# transformer inductance 16000H??

Discussion in 'General Electronics Discussion' started by komalbarun, May 18, 2013.

1. ### komalbarun

67
0
Nov 25, 2011
Am a bit confused...

20:1 step down transformer, 240V to 12V @ 0.3 A 3.6VA.

what is the indcutor's primary coil's and secondary coil's inductance?

I get 16000H for primary and 40H for secondary coil !!?

pls help..I think my calculus is wrong or maybe it's my concept about the transformer itself which is wrong xD

Last edited: May 18, 2013
2. ### BobK

7,682
1,688
Jan 5, 2010
16000H sounds a little high. How did you measure it?

The ratio is correct though: the square of the ratio of the windings.

Bob

Last edited: May 18, 2013
3. ### komalbarun

67
0
Nov 25, 2011
well...
V = -L I ?

Pin = Pout, so ,
240V x I = 3.6VA
I = 3.6/240 V = 0.015A

240 = -L 0.015
-L = 240/0.015 = 16000

am I making a mistake somewhere?

Last edited: May 18, 2013
4. ### duke37

5,364
771
Jan 9, 2011
Not V = I * L but V = I * Xl

Xl = 2*pi*F*L

You are too high by a factor of about 300.

5. ### komalbarun

67
0
Nov 25, 2011
how do I calculate the Xl if I don't know the L or vice-versa?

how do I use 12V @ 0,3A 3.6 VA to calculate the L (if possible)?

6. ### duke37

5,364
771
Jan 9, 2011
You measured Xl NOT L as I pointed out in the first equation.

Transposing the second equation (can you do this?)

L = Xl/(2*pi*F)

The 0.3A is the maximum current that the transformer can provide in the load without getting too hot or dropping too much voltage. It has nothing to do with inductance.

7. ### Raven Luni

798
8
Oct 15, 2011
Is it just me or are transformers much easier to understand than plain inductors?

8. ### komalbarun

67
0
Nov 25, 2011
thnx for that, its good to know

9. ### komalbarun

67
0
Nov 25, 2011
lol I just understood what you meant by this xD, so if am understanding right :

16000 = 2 * pi * f * L?

16000 = 2 * pi * 50 * L

L = 16000/ approx. 314
L = 50H ?

Last edited: May 19, 2013
10. ### duke37

5,364
771
Jan 9, 2011
That looks right to me.

Raven
A simple transformer is relatively easy to understand but as soon as non linear effects or energy transfers are included, my mind boggles. Inductors can be used in so many ways.