Hello!

I need some help with how to calculate, I want to found out the thermal resistance of a transformer, in order to choose a suitable heatsink for natural cooling.

I assume that I need to find out the operating temperature in order to get the thermal resistance from using this equation:

Rth=delta T /(Pcore + P,cu,winding)

*My question is how do I calculate the operating temperature in this transformer?

I have chosen a transformer core ETD49/25/16 (3F3) and have calculated the core and winding losses. Core loss=4 W and the winding loss=7W, so total loss is 11W.

The area of the copper wire are: A,cu=1.7671 mm^2.

Np=15

Ns=14

The thermal resistance of copper are calculated as: Rthcu,wire=(Rth,cu*l)/A=(0.00250626*0.5mm)/211mm^2 = 5.939*10^-6 C/W

Where l is the air-gap between the copper wire and the core.

Rth,cu=1/(399 W/mC)

Thermal resistance of air:

Rth,air=26.7 mC/W

Thermal resistance of wire isolation:

Rth,isolation=6.5359 mC/W

Thermal resistance of core material ferrite:

Rth=8 C/W

P.S. don't know if it helps, but have drawn a picture of the EI-core and the heatsink placement, the primary winding and the secondary winding are separated by using bobbin/isolation.

Thanks for any help!

//Stenberg

I need some help with how to calculate, I want to found out the thermal resistance of a transformer, in order to choose a suitable heatsink for natural cooling.

I assume that I need to find out the operating temperature in order to get the thermal resistance from using this equation:

Rth=delta T /(Pcore + P,cu,winding)

*My question is how do I calculate the operating temperature in this transformer?

I have chosen a transformer core ETD49/25/16 (3F3) and have calculated the core and winding losses. Core loss=4 W and the winding loss=7W, so total loss is 11W.

The area of the copper wire are: A,cu=1.7671 mm^2.

Np=15

Ns=14

The thermal resistance of copper are calculated as: Rthcu,wire=(Rth,cu*l)/A=(0.00250626*0.5mm)/211mm^2 = 5.939*10^-6 C/W

Where l is the air-gap between the copper wire and the core.

Rth,cu=1/(399 W/mC)

Thermal resistance of air:

Rth,air=26.7 mC/W

Thermal resistance of wire isolation:

Rth,isolation=6.5359 mC/W

Thermal resistance of core material ferrite:

Rth=8 C/W

P.S. don't know if it helps, but have drawn a picture of the EI-core and the heatsink placement, the primary winding and the secondary winding are separated by using bobbin/isolation.

Thanks for any help!

//Stenberg