I have a rough count of 21 words there and most are multisylablic.

Then just this morning I was working on a DC power supply and raveling at the large inductors at the DC input.

And those inductors are there for the purpose of attenuating what exactly? Not the DC input voltage. Could it be the AC noise? Yeah that's the ticket.

 

And those inductors are there for the purpose of attenuating what exactly? Not the DC input voltage. Could it be the AC noise? Yeah that's the ticket.

dude this post is not a debate about AC/DC I apologise if I didn't make it clear, but with the current graphs for inductors that are cases where the charge and discharge curves have a DC offset (i.e. still AC input but only in the postive region), I am looking for an inductor that does it in both regions.

 

And those inductors are there for the purpose of attenuating what exactly? Not the DC input voltage. Could it be the AC noise? Yeah that's the ticket.

if you google inductor current graphs you will understand what I mean

 

There is nothing magic about current graphs for inductors. Voltage is voltage and current is current, and a design is done by paying attention to all the details. You need the graphs for your purposes, I can do the math and physics. You said you could not find a manufacturer and I believe you and take you at your word. So let us know how it works out for you.

 

There is nothing magic about current graphs for inductors. Voltage is voltage and current is current, and a design is done by paying attention to all the details. You need the graphs for your purposes, I can do the math and physics. You said you could not find a manufacturer and I believe you and take you at your word. So let us know how it works out for you.

 

Let me repeat this in words of one syllable or less.

1. Inductors don't have DC offsets.
2. Inductors only work in AC circuits.
3. There are no DC applications for inductors.

Gee, I guess those big inductors in MRI units that never see current flow in the other direction don't have a DC offset. And apparently operating with the same current for months on end doesn't qualify as a DC application.

Then there's all of those old cars with ignition coils in them -- the current in the primary doesn't reverse direction. Why isn't that a DC offset?

 

Gee, I guess those big inductors in MRI units that never see current flow in the other direction don't have a DC offset. And apparently operating with the same current for months on end doesn't qualify as a DC application.

Then there's all of those old cars with ignition coils in them -- the current in the primary doesn't reverse direction. Why isn't that a DC offset?

The current is not constant either. As far as the MRI, I just had one, and it is not my impression that the same current flows all the time. There are definite on-off cycles. My evidence for this is presence of a previously unknown metal object in my forearm which caused the test to be aborted.

I guess I would ask how any of that is relevant to the design of an inductor. It has a measureable inductance, measureable mechanical specifications, and it has voltage and current limits.

 

Direct current (DC) is a flow of electrical charge carriers that always takes place in the same direction. The current need not always have the same magnitude, but if it is to be defined as dc, the direction of the charge carrier flow must never reverse. This contrasts with alternating current which varies the direction of flow.

I've recently noted a trend on this board of those who define a direct current as a current that since the beginning of time and forever and ever does not change one iota.

Hence even the humble AA cell battery is a source of AC current as it once did not exist and one day will be exhausted.

 

..a previously unknown metal object in my forearm ....

Umm, so you're a cyborg?

 

Umm, so you're a cyborg?

Not exactly. I have no idea when or how it happened; I've never served in the military, or been shot at. According to the radiologist, it is about 7mm long and bright as can be on the x-ray. I guess I'll have to get it removed if I want the complete MRI. I think I need something more substantial than that to be assimilated by the collective.

 

I've recently noted a trend on this board of those who define a direct current as a current that since the beginning of time and forever and ever does not change one iota.

Hence even the humble AA cell battery is a source of AC current as it once did not exist and one day will be exhausted.

And we can use the tools of calculus to determine if the time variation of voltage and current produce significant effects. In the case of inductors we can see that very small values of di/dt produce very small values of voltage difference across the inductor. Equally we can see that large values of di/dt produce correspondingly large voltages across the inductor. We also note that as di/dt approaches zero the voltage across the inductor goes to zero as well regardless of any DC offset on one end of the inductor or the other.

 

I've recently noted a trend on this board of those who define a direct current as a current that since the beginning of time and forever and ever does not change one iota.

Hence even the humble AA cell battery is a source of AC current as it once did not exist and one day will be exhausted.

Sounds like the same people who define a constant voltage source as a constant current source that continually varies its current to keep the voltage steady via the use of a voltage regulator circuit.

 

22 uH 19 amps
http://www.mouser.com/Passive-Compo...ls/Fixed-Inductors/_/N-wpcz?P=1z0wrhcZ1z0wpak

10 uH 26 amps
http://www.mouser.com/ProductDetail/Coilcraft/VER2923-103KL/?qs=zCSbvcPd3pYFGNEVSZE3iw==

These can be ordered through au.mouser.com

 

Not exactly. I have no idea when or how it happened; I've never served in the military, or been shot at.

Did your vet chip you instead of the dog?

ak

 

Did your vet chip you instead of the dog?

ak

Dog was chipped before we got her, so probably a low probability of that.

 

Dog was chipped before we got her, so probably a low probability of that.

Broken hypodermic needle? It does happen.

 

If you choose to wind your own, then realize, I gave directions for an air core inductor. The toroid inductors are low permeability powdered iron cores, and represent the latest improvement in old technology. Air core will suffice for human ear applications, but more precision is needed in scientific applications

Short version, if money is tight, roll your own. Without exact permeability curves, there are too many different values being made to use an unknown toroid, or invest in a capacitor/inductor meter, then you could scavenge and use recovered toroid inductors.

 

The current is not constant either. As far as the MRI, I just had one, and it is not my impression that the same current flows all the time. There are definite on-off cycles. My evidence for this is presence of a previously unknown metal object in my forearm which caused the test to be aborted.

I guess I would ask how any of that is relevant to the design of an inductor. It has a measureable inductance, measureable mechanical specifications, and it has voltage and current limits.

The superconducting background field magnet in an MRI is typically in the range of 5 to 7 tesla with a hundred amp of current and several dozen henries of inductance. They typically charge at just a couple of volts. Calculate the amount of time it takes to ramp such an inductor and you will quickly see why they are held constant. Plus, they are operated in persistent mode where a superconducting shunt is placed across the coil once they are at their operating current and the current supply is removed. They then sit there looking stupid at that current until they are serviced again which is commonly several months later and the current is topped off because they lose a couple of percent due to parasitics.

 

The superconducting background field magnet in an MRI is typically in the range of 5 to 7 tesla with a hundred amp of current and several dozen henries of inductance. They typically charge at just a couple of volts. Calculate the amount of time it takes to ramp such an inductor and you will quickly see why they are held constant. Plus, they are operated in persistent mode where a superconducting shunt is placed across the coil once they are at their operating current and the current supply is removed. They then sit there looking stupid at that current until they are serviced again which is commonly several months later and the current is topped off because they lose a couple of percent due to parasitics.

So what exactly is changing in the process of creating the image?

 

So what exactly is changing in the process of creating the image?

Not the background field.

You have an a second RF generator that superimposes an additional time-changing field that the protons in water respond to and, when this field is cycled, they precess back to their aligned state due to the background field and sensors detect the resulting RF emissions and map it into an image.