# Wire to RF toroidal coils?

1. ## Wire to RF toroidal coils?

I need to wind up a few toroidal coils on T130 and T50. F=over 10MHz, AC current up to 3A.
Number of turns 4 to 10.
For T130 with 7 turn is lenght of wire 300mm.

I looked at the wires available and calculated the resistance including the skin effect

1x 1,20mm 75,6mOhm
1x 0,70mm 132.6mOhm 4|| 31,2mOhm
1x 0,35mm 272.2mOhm 8|| 34,0mOhm

Yes, it would have HF cable for exmaple 37x0,14 R=18,4mOhm, but I don't and I don't want to give \$ 11 for 150g, when I have many kg 0.7mm.
I would like to use 4x0,7mm.
The question is how to wind it up?
Like 4 wires next to each other?
Or as twist, how many turn per meter?
What do you recommend?

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2. ## Re: Wire to RF toroidal coils?

To factor in only skin effect will underestimate the AC resistance, there's also proximity effect. Respectively, parallel connection of 4 wires will hardly achieve quarter resistance. Study the stranding scheme of litz wire to understand what's optimal. For low number of strands, twisting is O.K.

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