Building a transformer

[Stiffe]

Hey all
I am trying to design a step down transformer for a class

the input voltage would be 120Vac (socket) and would need to be step down to 28vac
I know that

Vs/Vp = Ns/Np

If i chose lets say 300 windings for the primary side the seconday side would then have 70.
My question is what diameter and type of wire do i use to wrap the core? and what type of core should i think about using?

thanks

 

[jmcoreymv]

The thickness of the wire should be determined by the current needed.

 

[bobsmith1492]

... and the size of the core also depends on the current required - probably just an iron core since it's just 60Hz.

Also, this forum isn't for homework.... :|

 

[Mark R]

1) Decide what power you require, and what range of voltages for input and output are acceptable.
2) Choose a core material - grain-oriented silicon steel, amorphous metal alloy, etc. and a core construction e.g. lamination, etc and core shape: C, EI, toroidal, etc.
3) Select an appropriate core size - either by calculation from the core properties (permeability, effective area, etc.) or use the tables provided by the manufacturer
4) Calculate the number of turns on the primary, so that you get a reasonable magnetising current in the primary at no-load, using the core properties provided by the manufacturer. Ensure that there is a large clearance between B at normal operation and Bsat.
5) If necessary, repeat step 4 modifing the parameters (desired magnetisation current, core size, etc.) to ensure that your design is satisfactory
6) Calclate the turns on the secondary
7) Calculate power losses in the copper and in the core. Calculate temperature rises for the core and windings and ensure that they don't exceed their rated temperatures, or the rated temperature of the insulation
8) Modify number of turns, core size, wire guage, etc. until step 7 gives a satisfactory result

 

[jagec]

I'd help you, but in my opinion, it's rather socially irresponsible to build a transformer.

They just use APPALLING levels of energon.

 

[PowerEngineer]

This might help...