DC saturation and decreasing permeability when stacking torroid cores

[slic123]

Hi,

We are designing an LC filter that will have inductor made of torroid core MS-184125-2 from Micrometals, datasheet.
Nominal current of the filter (and inductor) is 40A, we want to have an inductance of around 70 uH and for that we need 15 turns of wire. When calculating DC saturation from the datasheet at this number of turns and 40A of current it comes out that the permeability will decrease to about 30% and we end up with 22uH inductance.
My question is what will happen if we stack two torroid cores mentioned above regarding the DC saturation. We are going to need less number of turns to get the same inductance (11 instead of 15) but will the cores saturate at the same rate (following the same curve from datasheet)? So no matter the two cores, permeability decrease will be lower only due to less turns needed for the same inductance?

Unfortunately we are not able to test the saturation in our lab.

Thank you in advance!

 

[FvM]

You can easily answer the question yourself, when you consider that the unit of magnetic field strength is A/m. Respectively the horizontal (current) axis of saturation curve doesn't change when you stack multiple cores. For a specific core material, saturation limit NI depends only on magnetic length not cross section.

 

[Easy peasy]

2 cores = double the AL value - all else being equal - the nature of all iron powder cores is that the zero current L is quite high and the L at design full current is somewhat less,

going to very large low mu cores lowers this difference at the expense of more core and more copper . . .

--- Updated Mar 16, 2024 ---

Just from a quick look at the graphs, 2 cores at 400 ampere turns gives ~ 210 nH/T^2

400 A.T / 40A = 10 turns, 10^2 x 210E-9 = 21uH

So more or bigger cores needed

 

[Easy peasy]

just looking again for 4 stacked cores @ 400 A.t, AL = 4 x 140E-9 say ( from graph ) = 560 nH/T^2

400 A.t at 40A = 10 turns, 10^2 x 560 AL = 56uH

so still a way off with 4 cores.

indeed - if you calc the energy stored for 40A & 70uH - you see it is off the graph for that core ( 56,000 uJ )

 

[slic123]

Thank you for your replies, indeed I also came to realisation that the most practital solution would be to use bigger cores. We also considered using cores that are harder do saturate in same dimensions as that core from above, but they come at around 4 to 5 times the cost and from what we found out they are hard co come by.

Finally, we will go with reduced inductance - less turns and therefore less filter attenuation.