EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: julian1 on August 16, 2016, 08:43:02 am
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Looking at pictures of 300VA versus 160VA toroids on Ebay - and the larger ones appear to use fewer turns on the secondary (and presumably primaries too), for the same output voltage.
Obviously the secondary is also a larger gauge and higher current carrying wire.
Is this a general rule, and if so does that mean larger toroids would reduce the work required - if one wanted to adapt one by winding on additional secondaries at other voltage outputs.
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For a given input voltage and frequency, and the same core material (almost always laminated iron), the number of turns is inversely proportional to the cross section of the core. :)
Tim
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A transformer is not perfect, its windings have resistance that causes the secondary voltage to drop with a load. Its rated voltage is when it has its rated load.
A large transformer has windings with low resistance so a 12V transformer might have a secondary that produces 13V with no load. A cheap small transformer has high resistance windings so it is made to produce maybe 15V with no load then its secondary has more windings than the larger transformer.
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Well, the peak magnetic flux density (B) in the core of the transformer will mostly be determined by the ferromagnetic material used for the core, but that value is usually going to be between 1.3T and 1.8T.
If you compared two different size transformers made with the same core material, used on the same frequency and designed for the same peak flux density (B), then the higher power transformer is going to have a larger cross-section of the core, meaning that the peak magnetic flux is going to be higher, resulting in more volts per turn - meaning you need less turns around the core to achieve the same voltage on the output (exactly what you observed).
The wire is naturally going to have to be thicker, because it needs to carry more current, since the bigger transformer is capable of delivering more power.
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I gave Tim a STAR just for managing to keep it to one sentence. I know how hard that was.
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I gave Tim a STAR just for managing to keep it to one sentence. I know how hard that was.
I suspect my posts have an inverse-power law, where the average is "very long" and the outliers are the one-liners... :o :o :-DD
Tim
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I gave Tim a STAR just for managing to keep it to one sentence. I know how hard that was.
I suspect my posts have an inverse-power law, where the average is "very long" and the outliers are the one-liners... :o :o :-DD
Tim
Feeling rather self-conscious at the moment..... :-[