[SOLVED] Wind a 2.2uH torroid inductor

Hi

I'm new to inductor winding. When i searched in google i found the methods to wind, But i want to know
1.How can I select a toroid core ?. I found some codes T30-10 etc.
2. Is the wire gauge a factor?. If I selected one core, How to determine which gauge wire need to use?
3. Atlast how can I know whether the 2.2uH inductance reached?

I cant relate these things please help..

Thanks in advance:wink:

Hi,

2) you need to choos wire gauge for the desired current and the desired power loss
3) Usually cores come with an "A_L" value. L = A_L x n^2

Klaus

for 2u2H a plastic toroid (air cored) will work too...

Hi
Depends on the frequency!
2.2 uH @100 khz or 2.2 uH @10 MHz is not the same...

Depends on the application (current)

Example for air:
coil diameter:10mm
wire diameter:0.5mm
#windings:25
coil length:20mm

L=2uH, Q(30MHz)=290, fres=150MHz

hello niki, how do you justify that unusual statement? if I wind a litz winding on a plastic (air) toroid to be 2u2H at 100kHz say - it will be 2u2H at 10MHz also - the losses may be different but the inductance is fixed and invariant - like length, - how do you say it changes?

Hi Easy peasy
There is allways an optimal range for a inductor value. It's almost impossible to have a 10mH inductor at 1GHz.
The same story for capacitors: C = 100uF at 1Ghz is impossible.

Hi,

I don't agree. I understand that one can not use the complete energy that is stored in a 100uF capacitor at 1GHz frequency.

If you have 100uF ... it should be independent of frequency.
For sure you don't get the theoretical xc... which is incredibly low at 1GHz...but this is caused by ESR and ESL..but not by a "variable" capacitance.

Compare it with a bottle. It has a volume of one liter.
You may fill in water in 10 seconds and you may empty it within 10s.
But you cant't fill it in 1ms and empty it in 1ms...or 1us..but it has a volume of 1 liter

Klaus

Easy peasy said:

hello niki, how do you justify that unusual statement? if I wind a litz winding on a plastic (air) toroid to be 2u2H at 100kHz say - it will be 2u2H at 10MHz also - the losses may be different but the inductance is fixed and invariant - like length, - how do you say it changes?

Click to expand...

Frequency can affect inductance in many ways. These are skin effect that can be minimized (but not eliminatd) using litz wires, proximity effect and parasitic capacitance.

people are talking about losses and parasitic capacitance, at higher frequencies these take effect yes - but the intrinsic L is still there, hence the self resonant frequency - without the L the SRF would be very high indeed, above the SRF the "L" is capacitive in the circuit - due to parallel winding capacitance - but the L is still there...

Easy peasy you are right as far as you are referring to parasitic capacitance only. The L itself is not affected in frequency, but the total behavior of the component will be seen as the L was changed. Different things are skin effect and proximity effect. They affect directly the self-inductance since they modify the current distribution inside the conductor.

@ albbg, the current distribution in a choke does not change so much that the net average current position changes and changes the inductance, in a planar choke the higher frequencies tend to crowd around the inner periphery of the winding - but here the 1st order L is determined by the gap and amount of fringing B field on the gap.

The only time such behaviour actually noticeably changes inductance is for the leakage inductance of a transformer - here the high frequency currents tend to move closer together - lowering L leak - but this is still a 2nd order effect.

Litz on a air core is not affected - nor is copper tube..

Hi,

I have iron powder core (black coloured). My application for this inductor is in a boost circuit, which switches in 0.55 MHz. The current through inductor I need is 6A. Well, the resonance freq matters here?. Is there any way to get the spec of the Core, which I have now (from old inductor) ? I mean TO-37, TO-30 etc.

Is there any way to get the spec of the Core, which I have now (from old inductor) ? I mean TO-37, TO-30 etc.

Click to expand...

Not sure if you even understand the powder core specification syntax (e.g. T30-10). First number is core size, second core material. Datasheets and tables of Al values are widely available on the internet. Material -10 has low µr of only 6, T30-10 Al value is 2.5 nH/n² (25 µH/100 turns).

Hi Vishnuk,

1.How can I select a toroid core ?. I found some codes T30-10 etc.

Click to expand...

There are many ways to wind a 2.2µH inductor. Using a toroidal core is just one of them. You can also wind the coil in air, or you can use a solenoidal ferrite core, etc.

If you have decided you want to ujse a toroidal core, then it's time to go on and choose one. For this you first need to know some basic things in addition to the required inductance:

- The current the coil has to carry continuously;
- The peak current at which there shall not be too much saturation, or else, how much inductance reduction is acceptable at what current;
- The operating frequency, and the losses you are willing to accept;
- Size, weight, cost restrictions;

So, selecting the optimal core is really a little art, and experience helps a lot. But to get started, you can use the core data given by manufacturers. The aim is to choose a core that allows getting the required inductance with a reasonable number of turns, that does not saturate when the max current is flowing, that has enough winding space to accomodate the required wire thickness with that number of turns, that has low enough loss, and that isn't too large, too heavy, nor too expensive.

2. Is the wire gauge a factor?. If I selected one core, How to determine which gauge wire need to use?

Click to expand...

As a first approximation, for relatively low frequency coils where skin effect isn't too important, a cross sectional area of 1mm² for every 3A of average current is a good starting point. In very small coils you can often get away with significantly less cross section, while in high frequency coils you might need thicker wire. To validate and correct the design, once you know the number of turns and thus the total wire length, you can calculate the AC resistance of that wire, considering skin effect, for the operating frequency, and then calculate how much power loss that resistance will cause, and decide whether or not it's acceptable. But many times your current will be a mix of AC and DC, and for the DC part there is no skin effect. So, for applications where the AC component is small, you can simply use the DC resistance.

3. Atlast how can I know whether the 2.2uH inductance reached?

Click to expand...

Core manufacturers tell you how many turns on which core produce how much inductance. To confirm that all is well, you can measure the inductance. Methods are an inductance meter, of course, or a dipmeter, or you can make a test circuit that basically measures the current rise per time for a given applied voltage, using an oscilloscope.

I have iron powder core (black coloured).

Click to expand...

Caution with that. Those black cores are usually ferrite, not powedered iron. Ferrite comes in a large range of permeability, roughly from 10 to 10000! And you need to have considerable experience to have any chance at telling them apart by sight, so you have to measure them!

Powdered iron toroids typically come in colors. For example, a red core with one black side is material 2, a yellow one with one black side is material 6, and a yellow one with one white side is material 26. These are numbers used by the American Micrometals company, probbaly the best known. Other manufacturers might use different numbers, but often use the same color code. Powdered iron cores come in permeabilities from 1 (which means it's just plastic, without any iron!) to about 100. And there is no logical relationship between the material's number and its permeability! You have to look up the data.

My application for this inductor is in a boost circuit, which switches in 0.55 MHz. The current through inductor I need is 6A.

Click to expand...

For that frequency it's better to use ferrite rather than powdered iron. But with ferrite you will need a core that has an air gap, or is otherwise open, such as a solenoid or a bobbin core. A ferrite toroid (ungapped) would have to be too large to store enough energy.

You can easily use an air-wound coil for this, without any core at all, but it will radiate a huge amount of interference.

A low permeability powdered iron toroid, such as material 2, would probably work well too, and be smaller and radiate less noise than an air coil. But not a "high permeability" powdered iron core like material 26. Too lossy.

My choice would probably be a ferrite bobbin core.

Well, the resonance freq matters here?

Click to expand...

For the boost converter to work properly, you need to keep the stray and inter-turn capacitance low enough so that the resonant frequency of that coil is very much higher than 550kHz. But that's easy, because you will need just a few turns on a core, and still not very many without a core!

Is there any way to get the spec of the Core, which I have now (from old inductor) ? I mean TO-37, TO-30 etc.

Click to expand...

Yes, but it's not too easy. You need to make a test winding (10 turns should be OK) and measure the resulting inductance. That allows you to calculate the AL value of that core. And then you measure its physical dimensions: Inner diameter, outer diameter, height. Thhen you go to the manufacturers' catalogs, you look for toroids having that size, and then you try to match your measured AL value to the published AL values of all the cores of that size, made from different types of ferrite. That should tell you at least roughly what core you have.

There are two problems with this. One is that the AL value of ferrite cores usually has a big tolerance, so you may not know well which of two or three candidate materials you have there. The other is that there are many ferrite materials, from several different manufacturers, that have roughly the same permability, and thus give roughly the same AL value for a given core size, but which differ in other characteristics, such as loss factor, saturation flux density, Curie temperature, temperature coefficient, and so on. To make sure you really have identified a ferrite core, you need to measure all of those too, and that's rather hard!

For your converter, I suggest that you simply wind an air coil to test it. Place the coil at some distance from the rest of the circuit, to keep it from interfering the small-signal parts of it. The longish wires will just add to the inductance. And when you can, look for some nice little ferrite bobbin core to wind the definitive coil on.

There are many programs and online calculators that can help you choose cores, calculate turn numbers, calculate air coils, etc. I sometime suse one called "mini ring core calculator". It's not perfect, but quite usable and practical.

You might also want to look up this page, to learn about basic electromagnetics:

https://ludens.cl/Electron/Magnet.html