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O-Cores. Finally the Real Donuts
Toroids are 30-40% lighter and more compact than E-I transformers. One reason is that the magnetic flux runs parallel to the grain orientation in all parts of the core and another that less wire is needed because the windings are distributed evenly over the entire core circumference, resulting in a shorter mean turn length.
The performance of a toroidal transformer may be further optimized with an O-core (like in O-ring). O cores are wound from a silicon steel strip, which is continuously pointed towards each end to produce a circular cross section.
They are more expensive to produce than regular toroids and inevitably involve some scrap losses when the strip is cut to shape, but on the other hand feature advantages, which sometimes are worth the extra cost.
Why should you consider the O-Core:
- Get more power in a smaller package and save 10%-15% in magnet wire .
- Save the cost of epoxy coating the cores.
Epoxy coating adds 20-30 % to the cost of a bare toroid. Taping with 50% overlap is sufficient core insulation because the rounded shape eliminates
the risk of edge cut through. The O-cores also eliminates the barrel shape of windings placed on a square core.
- Prolong the life of the winding machine. Heavy wire may be wound at reduced tension, reducing the risk of insulation damage and layer cut through.