I have an educational single phase step-down/step-up transformer which is fed by a 120V Variac (Variable Transformer) that allows you to add as many turns as you wish ON THE SECONDARY (Insulated wire is used). Currently I am using the transformer as a step-down transformer with TWO TURNS ON THE SECONDARY (Ns = 2). I measured values for Vs (Secondary Voltage), Np (Set amount of turns which cannot be changed), Ns = 2, Ip (Primary Current), & Is (Secondary Current) with a Primary Voltage (Vp) = 10% on variac = 11.5Vac (.10 x 115Vac)

How would I hand calculate these values for when Ns = 3 at 10% on the variac before physically adding an extra turn? I am very familiar with using the transformer ratios for calculations (Np/Ns = Is/Ip = Vp/Vs). However, my calculation is not adding up for the new Vp? Can Volts per turn be used to calculated new values?

 

Hi,

If you have 5v with one turn and 10v for two turns then you should have 15 volts for three turns.
If it does not work that way then there may be something else working too, such as load, or two turns being partially connected together when the variac dial is turned.

 

Hi,

If you have 5v with one turn and 10v for two turns then you should have 15 volts for three turns.
If it does not work that way then there may be something else working too, such as load, or two turns being partially connected together when the variac dial is turned.

Turns are insulated

 

Hi,

Oh yes i was talking about the variac. So i guess you are not experimenting with that but with actual full turns either added or removed on a transformer core.

 

Hi,

Oh yes i was talking about the variac. So i guess you are not experimenting with that but with actual full turns either added or removed on a transformer core.

Only with stepdown transformer thanks