Say for a given number of turns, I need a current carrying capacity thats greater than the wire I am winding it with. I know I can use multiple strands of lower guage wiring to handle higher currents, but what exactly do I base that on?

For example, if I need it to handle a current of 2 amps, can I use two strands 22 awg guage wires (22awg is rated for 0.92A)?

Also, what exactly is the winding technique for mulitple strands? Do I twist the wires together and then wind them as normal? (something like this?). If so, how tightly do the wires need to be twisted together?

 

If I remember correctly the current carrying capacity of wires are based on open air, at some temperature (not sure what). In a confined area of a transformer you will have to increase the safety factor by considerable margin.
I would lay the multiple strands side by side, if you twist them one wire will
probably cut into another and short out, eventually. They will also take up much more space. Just my 2c worth.

 

Well, if you lay two strands of the wire side by side, wouldnt that be affecting the turns ratio?

Anybody have anything else they want to add?

 

No, you're still putting the same number of turns on, just with two wires instead of one - it's called 'bifilar' winding - where you wind more than one wire at the same time, it's main advantage is that it gives excellent matching between the two windings.

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What exactly are the rules concerning current carrying capacitity with bifilar or trifilar winding? Is it additive? Such as pair of 23awg found bifilar has the current capacitity double of a single 23awg wire?

 

Yes it is!.

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Skin effect losses are also lower. Some transformers don't even use wire but thin varnished copper tape.

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Exactly as Nigel sais already.
The bigger distribution transformers are wound the same way.
11 kV / 400 / 230 Volts has quite often for the secondary coils 2 heavy duty strips of copper or alluminium wound in parrallel.
It would otherwise be very difficult to have strips of 1 inch² copper as secondary winding in case of a 1000 kVA transformer.

It does not affect the turns ratio because both windings have the same amount of turns and length.

In case of the smaller transformer which has 2 windings to give 2 Amps I would suggest to get wire which carries 1.5 Amp safely so you have a current carrying capacity of 3 Amps which you downgrade for 2 Amps to allowe for losses.

Why not by a 2 Amps transformer at whatever voltage you need ?

or is it the challenge of building one from scratch.

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