Ferrite core inductor/transformer

[Techman_7]

I am winding a ferrite core inductor . To have an airgap of around 0.8 mm, I put a piece of paper between the centre leg of 2 E cores. (Core used is EE19/8/5) Is it a feasible method to have the air-gap?

How to join / glue ferrite core halves for winding the ferrite core inductor / transformer??

Which solution or paste is used for it?? I used rubber based adhesive fevibond at the outer legs of E cores. But not getting desired results.

Is it necessary to varnish the ferrite core ???

I want to know the procedure of winding , gluing the ferrite cores??

Please , let me know...

 

[srizbf]

for the air-gap , inserting a paper can also be employed .
Provided the thickness of the paper is equal to your designed air-gap distance.

varnishing is not necessary.
What is that parameter that is not met when you say 'of not getting desired reults?'

Gluing can be carried out with loctite adhesive or any similar one (any acrylic or epoxy based /thermosetting epoxy resin adhesives).

I am attaching the doc for gluing guide for ferrite cores:

https://elnamagnetics.com/wp-content/uploads/library/Elna-Magnetics/Gluing_of_Ferrite_Cores.pdf

 

[Techman_7]

Not getting results means not getting the required inductance value. I used the formula --

N= √ (L ÷ AL value);

required L is 2.81 mH, Al value for E16 core (Not E19) is 212 nH for airgap of around 0.1 mm. I got 115 turns.

Please find the attached core datasheet...

 

[srizbf]

is the core purchased, belongs to N87 material group?

 

[smijesh]

From the above post I understood you are using EF16 core with N87 material.
The AL value of the core at 0.1mm gap is 212nH
(It is the gap between center leg, bot side legs are closed)
If you put a paper in between center leg, a small gap will affect side legs also. So the Al value of your method(paper in t=between center leg) will be less than 212nH
If you have 115 turns
Desired inductance = 212nH x 115 x 115 = 2.803mH (Normal tolerance ± 8%)
If you got un gaped core, I recommending to make gap on any one of the center leg(0.1mm) by emery paper or file
Hope it will be helpful to you

 

[FvM]

To achieve an effective air gap of 0.1 mm with an ungapped core, you need a spacer of 0.05 mm thickness.

By the way, what's the application of your inductor? Did you also calculate the saturation current?

 

[Techman_7]

yes the material is N87

 

[Techman_7]

For gluing the core , the where to apply the acrylic or epoxy based adhesive ?? Is it between the outer legs or at the joint of 2 E cores??

If the adhesive applied between outer legs , it may create additional airgap. So the total airgap will increase.

 

[smijesh]

General practice is applying glue on outer legs for gaped cores. Use very thin layer of adhesive. Off Couse the glue will create minor air gap ( 0.01mm to 0.03mm). If you facing the problem with this minor air gap, you can adjust the turns (one or two turns can be increased). Because your core air gap is very small (0.1mm).
You put little bit glue on the coil former also so it will arrest the movement of core form the coil former.
Better to select air curing glue. Put a small tension clip over the ferrite core while curing, it will ensure further creation of air gap while curing.
Hope this post will help to you

 

[srizbf]

a posting of what is currently being done by you (a photo or a drawing )
will help in identifying the problem.

 

[Techman_7]

Is it the polyester tape used on the E cores & between the windings on coil former???

Which is the popular air curing glue for ferrite cores?

 

[FvM]

You already suggested yourself a useful method to make the air gap: Apply a spacer (paper or foil) between the core halves in the center and adhesive between the outer legs. This way the glue does not increase the air gap.

The spacer is only 0.05 mm for 0.1 mm total air gap, flimsy or air mail paper might work. Polyester film is probably better.
In industry, cores are either clamped or glued with two component expoy resin (e.g. araldite). Curing at elevated temperatures increases the durability.