Multi layer coil design

[humanityrulz]

Hi ,
I got multilayer iron core coil , which has 5000 turns, 100mm iron rod( but coil winded 82mm only) and diameter 19mm. 0.315mm Copper wire used for winding. i want to findout L inductance of the coil, I gone through dfferent soucres which contain air core coil multilayer calculation, no iron core multi layer design formulas.. could please give me some ideas to findout inductance and other factors which I have to consider in coil designing like back emf or resoncance and q factor I think... This coil using for less than 500mA and 15 to 55V

[MrAl]

Hi there,


Although you gave quite a bit of information in your question unfortunately it still isnt enough. To calculate the inductance (or at least to estimate it) of an iron core inductor we also MUST know the permeability of the core. The permeability (abbreviated 'u' sometimes) is one of the things in a formula for the inductance, and it is a very important quality of the core that we must know before we can calculate the inductance.

For example, say we have a construction where we calculate an inductance of 100uH with a certain core that has a permeability of 200. Now if we build another inductor just like that one except for the core which we use a core that has a permeability of 400, the inductance comes out to 200uH instead of 100uH. That's not the end of it though, because we could have used a core that had a permeability of 2000, and then instead of 100uH we would have gotten 1000uH, which is 10 times more inductance.

So you see, the permeability of the core is a very important piece of information that we really need to work this out.

The permeability can be measured, but it's just as simple to measure the inductance and not be bothered with the permeability.
To measure the inductance you need a good inductance meter or better yet a scope and wave generator. If you can get either of these let me know and i'll post more information on how to measure the inductance of your coil.
Oh yeah, you can try using it in a resonant circuit with a capacitor of known value and see what frequency it operates at by measuring the frequency with a frequency counter. Of course you need a frequency counter to do this, and this isnt a great method anyway unless you really intend to use it in a resonant circuit.

Another little thing you should be aware of is that the inductance can change if the coil has a dc current running through it. You'd also have to know the current level and the curve for the core to calculate this out.

[humanityrulz]

Hi there,
Thank you for your detailed reply..

Although you gave quite a bit of information in your question unfortunately it still isnt enough. To calculate the inductance (or at least to estimate it) of an iron core inductor we also MUST know the permeability of the core. The permeability (abbreviated 'u' sometimes) is one of the things in a formula for the inductance, and it is a very important quality of the core that we must know before we can calculate the inductance.

For example, say we have a construction where we calculate an inductance of 100uH with a certain core that has a permeability of 200. Now if we build another inductor just like that one except for the core which we use a core that has a permeability of 400, the inductance comes out to 200uH instead of 100uH. That's not the end of it though, because we could have used a core that had a permeability of 2000, and then instead of 100uH we would have gotten 1000uH, which is 10 times more inductance. So you see, the permeability of the core is a very important piece of information that we really need to work this out.

I understand now.. after a while I found, MILD STEEL used for this core, I treid to findout relative permeability value of the mild steel , some are saying 200-800(permeabilty 2.51x10^-4to 1x10^-3) and some given only 2000(2.51x10^-3), but in wikipedia electrical steel permeability value given as 5x10^-3, So I will go for min and max value (2.51x10^-4, 2.51x10^-3) So could you tell me now what is the L, B and H value for multiple layer coil? Beacasue as I mentiond earlier all info I found about only single layer that toairgaped coils formulas..
I found 100ohm resistance across coil using multimeter.

[humanityrulz]

Hi there,
So you see, the permeability of the core is a very important piece of information that we really need to work this out.

The permeability can be measured, but it's just as simple to measure the inductance and not be bothered with the permeability.
To measure the inductance you need a good inductance meter or better yet a scope and wave generator. If you can get either of these let me know and i'll post more information on how to measure the inductance of your coil.
Oh yeah, you can try using it in a resonant circuit with a capacitor of known value and see what frequency it operates at by measuring the frequency with a frequency counter. Of course you need a frequency counter to do this, and this isnt a great method anyway unless you really intend to use it in a resonant circuit.

Another little thing you should be aware of is that the inductance can change if the coil has a dc current running through it. You'd also have to know the current level and the curve for the core to calculate this out.

I haven't got any inductance meter, but I got scope can you tell I can I measure inductance in scope please?
After this I want to improve the magnetic field with less power, the coil I got. So for this reason I am trying to know these things.
Igone through few websites, which mentoned about power loss and eddycurrents.. back emf, or reverse peak voltage like this can you tell me how can I prevent these without damaging other components in ckt..

Thank you in advance....

[humanityrulz]

Can anyone tell me.. how can I upload files or any images? is there any way or it banned in this forum?

[MrAl]

Hi again,


Some time ago this forum stopped allowing uploads of pics or at least it broke or something.
I use http://www.postimage.org now and that seems to work. You upload there and then bring the link here and include it with your post.

To measure the inductance with a scope you also need a square wave generator or sine wave generator. You excite the inductor with the square wave and then look at the response current with the scope, then do a calculation. Another way, if the choke is big enough, is to excite it at line frequency (50 or 60Hz) and check the current and do a different calculation. It depends on the coil however.
Can you post a picture so we can see what this looks like? If you post a picture that you take, take the picture with a ruler next to the coil and core so we can see how big this thing is. You could also measure the core and coil if you like, and the shape of the core, but a pic would help too.

The way you protect your circuit from back EMF or other problems sometimes associated with coils depends on the actual circuit it is being used in. You'd have to post a schematic too. For example, sometimes a simple diode works and sometimes you dont need anything.

[humanityrulz]

Hi MrAl,
Again..Thanks for info... finally I found inductance of the coil without iron core 3mH and with slug it is 600mH. So, I guess I need to consider the 600mH to find the capacitor value with frequency, correct me if I am wrong. I am designing ckt to run this coil @100mA current and 12V . By consuming low power , I want to run this coil with low power losses, So can you guide to design this please. I saw many designs in internet to control motor most are usnig H bridge ckt and Buck -boost converter, I want to do same with low cost components. Thanks in advance. .

[MrAl]

Hi again,


Are you saying you want to use an H bridge and Buck or do you want to do it another way?

I think i can help better if you should me a schematic of what you want to do, or describe it in detail.

[humanityrulz]

Hi again,


Are you saying you want to use an H bridge and Buck or do you want to do it another way?

I think i can help better if you should me a schematic of what you want to do, or describe it in detail.

HI Mr Al,
I am looking for better solution... ofcourse... with low power consume and less cost.. for this baisc coil opreration.

If you still didn't get me.. let me know....but here I am doing basic operation.. I thought it is better way to understand things in coil designing.

I am trying to learn things here, So I am happy to know any method which helps me to improve my knowledge... end of the day someone has to share their knowledge, or views. Thanks for your efforts, in this process Mr Al...

[MrAl]

Hello again,


Im still not exactly sure what you are asking here. You show a DC to DC converter with the apparent output going to the coil, but dont say what you are using that coil for exactly. Is that part of the converter or is that a separate filter?

[humanityrulz]

Hello again,


Im still not exactly sure what you are asking here. You show a DC to DC converter with the apparent output going to the coil, but dont say what you are using that coil for exactly. Is that part of the converter or is that a separate filter?

Hi Mr Al,
Sorry, I drawn wrongly, I was planned to use PIC or oscillator to run coil, the power supply for these IC's need 5V(pic) so I am using 12-5V DC-Dc converter.Also I thought coil need more power supply to produce strong magnetic feild, so I am using 12v power supply.
If it confuses you, forget what I siad, suggest me what I have to do , to run coil with low power and produce strong magnetic fields. How much power do I need to supply to coil(which I got ) to produce strong magnetic field, which components I have to use to run.
Any suggestions are helpful. Thank you in advance.

[MrAl]

Hello again,


So all you want to do is produce a strong magnetic field then using the coil?

[humanityrulz]

Hello again,


So all you want to do is produce a strong magnetic field then using the coil?

Hi Mr Al,
YES...indeed..... Controllable magnetic field with low power , low losses.... and also want measure how strong it's if possible.......any suggestions.or..comments....

Let me know the general applications and pros and cons of strong magnetic fileds please. will low frequency(50Hz-500Hz) magnetic signals interfere with high frequency RF signals(2.4GHz frequency band), if so how can I avoid that interception ? Because I noticed magnetic field presence interfer my radio signal(MHz).... so how can I avoid ?

[MrAl]

Hello again,


If you need to control the level of the field from a coil you would probably want to build a driver that can supply current to the coil. The driver may have to handle quite a bit of current and voltage, depending on how fast you need the field to change and how strong it has to be.

So tell me what you are doing...you are trying to generate a magnetic field on demand to test for interference on other devices?

Devices that receive signals of any kind usually rely to some degree on what the level of other local signals are, that they are low enough to not be detected while the signals of interest are.
A filter of some kind is often used for this purpose, but any filter has the tendency to respond not only to the frequency it is 'tuned' to, but will respond at least a little to other frequencies as well.
This means that given enough amplitude and close enough distance, you can interfere with almost any device with almost any frequency. Directivity also plays a part however, in that if you can make the reception directional you can reduce outside interference. Sometimes this requires shielding too.

[Bygar]

An easy way to measure inductance is a series circuit consisting of;
An oscillator of known frequency
A Potentiometer and possibly a selection of fixed resistors
A means to measure AC voltages at the frequency of the oscillator
The circuit is simple the unknown inductor is wired in series with the
potentiometer and maybe a fixed resistor, apply a signal from frequency source
measure the AC voltage across the resistor and then the AC voltage across the
inductor; adjust the potentiometer and resistor combination until the coil and
resistor voltages are equal
you have found the inductive re-actance of the inductor you most of the way
to the answer these values will allow you to calculate the inductance of the unknown
coil. And also the permeability of the core. The needed equations are found in the
Allied Radio Data Book. X(inductive reactance) = 2x(pi) x f x l.Your math should allow you
to shuffle the equation for the unknown. I believe you can download a copy of the
Data book (http://www.smc.com) this book also contains multi-layer coil equations.
Good luck