Gapping ferrite cores

[ronv]

I'm trying to build some ballasts. I have found the right cores and clips and "stuff" but I don't know the proper way to gap the e-cores. I understand it is the center leg that gets gapped but i'm not sure if i can do it or if i have to buy them gapped. Do I take it all off one side or 1/2 one each core? One gets gapped at 1 mm the other at .5 mm. The core is an E30/15/7.
Thanks for the help!

 

[crutschow]

You can do it yourself if you have the tools to remove the material without breaking the core.

You can put all the gap on one side if that's easier. The gap doesn't care where it is.

 

[ronsimpson]

For production you can gap the center leg. I do not for prototype or for low volume production.
>Get the cores made with a center leg gap. The cores are hard, brittle and will brake if you grind on them at home. I have not had luck doing it myself.
>Center leg gap helps reduce the magnetic field leaking from the transformer.
>I use transformer tape to gap all the legs of the core. Mylar tape. Tape across the core then cut off the excess tape.
>I have sheets of Mylar from 1/1000 to 1/10 inch thick. I cut small rectangles and tape them to the outside two legs.

 

[RCinFLA]

Look at chapter 13, page 14 in link: **broken link removed**

You will need a diamond grinding wheel to cut the ferrite. Center post gap is better since it has lower flux leakage then outside edge gapping.

Better if you can find a core with a gap that suits you needs. Ferrite: E Cores

 

[ronv]

cores

The mylar or Kapton tape sounds like the best for a couple of prototypes. So if the design calls for
1mm do I gap all three legs at 1mm?

 

[colin55]

If the total is 1mm, you need 0.5mm in the centre and 0.5mm on each outer (as each outer has half the flux flowing through each outer).

 

[ronv]

Thanks everyone !

 

[MrAl]

Hi,

I have to recommend applying the gap all the way across all three legs of the E. When you do that, the gap is in the magnetic path twice instead of once so you use half the total required gap. At least you dont have to grind anything that way.
You should also verify the inductance with a test or two just to make sure everything works as planned with the applied gap.

Just to note, i have gapped ferrite toroids before by cracking the core in to 4 pieces and then putting the pieces back together. It's interesting to note how it affects the core performance. The break doesnt always come out as clean as we would like it though.

 

[ronv]

More questions

Turns out the ungapped cores are only the beginning. The cores i found that match the spec for the inverter can only be purchased in lots of 850. This leads to more questions. I think I know the answers but since I don't know anything about magnetics I better ask.

1- Can I use a hotter ferrite? The spec calls for N27 - Can I use N87 without any other changes?
2- Can I use a larger core without any problem.

Thanks again

 

[MrAl]

Hi,

You usually have to get the material right if it has a gap, as part of the design counts on having a certain permeability, and other core materials wont have the same permeability and other core sizes wont work out to the same inductance. If this design has already been worked out and tried then it's highly recommended to use the same core type and size.
If you wanted to get around this you'd have to do some serious testing to make sure that every aspect of the design works just as well as with the old core type.

 

[colin55]

In the end it will all come down to experimentation.
Buy something and see how it goes.

 

[hmsahir4u]

The Method to Disassambled a ferrite core Transfarmer

Dear Ron,
I would like to share my experience about disassambling of a premade ferrite Transfarmer. Most people break down the transfarmer during disassambling process. Hope that it will be useful for you and all the community.
Method: Take an Iron Plate and put it on the stove. Put the core of Ferrite Transfarmer on it. After some time you can disassemble it with a small screw without breaking the core.
Haimd Mahmood Sahir,
Chiniot Pakistan.
sahirhm@hotmail.com
Cell # +92 345 7590486