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:

    http://ferrite.ru/uploads/pdf/products/pot/p_18_11.pdf
    Ordering code: B65651+0400A048
    Gap: 0.1 mm
    Material: N48

    l_e=25.9 mm
    mu_e=192

    Ferrite N48
    www.epcos.com/blob/528870/download/3/pdf-n48.pdf
    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
    3,957
    1,097
    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

    For your core
    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

    Well-Known Member

    Jun 17, 2014
    2,430
    490
    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.
     
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