relationship between core size and turns in transformer

Thread Starter


Joined Jun 28, 2008
hi, friends i got a problem need ur help .:)
i have two cores of size 1.5 * 2 and 1.5 * 2.5 i am surprised how many turns i have to use for primary in 1.5*2 core and how many in 1.5 * 2.5
iron core. detail is
for 220 volts 50/60 hz
for 275 volts 50/60 hz
and for secndary 24 volts when using 220 primary winding

i realy want to know if core size changes then how turns changes is there any easy formula to determine turns and core size . i found 400 tuns for core size 1.5*2 and 350 turns for core 1.5*2.5 is it rite for primary windings
i will be very thankfull to u if u can solve my problem . thanks

John Luciani

Joined Apr 3, 2007
To determine inductance the formula is

N^2 = L / AL

N is the number of turns, L is the inductance, AL is the nominal core inductance that
is specified in the manufacturers datasheet. There is a lot of information about transformer
design at

Your larger core has a larger cross sectional area (and larger AL) which reduces the
number of turns required to get the same inductance.

(* jcl *)