# calculate saturation current of ferrite pot core

Discussion in 'General Electronics Chat' started by darsie, Aug 26, 2014.

1. ### darsie Thread Starter New Member

Feb 19, 2010
15
0
Hi!

How do I calculate the saturation current of this P-core:

Ordering code: B65651+0400A048
Gap: 0.1 mm
Material: N48

l_e=25.9 mm
mu_e=192

Ferrite N48
Flux density (near saturation) (f = 10 kHz) B_S (25 �C)= 420 mT

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/toroid.html says:

B*2*pi*r=mu*N*I

So I assume substituting 2*pi*r with the core length will work
aproximately with a P-core, I do:

NI=B_S*l_e/mu = 0.42 T * 0.0259 m / (192 * 4E-7 * pi) = 45 A

I don't believe 45 A. I have a 26/16 P-core (without specs, 26 mm diameter, 16 mm high (per set with 2 halves)) with saturation current of 3.5 A. Even though the P1811 has 0.1 mm gap 45 A seem too large.

I want to know this before I buy the core.

Thanks, Bernhard

Last edited: Aug 26, 2014
2. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,174
1,188
You calculation are correct. You simply have N*I = 45 Amper-turns = magnetomotive force

Personally I use this equation

Use this B = ( AL * N * I )/Ae

AL = 400nH/n²
I is a current in Amps.
Ae - effective cross sectional area = 43mm²

So for example

I = 3A and N = 10 we have

B = (400 * 3 * 10)/43 = 279mT.

so for NI

B = ( AL * NI )/Ae

B*Ae = AL * NI

N*I = (Bmax * Ae)/AL = (420 * 43)/400 = 45A turns.

so for 10 turns we have I_sat = 45At/10t = 4.5A and don't forget that this is a peak value.

Last edited: Aug 27, 2014
3. ### MrAl Distinguished Member

Jun 17, 2014
3,733
790
Hi,

Dont forget that the saturation flux density can go down quite a bit with temperature, which means you should check out the temperature characteristics of the core material too.
Core heating can occur because of ambient temperature rise or power heating.