piller32 said:

Intro to transformers:

A transformer has 20 primary windings and 100 secondary windings.

If the secondary voltage is 25v, Find the Primary voltage.

Vp/Vs =Np/Ns

20p/100 =

Now i'am stuck Please explain.

Sometimes sums will hurt your head when you represent them as equations and

try to eat them all at once.

The secondary has 25V across it with 100 turns. So the secondary voltage per

turn is 25/100 or 0.25.

The primary voltage per turn is the same so the primary voltage is 20*0.25

or 5V.

Give yourself a new variable called the voltage per turn, Vt. Divide the

secondary voltage, Vs, by the number of secondary turns, Ns, to get Vt, the

voltage per turn.

Vt = Vs/Ns

= 25/100

= 0.25V

Having found the voltage per turn multiply it by the number of primary turns

to find the primary voltage.

Vp = Vt*Np

= 0.25*20

= 5V

Since you had an equation for Vt you can substitute it in the above and get

Vp = (Vs/Ns)*Np

= Vs*Np/Ns

= 25*20/100

= 5V

You can take your original equation...

Vp/Vs =Np/Ns

and convert it to what I had by multiplying both sides by Vs

Vs*Vp/Vs = Vs*Np/Ns

Vs/Vs, on the left hand side, is 1 so things cancel and you get

Vp = Vs*Np/Ns

Like before, then you plug in the values for Vs, Np and Ns and get

Vp = 25*20/100

= 5V

Like before.

What you're dealing with here is algebra, part of mathematics. You tried to

jump too far and got lost. The almost nice thing is that it's a practical

application so you can go back and say.... 'It's a transformer so the number

of volts per turn is the same' and move forward.

DNA