# Auto-Transformer Formula help Please..

Discussion in 'Homework Help' started by stinky111, Dec 4, 2011.

1. ### stinky111 Thread Starter Member

Apr 7, 2011
39
1
Hi All,

Im studying for a final & am having problems finding the formulas in my notes to solve the question below..

An auto-transformer is connected to a 230V a.c supply. the secondary voltage is 50V a.c and the load current is 8A. How much current flows to the common part of the winding??

Appriciate the formula to find the current flowing to common part of winding please guys?? (Final a week away & I have no more lectures beforehand)
Thx

2. ### jimkeith Active Member

Oct 26, 2011
539
99
Iout = Iin + Icom

Icom = Iout - Iin

Iin = Iout /Eratio

Icom = Iout - (Iout /Eratio)

Try this and see if it works

3. ### EL7819 New Member

Apr 15, 2011
20
0
Np/Ns=Vp/Vs=Is/Ip

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
This is partly true for the auto-transformer - to the degree that it relates the input primary terminal current to the secondary terminal current but it doesn't tell you what the common current is in the 'shared' part of the winding. Jimkeith's method is correct.

stinky111 likes this.
5. ### stinky111 Thread Starter Member

Apr 7, 2011
39
1
Thanks JimKeith,
so am i correct in saying:

Ratio = vp/vs= 230/50 = 4.6
Icom = Iout-(Iout/Eratio)
= 8a-(8a/4.6)
= 6.26A??
Thx..

Mar 6, 2009
5,448
783
Correct.

Apr 7, 2011
39
1
Thx heaps...