, it is built with different purpose in mind :confused:So basically I was trying to avoid winding a micro electromagnet and I thought replacing it with a standard SMD inductor will do but this is not the case :( What other options do I have :rolleyes:
 

CDRIVE

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Thanks you all for the great info on this, so it seems that the inductor although has the same components, it is built with different purpose in mind :confused:So basically I was trying to avoid winding a micro electromagnet and I thought replacing it with a standard SMD inductor will do but this is not the case :( What other options do I have :rolleyes:
I don't think what you're attempting to do is clear. If you're trying to use an SMD inductor as an electromagnet it ain't gonna happen in this world. Though it may move a compass vane! :)

Chris
 

meedo74

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It is no different than moving the compass vane, I need only to flip a little compass vane like (metal chip) of a 2 mm diameter, so the electromagnet is not to hold a weight of any kind, it is a mechanical project but for this small actuator I need an electromagnet that is so tiny as 2 mm diameter (all in all, core and wingdings), and this is hard to find :confused:
 

(*steve*)

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You would need to start reading the datasheets of SMD inductors. You'll need to find one that's "wound" the right way (I.e. The axis is correct) and has an open magnetic circuit (I.e. Is not manually shielded -- a toroid is unlikely in a small form factor) and can withstand a significant DC current.

Then you'll have to experiment.

Oh, and on a technical note, even a straight piece of wire is an inductor!
 

hevans1944

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An electromagnet, any size, uses a ferromagnetic material (soft iron or silicon transformer steel or ceramic ferrites) for the core and an open (air gap) magnetic circuit path. Wire is wound around the core to create the magnetic field produced by the electromagnet.

The core intensifies and confines the electromagnetic field within the core except on the ends where the field "escapes" into the surrounding medium, usually air. The air gap allows the field to attract nearby ferromagnetic objects. Every electromagnet has two magnetic poles between which the magnetic field propagates. Most electromagnets use a ferromagnetic circuit to bring one pole physically close to the other pole, the magnetic field then being mostly confined to the volume between the two poles. A horseshoe magnet is a common example. This is not absolutely necessary: the poles on either end of the core can be left open, with considerably reduced magnet field intensity at either pole.

If you need a really tiny electromagnet you might try disassembling things that have tiny parts. A battery powered wristwatch comes to mind... surely there is an electromagnetic component in there somewhere! You could possibly wind your own electromagnet, as @Alec_t suggested using a length of soft iron wire, such as florist wire (green painted, soft iron wire used to tie up flower arrangements). Leave a generous length in addition to whatever length you make the coil so you can fold it back to serve as the other magnetic pole, cutting it off even with the other end.

There are so-called "pot cores" that come in two parts, one of which you will discard and the other you will use as an electromagnet having a magnetic core and one magnetic pole in the center, surrounded by a cup of magnetic material for the other pole. The outer rim of the "cup" is one magnetic pole and the center stem on which the coil is wound is the other magnetic pole.

Normally the other half of a pot core is placed over the stem half to form a closed magnetic path with minimal external magnetic field. For your electromagnet application you would not use this piece. Problem is, I have never seen a pot core made in a 2 mm diameter size. You might be able to start with a 2 mm diameter solid ferrite, or soft iron, rod and machine an internal annulus to form a post on which to place your coil. Perhaps use a CNC water-jet cutter or CNC wire EDM for this. Ferrite is a brittle ceramic and otherwise difficult to machine, but the small dimensions present a challenge even if soft iron is used.

You want to compromise with the diameter of the internal center post, leaving enough to allow a coil to slip over it easily (coil is wound externally before being placed on the center post) but also large enough to form an effective magnetic pole with the cup edge that will attract whatever small ferromagnetic objects you are trying to attract. It would help a lot if you would tell us what you are trying to DO.
 

CDRIVE

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It would help a lot if you would tell us what you are trying to DO.
Hop, let's get real here. You know that's a totally unrealistic request. EP stats indicate that imperative information isn't divulged until we've veered off into countless dead ends or a thread receives archive status. :D

Chris
 

hevans1944

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My guess is that this little metal chip is intended as one 'pixel' in a display matrix (digital micromirror).
Well, if so, Texas Instruments beat 'em to it with their DLP (digital light projector) product. I recently viewed a movie in a theater with 4K resolution that used the TI DLP to project color images on a huge theater screen. The resolution rivaled the images from a 70mm IMAX film projection. Quite excellent. Now if I could just afford to buy a home theater version of 4K with a 60" or so (diagonal measurement) slightly curved LED screen, Dolby surround sound, leather reclining chairs, and 4K streaming media... I would never get anything done.
 

CDRIVE

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Damn, I hate when I do that! He did answer the question but even after going back to post 1 I still missed it. More embarrassing than missing it was the fact that meedo posted it as a reply to ME! :rolleyes:

Sometimes I look in the mirror and say.. "What are you looking at Dummy"?
Chris
 

pgib8

Jul 26, 2015
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The most significant difference is this:
An electromagnet, you keep pumping current through it, in the same direction, doesn't have to be a lot necessarily but its DC and you use like an iron core. This means more an more of the magnetic domains within the iron start lining up until the core is completely saturated. No more magnetic field strength can be added and the electromagnet no longer behaves like an inductor, but now it behaves just like a copper wire.
With an inductor you never want it to saturate. When the inductor saturates it essentially acts like a short-circuit. Inductors are used in AC only, their purpose is generally to oppose any change in current (so in a way they act like resistors for AC but short circuits for DC).
 

AnalogKid

Jun 10, 2015
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No more magnetic field strength can be added and the electromagnet no longer behaves like an inductor, but now it behaves just like a copper wire.
First I've *ever* heard of a DC straight bar electromagnet "saturating", let alone "no long behav[ing]". anyone else?
With an inductor you never want it to saturate.
Except when you do.
Inductors are used in AC only, their purpose is generally to oppose any change in current
Um, no. Their purpose is to store energy in a magnetic field. Power conversion is the single most common use for inductors, both stand-alone and as parts of a transformer. In all of those millions of applications, the inductors' "purpose" is not to oppose anything.

Pendanticity-rich environment...

ak
 
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hevans1944

Hop - AC8NS
Jun 21, 2012
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When the ferromagnetic core of an inductor saturates, the main thing that happens is the relative permeability of the core approaches unity. The induced magnetic field at this point still exists, and an increasing current in the inductor will slightly increase the strength of the magnetic field, but not anywhere nearly as much as before the core saturated. And of course the effective inductance takes a nose dive, so if AC excitation is involved the current increases greatly at the positive and negative peaks. It is quite common in some applications to use a saturable inductor. Magnetic amplifiers, for example, depend on core saturation for their operation. See this Wikipedia article for more information.
 

pgib8

Jul 26, 2015
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Hey AnalogKid, I was just testing you, looks like you passed although you didn't get the A but close anyways. Often times I don't know what I'm talking about, so I just throw stuff out there :p
 

AnalogKid

Jun 10, 2015
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Hey AnalogKid, I was just testing you,
No, you weren't.
looks like you passed
How would you know.
Often times
Don't sell yourself short.
I don't know what I'm talking about, so I just throw stuff out there
Often times a newbie asking an honest question doesn't know how to distinguish between an experienced response and careless disregard from someone who don't know what he talking about.

ak
 
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