the world of inductors and me...newbie questions!

J

JGalt

New member
So I am trying to increase my level of understanding of inductors, and I've been reading and will be continuing to read the zillions of papers online about them. The thing is, I have to make sure my understanding of ALL inductors is consistent. For instance, when I'm reading something thats talking about the inductor in a switchmode power supply, I have to make sure that doesn't conflict with my understanding of inductors in an electromagnet. Otherwise somethings wrong with my thinking.
The types of inductors I need to reconcile together are:

-inductors used in SMPS
-transformers
-DC electromagnets
-AC electromagnets
-solenoids
-Inductive heating

I of course realize, these are all the same thing, just with different aspects of them exploited or enhanced for different purposes. However, I am looking for a mental model that works for all of them simultaneously, and doesn't fall apart when I switch thinking from one to the other. Thats how I will know my understanding is complete.

So here are some questions I have so far:

Scenario: DC electromagnet with no metal objects in its vicinity
Question: Steady state electrical power consumption in this case is purely DC resistance of coil, yes?

Scenario: DC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
Question: Steady state electrical power consumption is still just DC resistance of coil?
Question: Static pulling force requires no additional electrical force steady-state, because its not doing any work?
Question: If object is "unclamped" and pulled against and away from the magnet, does the electrical power consumption go up? Work is being done.

Scenario: DC electromagnet with metal object in its vicinity, but object free to be pulled towards magnet:
Question: What is the electrical power consumption as the object is being pulled towards the magnet?

Scenario: AC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
Question: Steady state electrical power consumption is still just DC resistance of coil?
Question: Static pulling force requires no additional electrical force steady-state, because its not doing any work?

Scenario: AC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
Question: Unlike DC electromagnet, object heats up from magnetic flux, so additional electrical power is required, even though object cant move.

I have more questions but this is probably enough for now! Thank you for any help!!!
 
N

nickb

New member
No one else had a go so I'll try..

Scenario: DC electromagnet with no metal objects in its vicinity
1)Question: Steady state electrical power consumption in this case is purely DC resistance of coil, yes?
Yes


2)Scenario: DC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
a)Question: Steady state electrical power consumption is still just DC resistance of coil?
Yes
b)Question: Static pulling force requires no additional electrical force steady-state, because its not doing any work?
Yes
c)Question: If object is "unclamped" and pulled against and away from the magnet, does the electrical power consumption go up? Work is being done.
Work is done pulling the object and therefore the energy consumption will temporarily be reduced. As the object is moved away so the inductance will decrease from La to Lb.
Now,
Initial energy in inductor = La * i^2
Final energy in inductor = Lb * i^2
Increase in electrical energy = (Lb-La) * i^2; Lb < La so this is a decrease and energy is returned to the generator.


3)Scenario: DC electromagnet with metal object in its vicinity, but object free to be pulled towards magnet:
Question: What is the electrical power consumption as the object is being pulled towards the magnet?
This is the converse of (2) so energy has to be supplied by the generator.


4) Scenario: AC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
a) Question: Steady state electrical power consumption is still just DC resistance of coil?
Well it's an AC circuit so there is real and imaginary (reactive) power. Only the real power is dissipated in the DC resistance. The imaginary power is returned to the generator.

b)Question: Static pulling force requires no additional electrical force steady-state, because its not doing any work?
Yes

5)Scenario: AC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
Question: Unlike DC electromagnet, object heats up from magnetic flux, so additional electrical power is required, even though object cant move.
Yes. Currents will be induced into the metal and those will dissipate energy due to the metal's resistance.
 
J

JGalt

New member
nickb said:
No one else had a go so I'll try..

Scenario: DC electromagnet with no metal objects in its vicinity
1)Question: Steady state electrical power consumption in this case is purely DC resistance of coil, yes?
Yes


2)Scenario: DC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
a)Question: Steady state electrical power consumption is still just DC resistance of coil?
Yes
b)Question: Static pulling force requires no additional electrical force steady-state, because its not doing any work?
Yes
c)Question: If object is "unclamped" and pulled against and away from the magnet, does the electrical power consumption go up? Work is being done.
Work is done pulling the object and therefore the energy consumption will temporarily be reduced. As the object is moved away so the inductance will decrease from La to Lb.
Now,
Initial energy in inductor = La * i^2
Final energy in inductor = Lb * i^2
Increase in electrical energy = (Lb-La) * i^2; Lb < La so this is a decrease and energy is returned to the generator.


3)Scenario: DC electromagnet with metal object in its vicinity, but object free to be pulled towards magnet:
Question: What is the electrical power consumption as the object is being pulled towards the magnet?
This is the converse of (2) so energy has to be supplied by the generator.


4) Scenario: AC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
a) Question: Steady state electrical power consumption is still just DC resistance of coil?
Well it's an AC circuit so there is real and imaginary (reactive) power. Only the real power is dissipated in the DC resistance. The imaginary power is returned to the generator.

b)Question: Static pulling force requires no additional electrical force steady-state, because its not doing any work?
Yes

5)Scenario: AC electromagnet with metal object in its vicinity, but object secured in place relative to electromagnet and cant move.
Question: Unlike DC electromagnet, object heats up from magnetic flux, so additional electrical power is required, even though object cant move.
Yes. Currents will be induced into the metal and those will dissipate energy due to the metal's resistance.
Click to expand...


Thank you!!! I did not expect power to go down in 2)c) but I suppose it makes sense as the converse of 3). It just seems intuitively that more power is required to "pull against" the force moving the object away, but I can see how that is not necessarily true, or at least, is not supported.
 
N

nickb

New member
Sorry, I made an error. The energy is 0.5*L*i^2. not L*i^2. Doesn't make any difference to the conclusions tho'
 
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