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Output voltage of transformer depends on ratio of winding count on primary and secondary coils, but is there an impact on transformer performance by actual winding count?

Say, i want to have 1:2 ratio, i could wind 10:20 or 100:200 windings.

In general, more windings - bigger the resistance, inductance and cost. Is there any point in winding more or is winding count kept to absolute minimum? How minimal winding count is determined?

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The induced magnetic field is proportional to ampere-turns, that's current times number of turns. Electrical energy is converted to magnetic energy in the core and back to electrical. The core must be big enough to hold that without saturating. For a 100 VA transformer you want to transfer more energy magnetically than for a 10 VA transformer. The 100 VA is larger because it has more turns to build up a stronger field, and also needs a bigger core to avoid it saturating.

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Great answer. Do you know what equations govern this, or how to estimate the number? What if there is no core - just air... I suppose the coils themselves will saturate!? – Hans-Peter E. Kristiansen Sep 29 '12 at 1:16
@Hans-Peter - An iron core transformer will have hysteresis loss, which the air core transformer won't have. But an air core has a lot of leakage, and is therefore not suitable as a power transformer. An iron core concentrates the magnetic field, and you won't get a strong field outside it. Calculations are complex, because they depend on shape, size, material, construction of core and windings. This site may get you started. – stevenvh Sep 29 '12 at 9:46

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