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I am designing an inductor for high current where i need Air gap of 6mm in order to avoid saturation.. But the thing is I am not able to find the air the ferrite material which has airgap of 6mm(one side).. So I thought of keeping a plastic of 2mm on both the legs which also make 2mm gap on the center...which makes effective air gap of 6mm (That's what i believe).

The AL value for individual gaps are given in the datasheet but that value is for middle gapped...

My concern is if i keep gap on both the legs like i mentioned, do i get the AL value mentioned in the datasheet for the airgap?

How does it make a difference by adding gap on legs?

enter image description here

Manjesh Gowda
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  • Assuming E cores, the outer legs are effectively in parallel so their 2mm gaps don't add up, giving 2mm outer + 2mm centre = 4mm. So I think you'll need 3mm in each gap. –  Dec 07 '20 at 15:49

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I believe that by adding 2mm on both the side gives effective air gap of 6mm..is thst right?

Nearly correct - it produces a 4 mm air gap. You have two magnetic circuits in parallel with the centre limb being common - so each parallel magnetic circuit only has a 4 mm gap: -

enter image description here

Red is subject to 2x 2mm gaps and so is blue.

How does it make a difference by adding gap on legs?

That's fine - distributing the gap in several places is acceptable.

My concern is if i keep gap on both the legs like i mentioned, do i get the AL value mentioned in the datasheet for the airgap?

Please link to the data sheet to be sure but probably, yes.

Andy aka
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  • Distributing the air gap in as many parts as possible is actually preferred for many purposes. That's one of the advantages of powder cores; they inherently have a distributed air gap depending on the ratio of ferrite/permalloy/iron/whatever to binder and filler. – Hearth Dec 07 '20 at 16:09
  • @Hearth spot on. – Andy aka Dec 07 '20 at 16:10
  • Doesn't having the gap on the outer legs create more EMI noise? Or is that only for transformers? – Aaron Dec 07 '20 at 16:37
  • @Aaron it's swings and roundabouts really and yes it will/can produce more EMI but that may or may not be a problem. – Andy aka Dec 07 '20 at 16:39
  • An additional note: If possible you should keep the windings and any other conductive materials away from the gaps to avoid additional fringing field losses. – John D Dec 07 '20 at 18:50
  • @JohnD another spot on! – Andy aka Dec 07 '20 at 18:51
  • Here I am going to use 2 E cores..I was thinking having 2mm airgap on both the legs makes the airgap of 2mm in middle aswell.. so it will be of 6mm airgap in total.. I will attach the link for the datasheet https://www.tdk-electronics.tdk.com/inf/80/db/fer/e_70_33_32.pdf Please let know if I have to worry about any other things.. Thank you Note: AL value for Gap of 4mm is wrong. I checked with tool..just for your info Please let me know...Thank you – Manjesh Gowda Dec 07 '20 at 20:58
  • Material type @ManjeshGowda ???. – Andy aka Dec 07 '20 at 21:41
  • N87 .. Thank you – Manjesh Gowda Dec 08 '20 at 08:06
  • @ManjeshGowda I'm unsure what tool you are talking about but with a 2 mm physical distance between cores, the effective air gap will be 4 mm. I can only answer on information you tell me. [This recent answer I did](https://electronics.stackexchange.com/questions/535264/how-to-correctly-use-the-formula-for-calculating-the-air-gap-in-a-pulse-transfor/535351#535351) shows a tear-down of the gap formula and how the permeability changes. So see if this ties in with your tool. – Andy aka Dec 08 '20 at 10:13
  • @Andyaka I was talking about a magnetics tool from TDK which gives direct answers for all the values.. Now i got the idea about the air gap.. And also when i looked into your formula for peak magnetic desnity B=μ0⋅μe⋅H where H is the peak current multiplied by number of turns and then divided by ℓe. I have a different formulas to calculate this but I am not sure which is the proper one..B= L *Imax whole divided by N*Amin.. another one is B= Imax*μ0⋅μr*N whole divided by Airgap(mm)..Where μr is 1 for airgap.. I dont know which one to follow.. But each one gives different answers.. let me know – Manjesh Gowda Dec 08 '20 at 10:50
  • I can't let you know anything. You have a formula and so do I. Mine works and is proven to work and I'm not about to debug your formula or how you use it or whether it's right. This site is a question and answer service and can't be used to evolve a series of questions because that attracts moderators to close down the discussion. If you want to raise a new question about the formulas then please do but, as far as I'm concerned, your original question is answered (whether you believe it or not). This site is definitely not a forum. – Andy aka Dec 08 '20 at 10:55
  • @Andyaka You cleared my doubt..I marked the answer. Thank you – Manjesh Gowda Dec 08 '20 at 19:43