# e 25 core

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#### nimitha

##### New Member
How can I wind a e25 transformer with a turns ratio 1:1.5? How many turns is required? In our paper nothing is specified about the inductance. so we wound the transformer with 10 primary and 15 secondary turns. 12V input is given to the primary. But we didn't get anything in the secondary.

#### Dick Cappels

##### Active Member
The number of turns required depends on the application of the transformer. If it doesn't seem to work with 10 turns primary and 15 turns secondary you may need to multiply the turns by some number or increase the drive frequency by some number. This is because the inductance of the primary will cause current to flow that has nothing to do with the secondary and if this current is too high the voltage drop in the primary winding will leave little to drive the secondary. Current through this inductance decreases with the number of turns and decreases with frequency. Keep the amplitude of the primary winding low at the start.

#### ronsimpson

##### Well-Known Member
In our paper nothing is specified about the inductance.
We need more information. Can you send "the paper"?

#### Flyback

##### Well-Known Member
yes , your "12v input" i hope is not DC like it sounds, becuase DC and transformers dont mix well

#### nimitha

##### New Member
No sir we have got this 12v input from the output of 230/12v transformer. And hence the supply given is ac.

#### Flyback

##### Well-Known Member
so you are transforming the output of a transformer? Why is it you do this?
Are you trying to build an smps with a 12v input?...if so then i will send you relevant theory paper on winding your e25

#### atferrari

##### Well-Known Member
Keep the amplitude of the primary winding low at the start.
Sorry for the question Dick. Amplitude of the input voltage you mean?

#### ronsimpson

##### Well-Known Member
No sir we have got this 12v input from the output of 230/12v transformer.
So you are working at 50 or 60hz, AC.
Is the "e25 transformer" about 2.5cm in size.
Do you have a way to measure inductance?
10 turns is very low for 50 to 60 hz.
Can you attach a picture?
What kind of wire?
What type of insulation? Is it like paint?
What is the resistance of each winding? About zero ohms?

#### dr pepper

##### Well-Known Member
An E25 from memory is a ferrite core, and is not really suitable for 50/60hz, more like 50 / 60 khz.
You'd be better rectifying the 12v ac and then chopping it at a higher frequency.

#### Dick Cappels

##### Active Member
atferrari Yes, I meant to refer to the voltage on the primary winding. After it starts to work he can experiment with gapping the core to prevent saturation.

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