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hevans1944
Hop - AC8NS
Sorry, Chris. If you feel the need to scroll, check out post #11. Your reply in post #12 probably nailed it. I have seen electromechanical annunciators that use electromagnets to flip vanes to display, for example, sports scores. These are usually quite large because they are viewed from afar. To build something similar with dimensions on the order of 2 mm sounds like a persistent pixel application: turn the pixel on or off with a short pulse and it remains in the last state. Maybe arrange them in three colors for a colored pixel display. Or maybe suspend the metal "chips" in some sort of liquid and use a magnetic field to make them visible or invisible. Easy to guess possible applications of a micro-manipulator for metal chips, not so easy to implement it. And, as we all know, Texas Instruments has already done it with tens of thousands of DLP (Digital Light Projection) micro-mirrors, so why re-invent that particular wheel?
Since the OP is a mechanical engineer, maybe they will post a sketch of how their billion-mark invention is supposed to work? Then perhaps we pesky electroniker types can describe how to make it actually work. The devil is always in the details.
Since the OP is a mechanical engineer, maybe they will post a sketch of how their billion-mark invention is supposed to work? Then perhaps we pesky electroniker types can describe how to make it actually work. The devil is always in the details.
Maybe I got my wires crossed but here are some things I remember (and get ready to scroll buddy).
One of my jobs I was doing firmware work for a synchronous switching device for high voltage breakers. The device’s purpose was to try to time the opening or closing of the contacts relative to the AC voltage. When to open or close the breaker always depended on what the load was. With a transformer the breaker ideally would open very shortly after a zero crossing, to draw an arc and allow the contacts to separate as far as possible by the time the next zero crossing came around, which is when the current would get interrupted. If this is not the case and the current is interrupted too soon, the reverse voltage spike from the transformer will reignite the arc and bad things will happen to the system. So then I worked on an algorithm that was a little more advanced (I didn’t invent it, disclaimer). In this advanced algorithm, also for transformer switching, it would consider the residual flux in the transformer’s core. This is where I first learned about magnetic saturation. It’s like this, during the AC cycle the magnetic field in the core always changes polarity, but the polarity doesn’t like instantly change. First it is decreased, then it is increased in the other direction and back and forth. When the transformer is de-energized, it turns out that some of this flux remains. When the transformer is energized again, we may not think of this right away, but the residual flux could be in an unfavorable direction compared to the initial direction of current. So instead of reducing the flux, it is possible it is adding to it and instead of magnetizing it in the other direction it’s adding even more into the same direction. Thus it becomes possible for the core to saturate and from what I remember it would drastically drop in impedance (kind of like a short circuit) and this would cause very high current spikes that are very bad for the system. You think the following was bs:
“…no longer behaves like an inductor, but now it behaves just like a copper wire.”
I think otherwise. When the inductor saturates, there will be a change in behavior and I believe this change is a drastic drop in impedance.
So you’ve never heard of a DC bar magnet saturating I see, I guess neither have I but I bet you it’s not that difficult to do. Why don’t you wrap some wire around a chunk of iron, add DC, and see how that interacts.
I figured with an inductor, you want these properties and that you don’t want it to saturate, apparently there are some cases where you do, I just never heard of those so I was wrong with that statement. There are probably those among us that want inductors to saturate all the time, my bad.
I didn’t give you an A on your answer because you claim that the purpose of inductors is to store energy and you went one step further saying their purpose is NOT to oppose anything, and I strongly disagree with you there.
From my point of view the purpose of an inductor in most cases my friend is not to store energy, that’s just something it does. The purpose of driving a car up a hill is also not to store energy, even though that’s essentially what it does right? I said in most cases and I know there are superconducting energy storage thingies that have the purpose to store energy in magnetic fields, for super critical facilities like silicon fabrication stuff. That’s neither here nor there. From my experience, what makes me put down an inductor onto a schematic, what might that purpose be? The number one purpose for me is as a filter. Pass DC and block high frequencies in most cases for me. I think if you took all the schematics in the world and counted all the inductors, I wouldn’t be too surprised there if most of them were used for filtering purposes. The second most common purpose that I believe inductors are used for is for impedance matching. Ever drive on a long road with a power transmission line next to it and then you see like these 3 barrels? Those are really called reactors but their purpose is to add some inductance because the power lines are predominantly capacitive (and you want them to be) but when they are really long, it gets a bit too much there. I also still have a smith chart sitting near my desk from 2 weeks ago when I added a parallel inductor right before the feed of the antenna because it wasn’t matched very well, but now it is, thanks to the inductor with the wonderful purpose [in this scenario] of letting me match the impedance of a load in a tuned circuit.
Another purpose that I have used them for once, was to limit inrush current that would otherwise blow out a fuse. It was neat to see the current on the oscilloscope too. Instead of BAM, the current started at nothing and very slowly ramped up.
And why is that, because inherently an inductor wants to keep the current the same, whether its no current, positive, negative, doesn’t matter, whatever it is, it wants to keep it that way, and how does it do that? By “injecting” a voltage that opposes the change in current. Btw. this is the reverse of what a capacitor does, which wants to keep the voltage the same and will “inject” a current to make it so. Look at a buck converter for example. The moment you put 12V on the input of the inductor, do you get 12V at the output? No, why? Because the inductor OPPOSES the change in current and builds up a reverse voltage. Like 12 batteries one way are put together with 5 batteries going the other way, so in effect the other side of the inductor will be a much lower voltage (unless you keep the voltage applied for long enough of course). Something else you misunderstood me was when I’m talking about DC, I’m talking about 0Hz. When I say AC, it doesn’t have to mean that polarity actually changes, but for me, and other’s may look at this differently but for me, AC means that there is some change happening. A lightning strike for example for me is AC, even though current just goes in one direction.
So let’s get back to the original question about the electromagnet. When I read the question, I was thinking of an actuator type of magnet and not like something that is ringing a door bell. I’m thinking of for example an electric car lock actuator. Push one button, the door gets locked, push another button and the door gets unlocked. Maybe you don’t want this type of inductor to saturate but if it is designed for that, then there probably are just so many windings that it still has plenty of DC resistance and doesn’t short out so to speak. I also think I was right that generally speaking for an electromagnet you use a core because you want to channel and amplify the magnetic field for actuating something right? When used purely as inductor, you may still want a core to give it more inductance but it’s not necessarily as common as with electromagnets. Based on frequency there are losses. You start by laminating the core, then you switch to other materials such as a ferrite core and eventually the only thing that will do is an air core or maybe some kind of plastic or ceramic.
In regards to what I wrote before, maybe it wasn’t completely 100% accurate, and you’re right, I should have added the disclaimer that I could be wrong because too many people post stuff on forums as fact and it can be really misleading. In this sense dear Analog Kid, what you wrote in my opinion was wrong too, at least as wrong as what I wrote, so congratulations, you are a hypocrite :-D.
Anyways, I didn’t research any of this stuff recently, so I’m writing all of this from my understanding and with that of course, I could be wrong, so there is my disclaimer.
CHEERS!
One of my jobs I was doing firmware work for a synchronous switching device for high voltage breakers. The device’s purpose was to try to time the opening or closing of the contacts relative to the AC voltage. When to open or close the breaker always depended on what the load was. With a transformer the breaker ideally would open very shortly after a zero crossing, to draw an arc and allow the contacts to separate as far as possible by the time the next zero crossing came around, which is when the current would get interrupted. If this is not the case and the current is interrupted too soon, the reverse voltage spike from the transformer will reignite the arc and bad things will happen to the system. So then I worked on an algorithm that was a little more advanced (I didn’t invent it, disclaimer). In this advanced algorithm, also for transformer switching, it would consider the residual flux in the transformer’s core. This is where I first learned about magnetic saturation. It’s like this, during the AC cycle the magnetic field in the core always changes polarity, but the polarity doesn’t like instantly change. First it is decreased, then it is increased in the other direction and back and forth. When the transformer is de-energized, it turns out that some of this flux remains. When the transformer is energized again, we may not think of this right away, but the residual flux could be in an unfavorable direction compared to the initial direction of current. So instead of reducing the flux, it is possible it is adding to it and instead of magnetizing it in the other direction it’s adding even more into the same direction. Thus it becomes possible for the core to saturate and from what I remember it would drastically drop in impedance (kind of like a short circuit) and this would cause very high current spikes that are very bad for the system. You think the following was bs:
“…no longer behaves like an inductor, but now it behaves just like a copper wire.”
I think otherwise. When the inductor saturates, there will be a change in behavior and I believe this change is a drastic drop in impedance.
So you’ve never heard of a DC bar magnet saturating I see, I guess neither have I but I bet you it’s not that difficult to do. Why don’t you wrap some wire around a chunk of iron, add DC, and see how that interacts.
I figured with an inductor, you want these properties and that you don’t want it to saturate, apparently there are some cases where you do, I just never heard of those so I was wrong with that statement. There are probably those among us that want inductors to saturate all the time, my bad.
I didn’t give you an A on your answer because you claim that the purpose of inductors is to store energy and you went one step further saying their purpose is NOT to oppose anything, and I strongly disagree with you there.
From my point of view the purpose of an inductor in most cases my friend is not to store energy, that’s just something it does. The purpose of driving a car up a hill is also not to store energy, even though that’s essentially what it does right? I said in most cases and I know there are superconducting energy storage thingies that have the purpose to store energy in magnetic fields, for super critical facilities like silicon fabrication stuff. That’s neither here nor there. From my experience, what makes me put down an inductor onto a schematic, what might that purpose be? The number one purpose for me is as a filter. Pass DC and block high frequencies in most cases for me. I think if you took all the schematics in the world and counted all the inductors, I wouldn’t be too surprised there if most of them were used for filtering purposes. The second most common purpose that I believe inductors are used for is for impedance matching. Ever drive on a long road with a power transmission line next to it and then you see like these 3 barrels? Those are really called reactors but their purpose is to add some inductance because the power lines are predominantly capacitive (and you want them to be) but when they are really long, it gets a bit too much there. I also still have a smith chart sitting near my desk from 2 weeks ago when I added a parallel inductor right before the feed of the antenna because it wasn’t matched very well, but now it is, thanks to the inductor with the wonderful purpose [in this scenario] of letting me match the impedance of a load in a tuned circuit.
Another purpose that I have used them for once, was to limit inrush current that would otherwise blow out a fuse. It was neat to see the current on the oscilloscope too. Instead of BAM, the current started at nothing and very slowly ramped up.
And why is that, because inherently an inductor wants to keep the current the same, whether its no current, positive, negative, doesn’t matter, whatever it is, it wants to keep it that way, and how does it do that? By “injecting” a voltage that opposes the change in current. Btw. this is the reverse of what a capacitor does, which wants to keep the voltage the same and will “inject” a current to make it so. Look at a buck converter for example. The moment you put 12V on the input of the inductor, do you get 12V at the output? No, why? Because the inductor OPPOSES the change in current and builds up a reverse voltage. Like 12 batteries one way are put together with 5 batteries going the other way, so in effect the other side of the inductor will be a much lower voltage (unless you keep the voltage applied for long enough of course). Something else you misunderstood me was when I’m talking about DC, I’m talking about 0Hz. When I say AC, it doesn’t have to mean that polarity actually changes, but for me, and other’s may look at this differently but for me, AC means that there is some change happening. A lightning strike for example for me is AC, even though current just goes in one direction.
So let’s get back to the original question about the electromagnet. When I read the question, I was thinking of an actuator type of magnet and not like something that is ringing a door bell. I’m thinking of for example an electric car lock actuator. Push one button, the door gets locked, push another button and the door gets unlocked. Maybe you don’t want this type of inductor to saturate but if it is designed for that, then there probably are just so many windings that it still has plenty of DC resistance and doesn’t short out so to speak. I also think I was right that generally speaking for an electromagnet you use a core because you want to channel and amplify the magnetic field for actuating something right? When used purely as inductor, you may still want a core to give it more inductance but it’s not necessarily as common as with electromagnets. Based on frequency there are losses. You start by laminating the core, then you switch to other materials such as a ferrite core and eventually the only thing that will do is an air core or maybe some kind of plastic or ceramic.
In regards to what I wrote before, maybe it wasn’t completely 100% accurate, and you’re right, I should have added the disclaimer that I could be wrong because too many people post stuff on forums as fact and it can be really misleading. In this sense dear Analog Kid, what you wrote in my opinion was wrong too, at least as wrong as what I wrote, so congratulations, you are a hypocrite :-D.
Anyways, I didn’t research any of this stuff recently, so I’m writing all of this from my understanding and with that of course, I could be wrong, so there is my disclaimer.
CHEERS!
hevans1944
Hop - AC8NS
Sounds like you have a pretty good and practical understanding of inductors. Unfortunately none of our responses here have elicited any information from the OP about what they are actually trying to DO, so this thread is leading nowhere.
BTW, it is not uncommon for us human beans to be wrong. Less common is to realize it and admit the mistake, although that does occur fairly often (as the need arises) in this forum. No flaming allowed here.
Actually, it is impossible to do. The lines of force extend to infinity, a difficult space to overload or saturate. Diminished increase in field strength as a function of increasing coil current? - Of course. But saturation in the same sense (and with the same consequences) of a transformer core saturating? - No. And it's not that I "feel" that the answer is no; the answer is no.
I get from your writing that you have experienced-based opinions of how, and particularly *why*, an inductor does what it does. Those opinions are overly-simplistic, leading to inaccurate descriptions and conclusions. An inductor stores energy in its magnetic field, and a capacitor stores energy in its electric field. That is what they do, and it is all that they do. How they do that can lead to some very interesting behaviors and applications, but those applications are the *consequences* of how the components function, not the definition. This was resolved during the US Civil War and tightened up into the modern descriptions in 1884, so it's not like they still are under review.
You are looking at the application and deriving the function, where in fact the physics works in the other direction. The electrodynamics of how an inductor stores and releases energy are complex (literally, thanks to Oliver Heavyside). An inductor doesn't "resist" anything. It has an impedance to electron flow, but so do all electrical and electronic components. It's impedance is not a constant with frequency, but neither is the impedance of a capacitor in a complimentary way. And an inductor doesn't "inject a voltage". When the magnetic field surrounding a conductor varies (for any reason), that action induces a current. That induced current produces its own field, and thanks to the minus sign in Faraday's Law (1831), Lenz's Law (1834) defines that that field is of the opposite polarity to the inducing field. This can lead to a physical interaction with the structure producing the field, which is why it is hard to turn a loaded generator. Stoooopid minus sign.
ak
And just so the pendantics don't start to lose it - yes, I know that the induced field's opposite polarity is not caused by the minus sign, but described by it.
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I started to read the long post and was interested why someone would want to activate a breaker at a zero crossing of voltage. Surely a zero crossing of current would be the ideal time?
The next part of the post deals with what appear to be fudge factors to guess the zero crossing point of the current.
And concerning saturation, the core saturates, not the inductor. When the core is saturated it is like it has been replaced by air for any increase in flux.
A simple rule of thumb is that it then behaves like a wire rather than an inductor, but in reality it behaves like an air core inductor and will still incrementally store energy -- just a lot less!
The next part of the post deals with what appear to be fudge factors to guess the zero crossing point of the current.
And concerning saturation, the core saturates, not the inductor. When the core is saturated it is like it has been replaced by air for any increase in flux.
A simple rule of thumb is that it then behaves like a wire rather than an inductor, but in reality it behaves like an air core inductor and will still incrementally store energy -- just a lot less!
hevans1944
Hop - AC8NS
It would help a lot if you described in some detail what that "compass vane like (metal chip) of a 2 mm diameter" actually is. Does it pivot to allow it to be flipped? If so, how does it pivot? Is it magnetized? If magnetized, is one face one pole and the other face the other pole? How do you propose to generate a torque to flip the metal chip? Will you reverse the current through the itsy bitsy electromagnet? Once the metal chip is oriented in the desired direction, is it supposed to stay that way without the electromagnet remaining energized? How many of these metal chips will you be flipping? All at the same time, or sequentially? Can you provide a sketch of what you are trying to DO?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
CDRIVE
Hauling 10' pipe on a Trek Shift3
Hop, I'm changing my coffee brand to whatever you're drinking. It obviously contains a powerful ingredient of synthetic optimism!
Chris
You mean like with a syringe?
You know what I really enjoy are opportunities to teach interested people about a complicated subject and see them actually understand it and take enjoyment from learning something new. When you teach someone, 20% of effort can cover 80% understanding, while it will take 80% of effort to understand the remaining 20% of knowledge. A good teacher will know that sometimes it is not conducive to push the full 100% onto a student but that it is better to skip out on a few details that aren’t even necessarily relevant in practice but instead give the student a pretty darn good overall picture, give them some intuitive understanding.
If someone asked me about electricity, I may begin by relating it to water flow and pressure. Then of course you would come in and say “electricity is nothing like water”. Well I can only hope that you are not a teacher because I would feel really sorry for those students.
If you need to explain someone how to use a cordless drill, are you going to throw out the year it was invented and the people that invented it and whether or not there was a minus sign? … come on dude.
The sad thing in all this is, that it seems like you actually know a lot and this was a really good opportunity for you to teach me and others something they didn’t know, in a way that perhaps is easy to understand too. But instead you would rather dismantle a statement that is maybe 90% true because it isn’t 100%. Well if you do that, then you can always chip away another layer and find that your truth is actually 99.9% and correct it to 100.0%, then find again, it’s 99.9999% and so forth. This is the kind of person that you are, well good luck buddy and please excuse me, for my "overly-simplistic" opinions.
I'm on my phone and can't easily search for the context of the sniper of your post that ak quoted.
On the surface, the quote does seem a little off-base. Perhaps if I read more fully it would make more sense.
Nevertheless, you need to accept that different people have different opinions about analogies.
I am quite comfortable with descriptions at differing levels of abstraction which are shown to be false when you take a more detailed look, others are not.
We might argue the facts but we try to play the ball, not the man.
hevans1944
Hop - AC8NS
I am drinking an organic coffee imported from Ethiopia: Amaro Gayo. Didn't realize it contained a dose of optimism, but if that is so, I am sure it isn't synthetic. Very tasty coffee IMO. Rewarms in the microwave without loss of flavor or taste. Seasonal though; you have to purchase enough to have a supply when it is out of season.Hop, I'm changing my coffee brand to whatever you're drinking. It obviously contains a powerful ingredient of synthetic optimism!
Chris
That's what I suspected, too. But without confirmation or additional information from the OP, who knows?
CDRIVE
Hauling 10' pipe on a Trek Shift3
Guess(1):
It was a school project. The due date of which has long past, along with the OP.
Guess(2):
It's an "I'm gonna get rich"! idea that can't be divulged to the people who are expected design it.
Guess(3)
It's just another one of Steve's "Nubies Mystery Circuit Circus" entrees.
Chris
It was a school project. The due date of which has long past, along with the OP.
Guess(2):
It's an "I'm gonna get rich"! idea that can't be divulged to the people who are expected design it.
Guess(3)
It's just another one of Steve's "Nubies Mystery Circuit Circus" entrees.
Chris
