# Difference between transformer of bigger/smaller number of turns with same turns ratio.

Discussion in 'General Electronics Chat' started by supermankid, Mar 19, 2015.

1. ### supermankid Thread Starter Member

May 26, 2013
40
1
What is the difference between the transformer of turns ration
1000:100
or
100:10
or
10:1
The transfer ration is the same in all the transformers but what is the difference
in using the transformer with less turns or more turns?
Is it related to transfer efficiency? Then how do they determine how much turns is needed for certain voltage/current operation?
One last thing, the inductance of the coil depends on number of turns, cross sectional area
and the length. Can we exchange one term with other.
For eg.
less number of turns with more area of cross section.
or
smaller length with number of turns?
I know that I am mixiing two things, but seperate answer to these statements can
make sense(I believe).

2. ### PlasmaT Member

Feb 19, 2015
54
8
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3. ### uwed Member

Mar 16, 2015
64
17
Have a look at this picture (and let's asume R1 and R2 are negligible):
http://lh6.ggpht.com/_X6JnoL0U4BY/S2w08C4JK4I/AAAAAAAANqw/DbATVvPS8LQ/s1600-h/tmp3922_thumb3.jpg

Xm = 2*pi*f *Lm
Lm is proportional to N^2

If N is large, than Xm is large, and the current Im, which takes the shortcut through Xm without every reaching the load becomes very, very small small. This current Im does not contribute to the power transfer but creates losses at the input side (windings, wires, transmission lines), even at no-load. Generally, Xm has to be much larger than Rload to allow power transfer. Windings are expensive and have losses on their own, so an optimum has to be found, application-dependent.

Large number of N --> large Xm --> Im=0 --> lower operating cost
BUT higher material cost, more weight, increased copper losses

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4. ### uwed Member

Mar 16, 2015
64
17
From the simple viewpoint of power transfer and saturation you can exchange turns number and core cross section, but it will have strong effects on efficiency, cooling, Lm and cost. Therefore, it's an important optimization criterion. I don't understand what you mean with "length".

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5. ### supermankid Thread Starter Member

May 26, 2013
40
1
Like the length of solenoid.

The first two links gave the result.

If more turns then more flux and more current can be delivered on the load !

6. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
429
a ten turn primary and a one turn secondary is 10 to 1 ratio, but dont connect it to 120 volts., the number of turns in a primary winding is determined by many things, usually in turns per volt. the insulation had to be adequate to insulate adjacent turns, as well as layer to layer voltages. the size of the wire has to be adequate for the power level the transformer is designed for, and the number of turns in the secondary determined by the voltage ratio . actually if the transformer is a step up transformer, the highest voltage winding determines the insulation level and turn to turn voltage.

7. ### crutschow Expert

Mar 14, 2008
16,533
4,454
In a transformer the main factor in determining the number of primary windings is the maximum voltage and lowest frequency applied to the primary.
There must be primary sufficient turns so that the core doesn't saturate under these worst-case conditions otherwise the primary current becomes limited only by the primary wire resistance. The transformer size, shape, and core material all affect the minimum number of turns where saturation occurs.
Once the number of primary turns is established by this criteria, then the number of secondary turns follows from the turns ratio (output voltage) wanted.