Question about a transformer

[AkisTzortzis]

Hello

I would like to make a transformer with a primary winding of 5 Volts RMS and current of 40 Ampere RMS. Its secondary winding ought to be 35 Volts RMS and 4.5 Amps RMS.

I presume that means the turns ratio should be 1:7 (from 5 Volts to 35 Volts) ?

I am not sure how to select the core , would a toroidal be best? And how about the wire? How thick a wire I need to handle 40 Amps on the primary? And how many turns do I need? For example what is the difference between having 10 primary turns and 70 secondary, or 100 primary turns and 700 secondary?

As I need to have 40 Amps flowing through the primary, at 5 Volts RMS, do I take it that the primary winding would need to have a resistance of 0.125 Ohm? How do I go about choosing the right wire and right number of turns to achieve 0.125 Ohm? And how on earth do I measure such a small resistance?

Any help appreciated.

 

[the_edge]

Dont know for thorus, but if you want to use EI transformer, than these are dimensions for your specific application:

S=15cm^2 - surface of the Fe core,
N1=116, number of turns on primary,
N2=17, number of turns on secondary,
d1=4.5mm, on primary, (very tick wire, might be that my calculation is wrong)
d2=1.5mm, on secondary,

As you can see, its big since it is for 200W on primary... These are aproximate values, dont take them for granted...

 

[Awarapunshee]

Hello

I would like to make a transformer with a primary winding of 5 Volts RMS and current of 40 Ampere RMS. Its secondary winding ought to be 35 Volts RMS and 4.5 Amps RMS.

I presume that means the turns ratio should be 1:7 (from 5 Volts to 35 Volts) ?

I am not sure how to select the core , would a toroidal be best? And how about .........

You forgot to write the operating frequency?

 

[AkisTzortzis]

Audio frequencies

 

[Audioguru]

You want the resistance of the windings on a transformer to be as low as possible so that the output voltage doesn't change much when the load current changes.