# Air gap for inductor core

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?

• 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.
– user16324
Commented Dec 7, 2020 at 15:49

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: -

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.

• 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. Commented Dec 7, 2020 at 16:09
• @Hearth spot on. Commented Dec 7, 2020 at 16:10
• Doesn't having the gap on the outer legs create more EMI noise? Or is that only for transformers? Commented Dec 7, 2020 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. Commented Dec 7, 2020 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. Commented Dec 7, 2020 at 18:50