# Induced voltage on secondary of a transformer

Discussion in 'General Electronics Chat' started by wes, Jun 20, 2012.

1. ### wes Thread Starter Active Member

Aug 24, 2007
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Hi, I know that on a transformer, if the primary and secondary are of equal turns then the voltage induced on the secondary will be equal to the primary minus any losses like leakage flux and so on. Usually from what I have seen and learned is that the size of both windings are usually equal, but what if the secondary is say 1/2 the diameter of the primary but the same number of turns? Will the induced voltage on the secondary still be equal to the primary. The total coil length on the secondary would be 1/2 the primary's total coil length and I am not sure if that matters?

2. ### ErnieM AAC Fanatic!

Apr 24, 2011
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By "diameter" do you mean the physical size of the wire?

What circle are you looking at?

3. ### wes Thread Starter Active Member

Aug 24, 2007
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No, I mean the diameter of the entire coil of wire. Not the diameter of the wire itself.

4. ### DerStrom8 Well-Known Member

Feb 20, 2011
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usually the coils are wrapped right on the core with just a few thin pieces of insulation separating them. 1/2 the diameter but same number of turns would mean that it's wrapped closer to the core, which is impossible if the wire gauge stays the same.

Would you be able to draw a sketch of what you're thinking of? I'm not sure if I'm understanding you correctly

5. ### Brownout Well-Known Member

Jan 10, 2012
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Same number of turns = same voltage as the primary. Diameter doesn't matter in the first order.

6. ### DerStrom8 Well-Known Member

Feb 20, 2011
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In theory you're absolutely right, but something occurred to me--if you have one winding wrapped tightly to the core on one side, and wrapped very loosely on the other, the magnetic field will be weaker where the loose coil actually sits. That would mean losses, and the voltages probably won't be equal.

7. ### Brownout Well-Known Member

Jan 10, 2012
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Who said anything about loose widnings? The question is about diameter. BTW, my answer assumes that the flux linkage would not be affected by geometry.

8. ### DerStrom8 Well-Known Member

Feb 20, 2011
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Oh sorry, that was just the way my mind was going. The OP was asking about changing the diameter of the winding without changing the number of turns or the wire gauge. The only way I could think of that happening would be if one winding was wound more loosely than the other.

9. ### Brownout Well-Known Member

Jan 10, 2012
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This senario occurs often, as when the secondary is wound on top of the primary. The diameter of the primary is smaller then the secondary. Opposite of the OP's question, but illustrative of how turns, not relationship of the diameters, is important.

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10. ### DerStrom8 Well-Known Member

Feb 20, 2011
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That's a good point. I didn't even think about that

I also suppose the secondary could be lengthened so it's the same number of turns, but it's just not as thick.

As long as the losses are small enough to be ignored, I completely agree with you--same number of turns should mean the same voltage.

11. ### wes Thread Starter Active Member

Aug 24, 2007
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Here, I attached a picture of what I mean. Also I am talking if the distance between the two coils is kept constant even if the diameter is decreased.

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12. ### DerStrom8 Well-Known Member

Feb 20, 2011
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The questions should be handled here on the forum, not through private emails. That way, more people are able to learn as well.