# Inductor Help

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#### vonsproken

##### Member
Hi,

I have a toroid core and I'm wondering how much current I can put into it before it saturates,

So there are two data sheets, one is the core material and the other is the dimensions and AL.

The flux max density of the material is 0.4T, the cross section is 150mm^2, the field strength is 1000 A/m, the permeability 5000 and the mean diameter 50mm.

In a book I have found that B = uo ur H , uo permeability air, ur relative permeability and H is the field strength.
H must be equal to 63.66 A/m from this equation. This is the same regardless of whether the core is small or large, as these are from the material datasheet.

I also know that H = NI/l where N = numbers of turns, I current and l mean circumference.

This is my confusion, why do I have two completely different field strengths. I also have two equations that calculate H, one is a constant and the other depends on number of turns, current and mean circumference,

I'm trying to work out the maximum current I can put into an inductor before it saturates, I also have different core diameters and different number of windings.

So I guess all I want to know is how you calculate the saturation current with regards to cross-section, permeability and maximum flus density. Also an explanation of these two equations, why one is constant and the other clearly cannot be.

Thanks,
John

#### ChrisP58

##### Well-Known Member
Please post the part number of the core and it's datasheet.

#### dr pepper

##### Well-Known Member
Flux density is dependant on a few factors important ones being,
Voltage
Frequency
Permeability
The more turns you have the lower the flux, the lower the voltage the lower the flux, lowering frequency increase the flux.
There is a standard transformer equation for working it out, however an online tool is quicker:
http://www.daycounter.com/Calculators/Max-Flux-Density-Calculator.phtml

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