11-07-2018, 12:52 PM
(11-07-2018, 06:17 AM)Diabolical Artificer Wrote: "measure the size of the cross section and multiply calculated area by 0.92)" this gives you what?
Ah! Yes, if you do some calculations beforehand, you can calculate how many turns are needed, and then from wire tables, you can determine wire gauge.
What does the calculation above give? It gives you the cross-section occupied by iron.
If you have a a toroid, 100mm outside diameter, 60mm hole, and 25mm high, then the gross cross-sectional area is 500mm². Multiply this by 0.92 and you get 460mm² of actual iron (if wound with 0.1mm strip) or 0.95 giving 475mm² of iron if wound with 0.3mm strip.
Then, it is simple to calculate minimum turns needed. Just use N = V / (4.44 x B x A x f) where V= AC volts rms; A = area as calculated above; B = max flux density in tesla (use 1.6 T for iron toroid); f = frequency.
Using the minimum turns necessary means that the wire can be the biggest diameter, so resistance and losses are minimised. More turns reduces B, so the thing runs quieter and core losses are reduced, at the expense of more copper losses and more voltage droop on load.
